Power-law photoluminescence decay in quantum dots

Czech Academy of Sciences Publication Activity Database

Král, Karel; Menšík, Miroslav

2013-01-01

Roč. 5, č. 6 (2013), s. 608-610 ISSN 2164-6627 R&D Projects: GA MŠk(CZ) OC10007; GA MŠk LH12236; GA MŠk LH12186 Institutional support: RVO:68378271 ; RVO:61389013 Keywords : quantum dots * indirect gap * photoluminescence * electron-phonon interaction * non-adiabatic Subject RIV: BM - Solid Matter Physics ; Magnetism; JA - Electronics ; Optoelectronics, Electrical Engineering (UMCH-V)

Effect of shells on photoluminescence of aqueous CdTe quantum dots

International Nuclear Information System (INIS)

Yuan, Zhimin; Yang, Ping

2013-01-01

Graphical abstract: Size-tunable CdTe coated with several shells using an aqueous solution synthesis. CdTe/CdS/ZnS quantum dots exhibited high PL efficiency up to 80% which implies the promising applications for biomedical labeling. - Highlights: • CdTe quantum dots were fabricated using an aqueous synthesis. • CdS, ZnS, and CdS/ZnS shells were subsequently deposited on CdTe cores. • Outer ZnS shells provide an efficient confinement of electron and hole inside the QDs. • Inside CdS shells can reduce the strain on the QDs. • Aqueous CdTe/CdS/ZnS QDs exhibited high stability and photoluminescence efficiency of 80%. - Abstract: CdTe cores with various sizes were fabricated in aqueous solutions. Inorganic shells including CdS, ZnS, and CdS/ZnS were subsequently deposited on the cores through a similar aqueous procedure to investigate the effect of shells on the photoluminescence properties of the cores. In the case of CdTe/CdS/ZnS quantum dots, the outer ZnS shell provides an efficient confinement of electron and hole wavefunctions inside the quantum dots, while the middle CdS shell sandwiched between the CdTe core and ZnS shell can be introduced to obviously reduce the strain on the quantum dots because the lattice parameters of CdS is situated at the intermediate-level between those of CdTe and ZnS. In comparison with CdTe/ZnS core–shell quantum dots, the as-prepared water-soluble CdTe/CdS/ZnS quantum dots in our case can exhibit high photochemical stability and photoluminescence efficiency up to 80% in an aqueous solution, which implies the promising applications in the field of biomedical labeling

Ultrafast photoluminescence spectroscopy of InAs/GaAs quantum dots

Czech Academy of Sciences Publication Activity Database

Neudert, K.; Trojánek, F.; Kuldová, Karla; Oswald, Jiří; Hospodková, Alice; Malý, P.

2009-01-01

Roč. 6, č. 4 (2009), 853-856 ISSN 1862-6351 R&D Projects: GA ČR GA202/06/0718 Institutional research plan: CEZ:AV0Z10100521 Keywords : quantum dots * photoluminescence * MOVPE Subject RIV: BM - Solid Matter Physics ; Magnetism

Size dependence of upconversion photoluminescence in MPA capped CdTe quantum dots: Existence of upconversion bright point

Energy Technology Data Exchange (ETDEWEB)

Ananthakumar, S. [Crystal Growth Centre, Anna University, Chennai 600025 (India); Jayabalan, J., E-mail: jjaya@rrcat.gov.in [Laser Physics Applications Section, Raja Ramanna Centre for Advanced Technology, Indore 452013 (India); Singh, Asha; Khan, Salahuddin [Laser Physics Applications Section, Raja Ramanna Centre for Advanced Technology, Indore 452013 (India); Babu, S. Moorthy [Crystal Growth Centre, Anna University, Chennai 600025 (India); Chari, Rama [Laser Physics Applications Section, Raja Ramanna Centre for Advanced Technology, Indore 452013 (India)

2016-01-15

The photoluminescence (PL) from semiconductor quantum dots can show a “PL bright point”, that is the PL from as prepared quantum dots is maximum at a particular size. In this work we show that, for CdTe quantum dots, upconversion photoluminescence (UCPL) originating from nonlinear absorption shows a similar “UCPL bright point”. The PL and UCPL bright points occur at nearly the same size. The existence of a UCPL bright point has important implications for upconversion microscopy applications. - Highlights: • The size dependence of the upconversion photoluminescence (UCPL) spectrum of CdTe quantum dots has been reported. • We show that the UCPL from the CdTe quantum dots is highest at a particular size. • Thus the occurrence of a 'UCPL bright point' in CdTe quantum dots has been demonstrated. • It has been shown that the UCPL bright point occurs at nearly the same size as a normal bright point.

Size dependence of upconversion photoluminescence in MPA capped CdTe quantum dots: Existence of upconversion bright point

International Nuclear Information System (INIS)

Ananthakumar, S.; Jayabalan, J.; Singh, Asha; Khan, Salahuddin; Babu, S. Moorthy; Chari, Rama

2016-01-01

The photoluminescence (PL) from semiconductor quantum dots can show a “PL bright point”, that is the PL from as prepared quantum dots is maximum at a particular size. In this work we show that, for CdTe quantum dots, upconversion photoluminescence (UCPL) originating from nonlinear absorption shows a similar “UCPL bright point”. The PL and UCPL bright points occur at nearly the same size. The existence of a UCPL bright point has important implications for upconversion microscopy applications. - Highlights: • The size dependence of the upconversion photoluminescence (UCPL) spectrum of CdTe quantum dots has been reported. • We show that the UCPL from the CdTe quantum dots is highest at a particular size. • Thus the occurrence of a "UCPL bright point" in CdTe quantum dots has been demonstrated. • It has been shown that the UCPL bright point occurs at nearly the same size as a normal bright point.

Quantum dots with indirect band gap: power-law photoluminescence decay

Czech Academy of Sciences Publication Activity Database

Král, Karel; Menšík, Miroslav

2014-01-01

Roč. 11, č. 5 (2014), s. 507-512 ISSN 1708-5284 R&D Projects: GA MŠk LH12236; GA MŠk LH12186 Institutional support: RVO:68378271 ; RVO:61389013 Keywords : photoluminescence * quantum dots * electron-phonon interaction * inter-valley deformation potential interaction * power-law decay Subject RIV: BM - Solid Matter Physics ; Magnetism

Solvothermal tuning of photoluminescent graphene quantum dots: from preparation to photoluminescence mechanism

Science.gov (United States)

Qi, Bao-Ping; Zhang, Xiaoru; Shang, Bing-Bing; Xiang, Dongshan; Zhang, Shenghui

2018-02-01

Solvothermal synthesis was employed to tune the surface states of graphene quantum dots (GQDs). Two series of GQDs with the particle sizes from 2.6 to 4.5 nm were prepared as follows: (I) GQDs with the same size but different oxygen degrees; (II) GQDs with different core sizes but the similar surface chemistry. Both the large sizes and the high surface oxidation degrees led to the redshift photoluminescence (PL) of GQDs. Electrochemiluminescence (ECL) spectra from two series of GQDs were all in accordance with their PL spectra, respectively, which provided good evidence for the conjugated structures in GQDs responsible for PL. [Figure not available: see fulltext.

Photoluminescence efficiency in AlGaN quantum wells

Energy Technology Data Exchange (ETDEWEB)

Tamulaitis, G.; Mickevičius, J. [Institute of Applied Research and Semiconductor Physics Department, Vilnius University, Sauletekio av. 9-III, Vilnius LT-10222 (Lithuania); Jurkevičius, J., E-mail: jonas.jurkevicius@ff.vu.lt [Institute of Applied Research and Semiconductor Physics Department, Vilnius University, Sauletekio av. 9-III, Vilnius LT-10222 (Lithuania); Shur, M.S. [Department of ECE and CIE, Rensselaer Polytechnic Institute (United States); Shatalov, M.; Yang, J.; Gaska, R. [Sensor Electronic Technology, Inc. (United States)

2014-11-15

Photoluminescence spectroscopy of AlGaN/AlGaN multiple quantum wells under quasi-steady-state conditions in the temperature range from 8 to 300 K revealed a strong dependence of droop onset threshold on temperature that was explained by the influence of carrier delocalization. The delocalization at room temperature results predominantly in enhancement of bimolecular radiative recombination, while being favorable for enhancement of nonradiative recombination at low temperatures. Studies of stimulated emission confirmed the strong influence of carrier localization on droop.

Physico-chemical mechanism for the vapors sensitivity of photoluminescent InP quantum dots

Science.gov (United States)

Prosposito, P.; De Angelis, R.; De Matteis, F.; Hatami, F.; Masselink, W. T.; Zhang, H.; Casalboni, M.

2016-03-01

InP/InGaP surface quantum dots are interesting materials for optical chemical sensors since they present an intense emission at room temperature, whose intensity changes rapidly and reversibly depending on the composition of the environmental atmosphere. We present here their emission properties by time resolved photoluminescence spectroscopy investigation and we discuss the physico-chemical mechanism behind their sensitivity to the surrounding atmosphere. Photoluminescence transients in inert atmosphere (N2) and in solvent vapours of methanol, clorophorm, acetone and water were measured. The presence of vapors of clorophorm, acetone and water showed a very weak effect on the transient times, while an increase of up to 15% of the decay time was observed for methanol vapour exposure. On the basis of the vapor molecule nature (polarity, proticity, steric hindrance, etc.) and of the interaction of the vapor molecules with the quantum dots surface a sensing mechanism involving quantum dots non-radiative surface states is proposed.

Physico-chemical mechanism for the vapors sensitivity of photoluminescent InP quantum dots

International Nuclear Information System (INIS)

Prosposito, P.; De Angelis, R.; De Matteis, F.; Casalboni, M.; Hatami, F.; Masselink, W.T.; Zhang, H.

2016-01-01

InP/InGaP surface quantum dots are interesting materials for optical chemical sensors since they present an intense emission at room temperature, whose intensity changes rapidly and reversibly depending on the composition of the environmental atmosphere. We present here their emission properties by time resolved photoluminescence spectroscopy investigation and we discuss the physico-chemical mechanism behind their sensitivity to the surrounding atmosphere. Photoluminescence transients in inert atmosphere (N 2 ) and in solvent vapours of methanol, chloroform, acetone and water were measured. The presence of vapors of chloroform, acetone and water showed a very weak effect on the transient times, while an increase of up to 15% of the decay time was observed for methanol vapour exposure. On the basis of the vapor molecule nature (polarity, proticity, steric hindrance, etc.) and of the interaction of the vapor molecules with the quantum dots surface a sensing mechanism involving quantum dots non-radiative surface states is proposed. (paper)

Hydrothermal synthesis of two photoluminescent nitrogen-doped graphene quantum dots emitted green and khaki luminescence

International Nuclear Information System (INIS)

Zhu, Xiaohua; Zuo, Xiaoxi; Hu, Ruiping; Xiao, Xin; Liang, Yong; Nan, Junmin

2014-01-01

A simple and effective chemical synthesis of the photoluminescent nitrogen-doped graphene quantum dots (N-GQDs) biomaterial is reported. Using the hydrothermal treatment of graphene oxide (GO) in the presence of hydrogen peroxide (H 2 O 2 ) and ammonia, the N-GQDs are synthesized through H 2 O 2 exfoliating the GO into nanocrystals with lateral dimensions and ammonia passivating the generated active surface. Then, after a dialytic separation, two water-soluble N-GQDs with average size of about 2.1 nm/6.2 nm, which emit green/khaki luminescence and exhibit excitation dependent/independent photoluminescence (PL) behaviors, are obtained. In addition, it is also demonstrated that these two N-GQDs are stable over a broad pH range and have the upconversion PL property, showing this approach provides a simple and effective method to synthesize the functional N-GQDs. - Highlights: • Nitrogen-doped graphene quantum dots (N-GQDs) are prepared by hydrothermal routine. • Two N-GQDs with different size distribution emit green/khaki photoluminescence. • Two N-GQDs exhibit excitation-dependent/independent photoluminescence behaviors

Different approaches for sensing captopril based on functionalized graphene quantum dots as photoluminescent probe

Energy Technology Data Exchange (ETDEWEB)

Toloza, Carlos A.T.; Khan, Sarzamin; Silva, Renan L.D. [Department of Chemistry, Pontifical Catholic University of Rio de Janeiro (PUC-Rio), Rio de Janeiro 22451-900 (Brazil); Romani, Eric C.; Freire, F.L. [Department of Physics, Pontifical Catholic University of Rio de Janeiro (PUC-Rio), Rio de Janeiro 22451-900 (Brazil); Aucélio, Ricardo Q., E-mail: aucelior@puc-rio.br [Department of Chemistry, Pontifical Catholic University of Rio de Janeiro (PUC-Rio), Rio de Janeiro 22451-900 (Brazil)

2016-11-15

The determination of captopril is proposed using graphene quantum dots produced by the pyrolysis of citric acid and glutathione (GSH-GQDs). Captopril induces both quenching and spectral red-shifting in the photoluminescence from aqueous dispersions of GSH-GQDs. By employing Fe{sup 3+} as mediator (that enables signal quenching of GSH-GQDs), the presence of captopril restored the photoluminescence of quantum dots. Under optimized experimental conditions, the signal quenching from the GSH-GQDs as function of the concentration of captopril showed a linear response range covering three orders of magnitude (10{sup −6} to 10{sup −4} mol L{sup −1}). The proposed approaches were tested by determining captopril in simulated samples and in commercial pharmaceutical formulations. The measurement of either the spectral shifting observed of the GSH-GQDs probe or the photoluminescence switch on/off using GQDs-GSH-Fe{sup 3+} resulted in satisfactory recoveries of captopril, showing the quantitative sensing potential.

Growth and temperature dependent photoluminescence of InGaAs quantum dot chains

International Nuclear Information System (INIS)

Yang, Haeyeon; Kim, Dong-Jun; Colton, John S.; Park, Tyler; Meyer, David; Jones, Aaron M.; Thalman, Scott; Smith, Dallas; Clark, Ken; Brown, Steve

2014-01-01

Highlights: • We examine the optical properties of novel quantum dot chains. • Study shows that platelets evolve into quantum dots during heating of the InGaAs platelets encapsulated with GaAs. • Single stack of quantum dots emits light at room temperature. • Quantum dots are of high quality, confirmed by cross-section TEM images and photoluminescence. • Light emission at room temperature weakens beyond the detection limit when the quantum dots form above the critical annealing temperature. - Abstract: We report a study of growth and photoluminescence from a single stack of MBE-grown In 0.4 Ga 0.6 As quantum dot chains. The InGaAs epilayers were grown at a low temperature so that the resulting surfaces remain flat with platelets even though their thicknesses exceed the critical thickness of the conventional Stranski–Krastanov growth mode. The flat InGaAs layers were then annealed at elevated temperatures to induce the formation of quantum dot chains. A reflection high energy electron diffraction study suggests that, when the annealing temperature is at or below 480 °C, the surface of growth front remains flat during the periods of annealing and growth of a 10 nm thick GaAs capping layer. Surprisingly, transmission electron microscopy images do indicate the formation of quantum dot chains, however, so the dot-chains in those samples may form from precursory platelets during the period of temperature ramping and subsequent capping with GaAs due to intermixing of group III elements. The optical emission from the quantum dot layer demonstrates that there is a critical annealing temperature of 480–500 °C above which the properties of the low temperature growth approach are lost, as the optical properties begin to resemble those of quantum dots produced by the conventional Stranski–Krastanov technique

Absolute determination of photoluminescence quantum efficiency using an integrating sphere setup

International Nuclear Information System (INIS)

Leyre, S.; Coutino-Gonzalez, E.; Hofkens, J.; Joos, J. J.; Poelman, D.; Smet, P. F.; Ryckaert, J.; Meuret, Y.; Durinck, G.; Hanselaer, P.; Deconinck, G.

2014-01-01

An integrating sphere-based setup to obtain a quick and reliable determination of the internal quantum efficiency of strongly scattering luminescent materials is presented. In literature, two distinct but similar measurement procedures are frequently mentioned: a “two measurement” and a “three measurement” approach. Both methods are evaluated by applying the rigorous integrating sphere theory. It was found that both measurement procedures are valid. Additionally, the two methods are compared with respect to the uncertainty budget of the obtained values of the quantum efficiency. An inter-laboratory validation using the two distinct procedures was performed. The conclusions from the theoretical study were confirmed by the experimental data

Detection of CdSe quantum dot photoluminescence for security label on paper

Energy Technology Data Exchange (ETDEWEB)

Isnaeni,, E-mail: isnaeni@lipi.go.id; Sugiarto, Iyon Titok [Research Center for Physics, Indonesian Institute of Science, Building 442 Puspiptek Serpong, South Tangerang, Banten, Indonesia 15314 (Indonesia); Bilqis, Ratu; Suseno, Jatmiko Endro [Department of Physics, Diponegoro University, Jl. Prof. Soedarto, Tembalang, Semarang, Indonesia 50275 (Indonesia)

2016-02-08

CdSe quantum dot has great potential in various applications especially for emitting devices. One example potential application of CdSe quantum dot is security label for anti-counterfeiting. In this work, we present a practical approach of security label on paper using one and two colors of colloidal CdSe quantum dot, which is used as stamping ink on various types of paper. Under ambient condition, quantum dot is almost invisible. The quantum dot security label can be revealed by detecting emission of quantum dot using photoluminescence and cnc machine. The recorded quantum dot emission intensity is then analyzed using home-made program to reveal quantum dot pattern stamp having the word ’RAHASIA’. We found that security label using quantum dot works well on several types of paper. The quantum dot patterns can survive several days and further treatment is required to protect the quantum dot. Oxidation of quantum dot that occurred during this experiment reduced the emission intensity of quantum dot patterns.

Power-law photoluminescence decay in indirect gap quantum dots

Czech Academy of Sciences Publication Activity Database

Menšík, Miroslav; Král, Karel

2013-01-01

Roč. 111, November (2013), s. 170-174 ISSN 0167-9317 R&D Projects: GA MŠk(CZ) OC10007; GA MŠk LH12186; GA MŠk LH12236; GA ČR(CZ) GAP205/10/2280 Institutional support: RVO:61389013 ; RVO:68378271 Keywords : quantum dots * indirect gap transition * power-law photoluminescence decay Subject RIV: BM - Solid Matter Physics ; Magnetism; BE - Theoretical Physics (FZU-D) Impact factor: 1.338, year: 2013

Changes of photoluminescence of electron beam irradiated self-assembled InAs/GaAs quantum dots

Science.gov (United States)

Maliya; Aierken, Abuduwayiti; Li, Yudong; Zhou, Dong; Zhao, Xiaofan; Guo, Qi; Liu, Chaoming

2018-03-01

We investigate the effects of 1.0MeV electron beam irradiation on the photoluminescence of self-assembled InAs/GaAs quantum dots. After irradiation doses up to 1×1016e-/cm2 , photoluminescence of all samples was degraded dramatically and some additional radiation-induced changes in photo-carrier recombination from QDs, which include a slight increase in PL emission with low electron doses under different photo-injection condition in two samples, are also noticed. Different energy shift was observed in two samples with different Quantum Dot sizes. We attribute this remarkable phenomenon to combination of stress relaxation induced red-shift and In-Ga intermixing caused blue-shift.

Dense arrays of ordered pyramidal quantum dots with narrow linewidth photoluminescence spectra

Energy Technology Data Exchange (ETDEWEB)

Surrente, A; Gallo, P; Felici, M; Dwir, B; Rudra, A; Kapon, E, E-mail: alessandro.surrente@epfl.c [Laboratory of Physics of Nanostructures, Ecole Polytechnique Federale de Lausanne (EPFL), CH-1015 Lausanne (Switzerland)

2009-10-14

Arrays of site-controlled, pyramidal InGaAs/GaAs quantum dots (QDs) grown by organo-metallic chemical vapour deposition with densities comparable to those of self-assembled QDs (5 x 10{sup 9} cm{sup -2}) are demonstrated. The QDs exhibit high quality photoluminescence spectra with inhomogeneous broadening of only 6.5 meV. The QD dipole moment was estimated through the analysis of time-resolved photoluminescence measurements. Such ordered QD arrays should be useful for applications in active nanophotonic systems such as QD lasers, modulators and switches requiring high overlap of the optical modes with the QD active region.

Near-unity photoluminescence quantum yield in MoS2

KAUST Repository

Amani, Matin

2015-11-26

Two-dimensional (2D) transition metal dichalcogenides have emerged as a promising material system for optoelectronic applications, but their primary figure of merit, the room-temperature photoluminescence quantum yield (QY), is extremely low.The prototypical 2D material molybdenum disulfide (MoS2) is reported to have a maximum QYof 0.6%, which indicates a considerable defect density. Herewe report on an air-stable, solution-based chemical treatment by an organic superacid, which uniformly enhances the photoluminescence and minority carrier lifetime of MoS2 monolayers by more than two orders of magnitude.The treatment eliminates defect-mediated nonradiative recombination, thus resulting in a finalQYofmore than 95%, with a longest-observed lifetime of 10.8 0.6 nanoseconds. Our ability to obtain optoelectronic monolayers with near-perfect properties opens the door for the development of highly efficient light-emitting diodes, lasers, and solar cells based on 2D materials.

Near-unity photoluminescence quantum yield in MoS2

KAUST Repository

Amani, Matin; Lien, Der Hsien; Kiriya, Daisuke; Xiao, Jun; Azcatl, Angelica; Noh, Jiyoung; Madhvapathy, Surabhi R.; Addou, Rafik; Santosh, K. C.; Dubey, Madan; Cho, Kyeongjae; Wallace, Robert M.; Lee, Si Chen; He, Jr-Hau; Ager, Joel W.; Zhang, Xiang; Yablonovitch, Eli; Javey, Ali

2015-01-01

Two-dimensional (2D) transition metal dichalcogenides have emerged as a promising material system for optoelectronic applications, but their primary figure of merit, the room-temperature photoluminescence quantum yield (QY), is extremely low.The prototypical 2D material molybdenum disulfide (MoS2) is reported to have a maximum QYof 0.6%, which indicates a considerable defect density. Herewe report on an air-stable, solution-based chemical treatment by an organic superacid, which uniformly enhances the photoluminescence and minority carrier lifetime of MoS2 monolayers by more than two orders of magnitude.The treatment eliminates defect-mediated nonradiative recombination, thus resulting in a finalQYofmore than 95%, with a longest-observed lifetime of 10.8 0.6 nanoseconds. Our ability to obtain optoelectronic monolayers with near-perfect properties opens the door for the development of highly efficient light-emitting diodes, lasers, and solar cells based on 2D materials.

Magnetic enhancement of photoluminescence from blue-luminescent graphene quantum dots

Science.gov (United States)

Chen, Qi; Shi, Chentian; Zhang, Chunfeng; Pu, Songyang; Wang, Rui; Wu, Xuewei; Wang, Xiaoyong; Xue, Fei; Pan, Dengyu; Xiao, Min

2016-02-01

Graphene quantum-dots (GQDs) have been predicted and demonstrated with fascinating optical and magnetic properties. However, the magnetic effect on the optical properties remains experimentally unexplored. Here, we conduct a magneto-photoluminescence study on the blue-luminescence GQDs at cryogenic temperatures with magnetic field up to 10 T. When the magnetic field is applied, a remarkable enhancement of photoluminescence emission has been observed together with an insignificant change in circular polarization. The results have been well explained by the scenario of magnetic-field-controlled singlet-triplet mixing in GQDs owing to the Zeeman splitting of triplet states, which is further verified by temperature-dependent experiments. This work uncovers the pivotal role of intersystem crossing in GQDs, which is instrumental for their potential applications such as light-emitting diodes, photodynamic therapy, and spintronic devices.

Using quantum dot photoluminescence for load detection

Science.gov (United States)

Moebius, M.; Martin, J.; Hartwig, M.; Baumann, R. R.; Otto, T.; Gessner, T.

2016-08-01

We propose a novel concept for an integrable and flexible sensor capable to visualize mechanical impacts on lightweight structures by quenching the photoluminescence (PL) of CdSe quantum dots. Considering the requirements such as visibility, storage time and high optical contrast of PL quenching with low power consumption, we have investigated a symmetrical and an asymmetrical layer stack consisting of semiconductor organic N,N,N',N'-Tetrakis(3-methylphenyl)-3,3'-dimethylbenzidine (HMTPD) and CdSe quantum dots with elongated CdS shell. Time-resolved series of PL spectra from layer stacks with applied voltages of different polarity and simultaneous observation of power consumption have shown that a variety of mechanisms such as photo-induced charge separation and charge injection, cause PL quenching. However, mechanisms such as screening of external field as well as Auger-assisted charge ejection is working contrary to that. Investigations regarding the influence of illumination revealed that the positive biased asymmetrical layer stack is the preferred sensor configuration, due to a charge carrier injection at voltages of 10 V without the need of coincident illumination.

Using quantum dot photoluminescence for load detection

Directory of Open Access Journals (Sweden)

M. Moebius

2016-08-01

Full Text Available We propose a novel concept for an integrable and flexible sensor capable to visualize mechanical impacts on lightweight structures by quenching the photoluminescence (PL of CdSe quantum dots. Considering the requirements such as visibility, storage time and high optical contrast of PL quenching with low power consumption, we have investigated a symmetrical and an asymmetrical layer stack consisting of semiconductor organic N,N,N′,N′-Tetrakis(3-methylphenyl-3,3′-dimethylbenzidine (HMTPD and CdSe quantum dots with elongated CdS shell. Time-resolved series of PL spectra from layer stacks with applied voltages of different polarity and simultaneous observation of power consumption have shown that a variety of mechanisms such as photo-induced charge separation and charge injection, cause PL quenching. However, mechanisms such as screening of external field as well as Auger-assisted charge ejection is working contrary to that. Investigations regarding the influence of illumination revealed that the positive biased asymmetrical layer stack is the preferred sensor configuration, due to a charge carrier injection at voltages of 10 V without the need of coincident illumination.

On quantum harmonic oscillator being subjected to absolute ...

Indian Academy of Sciences (India)

On quantum harmonic oscillator being subjected to absolute potential state. SWAMI NITYAYOGANANDA. Ramakrishna Mission Ashrama, R.K. Beach, Visakhapatnam 530 003, India. E-mail: nityayogananda@gmail.com. MS received 1 May 2015; accepted 6 May 2016; published online 3 December 2016. Abstract.

Near-unity photoluminescence quantum yield in MoS.sub.2

Science.gov (United States)

Amani, Matin; Lien, Der-Hsien; Kiriya, Daisuke; Bullock, James; Javey, Ali

2017-12-26

Two-dimensional (2D) transition-metal dichalcogenides have emerged as a promising material system for optoelectronic applications, but their primary figure-of-merit, the room-temperature photoluminescence quantum yield (QY) is extremely poor. The prototypical 2D material, MoS.sub.2 is reported to have a maximum QY of 0.6% which indicates a considerable defect density. We report on an air-stable solution-based chemical treatment by an organic superacid which uniformly enhances the photoluminescence and minority carrier lifetime of MoS.sub.2 monolayers by over two orders of magnitude. The treatment eliminates defect-mediated non-radiative recombination, thus resulting in a final QY of over 95% with a longest observed lifetime of 10.8.+-.0.6 nanoseconds. Obtaining perfect optoelectronic monolayers opens the door for highly efficient light emitting diodes, lasers, and solar cells based on 2D materials.

Temperature-dependent photoluminescence study of InP/ZnS quantum dots

Science.gov (United States)

Thuy Pham, Thi; Tran, Thi Kim Chi; Liem Nguyen, Quang

2011-06-01

This paper reports on the temperature-dependent photoluminescence of InP/ZnS quantum dots under 532 nm excitation, which is above the InP transition energy but well below that of ZnS. The overall photoluminescence spectra show two spectral components. The higher-energy one (named X) is assigned to originate from the excitonic transition; while the low-energy spectral component (named I) is normally interpreted as resulting from lattice imperfections in the crystalline structure of InP/ZnS quantum dots (QDs). Peak positions of both the X and I emissions vary similarly with increasing temperature and the same as the InP bandgap narrowing with temperature. In the temperature range from 15 to 80 K, the ratio of the integrated intensity from the X and the I emissions decreases gradually and then this ratio increases fast at temperatures higher than 80 K. This could result from a population of charge carriers in the lattice imperfection states at a temperature below 80 K to increase the I emission but then with these charge carriers being released to contribute to the X emission.

Interface and photoluminescence characteristics of graphene-(GaN/InGaN){sub n} multiple quantum wells hybrid structure

Energy Technology Data Exchange (ETDEWEB)

Wang, Liancheng, E-mail: wanglc@semi.ac.cn, E-mail: lzq@semi.ac.cn, E-mail: zh.zhang@hebut.edu.cn [Engineering Product Development Pillar (EPD), Singapore University of Technology & Design (SUTD), 8 Somapah Road, Singapore 487372 (Singapore); Semiconductor Lighting Technology Research and Development Center, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083 (China); Mind Star (Beijing) Technology Co., Ltd., Zhongguancun South Street, Haidian District, No. 45 Hing Fat Building 1001, Beijing 100872 (China); Liu, Zhiqiang, E-mail: wanglc@semi.ac.cn, E-mail: lzq@semi.ac.cn, E-mail: zh.zhang@hebut.edu.cn; Tian, Ying Dong; Yi, Xiaoyan; Wang, Junxi; Li, Jinmin; Wang, Guohong [Semiconductor Lighting Technology Research and Development Center, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083 (China); Zhang, Zi-Hui, E-mail: wanglc@semi.ac.cn, E-mail: lzq@semi.ac.cn, E-mail: zh.zhang@hebut.edu.cn [Key Laboratory of Electronic Materials and Devices of Tianjin, School of Electronics and Information Engineering, Hebei University of Technology, Tianjin 300401 (China)

2016-04-14

The effects of graphene on the optical properties of active system, e.g., the InGaN/GaN multiple quantum wells, are thoroughly investigated and clarified. Here, we have investigated the mechanisms accounting for the photoluminescence reduction for the graphene covered GaN/InGaN multiple quantum wells hybrid structure. Compared to the bare multiple quantum wells, the photoluminescence intensity of graphene covered multiple quantum wells showed a 39% decrease after excluding the graphene absorption losses. The responsible mechanisms have been identified with the following factors: (1) the graphene two dimensional hole gas intensifies the polarization field in multiple quantum wells, thus steepening the quantum well band profile and causing hole-electron pairs to further separate; (2) a lower affinity of graphene compared to air leading to a weaker capability to confine the excited hot electrons in multiple quantum wells; and (3) exciton transfer through non-radiative energy transfer process. These factors are theoretically analysed based on advanced physical models of semiconductor devices calculations and experimentally verified by varying structural parameters, such as the indium fraction in multiple quantum wells and the thickness of the last GaN quantum barrier spacer layer.

Photoluminescence intermittency of semiconductor quantum dots in dielectric environments

Energy Technology Data Exchange (ETDEWEB)

Isaac, A.

2006-08-11

The experimental studies presented in this thesis deal with the photoluminescence intermittency of semiconductor quantum dots in different dielectric environments. Detailed analysis of intermittency statistics from single capped CdSe/ZnS, uncapped CdSe and water dispersed CdSe/ZnS QDs in different matrices provide experimental evidence for the model of photoionization with a charge ejected into the surrounding matrix as the source of PL intermittency phenomenon. We propose a self-trapping model to explain the increase of dark state lifetimes with the dielectric constant of the matrix. (orig.)

Excitation density dependence of the photoluminescence from CdxHg1-xTe multiple quantum wells

International Nuclear Information System (INIS)

Tonheim, C R; Selvig, E; Nicolas, S; Breivik, M; Haakenaasen, R; Gunnaes, A E

2008-01-01

A study of the photoluminescence from a four-period Cd x Hg 1-x Te multiple quantum well structure at 11 K as a function of excitation density is presented. High-resolution X-ray diffraction and transmission electron microscopy revealed that the quantum well structure is of high quality. This was supported by the narrow photoluminescence peak originating in the ground state electron - heavy hole transition, with a full width at half maximum of only 7.4 meV for an excitation density of 1.3 W/cm 2 . When the excitation density was increased from 1.3 to 23.4 W/cm 2 , the peak position was shifted toward higher energy by 2.6 meV and the full width at half maximum increased from 7.4 to 10.9 meV

Micro-photoluminescence of GaAs/AlGaAs triple concentric quantum rings.

Science.gov (United States)

Abbarchi, Marco; Cavigli, Lucia; Somaschini, Claudio; Bietti, Sergio; Gurioli, Massimo; Vinattieri, Anna; Sanguinetti, Stefano

2011-10-31

A systematic optical study, including micro, ensemble and time resolved photoluminescence of GaAs/AlGaAs triple concentric quantum rings, self-assembled via droplet epitaxy, is presented. Clear emission from localized states belonging to the ring structures is reported. The triple rings show a fast decay dynamics, around 40 ps, which is expected to be useful for ultrafast optical switching applications.

Influence of 3D aggregation on the photoluminescence dynamics of CdSe quantum dot films

Energy Technology Data Exchange (ETDEWEB)

Alejo, T. [Departamento de Química Física, Facultad de Ciencias Químicas, Universidad de Salamanca, E-37008 Salamanca (Spain); Paulo, Pedro M.R. [Centro de Química Estrutural, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais 1, 1049-001 Lisboa (Portugal); Merchán, M.D. [Departamento de Química Física, Facultad de Ciencias Químicas, Universidad de Salamanca, E-37008 Salamanca (Spain); Garcia-Fernandez, Emilio; Costa, Sílvia M.B. [Centro de Química Estrutural, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais 1, 1049-001 Lisboa (Portugal); Velázquez, M.M., E-mail: mvsal@usal.es [Departamento de Química Física, Facultad de Ciencias Químicas, Universidad de Salamanca, E-37008 Salamanca (Spain)

2017-03-15

Thin films of semiconductor CdSe quantum dots, QDs, directly deposited onto quartz as well as onto a Langmuir-Blodgett film of the Gemini surfactant ethyl-bis (dimethyl octadecyl ammonium bromide have been prepared and their photoluminescence properties were characterized by confocal fluorescence lifetime microscopy. 3D aggregates of QDs were observed in QD films directly deposited onto the solid while the Gemini surfactant film avoids the 3D aggregation. The photoluminescence decay analysis was performed by a phenomenological model previously proposed by us which considers that the luminescence dynamics is affected by energy transport and trapping processes and the relative contribution of these processes depends on film morphology. Thus, in the non-aggregated and more homogeneous QD films, QDs deposited onto the surfactant, the relative contribution of the energy transport process increases with trap concentration while 3D aggregation favors the energy transport even at low density of energy traps. - Highlights: • Photoluminescence dynamics of QDs films. • Photoluminescence response related to energy transport and trapping processes. • Dependence of photoluminescence dynamics on film morphology.

Influence of 3D aggregation on the photoluminescence dynamics of CdSe quantum dot films

International Nuclear Information System (INIS)

Alejo, T.; Paulo, Pedro M.R.; Merchán, M.D.; Garcia-Fernandez, Emilio; Costa, Sílvia M.B.; Velázquez, M.M.

2017-01-01

Thin films of semiconductor CdSe quantum dots, QDs, directly deposited onto quartz as well as onto a Langmuir-Blodgett film of the Gemini surfactant ethyl-bis (dimethyl octadecyl ammonium bromide have been prepared and their photoluminescence properties were characterized by confocal fluorescence lifetime microscopy. 3D aggregates of QDs were observed in QD films directly deposited onto the solid while the Gemini surfactant film avoids the 3D aggregation. The photoluminescence decay analysis was performed by a phenomenological model previously proposed by us which considers that the luminescence dynamics is affected by energy transport and trapping processes and the relative contribution of these processes depends on film morphology. Thus, in the non-aggregated and more homogeneous QD films, QDs deposited onto the surfactant, the relative contribution of the energy transport process increases with trap concentration while 3D aggregation favors the energy transport even at low density of energy traps. - Highlights: • Photoluminescence dynamics of QDs films. • Photoluminescence response related to energy transport and trapping processes. • Dependence of photoluminescence dynamics on film morphology.

Dilute nitride InNP quantum dots: Growth and photoluminescence mechanism

Energy Technology Data Exchange (ETDEWEB)

Kuang, Y. J. [Department of Physics, University of California, San Diego, La Jolla, California 92093 (United States); Takabayashi, K.; Kamiya, I. [Quantum Interface Laboratory, Toyota Technological Institute, Nagoya 468-8511 (Japan); Sukrittanon, S. [Material Science and Engineering Program, University of California, San Diego, La Jolla, California 92093 (United States); Pan, J. L.; Tu, C. W. [Department of Electrical and Computer Engineering, University of California, San Diego, La Jolla, California 92093 (United States)

2014-10-27

Self-assembled dilute nitride InNP quantum dots (QDs) in GaP matrix grown under the Stranski-Krastanov mode by gas-source molecular beam epitaxy are studied. The N-related localized states inside the InNP QDs provide a spatially direct recombination channel, in contrast to the spatially indirect channel through the strained In(N)P QDs/GaP interface states. The N incorporation into InP QDs therefore causes a blueshift and double-peak features in photoluminescence, which are not observed in other dilute nitride materials.

On the acceptor-related photoluminescence spectra of GaAs quantum-wire microcrystals: A model calculation

International Nuclear Information System (INIS)

Oliveira, L.E.; Porras Montenegro, N.; Latge, A.

1992-07-01

The acceptor-related photoluminescence spectrum of a GaAs quantum-wire microcrystal is theoretically investigated via a model calculation within the effective-mass approximation, with the acceptor envelope wave functions and binding energies calculated through a variational procedure. Typical theoretical photoluminescence spectra show two peaks associated to transitions from the n = 1 conduction subband electron gas to acceptors at the on-center and on-edge positions in the wire in good agreement with the recent experimental results by Hirum et al. (Appl. Phys. Lett. 59, 431 (1991)). (author). 14 refs, 3 figs

Plasmon resonance-induced photoluminescence enhancement of CdTe/Cds quantum dots thin films

Energy Technology Data Exchange (ETDEWEB)

Wang, Hongyu [Nanjing University of Posts and Telecommunications, Nanjing 210003 (China); National Laboratory of Solid State Microstructure and School of Electronic Science and Engineering, Nanjing University, Nanjing 210093 (China); Xu, Ling, E-mail: xuling@nju.edu.cn [National Laboratory of Solid State Microstructure and School of Electronic Science and Engineering, Nanjing University, Nanjing 210093 (China); Wu, Yangqing; Xu, Jun; Ma, Zhongyuan; Chen, Kunji [National Laboratory of Solid State Microstructure and School of Electronic Science and Engineering, Nanjing University, Nanjing 210093 (China)

2016-11-30

Highlights: • CdTe/CdS quantum dots/Au nano-rods nano-composite films were fabricated. • PL intensity of the quantum dots films was enhanced due to Au nanorods. • Internal quantum efficiency increased due to localized surface plasmon resonance. • The lifetimes of quantum dots films decreased after interaction with Au nano-rods. - Abstract: CdTe/CdS quantum dots/Au nano-rods nano-composite films were fabricated on planar Si substrates. The optical properties of all samples were investigated and the corresponding simulations were studied. It was found that the photoluminescence intensity of the CdTe/CdS quantum dots films was enhanced about 9-fold after the incorporation of Au nano-rods, the internal quantum efficiency increased from 24.3% to 35.2% due to the localized surface plasmon resonance. The time-resolved luminescence decay curves showed that the lifetimes of CdTe/CdS quantum dots films decreased to 2.8 ns after interaction with Au nano-rods. The results of finite-difference time-domain simulation indicated that Au nano-rods induced the localization of electric field, which enhanced the PL intensity of quantum dots films in the vicinity of Au nano-rods.

Crystal habit dependent quantum confined photoluminescence of zinc oxide nanostructures

International Nuclear Information System (INIS)

Arellano, Ian Harvey J.; Payawan, Leon Jr. M.; Sarmago, Roland V.

2008-01-01

Diverse zinc oxide crystal habits namely wire, rods, tubes, whiskers and tetrapods were synthesized via hydrothermal and carbothermal reduction routes. A vapor current induced regionalization in the carbothermal synthesis lead to the isolation of these crystal habits for characterization. The surface morphology of the nanostructures was analyzed via field emission scanning electron microscopy (FESEM). The morphology and crystallinity of the as-synthesized nanostructure architectural motifs were related to their photoluminescence (PL). The photoluminescence at 157 nm was taken using F2 excimer laser and a crystal habit dependent response was observed. X-ray diffraction (XRD) analyses were conducted to deduce the degree of crystallinity showing results consistent with the excitonic emission at the band edge and visible emission at the electron-hole recombination sites. The presence of minimal crystal defects which gave the green emission was supported by energy dispersive spectroscopy (EDS) data. Transmission spectroscopy for the tetrapods exhibited an interesting PL reduction associated with high-energy deep traps in the nanostructures. Furthermore, some intensity dependent characteristics were deduced indicating quantum confined properties of these nano structures. (author)

Polarized Fine Structure in the Photoluminescence Excitation Spectrum of a Negatively Charged Quantum Dot

Science.gov (United States)

Ware, M. E.; Stinaff, E. A.; Gammon, D.; Doty, M. F.; Bracker, A. S.; Gershoni, D.; Korenev, V. L.; Bădescu, Ş. C.; Lyanda-Geller, Y.; Reinecke, T. L.

2005-10-01

We report polarized photoluminescence excitation spectroscopy of the negative trion in single charge-tunable InAs/GaAs quantum dots. The spectrum exhibits a p-shell resonance with polarized fine structure arising from the direct excitation of the electron spin triplet states. The energy splitting arises from the axially symmetric electron-hole exchange interaction. The magnitude and sign of the polarization are understood from the spin character of the triplet states and a small amount of quantum dot asymmetry, which mixes the wave functions through asymmetric e-e and e-h exchange interactions.

Investigation of reactive-ion-etch-induced damage of InP/InGaAs multiple quantum wells by photoluminescence

DEFF Research Database (Denmark)

Steffensen, O. M.; Birkedal, Dan; Hanberg, J.

1995-01-01

The effects of CH4/H2 reactive ion etching (RIE) on the optical properties of an InP/InGaAs multiple-quantum-well structure have been investigated by low-temperature photoluminescence (PL). The structure consisted of eight InGaAs quantum wells, lattice matched to InP, with nominal thicknesses of 0...

Photoluminescence and electroluminescence from Ge/strained GeSn/Ge quantum wells

Energy Technology Data Exchange (ETDEWEB)

Lin, Chung-Yi; Chang, Chih-Chiang [Department of Electrical Engineering, Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei 10617, Taiwan (China); Huang, Chih-Hsiung; Huang, Shih-Hsien [Department of Electrical Engineering, Graduate Institute of Electronics Engineering, National Taiwan University, Taipei 10617, Taiwan (China); Liu, C. W., E-mail: chee@cc.ee.ntu.edu.tw [Department of Electrical Engineering, Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei 10617, Taiwan (China); Department of Electrical Engineering, Graduate Institute of Electronics Engineering, National Taiwan University, Taipei 10617, Taiwan (China); National Nano Device Labs, Hsinchu 30077, Taiwan (China); Huang, Yi-Chiau; Chung, Hua; Chang, Chorng-Ping [Applied Materials Inc., Sunnyvale, California 94085 (United States)

2016-08-29

Ge/strained GeSn/Ge quantum wells are grown on a 300 mm Si substrate by chemical vapor deposition. The direct bandgap emission from strained GeSn is observed in the photoluminescence spectra and is enhanced by Al{sub 2}O{sub 3}/SiO{sub 2} passivation due to the field effect. The electroluminescence of the direct bandgap emission of strained GeSn is also observed from the Ni/Al{sub 2}O{sub 3}/GeSn metal-insulator-semiconductor tunneling diodes. Electroluminescence is a good indicator of GeSn material quality, since defects in GeSn layers degrade the electroluminescence intensity significantly. At the accumulation bias, the holes in the Ni gate electrode tunnel to the strained n-type GeSn layer through the ultrathin Al{sub 2}O{sub 3} and recombine radiatively with electrons. The emission wavelength of photoluminescence and electroluminescence can be tuned by the Sn content.

Impact of light polarization on photoluminescence intensity and quantum efficiency in AlGaN and AlInGaN layers

Science.gov (United States)

Netzel, C.; Knauer, A.; Weyers, M.

2012-12-01

We analyzed emission intensity, quantum efficiency, and emitted light polarization of c-plane AlGaN and AlInGaN layers (λ = 320-350 nm) by temperature dependent photoluminescence. Low indium content in AlInGaN structures causes a significant intensity increase by change of the polarization of the emitted light. Polarization changes from E ⊥ c to E ‖ c with increasing aluminum content. It switches back to E ⊥ c with the incorporation of indium. The polarization degree decreases with temperature. This temperature dependence can corrupt internal quantum efficiency determination by temperature dependent photoluminescence.

Photoluminescence properties of a novel conjugate of water-soluble CdTe quantum dots to guanine

Energy Technology Data Exchange (ETDEWEB)

Feng Xuejiao [North-East Normal University, Changchun 130024 (China); Shang, Qingkun, E-mail: shangqk995@nenu.edu.c [North-East Normal University, Changchun 130024 (China); Liu Hongjian [Relia Diagnostic Systems, Burlingame, CA 94010 (United States); Wang Wenlan; Wang Zhidan; Liu Junyu [North-East Normal University, Changchun 130024 (China)

2010-04-15

A novel conjugate of water-soluble CdTe quantum dots to a small biomolecule guanine has been obtained in aqueous phase. The photoluminescence property and the stability of the conjugate increased comparing to CdTe QDs. The interaction between CdTe QDs and guanine was studied by TEM, fluorescence microscope and photoluminescence (PL), IR, UV-Vis spectra. The effects of reflux time, pH value, ionic strength, and the ratio of CdTe QDs to guanine on the photoluminescence properties of conjugate were investigated in detail. The results show that guanine has a great influence on both the photoluminescence property and stability of thioglycolic acid-stabilized CdTe QDs. The formation of coordination and hydrogen bond between guanine molecules and CdTe including thioglycolic acid on its surface may effectively enhance the PL intensity and stability of CdTe QDs. The maximum PL intensity of the conjugate was obtained on the condition with lower ionic strength, less than 30 min reflux time, neutral pH value and 6/1 as molar ratio of guanine to CdTe.

Dewetting-Induced Photoluminescent Enhancement of Poly(lauryl methacrylate)/Quantum Dot Thin Films.

Science.gov (United States)

Geldmeier, Jeffrey; Rile, Lexy; Yoon, Young Jun; Jung, Jaehan; Lin, Zhiqun; Tsukruk, Vladimir V

2017-12-19

A new method for enhancing photoluminescence from quantum dot (QD)/polymer nanocomposite films is proposed. Poly(lauryl methacrylate) (PLMA) thin films containing embedded QDs are intentionally allowed to undergo dewetting on substrates by exposure to a nonsolvent vapor. After controlled dewetting, films exhibited typical dewetting morphologies with increased amounts of scattering that served to outcouple photoluminescence from the film and reduce internal light propagation within the film. Up to a 5-fold enhancement of the film emission was achieved depending on material factors such as the initial film thickness and QD concentration within the film. An increase in initial film thickness was shown to increase the dewetted maximum feature size and its characteristic length until a critical thickness was reached where dewetting became inhibited. A unique light exposure-based photopatterning method is also presented for the creation of high contrast emissive patterns as guided by spatially controlled dewetting.

Tuning the Photoluminescence of Graphene Quantum Dots by Photochemical Doping with Nitrogen

Directory of Open Access Journals (Sweden)

Xiaofen Xu

2017-11-01

Full Text Available Nitrogen-doped graphene quantum dots (NGQDs were synthesized by irradiating graphene quantum dots (GQDs in an NH3 atmosphere. The photoluminescence (PL properties of the GQDs and the NGQDs samples were investigated. Compared with GQDs, a clear PL blue-shift of NGQDs could be achieved by regulating the irradiating time. The NGQDs obtained by irradiation of GQDs for 70 min had a high N content of 15.34 at % and a PL blue-shift of about 47 nm. This may be due to the fact that photochemical doping of GQDs with nitrogen can significantly enhance the contents of pyridine-like nitrogen, and also effectively decrease the contents of oxygen functional groups of NGQDs, thus leading to the observed obvious PL blue-shift.

Photoluminescence of patterned CdSe quantum dot for anti-counterfeiting label on paper

International Nuclear Information System (INIS)

Isnaeni,; Yulianto, Nursidik; Suliyanti, Maria Margaretha

2016-01-01

We successfully developed a method utilizing colloidal CdSe nanocrystalline quantum dot for anti-counterfeiting label on a piece of glossy paper. We deposited numbers and lines patterns of toluene soluble CdSe quantum dot using rubber stamper on a glossy paper. The width of line pattern was about 1-2 mm with 1-2 mm separation between lines. It required less than one minute for deposited CdSe quantum dot on glossy paper to dry and become invisible by naked eyes. However, patterned quantum dot become visible using long-pass filter glasses upon excitation of UV lamp or blue laser. We characterized photoluminescence of line patterns of quantum dot, and we found that emission boundaries of line patterns were clearly observed. The error of line size and shape were mainly due to defect of the original stamper. The emission peak wavelength of CdSe quantum dot was 629 nm. The emission spectrum of deposited quantum dot has full width at half maximum (FWHM) of 30-40 nm. The spectra similarity between deposited quantum dot and the original quantum dot in solution proved that our stamping method can be simply applied on glossy paper without changing basic optical property of the quantum dot. Further development of this technique is potential for anti-counterfeiting label on very important documents or objects.

Photoluminescence of patterned CdSe quantum dot for anti-counterfeiting label on paper

Energy Technology Data Exchange (ETDEWEB)

Isnaeni,, E-mail: isnaeni@lipi.go.id; Yulianto, Nursidik; Suliyanti, Maria Margaretha [Research Center for Physics, Indonesian Institute of Sciences, Building 442, Kawasan Puspiptek, South Tangerang,Banten 15314 Indonesia (Indonesia)

2016-03-11

We successfully developed a method utilizing colloidal CdSe nanocrystalline quantum dot for anti-counterfeiting label on a piece of glossy paper. We deposited numbers and lines patterns of toluene soluble CdSe quantum dot using rubber stamper on a glossy paper. The width of line pattern was about 1-2 mm with 1-2 mm separation between lines. It required less than one minute for deposited CdSe quantum dot on glossy paper to dry and become invisible by naked eyes. However, patterned quantum dot become visible using long-pass filter glasses upon excitation of UV lamp or blue laser. We characterized photoluminescence of line patterns of quantum dot, and we found that emission boundaries of line patterns were clearly observed. The error of line size and shape were mainly due to defect of the original stamper. The emission peak wavelength of CdSe quantum dot was 629 nm. The emission spectrum of deposited quantum dot has full width at half maximum (FWHM) of 30-40 nm. The spectra similarity between deposited quantum dot and the original quantum dot in solution proved that our stamping method can be simply applied on glossy paper without changing basic optical property of the quantum dot. Further development of this technique is potential for anti-counterfeiting label on very important documents or objects.

Quantification of thyroxine by the selective photoluminescence quenching of L-cysteine–ZnS quantum dots in aqueous solution containing hexadecyltrimethylammonium bromide

International Nuclear Information System (INIS)

Khan, Sarzamin; Carneiro, Leonardo S.A.; Romani, Eric C.; Larrudé, Dunieskys G.; Aucelio, Ricardo Q.

2014-01-01

The determination of L-thyroxine is proposed based on the photoluminescence quenching effect caused on the L-cysteine modified ZnS quantum dots (L-cysteine ZnS QDs) aqueous dispersion. Under optimum conditions, the analytical response followed a Stern–Volmer model and the experimental conditions were adjusted to enable a robust and reproducible photoluminescence signal. The linear response observed in the quantum dots aqueous dispersion covered the L-thyroxine concentration from the LOQ (2.0×10 −8 mol L −1 ) to 4.0×10 −6 mol L −1 . The approach was tested in the determination of L-thyroxine in pharmaceutical formulations used to treat patients with thyroid gland disorder. The percent recoveries in controlled samples were between 93.3 and 103%. Analyte fortified saliva was also evaluated as a possible sample for L-thyroxine monitoring of a patient under treatment. It was identified a static type of photoluminescence quenching caused by L-thyroxine. - Highlights: • L-cysteine ZnS QDs were used as a photoluminescent probe to detect L-thyroxine. • Intensity of probe decreases following a Stern–Volmer model. • The method can detect down ng L −1 levels of L-thyroxine in the probe dispersion. • Method was used to determinate of L-thyroxine in saliva and in pharmaceuticals. • Mechanism of interaction between L-thyroxine and quantum dots was studied

Combined atomic force microscopy and photoluminescence imaging to select single InAs/GaAs quantum dots for quantum photonic devices.

Science.gov (United States)

Sapienza, Luca; Liu, Jin; Song, Jin Dong; Fält, Stefan; Wegscheider, Werner; Badolato, Antonio; Srinivasan, Kartik

2017-07-24

We report on a combined photoluminescence imaging and atomic force microscopy study of single, isolated self-assembled InAs quantum dots. The motivation of this work is to determine an approach that allows to assess single quantum dots as candidates for quantum nanophotonic devices. By combining optical and scanning probe characterization techniques, we find that single quantum dots often appear in the vicinity of comparatively large topographic features. Despite this, the quantum dots generally do not exhibit significant differences in their non-resonantly pumped emission spectra in comparison to quantum dots appearing in defect-free regions, and this behavior is observed across multiple wafers produced in different growth chambers. Such large surface features are nevertheless a detriment to applications in which single quantum dots are embedded within nanofabricated photonic devices: they are likely to cause large spectral shifts in the wavelength of cavity modes designed to resonantly enhance the quantum dot emission, thereby resulting in a nominally perfectly-fabricated single quantum dot device failing to behave in accordance with design. We anticipate that the approach of screening quantum dots not only based on their optical properties, but also their surrounding surface topographies, will be necessary to improve the yield of single quantum dot nanophotonic devices.

Photoluminescence related to Gd3+:N-vacancy complex in GaN:Gd multi-quantum wells

International Nuclear Information System (INIS)

Almokhtar, Mohamed; Emura, Shuichi; Koide, Akihiro; Fujikawa, Takashi; Asahi, Hajime

2015-01-01

Highlights: • We grew Gd-doped GaN multi-quantum wells (MQWs) with quantum layer thickness of one nm by MBE. • The X-ray absorption near edge structure spectra observed at Gd LIII-edge indicate a nitrogen vacancy adjacent to Gd substituting the Ga ion in Gd-doped GaN MQW. • The photoluminescence of the samples is discussed considering the formation of a Gd 3+ :Nitrogen-vacancy complex. • A model is presented considering exciton-polaron formation trapped in defect sites around the Gd 3+ :N-vacancy complex in Gd-doped GaN MQWs. - Abstract: The photoluminescence of Gd-doped GaN multi-quantum wells (MQWs) is presented and discussed considering the formation of a Gd 3+ :Nitrogen-vacancy (N-vacancy) complex. A lower energy photoluminescence peak was observed for the Gd-doped GaN MQW sample with respect to the main peak assigned to a neutral donor bound exciton (D 0 X) of the undoped GaN MQW sample. The X-ray absorption near edge structure spectrum observed at Gd L III -edge indicates a nitrogen vacancy adjacent to the Gd substituting the Ga ion in Gd-doped GaN MQW sample. Local stresses around the Gd dopants in Gd-doped GaN matrix generated due to the larger diameter of the Gd 3+ ion with respect to the Ga 3+ ion can be relieved by the creation of vacancies. The lower formation energy of N-vacancies in GaN matrix introduce them as a preferred candidate to relieve the generated stresses. A Gd 3+ :N-vacancy complex consisting of a Gd 3+ ion and the created nitrogen vacancy adjacent to the Gd 3+ dopant is likely to form in GaN:Gd matrix. The lower photoluminescence peak energy observed in the Gd-doped GaN MQW sample is assigned to the recombination of an exciton captured at the Gd 3+ :N-vacancy complex forming a small polaron-like state. A model is presented considering the small exciton-polaron population in defect sites captured around the Gd 3+ ions in the Gd-doped GaN

Enhanced quantum yield of photoluminescent porous silicon prepared by supercritical drying

Energy Technology Data Exchange (ETDEWEB)

Joo, Jinmyoung [Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093 (United States); Biomedical Engineering Research Center, Asan Institute for Life Sciences, Asan Medical Center, University of Ulsan College of Medicine, Seoul 05505 (Korea, Republic of); Defforge, Thomas; Gautier, Gael, E-mail: msailor@ucsd.edu, E-mail: gael.gautier@univ-tours.fr, E-mail: lcanham@psivida.com [Universite Francois Rabelais de Tours, CNRS CEA, INSA-CVL, GREMAN UMR 7347, 37071 Tours Cedex 2 (France); Loni, Armando [pSiMedica Ltd., Malvern Hills Science Park, Geraldine Road, Malvern, Worcestershire WR14 3SZ (United Kingdom); Kim, Dokyoung; Sailor, Michael J., E-mail: msailor@ucsd.edu, E-mail: gael.gautier@univ-tours.fr, E-mail: lcanham@psivida.com [Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093 (United States); Li, Z. Y. [Nanoscale Physics Research Laboratory, School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT (United Kingdom); Canham, Leigh T., E-mail: msailor@ucsd.edu, E-mail: gael.gautier@univ-tours.fr, E-mail: lcanham@psivida.com [pSiMedica Ltd., Malvern Hills Science Park, Geraldine Road, Malvern, Worcestershire WR14 3SZ (United Kingdom); Nanoscale Physics Research Laboratory, School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT (United Kingdom)

2016-04-11

The effect of supercritical drying (SCD) on the preparation of porous silicon (pSi) powders has been investigated in terms of photoluminescence (PL) efficiency. Since the pSi contains closely spaced and possibly interconnected Si nanocrystals (<5 nm), pore collapse and morphological changes within the nanocrystalline structure after common drying processes can affect PL efficiency. We report the highly beneficial effects of using SCD for preparation of photoluminescent pSi powders. Significantly higher surface areas and pore volumes have been realized by utilizing SCD (with CO{sub 2} solvent) instead of air-drying. Correspondingly, the pSi powders better retain the porous structure and the nano-sized silicon grains, thus minimizing the formation of non-radiative defects during liquid evaporation (air drying). The SCD process also minimizes capillary-stress induced contact of neighboring nanocrystals, resulting in lower exciton migration levels within the network. A significant enhancement of the PL quantum yield (>32% at room temperature) has been achieved, prompting the need for further detailed studies to establish the dominant causes of such an improvement.

Efficiency droop suppression of distance-engineered surface plasmon-coupled photoluminescence in GaN-based quantum well LEDs

Directory of Open Access Journals (Sweden)

Yufeng Li

2017-11-01

Full Text Available Ag coated microgroove with extreme large aspect-ratio of 500:1 was fabricated on p-GaN capping layer to investigate the coupling behavior between quantum wells and surface plasmon in highly spatial resolution. Significant photoluminescence enhancement was observed when the distance between Ag film and QWs was reduced from 220 nm to about 20 nm. A maximum enhancement ratio of 18-fold was achieved at the groove bottom where the surface plasmonic coupling was considered the strongest. Such enhancement ratio was found highly affected by the excitation power density. It also shows high correlation to the internal quantum efficiency as a function of coupling effect and a maximum Purcell Factor of 1.75 was estimated at maximum coupling effect, which matches number calculated independently from the time-resolved photoluminescence measurement. With such Purcell Factor, the efficiency was greatly enhanced and the droop was significantly suppressed.

Quantification of thyroxine by the selective photoluminescence quenching of L-cysteine–ZnS quantum dots in aqueous solution containing hexadecyltrimethylammonium bromide

Energy Technology Data Exchange (ETDEWEB)

Khan, Sarzamin; Carneiro, Leonardo S.A. [Chemistry Department, Pontifícia Universidade Católica do Rio de Janeiro, 22451-900 Rio de Janeiro-RJ (Brazil); Romani, Eric C.; Larrudé, Dunieskys G. [Physics Department, Pontifícia Universidade Católica do Rio de Janeiro, 22451-900, Rio de Janeiro-RJ (Brazil); Aucelio, Ricardo Q., E-mail: aucelior@puc-rio.br [Chemistry Department, Pontifícia Universidade Católica do Rio de Janeiro, 22451-900 Rio de Janeiro-RJ (Brazil)

2014-12-15

The determination of L-thyroxine is proposed based on the photoluminescence quenching effect caused on the L-cysteine modified ZnS quantum dots (L-cysteine ZnS QDs) aqueous dispersion. Under optimum conditions, the analytical response followed a Stern–Volmer model and the experimental conditions were adjusted to enable a robust and reproducible photoluminescence signal. The linear response observed in the quantum dots aqueous dispersion covered the L-thyroxine concentration from the LOQ (2.0×10{sup −8} mol L{sup −1}) to 4.0×10{sup −6} mol L{sup −1}. The approach was tested in the determination of L-thyroxine in pharmaceutical formulations used to treat patients with thyroid gland disorder. The percent recoveries in controlled samples were between 93.3 and 103%. Analyte fortified saliva was also evaluated as a possible sample for L-thyroxine monitoring of a patient under treatment. It was identified a static type of photoluminescence quenching caused by L-thyroxine. - Highlights: • L-cysteine ZnS QDs were used as a photoluminescent probe to detect L-thyroxine. • Intensity of probe decreases following a Stern–Volmer model. • The method can detect down ng L{sup −1} levels of L-thyroxine in the probe dispersion. • Method was used to determinate of L-thyroxine in saliva and in pharmaceuticals. • Mechanism of interaction between L-thyroxine and quantum dots was studied.

Excitation density dependence of the photoluminescence from Cd{sub x}Hg{sub 1-x}Te multiple quantum wells

Energy Technology Data Exchange (ETDEWEB)

Tonheim, C R; Selvig, E; Nicolas, S; Breivik, M; Haakenaasen, R [Norwegian Defence Research Establishment, PO Box 25, N-2027 Kjeller (Norway); Gunnaes, A E [Department of Physics, University of Oslo, Boks 1048 Blindern, N-0316 Oslo (Norway)], E-mail: celin.tonheim@ffi.no

2008-03-15

A study of the photoluminescence from a four-period Cd{sub x}Hg{sub 1-x}Te multiple quantum well structure at 11 K as a function of excitation density is presented. High-resolution X-ray diffraction and transmission electron microscopy revealed that the quantum well structure is of high quality. This was supported by the narrow photoluminescence peak originating in the ground state electron - heavy hole transition, with a full width at half maximum of only 7.4 meV for an excitation density of 1.3 W/cm{sup 2}. When the excitation density was increased from 1.3 to 23.4 W/cm{sup 2}, the peak position was shifted toward higher energy by 2.6 meV and the full width at half maximum increased from 7.4 to 10.9 meV.

Excitation dependence of photoluminescence in silicon quantum dots

International Nuclear Information System (INIS)

Wen Xiaoming; Lap Van Dao; Hannaford, Peter; Cho, E-C; Cho, Young H; Green, Martin A

2007-01-01

We have studied the optical properties of silicon quantum dots (QDs) embedded in a silicon oxide matrix using photoluminescence (PL) and time-resolved PL. A broad luminescence band is observed in the red region, in which the time evolution exhibits a stretched exponential decay. With increasing excitation intensity a significant saturation effect is observed. Direct electron-hole recombination is the dominant effect in the red band. A relatively narrow peak appears around 1.5 eV, which is attributed to the interface states overlapping with transition from the ground state of the silicon QDs. The saturation factor increases slowly with detection photon energy between 1.5 and 1.8 eV, which is attributed to the emission from zero-phonon electron-hole recombination. At higher photon energies the significantly increased saturation factor suggests a different emission mechanism, most likely the defect states from silicon, silicon oxide or silicon rich oxide

Photoluminescence and magnetophotoluminescence studies in GaInNAs/GaAs quantum wells

Science.gov (United States)

Segura, J.; Garro, N.; Cantarero, A.; Miguel-Sánchez, J.; Guzmán, A.; Hierro, A.

2007-04-01

We investigate the effects of electron and hole localization in the emission of a GaInNAs/GaAs single quantum well at low temperatures. Photoluminescence measurements varying the excitation density and under magnetic fields up to 14 T have been carried out. The results indicate that electrons are strongly localized in these systems due to small fluctuations in the nitrogen content of the quaternary alloy. The low linear diamagnetic shift of the emission points out the weakness of the Coulomb correlation between electrons and holes and suggests an additional partial localization of the holes.

Exploration of CdTe quantum dots as mesoscale pressure sensors via time-resolved shock-compression photoluminescent emission spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Kang, Zhitao [Georgia Tech Research Institute, Georgia Institute of Technology, Atlanta, Georgia 30332-0826 (United States); School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0245 (United States); Banishev, Alexandr A.; Christensen, James; Dlott, Dana D. [School of Chemical Sciences and Fredrick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Lee, Gyuhyon; Scripka, David A.; Breidenich, Jennifer; Summers, Christopher J.; Thadhani, Naresh N., E-mail: naresh.thadhani@mse.gatech.edu [School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0245 (United States); Xiao, Pan [LNM, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190 (China); George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0405 (United States); Zhou, Min [George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0405 (United States)

2016-07-28

The nanometer size of CdTe quantum dots (QDs) and their unique optical properties, including size-tunable narrow photoluminescent emission, broad absorption, fast photoluminescence decay, and negligible light scattering, are ideal features for spectrally tagging the shock response of localized regions in highly heterogeneous materials such as particulate media. In this work, the time-resolved laser-excited photoluminescence response of QDs to shock-compression was investigated to explore their utilization as mesoscale sensors for pressure measurements and in situ diagnostics during shock loading experiments. Laser-driven shock-compression experiments with steady-state shock pressures ranging from 2.0 to 13 GPa were performed on nanocomposite films of CdTe QDs dispersed in a soft polyvinyl alcohol polymer matrix and in a hard inorganic sodium silicate glass matrix. Time-resolved photoluminescent emission spectroscopy was used to correlate photoluminescence changes with the history of shock pressure and the dynamics of the matrix material surrounding the QDs. The results revealed pressure-induced blueshifts in emitted wavelength, decreases in photoluminescent emission intensity, reductions in peak width, and matrix-dependent response times. Data obtained for these QD response characteristics serve as indicators for their use as possible time-resolved diagnostics of the dynamic shock-compression response of matrix materials in which such QDs are embedded as in situ sensors.

Exploration of CdTe quantum dots as mesoscale pressure sensors via time-resolved shock-compression photoluminescent emission spectroscopy

International Nuclear Information System (INIS)

Kang, Zhitao; Banishev, Alexandr A.; Christensen, James; Dlott, Dana D.; Lee, Gyuhyon; Scripka, David A.; Breidenich, Jennifer; Summers, Christopher J.; Thadhani, Naresh N.; Xiao, Pan; Zhou, Min

2016-01-01

The nanometer size of CdTe quantum dots (QDs) and their unique optical properties, including size-tunable narrow photoluminescent emission, broad absorption, fast photoluminescence decay, and negligible light scattering, are ideal features for spectrally tagging the shock response of localized regions in highly heterogeneous materials such as particulate media. In this work, the time-resolved laser-excited photoluminescence response of QDs to shock-compression was investigated to explore their utilization as mesoscale sensors for pressure measurements and in situ diagnostics during shock loading experiments. Laser-driven shock-compression experiments with steady-state shock pressures ranging from 2.0 to 13 GPa were performed on nanocomposite films of CdTe QDs dispersed in a soft polyvinyl alcohol polymer matrix and in a hard inorganic sodium silicate glass matrix. Time-resolved photoluminescent emission spectroscopy was used to correlate photoluminescence changes with the history of shock pressure and the dynamics of the matrix material surrounding the QDs. The results revealed pressure-induced blueshifts in emitted wavelength, decreases in photoluminescent emission intensity, reductions in peak width, and matrix-dependent response times. Data obtained for these QD response characteristics serve as indicators for their use as possible time-resolved diagnostics of the dynamic shock-compression response of matrix materials in which such QDs are embedded as in situ sensors.

Influence of near-field coupling from Ag surface plasmons on InGaN/GaN quantum-well photoluminescence

DEFF Research Database (Denmark)

Fadil, Ahmed; Iida, Daisuke; Chen, Yuntian

2016-01-01

We have investigated the borderline between photoluminescence quenching and enhancement of InGaN/GaN quantum-wells due to Ag nanoparticles and their surface plasmon modes. By embedding Ag nanoparticles inside nanohole structures on the p-type layer GaN, luminescence quenching is observed...

Photoluminescence of a single InAs/AlAs quantum dot

International Nuclear Information System (INIS)

Shamirzaev, T.S.; Zhuravlev, K.S.; Larsson, M.; Holtz, P.O.

2008-01-01

Micro-photoluminescence (μ-PL) of a simple InAs/AlAs quantum dot (QD) has been studied. It has been found that the μ-PL emission related to the recombination in a single QD is strongly broadened probably due to spectral diffusion. Emissions related to the recombination of biexcitons and excitons occupying excited levels of the QD are observed in μ-PL spectra at high excitation power densities. A red shift of the μ-PL emissions related to recombination of excitons in the ground and excited levels of the QD with increasing excitation power gives clear evidence for type I alignment of the InAs/AlAs QD. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

On determining absolute entropy without quantum theory or the third law of thermodynamics

Science.gov (United States)

Steane, Andrew M.

2016-04-01

We employ classical thermodynamics to gain information about absolute entropy, without recourse to statistical methods, quantum mechanics or the third law of thermodynamics. The Gibbs-Duhem equation yields various simple methods to determine the absolute entropy of a fluid. We also study the entropy of an ideal gas and the ionization of a plasma in thermal equilibrium. A single measurement of the degree of ionization can be used to determine an unknown constant in the entropy equation, and thus determine the absolute entropy of a gas. It follows from all these examples that the value of entropy at absolute zero temperature does not need to be assigned by postulate, but can be deduced empirically.

Femtosecond pulsed laser ablation in microfluidics for synthesis of photoluminescent ZnSe quantum dots

Energy Technology Data Exchange (ETDEWEB)

Yang, Chao, E-mail: chaoyangscu@gmail.com [College of Electronics and Information Engineering, Sichuan University, No. 24 South Section 1, 1st Ring Road, Chengdu 610064 (China); Feng, Guoying, E-mail: guoing_feng@scu.edu.cn [College of Electronics and Information Engineering, Sichuan University, No. 24 South Section 1, 1st Ring Road, Chengdu 610064 (China); Dai, Shenyu, E-mail: 232127079@qq.com [College of Electronics and Information Engineering, Sichuan University, No. 24 South Section 1, 1st Ring Road, Chengdu 610064 (China); Wang, Shutong, E-mail: wangshutong.scu@gmail.com [College of Electronics and Information Engineering, Sichuan University, No. 24 South Section 1, 1st Ring Road, Chengdu 610064 (China); Li, Guang, E-mail: 632524844@qq.com [College of Electronics and Information Engineering, Sichuan University, No. 24 South Section 1, 1st Ring Road, Chengdu 610064 (China); Zhang, Hua [College of Electronics and Information Engineering, Sichuan University, No. 24 South Section 1, 1st Ring Road, Chengdu 610064 (China); Zhou, Shouhuan, E-mail: zhoush@scu.edu.cn [College of Electronics and Information Engineering, Sichuan University, No. 24 South Section 1, 1st Ring Road, Chengdu 610064 (China); North China Research Institute of Electro-Optics, 4 Jiuxianqiao Street, Chaoyang District, Beijing 100015 (China)

2017-08-31

Highlights: • A novel method for synthesis and coating of quantum dots by ultrafast laser pulses. • Mild and “green” synthesis method without toxic chemicals. • Enhanced bright green light emission without doped transition metal ions. • Ultrafast laser and coating layer enhanced the emission originated from defects. - Abstract: A simple but new toxic chemical free method, Femtosecond Laser Ablation in Microfluidics (FLAM) was proposed for the first time. ZnSe quantum dots of 4–6 nm were synthesized and with the use of hyperbranched Polyethyleneimine (PEI) as both structural and functional coated layer. These aqueous nanosized micelles consisting of quantum dots exhibit deep defect states emission of bright green light centered at 500 nm. A possible mechanism for the enhanced board band emission was discussed. The properties of toxic matters free and enhanced photoluminescence without doped transition metal ions demonstrate an application potential for biomedical imaging.

Femtosecond pulsed laser ablation in microfluidics for synthesis of photoluminescent ZnSe quantum dots

International Nuclear Information System (INIS)

Yang, Chao; Feng, Guoying; Dai, Shenyu; Wang, Shutong; Li, Guang; Zhang, Hua; Zhou, Shouhuan

2017-01-01

Highlights: • A novel method for synthesis and coating of quantum dots by ultrafast laser pulses. • Mild and “green” synthesis method without toxic chemicals. • Enhanced bright green light emission without doped transition metal ions. • Ultrafast laser and coating layer enhanced the emission originated from defects. - Abstract: A simple but new toxic chemical free method, Femtosecond Laser Ablation in Microfluidics (FLAM) was proposed for the first time. ZnSe quantum dots of 4–6 nm were synthesized and with the use of hyperbranched Polyethyleneimine (PEI) as both structural and functional coated layer. These aqueous nanosized micelles consisting of quantum dots exhibit deep defect states emission of bright green light centered at 500 nm. A possible mechanism for the enhanced board band emission was discussed. The properties of toxic matters free and enhanced photoluminescence without doped transition metal ions demonstrate an application potential for biomedical imaging.

Violet-to-Blue Gain and Lasing from Colloidal CdS Nanoplatelets: Low-Threshold Stimulated Emission Despite Low Photoluminescence Quantum Yield

Energy Technology Data Exchange (ETDEWEB)

Diroll, Benjamin T.; Talapin, Dmitri V.; Schaller, Richard D.

2017-02-13

Amplified spontaneous emission (ASE) and lasing from solution-processed materials are demonstrated in the challenging violet-to-blue (430–490 nm) spectral region for colloidal nanoplatelets of CdS and newly synthesized core/shell CdS/ZnS nanoplatelets. Despite modest band-edge photoluminescence quantum yields of 2% or less for single excitons, which we show results from hole trapping, the samples exhibit low ASE thresholds. Furthermore, four-monolayer CdS samples show ASE at shorter wavelengths than any reported film of colloidal quantum-confined material. This work underlines that low quantum yields for single excitons do not necessarily lead to a poor gain medium. The low ASE thresholds originate from negligible dispersion in thickness, large absorption cross sections of 2.8 × 10–14 cm–2, and rather slow (150 to 300 ps) biexciton recombination. We show that under higher-fluence excitation, ASE can kinetically outcompete hole trapping. Using nanoplatelets as the gain medium, lasing is observed in a linear optical cavity. This work confirms the fundamental advantages of colloidal quantum well structures as gain media, even in the absence of high photoluminescence efficiency.

Surface photovoltage and photoluminescence spectroscopy of self-assembled InAs/InP quantum wires

International Nuclear Information System (INIS)

Donchev, V; Ivanov, T S; Borisov, K; Angelova, T; Cros, A; Cantarero, A; Fuster, D; Shtinkov, N; Gonzalez, Y; Gonzalez, L

2010-01-01

The optical properties of InAs/InP multi-layer quantum wire (QWR) structures of various spacer thicknesses have been investigated by means of room temperature surface photovoltage and photoluminescence spectroscopy. Combined with empirical tight binding calculations, the spectra have revealed transitions assigned to QWR families with heights equal to integer number of 5, 6 and 7 monolayers. From the comparison of the experimental and theoretical results the atomic concentration of phosphorus in the wires has been estimated.

Surface photovoltage and photoluminescence spectroscopy of self-assembled InAs/InP quantum wires

Science.gov (United States)

Donchev, V.; Ivanov, T. S.; Angelova, T.; Cros, A.; Cantarero, A.; Shtinkov, N.; Borisov, K.; Fuster, D.; González, Y.; González, L.

2010-02-01

The optical properties of InAs/InP multi-layer quantum wire (QWR) structures of various spacer thicknesses have been investigated by means of room temperature surface photovoltage and photoluminescence spectroscopy. Combined with empirical tight binding calculations, the spectra have revealed transitions assigned to QWR families with heights equal to integer number of 5, 6 and 7 monolayers. From the comparison of the experimental and theoretical results the atomic concentration of phosphorus in the wires has been estimated.

Chemical sensitivity of InP/In0.48Ga0.52P surface quantum dots studied by time-resolved photoluminescence spectroscopy

International Nuclear Information System (INIS)

De Angelis, Roberta; Casalboni, Mauro; De Matteis, Fabio; Hatami, Fariba; Masselink, William T.; Zhang, Hong; Prosposito, Paolo

2015-01-01

InP/InGaP surface quantum dots represent an attractive material for optical chemical sensors since they show a remarkable near infra-red emission at room temperature, whose intensity increases rapidly and reversibly depending on the composition of the environmental atmosphere. We show here their emission properties by time resolved photoluminescence spectroscopy investigation. Photoluminescence transients with and without chemical solvent vapours (methanol, clorophorm, acetone and water) were fitted with a 3-exponential decay law with times of about 0.5 ns, 2 ns and 7 ns. The measurements revealed a weak effect on clorophorm, acetone and water, while the initial decay time of InP surface quantum dots increases (up to 15%) upon methanol vapour exposure, indicating that the organic molecules efficiently saturate QD non-radiative surface states. - Highlights: • InP SQDs emission depends on the presence of solvent vapours in the atmosphere. • TR photoluminescence transients were fitted with a 3-exponential decay law. • The initial decay time increases (up to 15%) upon methanol vapour exposure. • Organic molecules efficiently saturate QD non-radiative surface states.

Photoluminescence as a tool for characterizing point defects in semiconductors

Science.gov (United States)

Reshchikov, Michael

2012-02-01

Photoluminescence is one of the most powerful tools used to study optically-active point defects in semiconductors, especially in wide-bandgap materials. Gallium nitride (GaN) and zinc oxide (ZnO) have attracted considerable attention in the last two decades due to their prospects in optoelectronics applications, including blue and ultraviolet light-emitting devices. However, in spite of many years of extensive studies and a great number of publications on photoluminescence from GaN and ZnO, only a few defect-related luminescence bands are reliably identified. Among them are the Zn-related blue band in GaN, Cu-related green band and Li-related orange band in ZnO. Numerous suggestions for the identification of other luminescence bands, such as the yellow band in GaN, or green and yellow bands in ZnO, do not stand up under scrutiny. In these conditions, it is important to classify the defect-related luminescence bands and find their unique characteristics. In this presentation, we will review the origin of the major luminescence bands in GaN and ZnO. Through simulations of the temperature and excitation intensity dependences of photoluminescence and by employing phenomenological models we are able to obtain important characteristics of point defects such as carrier capture cross-sections for defects, concentrations of defects, and their charge states. These models are also used to find the absolute internal quantum efficiency of photoluminescence and obtain information about nonradiative defects. Results from photoluminescence measurements will be compared with results of the first-principle calculations, as well as with the experimental data obtained by other techniques such as positron annihilation spectroscopy, deep-level transient spectroscopy, and secondary ion mass spectrometry.

The relation between photoluminescence properties and gas pressure with [0001] InGaN single quantum well systems

Energy Technology Data Exchange (ETDEWEB)

Tsutsumi, Toshiaki [Department of Nanosystem Sciences, Yokohama City University, Yokohama 236-0027 (Japan); Alfieri, Giovanni; Kawakami, Yoichi [Department of Electronic Science and Engineering, Kyoto University, Kyotodaigaku-katsura, Nishikyo, Kyoto 615-8510 (Japan); Micheletto, Ruggero, E-mail: ruggero@yokohama-cu.ac.jp [Department of Nanosystem Sciences, Yokohama City University, Yokohama 236-0027 (Japan)

2017-01-15

Highlights: • Photoluminescence of InGaN device is variable, there is no clear explanation for this. • We perform an ad-hoc absorption procedure, found that gases on the surface reduce emission. • We found that variability is related to the pressure of the gas in which the sample is immersed. • We point out the role of oxygen as major player in the reduction of photoluminescence. • A model is proposed and explains successfully the dynamical optical processes observed. - Abstract: We show for the first time that photoluminescence of InGaN single quantum wells (SQW) devices is related to the gas pressure in which the sample is immersed, also we give a model of the phenomena to suggest a possible cause. Our model shows a direct relation between experimental behavior and molecular coverage dynamics. This strongly suggests that the driving force of photoluminescence decrease is oxygen covering the surface of the device with a time dynamics that depends on the gas pressure. This aims to contribute to the understanding of the physical mechanism of the so-called optical memory effect and blinking phenomenon observed in these devices.

Photoluminescence up-conversion in five Inx(Al0.17Ga0.83)1-xAs/ Al0.17Ga0.83As quantum wells with different x values

DEFF Research Database (Denmark)

Machida, S.; Tadakuma, T.; Satake, A.

Photoluminescence (PL) up-conversion in a unique system with five different quantum wells has been investigated. Anti-Stokes PL intensity observed shows dramatic dependence on where carriers are resonantly photoexcited, indicating nonlinear processes with spatial position dependence.......Photoluminescence (PL) up-conversion in a unique system with five different quantum wells has been investigated. Anti-Stokes PL intensity observed shows dramatic dependence on where carriers are resonantly photoexcited, indicating nonlinear processes with spatial position dependence....

Quantum efficiency of silica-coated rare-earth doped yttrium silicate

International Nuclear Information System (INIS)

Cervantes-Vásquez, D.; Contreras, O.E.; Hirata, G.A.

2013-01-01

The photoluminescent properties of rare earth-activated white-emitting Y 2 SiO 5 :Ce,Tb nanocrystalline phosphor prepared by two different methods, pressure-assisted combustion synthesis and sol–gel, were studied. The synthesized phosphor samples were post-annealed at 1373 K and 1623 K in order to obtain the X1-Y 2 SiO 5 and X2-Y 2 SiO 5 phases, respectively, which were confirmed by X-ray diffraction measurements. Photoluminescence analysis showed the contribution of two blue-emission bands within the 380–450 nm region originating from 5d–4f transitions in Ce 3+ ions and a well-defined green emission of Tb 3+ ions located at 545 nm corresponding to 5 D 4 → 7 F 5 electronic transitions. Thereafter, Y 2 SiO 5 :Ce,Tb powders were coated with colloidal silica in order to investigate the effect of silica coatings on their luminescent properties. Absolute fluorescence quantum efficiency measurements were carefully performed, which revealed an increase of 12% of efficiency in coated compared with bare-Y 2 SiO 5 :Ce,Tb phosphor. -- Highlights: • Y 2 SiO 5 :Ce,Tb phosphor powders were successfully coated with colloidal silica. • Post-annealing treatments improved the quantum efficiency of silica-coated Y 2 SiO 5 :Ce,Tb phosphors. • Absolute fluorescence quantum efficiency measurements showed an increase of 12%

Blue photoluminescent carbon nanodots from limeade

Energy Technology Data Exchange (ETDEWEB)

Suvarnaphaet, Phitsini [Department of Physics, Faculty of Science, Mahidol University, Bangkok 10400 (Thailand); ThEP Center, Commission of Higher Education, 328 Si Ayuthaya Rd (Thailand); Tiwary, Chandra Sekhar [Department of Materials Science and Nano Engineering, Rice University, Houston, TX 7005 (United States); Wetcharungsri, Jutaphet; Porntheeraphat, Supanit [NECTEC, National Science and Technology Development Agency (NSTDA), Thailand Science Park, Pathumthani 12120 (Thailand); Hoonsawat, Rassmidara [Department of Physics, Faculty of Science, Mahidol University, Bangkok 10400 (Thailand); ThEP Center, Commission of Higher Education, 328 Si Ayuthaya Rd (Thailand); Ajayan, Pulickel Madhavapanicker [Department of Materials Science and Nano Engineering, Rice University, Houston, TX 7005 (United States); Tang, I-Ming [Department of Physics, Faculty of Science, Mahidol University, Bangkok 10400 (Thailand); Department of Material Science, Faculty of Science, Kasetsart University, Bangkok 10400 (Thailand); ThEP Center, Commission of Higher Education, 328 Si Ayuthaya Rd (Thailand); Asanithi, Piyapong, E-mail: asanithi@hotmail.com [Department of Physics, Faculty of Science, King Mongkut' s University of Technology Thonburi, Bangkok 10140 (Thailand); ThEP Center, Commission of Higher Education, 328 Si Ayuthaya Rd (Thailand)

2016-12-01

Carbon-based photoluminescent nanodot has currently been one of the promising materials for various applications. The remaining challenges are the carbon sources and the simple synthetic processes that enhance the quantum yield, photostability and biocompatibility of the nanodots. In this work, the synthesis of blue photoluminescent carbon nanodots from limeade via a single-step hydrothermal carbonization process is presented. Lime carbon nanodot (L-CnD), whose the quantum yield exceeding 50% for the 490 nm emission in gram-scale amounts, has the structure of graphene core functionalized with the oxygen functional groups. The micron-sized flake of the as-prepared L-CnD powder exhibits multicolor emission depending on an excitation wavelength. The L-CnDs are demonstrated for rapidly ferric-ion (Fe{sup 3+}) detection in water compared to Fe{sup 2+}, Cu{sup 2+}, Co{sup 2+}, Zn{sup 2+}, Mn{sup 2+} and Ni{sup 2+} ions. The photoluminescence quenching of L-CnD solution under UV light is used to distinguish the Fe{sup 3+} ions from others by naked eyes as low concentration as 100 μM. Additionally, L-CnDs provide exceptional photostability and biocompatibility for imaging yeast cell morphology. Changes in morphology of living yeast cells, i.e. cell shape variation, and budding, can be observed in a minute-period until more than an hour without the photoluminescent intensity loss. - Highlights: • Photoluminescent carbon nanodots are synthesized from limeade. • The quantum yield of lime carbon nanodots is higher than 50%. • The lime carbon nanodots can be applied for detecting of Fe{sup 3+} ions and for imaging living yeast cells.

Enhancement of photoluminescence from GaInNAsSb quantum wells upon annealing: improvement of material quality and carrier collection by the quantum well

International Nuclear Information System (INIS)

Baranowski, M; Kudrawiec, R; Latkowska, M; Syperek, M; Misiewicz, J; Sarmiento, T; Harris, J S

2013-01-01

In this study we apply time resolved photoluminescence and contactless electroreflectance to study the carrier collection efficiency of a GaInNAsSb/GaAs quantum well (QW). We show that the enhancement of photoluminescence from GaInNAsSb quantum wells annealed at different temperatures originates not only from (i) the improvement of the optical quality of the GaInNAsSb material (i.e., removal of point defects, which are the source of nonradiative recombination) but it is also affected by (ii) the improvement of carrier collection by the QW region. The total PL efficiency is the product of these two factors, for which the optimal annealing temperatures are found to be ∼700 °C and ∼760 °C, respectively, whereas the optimal annealing temperature for the integrated PL intensity is found to be between the two temperatures and equals ∼720 °C. We connect the variation of the carrier collection efficiency with the modification of the band bending conditions in the investigated structure due to the Fermi level shift in the GaInNAsSb layer after annealing.

Green and fast synthesis of amino-functionalized graphene quantum dots with deep blue photoluminescence

Energy Technology Data Exchange (ETDEWEB)

Blanco, E., E-mail: eduardo.blanco@uca.es; Blanco, G.; Gonzalez-Leal, J. M.; Barrera, M. C.; Domínguez, M.; Ramirez-del-Solar, M. [University of Cádiz, Institute of Electron Microscopy and Materials (Spain)

2015-05-15

Graphene quantum dots (GQDs) were prepared using a top-down approach with a green microwave-assisted hydrothermal synthesis from ultrathin graphite, previously ultrasound delaminated. Results obtained by transmission electron microscopy and atomic force microscopy indicate that the so-fabricated GQDs are plates with 6 nm of average diameter, mostly single- or bi-layered. Photoluminescence characterization shows that the strongest emission occurs at 410–415 nm wavelength when the samples are excited at 310–320 nm wavelength. In addition to these down-conversion features, GQDs also exhibit up-conversion photoluminescence when excited in the range 560–800 nm wavelength, with broad emission peaks at 410–450 nm wavelength. Analysis of X-ray photoelectron spectroscopy measurements indicates a higher proportion of C–C sp{sup 2} than sp{sup 3} bonds, with the sp{sup 3} ones mainly located at the GQD surfaces. Also evidences of C–O and C–N bonds at the GQD surface have been observed. The combination of these results with Raman and ultraviolet–visible absorption experiments allows envisaging the GQDs to be composed of amino-functionalized sp{sup 2} islands with a high degree of surface oxidation. This would explain the photoluminescent properties observed in the samples under study. The combined up- and down-conversion photoluminescence processes would made these GQDs a powerful energy-transfer component in GQDs–TiO{sub 2} nanocomposite systems, which could be used in photocatalyst devices with superior performance compared to simple TiO{sub 2} systems.

Effects of InAlAs strain reducing layer on the photoluminescence properties of InAs quantum dots embedded in InGaAs/GaAs quantum wells

Energy Technology Data Exchange (ETDEWEB)

Kong, Lingmin, E-mail: konglm@qq.com [School of Marine Science and Technology, Zhejiang Ocean University, Zhoushan 316000 (China); Sun, Wei [SEM School of Electromechanical Engineering, Weifang Engineering Vocational College, Qingzhou 262500 (China); Feng, Zhe Chuan, E-mail: zcfeng@nut.edu.tw [Institute of Photonics and Optoelectronics, Department of Electrical Engineering, and Center for Emerging Material and Advanced Devices, National Taiwan University, Taipei 106-17, Taiwan (China); Xie, Sheng [School of Electronic and Information Engineering, Tianjin University, Tianjin 300072 (China); Zhou, Yunqing; Wang, Rui; Zhang, Cunxi; Zong, Zhaocun; Wang, Hongxia; Qiao, Qian [Department of Physics, Zhejiang Ocean University, Zhoushan 316000 (China); Wu, Zhengyun [Department of Physics, Xiamen University, Xiamen 361005 China (China)

2014-07-01

Two kinds of self-assembled quantum dots (QDs) embedded within InGaAs/GaAs quantum wells were grown by molecular beam epitaxy: one was capped with an InAlAs strain reducing (SR) layer, while the other was not. Their emission dynamics was investigated by time-resolved and temperature dependent (TD) photoluminescence (PL) measurements. A significant redshift can be observed in the emission peak position of InAs QDs with thin InAlAs SR cap layer, which results from SR effects. Different behaviors of the integrated PL intensity for the samples with or without InAlAs layer may be ascribed to the reduced carrier transition at higher temperature for the higher energy barrier of the InAlAs layer, and the TD mode of carrier migration. The PL decay time of quantum dots grown with InAlAs layer was much longer than that without the layer, which implies that the InAlAs layer with higher energy barrier may enhance the quantum restriction of carriers in InAs QDs. These observations are discussed from the viewpoint of strain compensation and potential barrier variation with SR layers. Our experiments also demonstrate that the main mode of carrier migration is quantum tunneling effect at lower temperature, while it is quantum transition at higher temperature. The results demonstrate the importance of InAlAs SR layer for the optical quality of InAs QDs. - Highlights: • InAs quantum dots (QDs) were grown on GaAs. • A thin InAlAs layer was grown on InAs QDs. • Temperature dependent photoluminescence (PL) and time-resolved PL were carried out. • Both a redshift and a double exponential decay of PL emission were generated by the InAlAs layer.

Red-shift of the photoluminescent emission peaks of CdTe quantum dots due to the synergistic interaction with carbon quantum dot mixtures

International Nuclear Information System (INIS)

Pelayo, E; Zazueta, A; López-Delgado, R; Ayón, A; Saucedo, E; Ruelas, R

2016-01-01

We report the relatively large red-shift effect observed in down-shifting carbon quantum dots (CQDs) that is anticipated to have a positive impact on the power conversion efficiency of solar cells. Specifically, with an excitation wavelength of 390 nm, CQDs of different sizes, exhibited down-shifted emission peaks centered around 425 nm. However, a solution comprised of a mixture of CQDs of different sizes, was observed to have an emission peak red-shifted to 515 nm. The effect could arise when larger carbon quantum dots capture the photons emitted by their smaller counterparts followed by the subsequent re-emission at longer wavelengths. Furthermore, the red-shift effect was also observed in CdTe QDs when added to a solution with the aforementioned mixture of Carbon QDs. Thus, whereas a solution solely comprised of a collection of CdTe QDs of different sizes, exhibited a down-shifted photoluminescence centered around 555 nm, the peak was observed to be further red-shifted to 580 nm when combined with the solution of CQDs of different sizes. The quantum dot characterization included crystal structure analysis as well as photon absorption and photoluminescence wavelengths. Subsequently, the synthesized QDs were dispersed in a polymeric layer of poly-methyl-methacrylate (PMMA) and incorporated on functional and previously characterized solar cells, to quantify their influence in the electrical performance of the photovoltaic structures. We discuss the synthesis and characterization of the produced Carbon and CdTe QDs, as well as the observed improvement in the power conversion efficiency of the fabricated photovoltaic devices. (paper)

Temperature dependence of photoluminescence from submonolayer deposited InGaAs/GaAs quantum dots

DEFF Research Database (Denmark)

Xu, Zhangcheng; Leosson, K.; Birkedal, Dan

2002-01-01

The temperature dependence of photoluminescence (PL) from self-assembled InGaAs quantum dots (QD's) grown by submonolayer deposition mode (non-SK mode), is investigated. It is found that the PL spectra are dominated by the ground-state transitions at low temperatures, but increasingly...... by the excited-state transitions at higher temperatures. The emission linewidth of the ground-state transitions of QDs ensembles first decreases and then increases with the increase of temperature, which results from the carrier transfer between dots via barrier states....

Carrier redistribution between different potential sites in semipolar (202¯1) InGaN quantum wells studied by near-field photoluminescence

KAUST Repository

Marcinkevičius, S.; Gelžinytė, K.; Zhao, Y.; Nakamura, S.; DenBaars, S. P.; Speck, J. S.

2014-01-01

© 2014 AIP Publishing LLC. Scanning near-field photoluminescence (PL) spectroscopy at different excitation powers was applied to study nanoscale properties of carrier localization and recombination in semipolar (202¯1) InGaN quantum wells (QWs

Surface-related reduction of photoluminescence in GaAs quantum wires and its recovery by new passivation

International Nuclear Information System (INIS)

Shiozaki, Nanako; Anantathanasarn, Sanguan; Sato, Taketomo; Hashizume, Tamotsu; Hasegawa, Hideki

2005-01-01

Etched GaAs quantum wires (QWRs) and selectively grown (SG) QWRs were fabricated, and dependence of their photoluminescence (PL) properties on QWR width (W) and QWR distance to surface (d) were investigated. PL intensity greatly reduced with reduction of W and d, due to non-radiative recombination through surface states. Surface passivation by growing a Si interface control layer (Si-ICL) on group III-terminated surfaces greatly improved PL properties

Enhanced photoluminescence of multilayer Ge quantum dots on Si(001) substrates by increased overgrowth temperature.

Science.gov (United States)

Liu, Zhi; Cheng, Buwen; Hu, Weixuan; Su, Shaojian; Li, Chuanbo; Wang, Qiming

2012-07-11

Four-bilayer Ge quantum dots (QDs) with Si spacers were grown on Si(001) substrates by ultrahigh vacuum chemical vapor deposition. In three samples, all Ge QDs were grown at 520 °C, while Si spacers were grown at various temperatures (520 °C, 550 °C, and 580 °C). Enhancement and redshift of room temperature photoluminescence (PL) were observed from the samples in which Si spacers were grown at a higher temperature. The enhancement of PL is explained by higher effective electrons capturing in the larger size Ge QDs. Quantum confinement of the Ge QDs is responsible for the redshift of PL spectra. The Ge QDs' size and content were investigated by atomic force microscopy and Raman scattering measurements.

Highly photoluminescent MoO{sub x} quantum dots: Facile synthesis and application in off-on Pi sensing in lake water samples

Energy Technology Data Exchange (ETDEWEB)

Xiao, Sai Jin [Jiangxi Key Laboratory of Mass Spectrometry and Instrumentation, East China University of Technology (ECUT), Nanchang 330013 (China); School of Chemistry, Biology and Material Science, ECUT, Nanchang 330013 (China); Zhao, Xiao Jing; Zuo, Jun [School of Chemistry, Biology and Material Science, ECUT, Nanchang 330013 (China); Huang, Hai Qing [State Key Laboratory Breeding Base of Nuclear Resources and Environment, ECUT, Nanchang 330013 (China); Zhang, Li, E-mail: zhangli8@ncu.edu.cn [College of Chemistry, Nanchang University, Nanchang 330031 (China)

2016-02-04

Molybdenum oxide (MoO{sub x}) is a well-studied transition-metal semiconductor material, and has a wider band gap than MoS{sub 2} which makes it become a promising versatile probe in a variety of fields, such as gas sensor, catalysis, energy storage ect. However, few MoO{sub x} nanomaterials possessing photoluminescence have been reported until now, not to mention the application as photoluminescent probes. Herein, a one-pot method is developed for facile synthesis of highly photoluminescent MoO{sub x} quantum dots (MoO{sub x} QDs) in which commercial molybdenum disulfide powder and hydrogen peroxide (H{sub 2}O{sub 2}) are involved as the precursor and oxidant, respectively. Compared with current synthesis methods, the proposed one has the advantages of rapid, one-pot, easily prepared, environment friendly as well as strong photoluminescence. The obtained MoO{sub x} QDs is further utilized as an efficient photoluminescent probe, and a new off-on sensor has been constructed for phosphate (Pi) determination in complicated lake water samples, attributed to the fact that the binding affinity of Eu{sup 3+} ions to the oxygen atoms from Pi is much higher than that from the surface of MoO{sub x} QDs. Under the optimal conditions, a good linear relationship was found between the enhanced photoluminescence intensity and Pi concentration in the range of 0.1–160.0 μM with the detection limit of 56 nM (3σ/k). The first application of the photoluminescent MoO{sub x} nanomaterials for ion photochemical sensing will open the gate of employing MoO{sub x} nanomaterials as versatile probes in a variety of fields, such as chemi-/bio-sensor, cell imaging, biomedical and so on. - Highlights: • Though increasing effort has been devoted to MoO{sub x} nanomaterials synthesis, only a few reports mentioning its photoluminescence property are available, while even no evidence has shown its applications in chemical and biological sensing. • Herein, a one-pot method possessing the

Brightly Luminescent and Color-Tunable Colloidal CH3NH3PbX3 (X = Br, I, Cl) Quantum Dots: Potential Alternatives for Display Technology.

Science.gov (United States)

Zhang, Feng; Zhong, Haizheng; Chen, Cheng; Wu, Xian-gang; Hu, Xiangmin; Huang, Hailong; Han, Junbo; Zou, Bingsuo; Dong, Yuping

2015-04-28

Organometal halide perovskites are inexpensive materials with desirable characteristics of color-tunable and narrow-band emissions for lighting and display technology, but they suffer from low photoluminescence quantum yields at low excitation fluencies. Here we developed a ligand-assisted reprecipitation strategy to fabricate brightly luminescent and color-tunable colloidal CH3NH3PbX3 (X = Br, I, Cl) quantum dots with absolute quantum yield up to 70% at room temperature and low excitation fluencies. To illustrate the photoluminescence enhancements in these quantum dots, we conducted comprehensive composition and surface characterizations and determined the time- and temperature-dependent photoluminescence spectra. Comparisons between small-sized CH3NH3PbBr3 quantum dots (average diameter 3.3 nm) and corresponding micrometer-sized bulk particles (2-8 μm) suggest that the intense increased photoluminescence quantum yield originates from the increase of exciton binding energy due to size reduction as well as proper chemical passivations of the Br-rich surface. We further demonstrated wide-color gamut white-light-emitting diodes using green emissive CH3NH3PbBr3 quantum dots and red emissive K2SiF6:Mn(4+) as color converters, providing enhanced color quality for display technology. Moreover, colloidal CH3NH3PbX3 quantum dots are expected to exhibit interesting nanoscale excitonic properties and also have other potential applications in lasers, electroluminescence devices, and optical sensors.

Self-assembly and photoluminescence evolution of hydrophilic and hydrophobic quantum dots in sol–gel processes

Energy Technology Data Exchange (ETDEWEB)

Yang, Ping, E-mail: mse_yangp@ujn.edu.cn [School of Material Science and Engineering, University of Jinan, Jinan 250022 (China); Matras-Postolek, Katarzyna [Faculty of Chemical Engineering and Technology, Cracow University of Technology, Krakow 31-155 (Poland); Song, Xueling; Zheng, Yan; Liu, Yumeng; Ding, Kun; Nie, Shijie [School of Material Science and Engineering, University of Jinan, Jinan 250022 (China)

2015-10-15

Graphical abstract: Highly luminescent quantum dots (QDs) with tunable photoluminescence (PL) wavelength were assembled into various morphologies including chain, hollow spheres, fibers, and ring structures through sol–gel processes. The PL properties during assembly as investigated. - Highlights: • Highly luminescent quantum dots (QDs) were synthesized from several ligands. • The evolution of PL in self-assembly via sol–gel processes was investigated. • CdTe QDs were assembled into a chain by controlling hydrolysis and condensation reactions. • Hollow spheres, fibers, and ring structures were created via CdSe/ZnS QDs in sol–gel processes. - Abstract: Highly luminescent quantum dots (QDs) with tunable photoluminescence (PL) wavelength were synthesized from several ligands to investigate the PL evolution in QD self-assembly via sol–gel processes. After ligand exchange, CdTe QDs were assembled into a chain by controlling the hydrolysis and condensation reaction of 3-mercaptopropyl-trimethoxysilane. The chain was then coated with a SiO{sub 2} shell from tetraethyl orthosilicate (TEOS). Hollow spheres, fibers, and ring structures were created from CdSe/ZnS QDs via various sol–gel processes. CdTe QDs revealed red-shifted and narrowed PL spectrum after assembly compared with their initial one. In contrast, the red-shift of PL spectra of CdSe/ZnS QDs is small. By optimizing experimental conditions, SiO{sub 2} spheres with multiple CdSe/ZnS QDs were fabricated using TEOS and MPS. The QDs in these SiO{sub 2} spheres retained their initial PL properties. This result is useful for application because of their high stability and high PL efficiency of 33%.

Highly photoluminescent and photostable CdSe quantum dot-nylon hybrid composites for efficient light conversion applications

Energy Technology Data Exchange (ETDEWEB)

Yuan Ying; Riehle, Frank-Stefan [Freiburg Materials Research Centre (FMF), University of Freiburg, Stefan-Meier-Str. 21, D-79104 Freiburg (Germany); Department of Microsystems Engineering (IMTEK), Georg Koehler Allee 103, University of Freiburg, D-79110 Freiburg (Germany); Nitschke, Roland [Life Imaging Center, Centre of Systems Biology, University of Freiburg Habsburgerstr. 49, D-79104 Freiburg (Germany); Centre for Biological Signalling Studies (BIOSS), University of Freiburg (Germany); Krueger, Michael, E-mail: michael.krueger@fmf.uni-freiburg.de [Freiburg Materials Research Centre (FMF), University of Freiburg, Stefan-Meier-Str. 21, D-79104 Freiburg (Germany); Department of Microsystems Engineering (IMTEK), Georg Koehler Allee 103, University of Freiburg, D-79110 Freiburg (Germany)

2012-02-15

Highlights: Black-Right-Pointing-Pointer A novel in situ synthesis approach for highly luminescent CdSe core QDs-nylon hybrid materials. Black-Right-Pointing-Pointer Potential applications for light and energy conversion are demonstrated. Black-Right-Pointing-Pointer Three dimensional structures out of this hybrid material are available. - Abstract: Highly photoluminescent hexadecylamine (HDA) capped core CdSe quantum dots (QDs) with fluorescent quantum yields (QYs) up to 60% were synthesized using a hot injection method and directly incorporated into nylon polymer. For the incorporation of crude CdSe QDs into nylon a simple reproducible and upscalable one pot approach was developed without the need of further purification steps. The photoluminescence (PL) properties of the core QDs and the resulting QD-polymer hybrid composites were investigated and compared. Red emitting hybrid materials exhibit a QY of 60% with a high potential for applications in direct light and energy conversion. The hybrid materials could be successfully utilized as LED conversion layers. By avoiding exposure to oxygen the hybrid films can be kept for a month without detecting a significant decrease in luminescence. Various three dimensional structures are easily available opening doors for further applications such as novel materials for fluorescence standard development in laser scanning microscopy (LSM).

Study of InGaN/GaN quantum dot systems by TEM techniques and photoluminescence spectroscopy

International Nuclear Information System (INIS)

Kashtiban, R J; Bangert, U; Harvey, A J; Sherliker, B; Halsall, M P

2010-01-01

InGaN/GaN multilayer quantum dot structures produced by MOCVD techniques on c-plane sapphire were studied by transmission electron microscopy (TEM) and photoluminescence (PL) techniques. Indium fluctuations ranging from 1-4 nm were observed with both energy filtered TEM (EFTEM) and high angle annular dark field (HAADF) scanning TEM. The existence of V-shaped defects with nucleation centres at the termination of threading dislocation were observed in HAADF images. There was also evidence of the formation of large quantum dots at low densities from lattice HRTEM images. This was further confirmed by PL measurements through the observation of a single sharp line at low power with the typical saturation behaviour at higher power excitation.

Correlation between Photoluminescence and Carrier Transport and a Simple In Situ Passivation Method for High-Bandgap Hybrid Perovskites.

Science.gov (United States)

Stoddard, Ryan J; Eickemeyer, Felix T; Katahara, John K; Hillhouse, Hugh W

2017-07-20

High-bandgap mixed-halide hybrid perovskites have higher open-circuit voltage deficits and lower carrier diffusion lengths than their lower-bandgap counterparts. We have developed a ligand-assisted crystallization (LAC) technique that introduces additives in situ during the solvent wash and developed a new method to dynamically measure the absolute intensity steady-state photoluminescence and the mean carrier diffusion length simultaneously. The measurements reveal four distinct regimes of material changes and show that photoluminescence brightening often coincides with losses in carrier transport, such as in degradation or phase segregation. Further, the measurements enabled optimization of LAC on the 1.75 eV bandgap FA 0.83 Cs 0.17 Pb(I 0.66 Br 0.34 ) 3 , resulting in an enhancement of the photoluminescence quantum yield (PLQY) of over an order of magnitude, an increase of 80 meV in the quasi-Fermi level splitting (to 1.29 eV), an increase in diffusion length by a factor of 3.5 (to over 1 μm), and enhanced open-circuit voltage and short-circuit current from photovoltaics fabricated from the LAC-treated films.

Time-resolved photoluminescence of Ga(NAsP) multiple quantum wells grown on Si substrate: Effects of rapid thermal annealing

Energy Technology Data Exchange (ETDEWEB)

Woscholski, R., E-mail: ronja.woscholski@physik.uni-marburg.de; Shakfa, M.K.; Gies, S.; Wiemer, M.; Rahimi-Iman, A.; Zimprich, M.; Reinhard, S.; Jandieri, K.; Baranovskii, S.D.; Heimbrodt, W.; Volz, K.; Stolz, W.; Koch, M.

2016-08-31

Time-resolved photoluminescence (TR-PL) spectroscopy has been used to study the impact of rapid thermal annealing (RTA) on the optical properties and carrier dynamics in Ga(NAsP) multiple quantum well heterostructures (MQWHs) grown on silicon substrates. TR-PL measurements reveal an enhancement in the PL efficiency when the RTA temperature is increased up to 925 °C. Then, the PL intensity dramatically decreases with the annealing temperature. This behavior is explained by the variation of the disorder degree in the studied structures. The analysis of the low-temperature emission-energy-dependent PL decay time enables us to characterize the disorder in the Ga(NAsP) MQWHs. The theoretically extracted energy-scales of disorder confirm the experimental observations. - Highlights: • Ga(NAsP) multiple quantum well heterostructures (MQWHs) grown on silicon substrates • Impact of rapid thermal annealing on the optical properties and carrier dynamics • Time resolved photoluminescence spectroscopy was applied. • PL transients became continuously faster with increasing annealing temperature. • Enhancement in the PL efficiency with increasing annealing temperature up to 925 °C.

Time-resolved photoluminescence of Ga(NAsP) multiple quantum wells grown on Si substrate: Effects of rapid thermal annealing

International Nuclear Information System (INIS)

Woscholski, R.; Shakfa, M.K.; Gies, S.; Wiemer, M.; Rahimi-Iman, A.; Zimprich, M.; Reinhard, S.; Jandieri, K.; Baranovskii, S.D.; Heimbrodt, W.; Volz, K.; Stolz, W.; Koch, M.

2016-01-01

Time-resolved photoluminescence (TR-PL) spectroscopy has been used to study the impact of rapid thermal annealing (RTA) on the optical properties and carrier dynamics in Ga(NAsP) multiple quantum well heterostructures (MQWHs) grown on silicon substrates. TR-PL measurements reveal an enhancement in the PL efficiency when the RTA temperature is increased up to 925 °C. Then, the PL intensity dramatically decreases with the annealing temperature. This behavior is explained by the variation of the disorder degree in the studied structures. The analysis of the low-temperature emission-energy-dependent PL decay time enables us to characterize the disorder in the Ga(NAsP) MQWHs. The theoretically extracted energy-scales of disorder confirm the experimental observations. - Highlights: • Ga(NAsP) multiple quantum well heterostructures (MQWHs) grown on silicon substrates • Impact of rapid thermal annealing on the optical properties and carrier dynamics • Time resolved photoluminescence spectroscopy was applied. • PL transients became continuously faster with increasing annealing temperature. • Enhancement in the PL efficiency with increasing annealing temperature up to 925 °C

Assignment of absolute stereostructures through quantum mechanics electronic and vibrational circular dichroism calculations.

Science.gov (United States)

Dai, Peng; Jiang, Nan; Tan, Ren-Xiang

2016-01-01

Elucidation of absolute configuration of chiral molecules including structurally complex natural products remains a challenging problem in organic chemistry. A reliable method for assigning the absolute stereostructure is to combine the experimental circular dichroism (CD) techniques such as electronic and vibrational CD (ECD and VCD), with quantum mechanics (QM) ECD and VCD calculations. The traditional QM methods as well as their continuing developments make them more applicable with accuracy. Taking some chiral natural products with diverse conformations as examples, this review describes the basic concepts and new developments of QM approaches for ECD and VCD calculations in solution and solid states.

Surface effects on the photoluminescence of Si quantum dots

International Nuclear Information System (INIS)

Wang, Chiang-Jing; Tsai, Meng-Yen; Chi, Cheng Chung; Perng, Tsong-Pyng

2009-01-01

Si quantum dots (SiQDs) with sizes ranging from 5 to 20 nm were fabricated by vapor condensation. They showed red photoluminescence (PL) in vacuum with the peak located at around 750 nm. After the specimen was exposed to air, the PL intensity became higher, and continued to increase during the PL test with a cycling of vacuum-air-vacuum. In pure oxygen, the PL intensity exhibited an irreversible decrease, while in nitrogen a smaller amount of reversible increase of PL intensity was observed. Furthermore, the PL intensity exhibited a remarkable enhancement if the SiQDs were treated with water. With HF treatment, the PL peak position showed a blue-shift to 680 nm, and was recovered after subsequent exposure to air. Si-O-H complexes were suggested to be responsible for this red luminescence. The irreversible decrease of PL intensity due to oxygen adsorption was speculated to be caused by the modification of chemical bonds on the surface. In the case of nitrogen adsorption, the PL change was attributed to the surface charging during adsorption.

Photoluminescence of anti-modulation doped near-surface GaAs/AlGaAs single quantum well structures exposed to hydrogen plasma

CERN Document Server

Bumaj, Y A; Goldkhan, R; Shtajn, N; Golombek, A; Nakov, V; Cheng, T S

2002-01-01

The anti-modulation Si-doped GaAs/AlGaAs structures with near-surface single quantum wells grown by molecular-beam epitaxy were exposed to hydrogen plasma at 260 deg C and investigated by low-temperature photoluminescence, photoluminescence excitation and photoreflectance spectroscopy. After hydrogenation, the quenching of the exciton luminescence for the below AlGaAs band gap excitation due to the increase of electric field in the structure has been observed. The effect is consistent with unpinning of Fermi level from mid gap of nominally undoped (p-type) GaAs cap layer due to passivation of surface states by hydrogen without neutralization of shallow impurities in the epilayers

Photoluminescent properties of single crystal diamond microneedles

Science.gov (United States)

Malykhin, Sergey A.; Ismagilov, Rinat R.; Tuyakova, Feruza T.; Obraztsova, Ekaterina A.; Fedotov, Pavel V.; Ermakova, Anna; Siyushev, Petr; Katamadze, Konstantin G.; Jelezko, Fedor; Rakovich, Yury P.; Obraztsov, Alexander N.

2018-01-01

Single crystal needle-like diamonds shaped as rectangular pyramids were produced by combination of chemical vapor deposition and selective oxidation with dimensions and geometrical characteristics depending on the deposition process parameters. Photoluminescence spectra and their dependencies on wavelength of excitation radiation reveal presence of nitrogen- and silicon-vacancy color centers in the diamond crystallites. Photoluminescence spectra, intensity mapping, and fluorescence lifetime imaging microscopy indicate that silicon-vacancy centers are concentrated at the crystallites apex while nitrogen-vacancy centers are distributed over the whole crystallite. Dependence of the photoluminescence on excitation radiation intensity demonstrates saturation and allows estimation of the color centers density. The combination of structural parameters, geometry and photoluminescent characteristics are prospective for advantageous applications of these diamond crystallites in quantum information processing and optical sensing.

Chemically modulated graphene quantum dot for tuning the photoluminescence as novel sensory probe

Science.gov (United States)

Hwang, Eunhee; Hwang, Hee Min; Shin, Yonghun; Yoon, Yeoheung; Lee, Hanleem; Yang, Junghee; Bak, Sora; Lee, Hyoyoung

2016-12-01

A band gap tuning of environmental-friendly graphene quantum dot (GQD) becomes a keen interest for novel applications such as photoluminescence (PL) sensor. Here, for tuning the band gap of GQD, a hexafluorohydroxypropanyl benzene (HFHPB) group acted as a receptor of a chemical warfare agent was chemically attached on the GQD via the diazonium coupling reaction of HFHPB diazonium salt, providing new HFHPB-GQD material. With a help of the electron withdrawing HFHPB group, the energy band gap of the HFHPB-GQD was widened and its PL decay life time decreased. As designed, after addition of dimethyl methyl phosphonate (DMMP), the PL intensity of HFHPB-GQD sensor sharply increased up to approximately 200% through a hydrogen bond with DMMP. The fast response and short recovery time was proven by quartz crystal microbalance (QCM) analysis. This HFHPB-GQD sensor shows highly sensitive to DMMP in comparison with GQD sensor without HFHPB and graphene. In addition, the HFHPB-GQD sensor showed high selectivity only to the phosphonate functional group among many other analytes and also stable enough for real device applications. Thus, the tuning of the band gap of the photoluminescent GQDs may open up new promising strategies for the molecular detection of target substrates.

Quantum efficiency of silica-coated rare-earth doped yttrium silicate

Energy Technology Data Exchange (ETDEWEB)

Cervantes-Vásquez, D., E-mail: dcervant@cnyn.unam.mx [Centro de Investigación Científica y de Educación Superior de Ensenada, Carretera Ensenada-Tijuana No. 3918, Zona Playitas, C.P. 22860 Ensenada, B.C., México (Mexico); Contreras, O.E.; Hirata, G.A. [Centro de Nanociencias y Nanotecnología, Universidad Nacional Autónoma de México, Km. 107 Carretera Tijuana-Ensenada, C.P. 22800 Ensenada, B.C., México (Mexico)

2013-11-15

The photoluminescent properties of rare earth-activated white-emitting Y{sub 2}SiO{sub 5}:Ce,Tb nanocrystalline phosphor prepared by two different methods, pressure-assisted combustion synthesis and sol–gel, were studied. The synthesized phosphor samples were post-annealed at 1373 K and 1623 K in order to obtain the X1-Y{sub 2}SiO{sub 5} and X2-Y{sub 2}SiO{sub 5} phases, respectively, which were confirmed by X-ray diffraction measurements. Photoluminescence analysis showed the contribution of two blue-emission bands within the 380–450 nm region originating from 5d–4f transitions in Ce{sup 3+} ions and a well-defined green emission of Tb{sup 3+} ions located at 545 nm corresponding to {sup 5}D{sub 4}→{sup 7}F{sub 5} electronic transitions. Thereafter, Y{sub 2}SiO{sub 5}:Ce,Tb powders were coated with colloidal silica in order to investigate the effect of silica coatings on their luminescent properties. Absolute fluorescence quantum efficiency measurements were carefully performed, which revealed an increase of 12% of efficiency in coated compared with bare-Y{sub 2}SiO{sub 5}:Ce,Tb phosphor. -- Highlights: • Y{sub 2}SiO{sub 5}:Ce,Tb phosphor powders were successfully coated with colloidal silica. • Post-annealing treatments improved the quantum efficiency of silica-coated Y{sub 2}SiO{sub 5}:Ce,Tb phosphors. • Absolute fluorescence quantum efficiency measurements showed an increase of 12%.

Photoluminescence spectrum changes of GaN quantum wells caused by the strong piezoelectric fields

Energy Technology Data Exchange (ETDEWEB)

Herrera, H.; Calderon, A. [CICATA-IPN, Av. Legaria 694, Col. Irrigacion, 11500 Mexico D.F. (Mexico); Gonzalez de la Cruz, G. [CINVESTAV-IPN, A.P. 14-740, 07000 Mexico D.F. (Mexico)

2006-07-01

Spontaneous and piezoelectric fields are known to be the key to understanding the optical properties of nitride heterostructures. This effect modifies the electronic states in the quantum well (QW) and the emission energy in the photoluminescence (PL) spectrum. These fields induce a reduction of the oscillator strength on the transition energy between the confined electron and hole states in GaN/Al{sub x}Ga{sub 1-x}N QW's and dramatically increase the carrier life time as the QW thickness increases. In this work, we solve analytically the Schroedinger equation for moderate electric fields when the electron-hole transition energy in the QW is larger than the energy gap of the GaN. Furthermore, the large redshifts of the PL energy position and the spatial separation of the electron and hole by several times of the Bohr radius caused by the strong piezoelectric fields are explained using a triangular potential in the Schrodinger equation. The transition energy calculations between the electron-hole pair as a function of the well width with the electric field as a fitting parameter are in agreement with the measured photoluminescence energy peaks. (Author)

Photoluminescence spectrum changes of GaN quantum wells caused by the strong piezoelectric fields

International Nuclear Information System (INIS)

Herrera, H.; Calderon, A.; Gonzalez de la Cruz, G.

2006-01-01

Spontaneous and piezoelectric fields are known to be the key to understanding the optical properties of nitride heterostructures. This effect modifies the electronic states in the quantum well (QW) and the emission energy in the photoluminescence (PL) spectrum. These fields induce a reduction of the oscillator strength on the transition energy between the confined electron and hole states in GaN/Al x Ga 1-x N QW's and dramatically increase the carrier life time as the QW thickness increases. In this work, we solve analytically the Schroedinger equation for moderate electric fields when the electron-hole transition energy in the QW is larger than the energy gap of the GaN. Furthermore, the large redshifts of the PL energy position and the spatial separation of the electron and hole by several times of the Bohr radius caused by the strong piezoelectric fields are explained using a triangular potential in the Schrodinger equation. The transition energy calculations between the electron-hole pair as a function of the well width with the electric field as a fitting parameter are in agreement with the measured photoluminescence energy peaks. (Author)

Classical and quantum dynamics of a gravitational theory with absolute teleparallelism

International Nuclear Information System (INIS)

Azeredo Campos, R. de.

1984-01-01

The dynamics of an alternative theory of gravitation with absolute teleparallelism is sustied. In the Cauchy problem of this theory four constraint relations are obtained, as in general relativity, because of the existence of the manifold mapping group. Propagation equations for the dynamical variables are also derived by applying Dirac's Hamiltonian methods. In addition, an algebra of generators related to the global Lorentz group and the correspondence principle leading to a quantum version of the theory are also discussed. (author) [pt

Strategy for synthesizing quantum dot-layered double hydroxide nanocomposites and their enhanced photoluminescence and photostability.

Science.gov (United States)

Cho, Seungho; Jung, Sungwook; Jeong, Sanghwa; Bang, Jiwon; Park, Joonhyuck; Park, Youngrong; Kim, Sungjee

2013-01-08

Layered double hydroxide-quantum dot (LDH-QD) composites are synthesized via a room temperature LDH formation reaction in the presence of QDs. InP/ZnS (core/shell) QD, a heavy metal free QD, is used as a model constituent. Interactions between QDs (with negative zeta potentials), decorated with dihydrolipoic acids, and inherently positively charged metal hydroxide layers of LDH during the LDH formations are induced to form the LDH-QD composites. The formation of the LDH-QD composites affords significantly enhanced photoluminescence quantum yields and thermal- and photostabilities compared to their QD counterparts. In addition, the fluorescence from the solid LDH-QD composite preserved the initial optical properties of the QD colloid solution without noticeable deteriorations such as red-shift or deep trap emission. Based on their advantageous optical properties, we also demonstrate the pseudo white light emitting diode, down-converted by the LDH-QD composites.

Visible photoluminescence from hydrogenated silicon particles suspended in a silane plasma

International Nuclear Information System (INIS)

Courteille, C.; Dorier, J.L.; Dutta, J.; Hollenstein, C.; Howling, A.A.; Stoto, T.

1994-09-01

Visible photoluminescence at room temperature has been observed in amorphous hydrogenated silicon particulates during their formation in a silane radio-frequency plasma. Oxygen injection along with mass spectrometry measurements demonstrate that oxygen has no influence on the photoluminescence. The appearance of visible photoluminescence coincides with a particle agglomeration phase as shown by laser light scattering experiments, and electron microscopy shows silicon nanocrystals within these particulates. These observations of visible photoluminescence are consistent with the model of quantum confinement in the silicon nanocrystals. (author) 5 figs., 45 refs

High Photoluminescence Quantum Yield in Band Gap Tunable Bromide Containing Mixed Halide Perovskites.

Science.gov (United States)

Sutter-Fella, Carolin M; Li, Yanbo; Amani, Matin; Ager, Joel W; Toma, Francesca M; Yablonovitch, Eli; Sharp, Ian D; Javey, Ali

2016-01-13

Hybrid organic-inorganic halide perovskite based semiconductor materials are attractive for use in a wide range of optoelectronic devices because they combine the advantages of suitable optoelectronic attributes and simultaneously low-cost solution processability. Here, we present a two-step low-pressure vapor-assisted solution process to grow high quality homogeneous CH3NH3PbI3-xBrx perovskite films over the full band gap range of 1.6-2.3 eV. Photoluminescence light-in versus light-out characterization techniques are used to provide new insights into the optoelectronic properties of Br-containing hybrid organic-inorganic perovskites as a function of optical carrier injection by employing pump-powers over a 6 orders of magnitude dynamic range. The internal luminescence quantum yield of wide band gap perovskites reaches impressive values up to 30%. This high quantum yield translates into substantial quasi-Fermi level splitting and high "luminescence or optically implied" open-circuit voltage. Most importantly, both attributes, high internal quantum yield and high optically implied open-circuit voltage, are demonstrated over the entire band gap range (1.6 eV ≤ Eg ≤ 2.3 eV). These results establish the versatility of Br-containing perovskite semiconductors for a variety of applications and especially for the use as high-quality top cell in tandem photovoltaic devices in combination with industry dominant Si bottom cells.

Photoluminescence of ZnS: Mn quantum dot by hydrothermal method

Directory of Open Access Journals (Sweden)

Yun Hu

2018-01-01

Full Text Available ZnS: Mn quantum dots (QDs with the average grain size from 4.2 to 7.2 nm were synthesized by a hydrothermal method. All samples were cubic zinc blende structure (β-ZnS measured using X-ray diffraction (XRD. And the main diffraction peaks of ZnS: Mn shifted slightly towards higher angle in comparison with the intrinsic ZnS because of the substitution of Mn2+ for Zn2+. Due to the small grain size (4-7 nm effect, the poor dispersion and serious reunion phenomenon for the samples were observed from transmission electron microscopy (TEM. ZnS: Mn QDs had four peaks centered at 466, 495, 522, and 554 nm, respectively, in the photoluminescence (PL spectra, in which the band at 554 nm absent in the intrinsic ZnS: Mn is attributed to the doping of Mn2+ in the lattice sites. As the concentration of Mn2+ increasing from 0% to 0.6 at%, the intensity of the PL emission also increased. But the concentration reached 0.9 at%, quenching of PL emission occurred. The peak in ZnS: Mn QDs observed at 490 cm-1 was originated from the stretching vibration of the Mn–O bonds in the Fourier transform infrared (FTIR spectra. And the small changes about this peak compared with the previous reports at 500 cm-1 can be attributed to the formation of quantum dots. This method we utilized to synthesize ZnS: Mn QDs is very simple, low cost, and applicable for other semiconductor QD materials.

Exciton-related nonlinear optical response and photoluminescence in dilute nitrogen InxGa1−xNyAs1−y/GaAs cylindrically shaped quantum dots

International Nuclear Information System (INIS)

Duque, C.M.; Morales, A.L.; Mora-Ramos, M.E.; Duque, C.A.

2014-01-01

An investigation of the effects of the dilute nitrogen contents in the exciton states of cylindrical In x Ga 1−x N y As 1−y /GaAs quantum dots is presented. The exciton states in the system are obtained within the effective mass theory and the band anti-crossing model. Exciton-related nonlinear optical absorption and refractive index change, as well as excitonic photoluminescence are studied with the help of the calculated exciton states. - Highlights: • Theoretical study of excitons in cylindrical In x Ga 1−x N y As 1−y /GaAs quantum dots. • Calculations of binding energy for different configurations of electron-hole pairs. • Nonlinear optical absorption and refractive index changes. • Dependence of photoluminescence energy transitions with several inputs

Optimal quantum error correcting codes from absolutely maximally entangled states

Science.gov (United States)

Raissi, Zahra; Gogolin, Christian; Riera, Arnau; Acín, Antonio

2018-02-01

Absolutely maximally entangled (AME) states are pure multi-partite generalizations of the bipartite maximally entangled states with the property that all reduced states of at most half the system size are in the maximally mixed state. AME states are of interest for multipartite teleportation and quantum secret sharing and have recently found new applications in the context of high-energy physics in toy models realizing the AdS/CFT-correspondence. We work out in detail the connection between AME states of minimal support and classical maximum distance separable (MDS) error correcting codes and, in particular, provide explicit closed form expressions for AME states of n parties with local dimension \

Electric Field Modulation of Semiconductor Quantum Dot Photoluminescence: Insights Into the Design of Robust Voltage-Sensitive Cellular Imaging Probes.

Science.gov (United States)

Rowland, Clare E; Susumu, Kimihiro; Stewart, Michael H; Oh, Eunkeu; Mäkinen, Antti J; O'Shaughnessy, Thomas J; Kushto, Gary; Wolak, Mason A; Erickson, Jeffrey S; Efros, Alexander L; Huston, Alan L; Delehanty, James B

2015-10-14

The intrinsic properties of quantum dots (QDs) and the growing ability to interface them controllably with living cells has far-reaching potential applications in probing cellular processes such as membrane action potential. We demonstrate that an electric field typical of those found in neuronal membranes results in suppression of the QD photoluminescence (PL) and, for the first time, that QD PL is able to track the action potential profile of a firing neuron with millisecond time resolution. This effect is shown to be connected with electric-field-driven QD ionization and consequent QD PL quenching, in contradiction with conventional wisdom that suppression of the QD PL is attributable to the quantum confined Stark effect.

Absolute spectroscopy near 7.8 {\\mu} m with a comb-locked extended-cavity quantum-cascade-laser

KAUST Repository

Lamperti, Marco; Alsaif, Bidoor; Gatti, Davide; Fermann, Martin; Laporta, Paolo; Farooq, Aamir; Marangoni, Marco

2017-01-01

We report the first experimental demonstration of frequency-locking of an extended-cavity quantum-cascade-laser (EC-QCL) to a near-infrared frequency comb. The locking scheme is applied to carry out absolute spectroscopy of N2O lines near 7.87 {\\mu

Composition Screening in Blue-Emitting Li4Sr1+xCa0.97-x(SiO4)2:Ce3+ Phosphors for High Quantum Efficiency and Thermally Stable Photoluminescence.

Science.gov (United States)

Zhang, Jingchen; Zhang, Jilin; Zhou, Wenli; Ji, Xiaoyu; Ma, Wentao; Qiu, Zhongxian; Yu, Liping; Li, Chengzhi; Xia, Zhiguo; Wang, Zhengliang; Lian, Shixun

2017-09-13

Photoluminescence quantum efficiency (QE) and thermal stability are important for phosphors used in phosphor-converted light-emitting diodes (pc-LEDs). Li 4 Sr 1+x Ca 0.97-x (SiO 4 ) 2 :0.03Ce 3+ (-0.7 ≤ x ≤ 1.0) phosphors were designed from the initial model of Li 4 SrCa(SiO 4 ) 2 :Ce 3+ , and their single-phased crystal structures were found to be located in the composition range of -0.4 ≤ x ≤ 0.7. Depending on the substitution of Sr 2+ for Ca 2+ ions, the absolute QE value of blue-emitting composition-optimized Li 4 Sr 1.4 Ca 0.57 (SiO 4 ) 2 :0.03Ce 3+ reaches ∼94%, and the emission intensity at 200 °C remains 95% of that at room temperature. Rietveld refinements and Raman spectral analyses suggest the increase of crystal rigidity, increase of force constant in CeO 6 , and decrease of vibrational frequency by increasing Sr 2+ content, which are responsible for the enhanced quantum efficiency and thermal stability. The present study points to a new strategy for future development of the pc-LEDs phosphors based on local structures correlation via composition screening.

MOVPE grown InGaAs quantum dots of high optical quality as seed layer for low-density InP quantum dots

International Nuclear Information System (INIS)

Richter, D; Hafenbrak, R; Joens, K D; Schulz, W-M; Eichfelder, M; Rossbach, R; Jetter, M; Michler, P

2010-01-01

To achieve a low density of optically active InP-quantum dots we used InGaAs islands embedded in GaAs as a seed layer. First, the structural InGaAs quantum dot properties and the influence of the annealing technique was investigated by atomic force microscope measurements. High-resolution micro-photoluminescence spectra reveal narrow photoluminescence lines, with linewidths down to 11 μeV and fine structure splittings of 25 μeV. Furthermore, using these InGaAs quantum dots as seed layer reduces the InP quantum dot density of optically active quantum dots drastically. InP quantum dot excitonic photoluminescence emission with a linewidth of 140 μeV has been observed.

Enhanced carrier collection efficiency and reduced quantum state absorption by electron doping in self-assembled quantum dot solar cells

Energy Technology Data Exchange (ETDEWEB)

Li, Tian, E-mail: tianlee@umd.edu, E-mail: dage@ece.umd.edu; Dagenais, Mario, E-mail: tianlee@umd.edu, E-mail: dage@ece.umd.edu [Department of Electrical Engineering, University of Maryland, College Park, Maryland 20742 (United States); Lu, Haofeng; Fu, Lan; Tan, Hark Hoe; Jagadish, Chennupati [Department of Electronic Materials Engineering, Research School of Physics and Engineering, The Australian National University, Canberra ACT 0200 (Australia)

2015-02-02

Reduced quantum dot (QD) absorption due to state filling effects and enhanced electron transport in doped QDs are demonstrated to play a key role in solar energy conversion. Reduced QD state absorption with increased n-doping is observed in the self-assembled In{sub 0.5}Ga{sub 0.5}As/GaAs QDs from high resolution below-bandgap external quantum efficiency (EQE) measurement, which is a direct consequence of the Pauli exclusion principle. We also show that besides partial filling of the quantum states, electron-doping produces negatively charged QDs that exert a repulsive Coulomb force on the mobile electrons, thus altering the electron trajectory and reducing the probability of electron capture, leading to an improved collection efficiency of photo-generated carriers, as indicated by an absolute above-bandgap EQE measurement. The resulting redistribution of the mobile electron in the planar direction is further validated by the observed photoluminescence intensity dependence on doping.

Internal quantum efficiency enhancement of GaInN/GaN quantum-well structures using Ag nanoparticles

DEFF Research Database (Denmark)

Iida, Daisuke; Fadil, Ahmed; Chen, Yuntian

2015-01-01

We report internal quantum efficiency enhancement of thin p-GaN green quantumwell structure using self-assembled Ag nanoparticles. Temperature dependent photoluminescence measurements are conducted to determine the internal quantum efficiency. The impact of excitation power density on the enhance......We report internal quantum efficiency enhancement of thin p-GaN green quantumwell structure using self-assembled Ag nanoparticles. Temperature dependent photoluminescence measurements are conducted to determine the internal quantum efficiency. The impact of excitation power density...

Effects of crossed states on photoluminescence excitation spectroscopy of InAs quantum dots

Directory of Open Access Journals (Sweden)

Lin Chien-Hung

2011-01-01

Full Text Available Abstract In this report, the influence of the intrinsic transitions between bound-to-delocalized states (crossed states or quasicontinuous density of electron-hole states on photoluminescence excitation (PLE spectra of InAs quantum dots (QDs was investigated. The InAs QDs were different in size, shape, and number of bound states. Results from the PLE spectroscopy at low temperature and under a high magnetic field (up to 14 T were compared. Our findings show that the profile of the PLE resonances associated with the bound transitions disintegrated and broadened. This was attributed to the coupling of the localized QD excited states to the crossed states and scattering of longitudinal acoustical (LA phonons. The degree of spectral linewidth broadening was larger for the excited state in smaller QDs because of the higher crossed joint density of states and scattering rate.

Bounds on absolutely maximally entangled states from shadow inequalities, and the quantum MacWilliams identity

Science.gov (United States)

Huber, Felix; Eltschka, Christopher; Siewert, Jens; Gühne, Otfried

2018-04-01

A pure multipartite quantum state is called absolutely maximally entangled (AME), if all reductions obtained by tracing out at least half of its parties are maximally mixed. Maximal entanglement is then present across every bipartition. The existence of such states is in many cases unclear. With the help of the weight enumerator machinery known from quantum error correction and the shadow inequalities, we obtain new bounds on the existence of AME states in dimensions larger than two. To complete the treatment on the weight enumerator machinery, the quantum MacWilliams identity is derived in the Bloch representation. Finally, we consider AME states whose subsystems have different local dimensions, and present an example for a 2×3×3×3 system that shows maximal entanglement across every bipartition.

Characteristics of exciton photoluminescence kinetics in low-dimensional silicon structures

CERN Document Server

Sachenko, A V; Manojlov, E G; Svechnikov, S V

2001-01-01

The time-resolved visible photoluminescence of porous nanocrystalline silicon films obtained by laser ablation have been measured within the temperature range 90-300 K. A study has been made of the interrelationship between photoluminescence characteristics (intensity, emission spectra, relaxation times, their temperature dependencies and structural and dielectric properties (size and shapes of Si nanocrystals, oxide phase of nanocrystal coating, porosity). A photoluminescence model is proposed that describes photon absorption and emission occurring in quantum-size Si nanocrystals while coupled subsystems of electron-hole pairs and excitons take part in the recombination. Possible excitonic Auger recombination mechanism in low-dimensional silicon structures is considered

The new Absolute Quantum Gravimeter (AQG): first results and perspectives

Science.gov (United States)

Bonvalot, Sylvain; Le Moigne, Nicolas; Merlet, Sebastien; Desruelle, Bruno; Lautier-Gaud, Jean; Menoret, Vincent; Vermeulen, Pierre

2016-04-01

Cold atom gravimetry represents one of the most innovative evolution in gravity instrumentation since the last 20 years. The concept of measuring the gravitational acceleration by dropping atoms and the development of the first instrumental devices during this last decade quickly revealed the promising perspectives of this new generation of gravity meters enabling accurate and absolute measurements of the Earth's gravity field for a wide range of applications (geophysics, geodesy, metrology, etc.). The Absolute Quantum Gravimeter (AQG) gravity meter, developed by MUQUANS (Talence, France - http://www.muquans.com/) with the support of RESIF, the French Seismologic and Geodetic Network (http://www.resif.fr/) belongs to this new generation of instruments. It also represents the first commercial device based on the utilization of advanced matter-wave interferometry techniques, which allow to characterize precisely the vertical acceleration experienced by a cloud of cold atoms. Recently, the first operational unit (AQG01) has been achieved as a compact transportable gravimeter with the aim of satisfying absolute gravity measurements in laboratory conditions under the following specifications: measurements the μGal level at a few Hz cycling frequency, sensitivity of 50μGal/√Hz, immunity to ground vibrations, easy and quickness of operation, automated continuous data acquisition for several months, etc. In order to evaluate the current performances of the AQG01, several experiments are carried out in collaboration between RESIF user's teams and the MUQUANS manufacturer on different reference gravity sites and laboratories in France. These measurements performed in indoor conditions including simultaneous observations with classical reference gravity instruments (corner-cube absolute gravity meters, relative superconducting meters) as well with the Cold Atom Gravity meter (CAG) developed by LNE-SYRTE, lead to a first objective characterization of the performances of

Photoluminescence study of the nitrogen content effect on GaAs/GaAs1-xNx/GaAs/AlGaAs: (Si) quantum well

International Nuclear Information System (INIS)

Hamdouni, A.; Bousbih, F.; Ben bouzid, S.; Aloulou, S.; Harmand, J.C.; Chtourou, R.

2008-01-01

We study the effect of nitrogen content in modulation-doped GaAs/GaAs 1-x N x /GaAs/GaAlAs:(Si) quantum well using low-temperature photoluminescence spectroscopy. The samples were grown on GaAs (001) substrates by molecular-beam epitaxy with different nitrogen compositions. The variation of the nitrogen composition from 0.04% to 0.32% associated to the bi-dimensional electron gas gives a new interaction mode between the nitrogen localized states and the GaAs 1-x N x /GaAs energies levels. The red-shift observed in photoluminescence spectra as function of nitrogen content has been interpreted in the frame of the band anticrossing model

Stochastic quantum confinement in nanocrystalline silicon layers: The role of quantum dots, quantum wires and localized states

International Nuclear Information System (INIS)

Ramírez-Porras, A.; García, O.; Vargas, C.; Corrales, A.; Solís, J.D.

2015-01-01

Highlights: • PL spectra of porous silicon samples have been studied using a stochastic model. • This model can deconvolute PL spectra into three components. • Quantum dots, quantum wires and localized states have been identified. • Nanostructure diameters are in the range from 2.2 nm to 4.0 nm. • Contributions from quantum wires are small compared to the others. - Abstract: Nanocrystallites of Silicon have been produced by electrochemical etching of crystal wafers. The obtained samples show photoluminescence in the red band of the visible spectrum when illuminated by ultraviolet light. The photoluminescence spectra can be deconvolved into three components according to a stochastic quantum confinement model: one band coming from Nanocrystalline dots, or quantum dots, one from Nanocrystalline wires, or quantum wires, and one from the presence of localized surface states related to silicon oxide. The results fit well within other published models

Stochastic quantum confinement in nanocrystalline silicon layers: The role of quantum dots, quantum wires and localized states

Energy Technology Data Exchange (ETDEWEB)

Ramírez-Porras, A., E-mail: aramirez@fisica.ucr.ac.cr [Centro de Investigación en Ciencia e Ingeniería de Materiales (CICIMA), Universidad de Costa Rica, San Pedro de Montes de Oca 11501 (Costa Rica); Escuela de Física, Universidad de Costa Rica, San Pedro de Montes de Oca 11501 (Costa Rica); García, O. [Escuela de Física, Universidad de Costa Rica, San Pedro de Montes de Oca 11501 (Costa Rica); Escuela de Química, Universidad de Costa Rica, San Pedro de Montes de Oca 11501 (Costa Rica); Vargas, C. [Escuela de Física, Universidad de Costa Rica, San Pedro de Montes de Oca 11501 (Costa Rica); Corrales, A. [Escuela de Física, Universidad de Costa Rica, San Pedro de Montes de Oca 11501 (Costa Rica); Escuela de Química, Universidad de Costa Rica, San Pedro de Montes de Oca 11501 (Costa Rica); Solís, J.D. [Escuela de Física, Universidad de Costa Rica, San Pedro de Montes de Oca 11501 (Costa Rica)

2015-08-30

Highlights: • PL spectra of porous silicon samples have been studied using a stochastic model. • This model can deconvolute PL spectra into three components. • Quantum dots, quantum wires and localized states have been identified. • Nanostructure diameters are in the range from 2.2 nm to 4.0 nm. • Contributions from quantum wires are small compared to the others. - Abstract: Nanocrystallites of Silicon have been produced by electrochemical etching of crystal wafers. The obtained samples show photoluminescence in the red band of the visible spectrum when illuminated by ultraviolet light. The photoluminescence spectra can be deconvolved into three components according to a stochastic quantum confinement model: one band coming from Nanocrystalline dots, or quantum dots, one from Nanocrystalline wires, or quantum wires, and one from the presence of localized surface states related to silicon oxide. The results fit well within other published models.

The photoluminescence decay time of self-assembled InAs quantum dots covered by InGaAs layers

International Nuclear Information System (INIS)

Shu, G W; Wang, C K; Wang, J S; Shen, J L; Hsiao, R S; Chou, W C; Chen, J F; Lin, T Y; Ko, C H; Lai, C M

2006-01-01

The temperature dependence of the time-resolved photoluminescence (PL) of self-assembled InAs quantum dots (QDs) with InGaAs covering layers was investigated. The PL decay time increases with temperature from 50 to 170 K, and then decreases as the temperature increases further above 170 K. A model based on the phonon-assisted transition between the QD ground state and the continuum state is used to explain the temperature dependence of the PL decay time. This result suggests that the continuum states are important in the carrier capture in self-assembled InAs QDs

Functionalization of graphene oxide nanostructures improves photoluminescence and facilitates their use as optical probes in preclinical imaging

Science.gov (United States)

Prabhakar, Neeraj; Näreoja, Tuomas; von Haartman, Eva; Şen Karaman, Didem; Burikov, Sergey A.; Dolenko, Tatiana A.; Deguchi, Takahiro; Mamaeva, Veronika; Hänninen, Pekka E.; Vlasov, Igor I.; Shenderova, Olga A.; Rosenholm, Jessica M.

2015-06-01

Recently reported photoluminescent nanographene oxides (nGOs), i.e. nanographene oxidised with a sulfuric/nitric acid mixture (SNOx method), have tuneable photoluminescence and are scalable, simple and fast to produce optical probes. This material belongs to the vast class of photoluminescent carbon nanostructures, including carbon dots, nanodiamonds (NDs), graphene quantum dots (GQDs), all of which demonstrate a variety of properties that are attractive for biomedical imaging such as low toxicity and stable photoluminescence. In this study, the nGOs were organically surface-modified with poly(ethylene glycol)-poly(ethylene imine) (PEG-PEI) copolymers tagged with folic acid as the affinity ligand for cancer cells expressing folate receptors. The functionalization enhanced both the cellular uptake and quantum efficiency of the photoluminescence as compared to non-modified nGOs. The nGOs exhibited an excitation dependent photoluminescence that facilitated their detection with a wide range of microscope configurations. The functionalized nGOs were non-toxic, they were retained in the stained cell population over a period of 8 days and they were distributed equally between daughter cells. We have evaluated their applicability in in vitro and in vivo (chicken embryo CAM) models to visualize and track migratory cancer cells. The good biocompatibility and easy detection of the functionalized nGOs suggest that they could address the limitations faced with quantum dots and organic fluorophores in long-term in vivo biomedical imaging.Recently reported photoluminescent nanographene oxides (nGOs), i.e. nanographene oxidised with a sulfuric/nitric acid mixture (SNOx method), have tuneable photoluminescence and are scalable, simple and fast to produce optical probes. This material belongs to the vast class of photoluminescent carbon nanostructures, including carbon dots, nanodiamonds (NDs), graphene quantum dots (GQDs), all of which demonstrate a variety of properties that are

Intense, stable and excitation wavelength-independent photoluminescence emission in the blue-violet region from phosphorene quantum dots

Science.gov (United States)

Ge, Shuaipeng; Zhang, Lisheng; Wang, Peijie; Fang, Yan

2016-01-01

Nanoscale phosphorene quantum dots (PQDs) with few-layer structures were fabricated by pulsed laser ablation of a bulk black phosphorus target in diethyl ether. An intense and stable photoluminescence (PL) emission of the PQDs in the blue-violet wavelength region is clearly observed for the first time, which is attributed to electronic transitions from the lowest unoccupied molecular orbital (LUMO) to the highest occupied molecular orbital (HOMO) and occupied molecular orbitals below the HOMO (H-1, H-2), respectively. Surprisingly, the PL emission peak positions of the PQDs are not red-shifted with progressively longer excitation wavelengths, which is in contrast to the cases of graphene and molybdenum disulphide quantum dots. This excitation wavelength-independence is derived from the saturated passivation on the periphery and surfaces of the PQDs by large numbers of electron-donating functional groups which cause the electron density on the PQDs to be dramatically increased and the band gap to be insensitive to the quantum size effect in the PQDs. This work suggests that PQDs with intense, stable and excitation wavelength-independent PL emission in the blue-violet region have a potential application as semiconductor-based blue-violet light irradiation sources. PMID:27265198

Polarized photoluminescence excitation spectroscopy of a-plane InGaN/GaN multiple quantum wells grown on r-plane sapphire

Energy Technology Data Exchange (ETDEWEB)

Kundys, D., E-mail: dmytro.kundys@manchester.ac.uk; Sutherland, D.; Badcock, T. J.; Dawson, P. [School of Physics and Astronomy, Photon Science Institute, University of Manchester, Manchester M13 9PL (United Kingdom); Schulz, S. [Photonics Theory group, Tyndall National Institute, Lee Maltings, Cork (Ireland); Oehler, F.; Kappers, M. J.; Oliver, R. A.; Humphreys, C. J. [Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, CB3 0FS (United Kingdom)

2014-03-21

We have performed a detailed study of the impact of basal plane stacking faults (BSFs) on the optical properties of both a-plane InGaN/GaN quantum wells (QWs) and GaN template samples grown on r-sapphire. In particular, we have used polarised photoluminescence excitation spectroscopy (P-PLE) to investigate the nature of the low temperature recombination as well as extracting information on the valence band (VB) polarisation anisotropy. Our low temperature P-PLE results revealed not only excitons associated with intersubband quantum well transitions and the GaN barrier material but also a transition associated with creation of excitons in BSFs. The strength of this BSF transition varied with detection energy across the quantum well emission suggesting that there is a significant contribution to the emission line width from changes in the local electronic environment of the QWs due to interactions with BSFs. Furthermore, we observed a corresponding progressive increase in the VB splitting of the QWs as the detection energy was varied across the quantum well emission spectrum.

Role of quantum-confined stark effect on bias dependent photoluminescence of N-polar GaN/InGaN multi-quantum disk amber light emitting diodes

Science.gov (United States)

Tangi, Malleswararao; Mishra, Pawan; Janjua, Bilal; Prabaswara, Aditya; Zhao, Chao; Priante, Davide; Min, Jung-Wook; Ng, Tien Khee; Ooi, Boon S.

2018-03-01

We study the impact of quantum-confined stark effect (QCSE) on bias dependent micro-photoluminescence emission of the quantum disk (Q-disk) based nanowires light emitting diodes (NWs-LED) exhibiting the amber colored emission. The NWs are found to be nitrogen polar (N-polar) verified using KOH wet chemical etching and valence band spectrum analysis of high-resolution X-ray photoelectron spectroscopy. The crystal structure and quality of the NWs were investigated by high-angle annular dark field - scanning transmission electron microscopy. The LEDs were fabricated to acquire the bias dependent micro-photoluminescence spectra. We observe a redshift and a blueshift of the μPL peak in the forward and reverse bias conditions, respectively, with reference to zero bias, which is in contrast to the metal-polar InGaN well-based LEDs in the literature. Such opposite shifts of μPL peak emission observed for N-polar NWs-LEDs, in our study, are due to the change in the direction of the internal piezoelectric field. The quenching of PL intensity, under the reverse bias conditions, is ascribed to the reduction of electron-hole overlap. Furthermore, the blueshift of μPL emission with increasing excitation power reveals the suppression of QCSE resulting from the photo-generated carriers. Thereby, our study confirms the presence of QCSE for NWs-LEDs from both bias and power dependent μPL measurements. Thus, this study serves to understand the QCSE in N-polar InGaN Q-disk NWs-LEDs and other related wide-bandgap nitride nanowires, in general.

Role of quantum-confined stark effect on bias dependent photoluminescence of N-polar GaN/InGaN multi-quantum disk amber light emitting diodes

KAUST Repository

Tangi, Malleswararao

2018-03-09

We study the impact of quantum-confined stark effect (QCSE) on bias dependent micro-photoluminescence emission of the quantum disk (Q-disk) based nanowires light emitting diodes (NWs-LED) exhibiting the amber colored emission. The NWs are found to be nitrogen polar (N-polar) verified using KOH wet chemical etching and valence band spectrum analysis of high-resolution X-ray photoelectron spectroscopy. The crystal structure and quality of the NWs were investigated by high-angle annular dark field - scanning transmission electron microscopy. The LEDs were fabricated to acquire the bias dependent micro-photoluminescence spectra. We observe a redshift and a blueshift of the μPL peak in the forward and reverse bias conditions, respectively, with reference to zero bias, which is in contrast to the metal-polar InGaN well-based LEDs in the literature. Such opposite shifts of μPL peak emission observed for N-polar NWs-LEDs, in our study, are due to the change in the direction of the internal piezoelectric field. The quenching of PL intensity, under the reverse bias conditions, is ascribed to the reduction of electron-hole overlap. Furthermore, the blueshift of μPL emission with increasing excitation power reveals the suppression of QCSE resulting from the photo-generated carriers. Thereby, our study confirms the presence of QCSE for NWs-LEDs from both bias and power dependent μPL measurements. Thus, this study serves to understand the QCSE in N-polar InGaN Q-disk NWs-LEDs and other related wide-bandgap nitride nanowires, in general.

Optical properties of the semiconductor quantum structure

International Nuclear Information System (INIS)

Haratizadeh, H.; Holtz, P.O.; Monemar, B.; Karlsoon, K.F.; Moskalenko, E.S.; Amano, H.; Akasaki, I.; Schoenfeld, W.V.; Garcia, J.M.; Petroff, P.M.

2004-01-01

Optical properties of the quantum structures have been discussed with emphasize of the AlGaN/GaN multiple quantum wells and InAs/GaAs quantum dot structures. We report on a detailed study of low temperature photoluminescence in Al 0 .07Ga 0 .93 N/GaN multiple quantum wells. The structures were nominally undoped multiple quantum well grown on sapphire substrate. The structure from discrete well width variations is here resolved in photoluminescence spectra. The results demonstrate that the theoretically estimated fields in this work are consistent with the experimental spectra

Photoluminescence of Diamondoid Crystals

Energy Technology Data Exchange (ETDEWEB)

Clay, William; /Stanford U., Phys. Dept. /Stanford U., Appl. Phys. Dept. /Stanford U., Geballe Lab.; Sasagawa, Takao; Iwasa, Akio; /TIT, Nagatsuta; Liu, Zhi; /LBNL, ALS; Dahl, Jeremy E.; /Stanford U., Phys. Dept. /Stanford U., Appl. Phys. Dept. /Stanford U., Geballe Lab.; Carlson, Robert M.K.; /Molecular Diamond Technologies, Chevron Technology Ventures; Kelly, Michael; Melos, Nicholas; /Stanford U., Phys. Dept. /Stanford U., Appl. Phys. Dept. /Stanford U., Geballe Lab.; Shen, Zhi-Xun; /Stanford U., Phys. Dept. /Stanford U., Appl. Phys. Dept. /Stanford U., Geballe Lab. /SIMES, Stanford

2012-04-03

The photoluminescence of diamondoids in the solid state is examined. All of the diamondoids are found to photoluminesce readily with initial excitation wavelengths ranging from 233 nm to 240 nm (5.3 eV). These excitation energies are more than 1 eV lower than any previously studied saturated hydrocarbon material. The emission is found to be heavily shifted from the absorption, with emission wavelengths of roughly 295 nm (4.2 eV) in all cases. In the dissolved state, however, no uorescence is observed for excitation wavelengths as short as 200 nm. We also discuss predictions and measurements of the quantum yield. Our predictions indicate that the maximum yield may be as high as 25%. Our measurement of one species, diamantane, gives a yield of 11%, the highest ever reported for a saturated hydrocarbon, even though it was likely not at the optimal excitation wavelength.

Effect of Ligand Exchange on the Photoluminescence Properties of Cu-Doped Zn-In-Se Quantum Dots

Science.gov (United States)

Dong, Xiaofei; Xu, Jianping; Yang, Hui; Zhang, Xiaosong; Mo, Zhaojun; Shi, Shaobo; Li, Lan; Yin, Shougen

2018-04-01

The surface-bound ligands of a semiconductor nanocrystal can affect its electron transition behavior. We investigate the photoluminescence (PL) properties of Cu-doped Zn-In-Se quantum dots (QDs) through the exchange of oleylamine with 6-mercaptohexanol (MCH). Fourier transform infrared and 1H nuclear magnetic resonance spectroscopies, and mass spectrometry reveal that the short-chain MCH molecules are bound to the QD surface. The emission peaks remain unchanged after ligand exchange, and the PL quantum yield is reduced from 49% to 38%. The effects of particle size and defect type on the change in PL behavior upon ligand substitution are excluded through high-resolution transmission electron microscopy, UV-Vis absorption, and PL spectroscopies. The origin of the decreased PL intensity is associated with increased ligand density and the stronger ligand electron-donating abilities of MCH-capped QDs that induce an increase in the nonradiative transition probability. A lower PL quenching transition temperature is observed for MCH-capped QDs and is associated with increasing electron-acoustic phonon coupling due to the lower melting temperature of MCH.

Infrared photoluminescence of high In-content InN/InGaN multiple-quantum-wells

Energy Technology Data Exchange (ETDEWEB)

Valdueza-Felip, Sirona; Naranjo, Fernando B.; Gonzalez-Herraez, Miguel [Electronics Department, University of Alcala, Alcala de Henares (Spain); Rigutti, Lorenzo; Julien, Francois H. [Institut d' Electronique Fondamentale, University of Paris Sud XI, UMR 8622 CNRS, Orsay (France); Lacroix, Bertrand; Ruterana, Pierre [Centre de Recherche sur les Ions les Materiaux et la Photonique (CIMAP), UMR 6252, CNRS, ENSICAEN, CEA, UCBN, Caen (France); Fernandez, Susana [Departamento de Energias Renovables, Energia Solar Fotovoltaica, CIEMAT, Madrid (Spain); Monroy, Eva [CEA Grenoble, INAC/SP2M, Grenoble (France)

2012-01-15

We report on the thermal evolution of the photoluminescence (PL) from high In-content InN/In{sub 0.9}Ga{sub 0.1}N multiple-quantum wells (MQWs) synthesized by plasma-assisted molecular-beam epitaxy on GaN-on-sapphire templates. The structural quality and the well/barrier thickness uniformity in the MQW structure are assessed by X-ray diffraction and transmission electron microscopy measurements. PL results are compared with the luminescence from a 1-{mu}m-thick InN reference sample. In both cases, the dominant low-temperature (5 K) PL emission peaks at {proportional_to}0.73 eV with a full width at half maximum of {proportional_to}86 meV. The InN layer displays an S-shape evolution of the emission peak energy with temperaure, explained in terms of carrier localization. A carrier localization energy of {proportional_to}12 meV is estimated for the InN layer, in good agreement with the expected carrier concentration. In the case of the MQW structure, an enhancement of the carrier localization associated to the piezoelectric field results in an improved thermal stability of the PL intensity, reaching an internal quantum efficiency of {proportional_to}16%. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Infrared photoluminescence of high In-content InN/InGaN multiple-quantum-wells

International Nuclear Information System (INIS)

Valdueza-Felip, Sirona; Naranjo, Fernando B.; Gonzalez-Herraez, Miguel; Rigutti, Lorenzo; Julien, Francois H.; Lacroix, Bertrand; Ruterana, Pierre; Fernandez, Susana; Monroy, Eva

2012-01-01

We report on the thermal evolution of the photoluminescence (PL) from high In-content InN/In 0.9 Ga 0.1 N multiple-quantum wells (MQWs) synthesized by plasma-assisted molecular-beam epitaxy on GaN-on-sapphire templates. The structural quality and the well/barrier thickness uniformity in the MQW structure are assessed by X-ray diffraction and transmission electron microscopy measurements. PL results are compared with the luminescence from a 1-μm-thick InN reference sample. In both cases, the dominant low-temperature (5 K) PL emission peaks at ∝0.73 eV with a full width at half maximum of ∝86 meV. The InN layer displays an S-shape evolution of the emission peak energy with temperature, explained in terms of carrier localization. A carrier localization energy of ∝12 meV is estimated for the InN layer, in good agreement with the expected carrier concentration. In the case of the MQW structure, an enhancement of the carrier localization associated to the piezoelectric field results in an improved thermal stability of the PL intensity, reaching an internal quantum efficiency of ∝16%. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Size dependent photoluminescence property of hydrothermally synthesized crystalline carbon quantum dots

Energy Technology Data Exchange (ETDEWEB)

Sarkar, S.; Banerjee, D.; Ghorai, U.K.; Das, N.S. [School of Material Science and Nanotechnology Jadavpur University, Kolkata 700032 (India); Chattopadhyay, K.K., E-mail: kalyan_chattopadhyay@yahoo.com [School of Material Science and Nanotechnology Jadavpur University, Kolkata 700032 (India); Thin Film and NanoScience Laboratory, Department of Physics, Jadavpur University, Kolkata 700032 (India)

2016-10-15

In this work, simple hydrothermal synthesis of water soluble Carbon quantum dots (CQDs) of different sizes has been reported. The effect of synthesis temperature and synthesis time on the particle size has also been shown. The structures of all the as-prepared samples were studied by field emission scanning electron microscope and high resolution transmission electron microscope. Fourier transformed infrared spectrophotometer analyzes the different bonding present in the sample whereas Raman spectrophotometer quantifies the hybridization state of the prepared samples. UV–vis spectrophotometer gives the variation of absorbance of all the samples with wavelength. Dynamic light scattering study shows the variation of particle size with deposition condition and corresponding zeta potential gives the idea about the stability of the CQD solutions. The photoluminescence (PL) properties of the as prepared CQDs were also studied in detail. It is noticed that with the increase of excitation wavelength, the PL emissions for the different samples were red shifted. The results have been explained in terms of the excitation dependent emission, variations in size of the CQD and presence of different functional groups on the surface of CQDs.

Size dependent photoluminescence property of hydrothermally synthesized crystalline carbon quantum dots

International Nuclear Information System (INIS)

Sarkar, S.; Banerjee, D.; Ghorai, U.K.; Das, N.S.; Chattopadhyay, K.K.

2016-01-01

In this work, simple hydrothermal synthesis of water soluble Carbon quantum dots (CQDs) of different sizes has been reported. The effect of synthesis temperature and synthesis time on the particle size has also been shown. The structures of all the as-prepared samples were studied by field emission scanning electron microscope and high resolution transmission electron microscope. Fourier transformed infrared spectrophotometer analyzes the different bonding present in the sample whereas Raman spectrophotometer quantifies the hybridization state of the prepared samples. UV–vis spectrophotometer gives the variation of absorbance of all the samples with wavelength. Dynamic light scattering study shows the variation of particle size with deposition condition and corresponding zeta potential gives the idea about the stability of the CQD solutions. The photoluminescence (PL) properties of the as prepared CQDs were also studied in detail. It is noticed that with the increase of excitation wavelength, the PL emissions for the different samples were red shifted. The results have been explained in terms of the excitation dependent emission, variations in size of the CQD and presence of different functional groups on the surface of CQDs.

Thermal activation of carriers from semiconductor quantum wells

International Nuclear Information System (INIS)

Johnston, M.B.; Herz, L.M.; Dao, L.V.; Gal, M.; Tan, H.H.; Jagadish, C.

1999-01-01

Full text: We have conducted a systematic investigation of the thermal excitation of carriers in confined states of quantum wells. Carriers may be injected into a sample containing a quantum well electrically or optically, once there they rapidly thermalise and are captured by the confined state of the quantum well. Typically electrons and holes recombine radiatively from their respective quantum well states. As a quantum well sample is heated from low temperatures (∼10K), phonon interactions increase which leads to carriers being excited from the well region into the higher energy, barrier region of the sample. Since carrier recombination from barrier regions is via non-radiative processes, there is strong temperature dependence of photoluminescence from the quantum well region. We measured quantum well photoluminescence as a function of excitation intensity and wavelength over the temperature range from 8K to 300K. In high quality InGaAs quantum wells we found unexpected intensity dependence of the spectrally integrated temperature dependent photoluminescence. We believe that this is evidence for by the existence of saturable states at the interfaces of the quantum wells

Quantum efficiency and oscillator strength of site-controlled InAs quantum dots

DEFF Research Database (Denmark)

Albert, F.; Stobbe, Søren; Schneider, C.

2010-01-01

We report on time-resolved photoluminescence spectroscopy to determine the oscillator strength (OS) and the quantum efficiency (QE) of site-controlled InAs quantum dots nucleating on patterned nanoholes. These two quantities are determined by measurements on site-controlled quantum dot (SCQD...

The nature of the photoluminescence in amorphized PZT

International Nuclear Information System (INIS)

Silva, M.S.; Cilense, M.; Orhan, E.; Goes, M.S.; Machado, M.A.C.; Santos, L.P.S.; Paiva-Santos, C.O.; Longo, E.; Varela, J.A.; Zaghete, M.A.; Pizani, P.S.

2005-01-01

The polymeric precursor method was used to synthesize lead zirconate titanate powder (PZT). The crystalline powder was then amorphized by a high-energy ball milling process during 120 h. A strong photoluminescence emission was observed at room temperature for the amorphized PZT powder. The powders were characterized by XRD and the percentage of amorphous phase was calculated through Rietveld refinement. The microstructure for both phases was investigated by TEM. The optical gap was calculated through the Wood and Tauc method using the UV-Vis. data. Quantum mechanical calculations were carried out to give an interpretation of the photoluminescence in terms of electronic structure

Surface modification effects on defect-related photoluminescence in colloidal CdS quantum dots.

Science.gov (United States)

Lee, TaeGi; Shimura, Kunio; Kim, DaeGwi

2018-05-03

We investigated the effects of surface modification on the defect-related photoluminescence (PL) band in colloidal CdS quantum dots (QDs). A size-selective photoetching process and a surface modification technique with a Cd(OH)2 layer enabled the preparation of size-controlled CdS QDs with high PL efficiency. The Stokes shift of the defect-related PL band before and after the surface modification was ∼1.0 eV and ∼0.63 eV, respectively. This difference in the Stokes shifts suggests that the origin of the defect-related PL band was changed by the surface modification. Analysis by X-ray photoelectron spectroscopy revealed that the surface of the CdS QDs before and after the surface modification was S rich and Cd rich, respectively. These results suggest that Cd-vacancy acceptors and S-vacancy donors affect PL processes in CdS QDs before and after the surface modification, respectively.

Quantum-well exciton polariton emission from multi-quantum-well wire structures

Science.gov (United States)

Kohl, M.; Heitmann, D.; Grambow, P.; Ploog, K.

The radiative decay of quantum-well exciton (QWE) polaritons in microstructured Al0.3Ga0.7As - GaAs multi-quantum wells (MQW) has been studied by photoluminescence spectroscopy. Periodic wire structures with lateral periodicities a = 250-500 nm and lateral widths t = 100-200 nm have been fabricated by plasma etching. The thickness of the QWs was 13 nm. In the QW wire samples the free-exciton photoluminescence was strongly reduced and the QWE polariton emission was observed as a maximum peaked at a 3 meV higher energy than the free QWE transition. In samples which had only a microstructured cladding layer, the free-exciton photoluminescence was dominant in the spectrum and the QWE polariton emission was observed as a shoulder on the high-energy side of the free QWE transition. In addition, two transitions at the low energy side of the free QWE photoluminescence were present in the microstructured samples, which were related to etching induced states.

Efficient Luminescence from Perovskite Quantum Dot Solids

KAUST Repository

Kim, Younghoon; Yassitepe, Emre; Voznyy, Oleksandr; Comin, Riccardo; Walters, Grant; Gong, Xiwen; Kanjanaboos, Pongsakorn; Nogueira, Ana F.; Sargent, Edward H.

2015-01-01

© 2015 American Chemical Society. Nanocrystals of CsPbX3 perovskites are promising materials for light-emitting optoelectronics because of their colloidal stability, optically tunable bandgap, bright photoluminescence, and excellent photoluminescence quantum yield. Despite their promise, nanocrystal-only films of CsPbX3 perovskites have not yet been fabricated; instead, highly insulating polymers have been relied upon to compensate for nanocrystals' unstable surfaces. We develop solution chemistry that enables single-step casting of perovskite nanocrystal films and overcomes problems in both perovskite quantum dot purification and film fabrication. Centrifugally cast films retain bright photoluminescence and achieve dense and homogeneous morphologies. The new materials offer a platform for optoelectronic applications of perovskite quantum dot solids.

Efficient Luminescence from Perovskite Quantum Dot Solids

KAUST Repository

Kim, Younghoon

2015-11-18

© 2015 American Chemical Society. Nanocrystals of CsPbX3 perovskites are promising materials for light-emitting optoelectronics because of their colloidal stability, optically tunable bandgap, bright photoluminescence, and excellent photoluminescence quantum yield. Despite their promise, nanocrystal-only films of CsPbX3 perovskites have not yet been fabricated; instead, highly insulating polymers have been relied upon to compensate for nanocrystals\\' unstable surfaces. We develop solution chemistry that enables single-step casting of perovskite nanocrystal films and overcomes problems in both perovskite quantum dot purification and film fabrication. Centrifugally cast films retain bright photoluminescence and achieve dense and homogeneous morphologies. The new materials offer a platform for optoelectronic applications of perovskite quantum dot solids.

Photoluminescence in Carborane-Stilbene Triads: A Structural, Spectroscopic, and Computational Study.

Science.gov (United States)

Cabrera-González, Justo; Viñas, Clara; Haukka, Matti; Bhattacharyya, Santanu; Gierschner, Johannes; Núñez, Rosario

2016-09-12

A set of triads in which o- and m-carborane clusters are bonded to two stilbene units through Ccluster -CH2 bonds was synthesized, and their structures were confirmed by X-ray diffraction. A study on the influence of the o- and m- isomers on the absorption and photoluminescence properties of the stilbene units in solution revealed no charge-transfer contributions in the lowest excited state, as confirmed by (TD)DFT calculations. The presence of one or two B-I groups in m-carborane derivatives does not affect the emission properties of the stilbenes in solution, probably due to the rather large distance between the iodo substituents and the fluorophore. Nevertheless, a significant redshift of the photoluminescence (PL) emission maximum in the solid state (thin films and powder samples) compared to solution was observed; this can be traced back to PL sensitization, most probably due to more densely packed stilbene moieties. Remarkably, the PL absolute quantum yields of powder samples are significantly higher than those in solution, and this was attributed to the restricted environment and the aforementioned sensitization. Thus, the bonding of the carborane clusters to two stilbene units preserves their PL behavior in solution, but produces significant changes in the solid state. Furthermore, iodinated species can be considered to be promising precursors for theranostic agents in which both imaging and therapeutic functions could possibly be combined. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Simple and greener synthesis of highly photoluminescence Mn{sup 2+}-doped ZnS quantum dots and its surface passivation mechanism

Energy Technology Data Exchange (ETDEWEB)

Wang, Yongbo; Liang, Xuhua; Ma, Xuan; Hu, Yahong [School of Chemical Engineering, Northwest University, No. 229 Taibai North Road, Xi’an, Shannxi, 710069 (China); Hu, Xiaoyun; Li, Xinghua [Department of Physics, Northwest University, No. 229 Taibai North Road, Xi’an, Shannxi, 710069 (China); Fan, Jun, E-mail: fanjun@nwu.edu.cn [School of Chemical Engineering, Northwest University, No. 229 Taibai North Road, Xi’an, Shannxi, 710069 (China)

2014-10-15

Graphical abstract: TEM and HRTEM (inset) images of the as-prepared Mn{sup 2+}-doped ZnS QDs and the passivation mechanism model of GSH-capped ZnS QDs (b). - Highlights: • Highly photoluminescent Mn{sup 2+}-doped ZnS quantum dots were synthesized by a simple synthetic method. • The effects of Mn{sup 2+} doping concentration, reaction time and temperature on PL intensity were investigated. • The mechanism of surface passivation was described. - Abstract: In this paper, we reported a simple synthetic method of highly photoluminescent (PL) and stable Mn{sup 2+}-doped ZnS quantum dots (QDs) with glutathione (GSH) as the capping molecule and focused on mechanism of the surface passivation of QDs. The Mn{sup 2+}-doped ZnS QDs that was synthesized in basic solution (pH 10) at 120 °C for 5 h exhibited blue trap-state emission around 418 nm and a strong orange-red emission at about 580 nm with an excitation wavelength of 330 nm. The optimum doping concentration is determined to be 1.5 at.%, and the present Mn{sup 2+}-doped ZnS QDs synthesized under the optimal reaction condition exhibited a quantum yield of 48%. High resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) indicated that the Mn{sup 2+}-doped ZnS QDs were 3–5 nm in size with a zinc blend structure. More importantly, the PL intensity and chemical stability can be improved using organic ligand modification strategies, it was found that GSH could passivate surface defects very efficiently by comparing and analyzing the results of the different organic ligands modification. The cadmium-free Mn{sup 2+}-doped ZnS QDs well-passivated with GSH as capping molecule acquired the advantages of strong PL and excellent chemical stability, which are important to QD applications.

Ratiometric photoluminescence sensing based on Ti3C2 MXene quantum dots as an intracellular pH sensor.

Science.gov (United States)

Chen, Xu; Sun, Xueke; Xu, Wen; Pan, Gencai; Zhou, Donglei; Zhu, Jinyang; Wang, He; Bai, Xue; Dong, Biao; Song, Hongwei

2018-01-18

Intracellular pH sensing is of importance and can be used as an indicator for monitoring the evolution of various diseases and the health of cells. Here, we developed a new class of surface-functionalized MXene quantum dots (QDs), Ti 3 C 2 , by the sonication cutting and hydrothermal approach and further explored their intracellular pH sensing. The functionalized Ti 3 C 2 QDs exhibit bright excitation-dependent blue photoluminescence (PL) originating from the size effect and surface defects. Meanwhile, Ti 3 C 2 QDs demonstrate a high PL response induced by the deprotonation of the surface defects. Furthermore, combining the highly pH sensitive Ti 3 C 2 QDs with the pH insensitive [Ru(dpp) 3 ]Cl 2 , we developed a ratiometric pH sensor to quantitatively monitor the intracellular pH values. These novel MXene quantum dots can serve as a promising platform for developing practical fluorescent nanosensors.

Quantum efficiency and oscillator strength of site-controlled InGaAs quantum dots

DEFF Research Database (Denmark)

Albert, F.; Schneider, C.; Stobbe, Søren

2010-01-01

We report on time-resolved photoluminescence spectroscopy to determine the oscillator strength (OS) and the quantum efficiency (QE) of site-controlled In(Ga)As quantum dots nucleating on patterned nanoholes. These two quantities are determined by measurements on site-controlled quantum dot (SCQD...

Photoluminescence investigation of type-II GaSb/GaAs quantum dots grown by liquid phase epitaxy

Science.gov (United States)

Wang, Yang; Hu, Shuhong; Xie, Hao; Lin, Hongyu; lu, Hongbo; Wang, Chao; Sun, Yan; Dai, Ning

2018-06-01

GaSb quantum dots (QDs) with an areal density of ∼1 × 1010 cm-2 are successfully grown by the modified (rapid slider) liquid phase epitaxy technique. The morphology of the QDs has been investigated by scanning electron microscope (SEM) and atom force microscope (AFM). The power-dependence and temperature-dependence photoluminescence (PL) spectra have been studied. The bright room-temperature PL suggests a good luminescence quality of GaSb QDs/GaAs matrix system. The type-II alignment of the GaSb QDs/GaAs matrix system is verified by the blue-shift of the QDs peak with the increase of excitation power. From the temperature-dependence PL spectra, the activation energy of QDs is determined to be 111 meV.

Enhanced photoluminescence from porous silicon by hydrogen-plasma etching

International Nuclear Information System (INIS)

Wang, Q.; Gu, C.Z.; Li, J.J.; Wang, Z.L.; Shi, C.Y.; Xu, P.; Zhu, K.; Liu, Y.L.

2005-01-01

Porous silicon (PS) was etched by hydrogen plasma. On the surface a large number of silicon nanocone arrays and nanocrystallites were formed. It is found that the photoluminescence of the H-etched porous silicon is highly enhanced. Correspondingly, three emission centers including red, green, and blue emissions are shown to contribute to the enhanced photoluminescence of the H-etched PS, which originate from the recombination of trapped electrons with free holes due to Si=O bonding at the surface of the silicon nanocrystallites, the quantum size confinement effect, and oxygen vacancy in the surface SiO 2 layer, respectively. In particular, the increase of SiO x (x<2) formed on the surface of the H-etched porous silicon plays a very important role in enhancing the photoluminescence properties

In-plane magneto-photoluminescence studies of modulation-doped GaAs/AlGaAs coupled double quantum wells

Energy Technology Data Exchange (ETDEWEB)

KIM,YONGMIN; PERRY,C.H.; SIMMONS,JERRY A.; KLEM,JOHN F.

2000-05-11

In-plane magnetic field photoluminescence spectra from n series of n-type modulation doped GaAs/Al{sub 0.3}Ga{sub 0.7}As coupled double quantum wells show distinctive doublet structures related to the tunnel-split ground sub-level states. The magnetic field behavior of the upper transition from the antisymmetric state strongly depends on sample mobility. In a lower mobility sample, the transition energy displays an N-type kink with field (namely a maximum followed by a minimum), whereas higher mobility samples have a linear dependence. The former is attributed to a coupling mechanism due to homogeneous broadening of the electron and hole states. The results are in good agreement with recent theoretical calculations.

Photoluminescence study of as-grown vertically standing wurtzite InP nanowire ensembles.

Science.gov (United States)

Iqbal, Azhar; Beech, Jason P; Anttu, Nicklas; Pistol, Mats-Erik; Samuelson, Lars; Borgström, Magnus T; Yartsev, Arkady

2013-03-22

We demonstrate a method that enables the study of photoluminescence of as-grown nanowires on a native substrate by non-destructively suppressing the contribution of substrate photoluminescence. This is achieved by using polarized photo-excitation and photoluminescence and by making an appropriate choice of incident angle of both excitation beam and photoluminescence collection direction. Using TE-polarized excitation at a wavelength of 488 nm at an incident angle of ∼70° we suppress the InP substrate photoluminescence relative to that of the InP nanowires by about 80 times. Consequently, the photoluminescence originating from the nanowires becomes comparable to and easily distinguishable from the substrate photoluminescence. The measured photoluminescence, which peaks at photon energies of ∼1.35 eV and ∼1.49 eV, corresponds to the InP substrate with zinc-blende crystal structure and to the InP nanowires with wurtzite crystal structure, respectively. The photoluminescence quantum yield of the nanowires was found to be ∼20 times lower than that of the InP substrate. The nanowires, grown vertically in a random ensemble, neither exhibit substantial emission polarization selectivity to the axis of the nanowires nor follow excitation polarization preferences observed previously for a single nanowire.

UV and air stability of high-efficiency photoluminescent silicon nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Yang, Jihua, E-mail: yangj@umn.edu [Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55455 (United States); Liptak, Richard [Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN 55455 (United States); Department of Physics and Optical Engineering, Rose-Hulman Institute of Technology, 5500 Wabash Ave, Terre Haute, IN 47803 (United States); Rowe, David; Wu, Jeslin [Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55455 (United States); Casey, James; Witker, David [Dow Corning Corporation, 2200 W. Salzburg Road, Midland, MI 48686 (United States); Campbell, Stephen A. [Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN 55455 (United States); Kortshagen, Uwe, E-mail: kortshagen@umn.edu [Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55455 (United States)

2014-12-30

The effects of UV light and air exposure on the photoluminescent properties of nonthermal plasma-synthesized silicon nanocrystals (Si NCs) were investigated. Si NCs with high-efficiency photoluminescence (PL) have been achieved via a post-synthesis hydrosilylation process. Photobleaching is observed within the first few hours of ultra-violet (UV) irradiation. Equilibrium is reached after ∼4 h of UV exposure wherein the Si NCs are able to retain 52% of the initially measured PL quantum yield (PLQY). UV-treated Si NCs showed recovery of PL with time. Gas-phase passivation of Si NCs by hydrogen afterglow injection improves PLQY and PL stability against UV and air exposure. Additionally, phosphorous doping can also improve UV stability of photoluminescent Si NCs.

Tailoring the photoluminescence polarization anisotropy of a single InAs quantum dash by a post-growth modification of its dielectric environment

Energy Technology Data Exchange (ETDEWEB)

Mrowiński, P.; Misiewicz, J.; Sęk, G. [Laboratory for Optical Spectroscopy of Nanostructures, Division of Experimental Physics, Faculty of Fundamental Problems of Technology, Wrocław University of Science and Technology, Wrocław (Poland); Tarnowski, K.; Olszewski, J.; Urbańczyk, W. [Division of Optics and Photonics, Faculty of Fundamental Problems of Technology, Wrocław University of Science and Technology, Wrocław (Poland); Somers, A.; Kamp, M. [Technische Physik & W. C. Röntgen-Center for Complex Material Systems, Universität Würzburg, Würzburg Germany (Germany); Reithmaier, J. P. [Institute of Nanostructure Technologies and Analytics (INA), CINSaT, University of Kassel, Heinrich-Plett-Str. 40, 34132 Kassel (Germany); Machnikowski, P. [Division of Theoretical Physics, Faculty of Fundamental Problems of Technology, Wrocław University of Science and Technology, Wrocław (Poland)

2016-08-21

Excitonic emission from single InAs/InGaAlAs/InP quantum dashes has been investigated in terms of controlling the polarization anisotropy by altering the shape of the processed sub-micrometer mesa structures. Photoluminescence has been measured from exemplary single quantum dashes emitting around 1.3 and 1.55 μm and placed inside rectangular mesas of various orientation, asymmetry, and sizes. The detected degree of linear polarization of bright exciton emission ranges from −0.1 to ca. 0.55, compared to 0.25 for dashes in unaltered or isotropic in-plane dielectric surrounding. These results are interpreted by numerical simulations using an emitter coupled with a single optical mode in such a mesa and outgoing in the direction normal to the sample surface.

Bidentate Ligand-passivated CsPbI3 Perovskite Nanocrystals for Stable Near-unity Photoluminescence Quantum Yield and Efficient Red Light-emitting Diodes

KAUST Repository

Pan, Jun

2017-12-17

Although halide perovskite nanocrystals (NCs) are promising materials for optoelectronic devices, they suffer severely from chemical and phase instabilities. Moreover, the common capping ligands like oleic acid and oleylamine that encapsulate the NCs will form an insulating layer, precluding their utility in optoelectronic devices. To overcome these limitations, we develop a post-synthesis passivation process for CsPbI3 NCs by using a bidentate ligand, namely 2,2’-Iminodibenzoic acid. Our passivated NCs exhibit narrow red photoluminescence with exceptional quantum yield (close to unity) and substantially improved stability. The passivated NCs enabled us to realize red light-emitting diodes (LEDs) with 5.02% external quantum efficiency and 748 cd/m2 luminance, surpassing by far LEDs made from the non-passivated NCs.

Bidentate Ligand-passivated CsPbI3 Perovskite Nanocrystals for Stable Near-unity Photoluminescence Quantum Yield and Efficient Red Light-emitting Diodes

KAUST Repository

Pan, Jun; Shang, Yuequn; Yin, Jun; de Bastiani, Michele; Peng, Wei; Dursun, Ibrahim; Sinatra, Lutfan; El-Zohry, Ahmed M.; Hedhili, Mohamed N.; Emwas, Abdul-Hamid M.; Mohammed, Omar F.; Ning, Zhijun; Bakr, Osman

2017-01-01

Although halide perovskite nanocrystals (NCs) are promising materials for optoelectronic devices, they suffer severely from chemical and phase instabilities. Moreover, the common capping ligands like oleic acid and oleylamine that encapsulate the NCs will form an insulating layer, precluding their utility in optoelectronic devices. To overcome these limitations, we develop a post-synthesis passivation process for CsPbI3 NCs by using a bidentate ligand, namely 2,2’-Iminodibenzoic acid. Our passivated NCs exhibit narrow red photoluminescence with exceptional quantum yield (close to unity) and substantially improved stability. The passivated NCs enabled us to realize red light-emitting diodes (LEDs) with 5.02% external quantum efficiency and 748 cd/m2 luminance, surpassing by far LEDs made from the non-passivated NCs.

Current measurement system utilizing cryogenic techniques for the absolute measurement of the magnetic flux quantum

International Nuclear Information System (INIS)

Endo, T.; Murayama, Y.; Sakamoto, Y.; Sakuraba, T.; Shiota, F.

1989-01-01

A series of systems composed of cryogenic devices such as a Josephson potentiometer and a cryogenic current comparator has been proposed and developed to precisely measure a current with any value up to 1 A. These systems will be used to measure the injected electrical energy with an uncertainty of the order of 0.01 ppm or less in the absolute measurement of the magnetic flux quantum by superconducting magnetic levitation. Some preliminary experiments are described

Highly photoluminescent europium tetraphenylimidodiphosphinate ternary complexes with heteroaromatic co-ligands. Solution and solid state studies

Energy Technology Data Exchange (ETDEWEB)

Pietraszkiewicz, Marek, E-mail: mpietraszkiewicz@ichf.edu.pl [Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw (Poland); Pietraszkiewicz, Oksana; Karpiuk, Jerzy; Majka, Alina [Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw (Poland); Dutkiewicz, Grzegorz; Borowiak, Teresa [Adam Mickiewicz University, Faculty of Chemistry, Department of Crystallography, Grunwaldzka 6, 60-780 Poznań (Poland); Kaczmarek, Anna M. [L3–Luminescent Lanthanide Lab, f-element coordination chemistry, Ghent University, Department of Inorganic and Physical Chemistry, Krijgslaan 281, Building S3, 9000 Gent (Belgium); Van Deun, Rik, E-mail: rik.vandeun@ugent.be [L3–Luminescent Lanthanide Lab, f-element coordination chemistry, Ghent University, Department of Inorganic and Physical Chemistry, Krijgslaan 281, Building S3, 9000 Gent (Belgium)

2016-02-15

Tetraphenylimidodiphosphinate (tpip) forms neutral 3:1 complexes with lanthanide ions. These complexes can accommodate one ancillary planar heterocyclic ligand to complement their coordination sphere of Eu{sup 3+} to coordination number 8. Several co-ligands were tested to form new complexes: 1,10-phenanthroline, bathophenanthroline, 2,4,6-tris(2-pyridyl)-1,3,5-triazine, dipyrido[3,2-f:2′,3′-h]quinoxaline and 2,2′:6′,2′′-terpyridine. The addition of heterocyclic N,N-bidentate co-ligands to the coordination sphere results in a dramatic (by a factor of 45–50) luminescence enhancement of the parent Eu(tpip){sub 3}. The solid-state measurements confirmed that the ancillary ligands strongly increased the photoluminescence quantum yield (PLQY) of the investigated complexes. - Highlights: • We have disovered highly photoluminescent ternary Eu(III) complexes. • They consist of Eu(III) tetraphenylimidodiphosphinate, and planar heterocyclic ligands. • The increase in photoluminescence quantum yields in solution is enhanced up to 50 times in solution. • The solid-state photoluminescence exceeds 80% at room temperature.

Highly photoluminescent europium tetraphenylimidodiphosphinate ternary complexes with heteroaromatic co-ligands. Solution and solid state studies

International Nuclear Information System (INIS)

Pietraszkiewicz, Marek; Pietraszkiewicz, Oksana; Karpiuk, Jerzy; Majka, Alina; Dutkiewicz, Grzegorz; Borowiak, Teresa; Kaczmarek, Anna M.; Van Deun, Rik

2016-01-01

Tetraphenylimidodiphosphinate (tpip) forms neutral 3:1 complexes with lanthanide ions. These complexes can accommodate one ancillary planar heterocyclic ligand to complement their coordination sphere of Eu 3+ to coordination number 8. Several co-ligands were tested to form new complexes: 1,10-phenanthroline, bathophenanthroline, 2,4,6-tris(2-pyridyl)-1,3,5-triazine, dipyrido[3,2-f:2′,3′-h]quinoxaline and 2,2′:6′,2′′-terpyridine. The addition of heterocyclic N,N-bidentate co-ligands to the coordination sphere results in a dramatic (by a factor of 45–50) luminescence enhancement of the parent Eu(tpip) 3 . The solid-state measurements confirmed that the ancillary ligands strongly increased the photoluminescence quantum yield (PLQY) of the investigated complexes. - Highlights: • We have disovered highly photoluminescent ternary Eu(III) complexes. • They consist of Eu(III) tetraphenylimidodiphosphinate, and planar heterocyclic ligands. • The increase in photoluminescence quantum yields in solution is enhanced up to 50 times in solution. • The solid-state photoluminescence exceeds 80% at room temperature.

Photoluminescent (PL) or electroluminescent (EL) quantum dots for display, lighting, and photomedicine (Conference Presentation)

Science.gov (United States)

Dong, Yajie

2017-02-01

Quantum dots (QDs) have gone through a long journey before finding their ways into the display field. This talk will briefly touch on the history before trying to answer several key questions related to QDs applications in display: What are QDs? How are they made? What properties do they have and Why? How can these properties be used to improve color and efficiency of display, in either photoluminescence (PL) or electroluminescence (EL) mode? And what are the remaining challenges for QDs wide adoption in display industry? Lastly, some most recent progresses in our UCF lab at both PL and EL fronts will be highlighted. For PL, a cadmium-free perovskite-polymer composite films with exceptionally narrow emission green peaks (FWHM 20 nm) and good water and thermal stability will be reported. Together with red quantum dots or PFS/KSF phosphors as down-converters for blue LEDs, a white-light source with 95% Rec. 2020 color gamut was demonstrated [1]. For EL, red quantum dot light emitting devices (QLEDs) with record luminance of 165,000 Cd/m2 has been obtained at a current density of 1000 mA/cm2 with a low driving voltage of 5.8 V and CIE coordinates of (0.69, 0.31). [2] The potential of using these QLEDs for light sources for integrated sensing platform [3] or high efficiency, high color quality hybrid white OLED [4] will be discussed. [1] Y. N. Wang, J. He, H. Chen, J. S. Chen, R. D. Zhu, P. Ma, A. Towers, Y. Lin, A. J. Gesquiere, S. T. Wu, Y. J. Dong. Ultrastable, Highly Luminescent Organic-Inorganic Perovskite - Polymer Composite Films, Advanced Materials, accepted, (2016). [2] Y. J. Dong, J.M. Caruge, Z. Q. Zhou, C. Hamilton, Z. Popovic, J. Ho, M. Stevenson, G. Liu, V. Bulovic, M. Bawendi, P. T. Kazlas, S. Coe-Sullivan, and J. Steckel Ultra-bright, Highly Efficient, Low Roll-off Inverted Quantum-Dot Light Emitting Devices (QLEDs). SID Symp. Dig. Tech. Pap. 46, 270-273 (2015). [3] J. He, H. Chen, S. T. Wu, and Y. J. Dong, Integrated Sensing Platform Based on Quantum

Quantum dot-polymer conjugates for stable luminescent displays.

Science.gov (United States)

Ghimire, Sushant; Sivadas, Anjaly; Yuyama, Ken-Ichi; Takano, Yuta; Francis, Raju; Biju, Vasudevanpillai

2018-05-23

The broad absorption of light in the UV-Vis-NIR region and the size-based tunable photoluminescence color of semiconductor quantum dots make these tiny crystals one of the most attractive antennae in solar cells and phosphors in electrooptical devices. One of the primary requirements for such real-world applications of quantum dots is their stable and uniform distribution in optically transparent matrices. In this work, we prepare transparent thin films of polymer-quantum dot conjugates, where CdSe/ZnS quantum dots are uniformly distributed at high densities in a chitosan-polystyrene copolymer (CS-g-PS) matrix. Here, quantum dots in an aqueous solution are conjugated to the copolymer by a phase transfer reaction. With the stable conjugation of quantum dots to the copolymer, we prevent undesired phase separation between the two and aggregation of quantum dots. Furthermore, the conjugate allows us to prepare transparent thin films in which quantum dots are uniformly distributed at high densities. The CS-g-PS copolymer helps us in not only preserving the photoluminescence properties of quantum dots in the film but also rendering excellent photostability to quantum dots at the ensemble and single particle levels, making the conjugate a promising material for photoluminescence-based devices.

Photoluminescence of double core/shell infrared (CdSeTe)/ZnS quantum dots conjugated to Pseudo rabies virus antibodies

Science.gov (United States)

Torchynska, T. V.; Casas Espinola, J. L.; Jaramillo Gómez, J. A.; Douda, J.; Gazarian, K.

2013-06-01

Double core CdSeTe/ZnS quantum dots (QDs) with emission at 800 nm (1.60 eV) have been studied by photoluminescence (PL) and Raman scattering methods in the non-conjugated state and after the conjugation to the Pseudo rabies virus (PRV) antibodies. The transformation of PL spectra, stimulated by the electric charge of antibodies, has been detected for the bioconjugated QDs. Raman scattering spectra are investigated with the aim to reveal the CdSeTe core compositions. The double core QD energy diagrams were designed that help to analyze the PL spectra and their transformation at the bioconjugation. It is revealed that the interface in double core QDs has the type II quantum well character that permits to explain the near IR optical transition (1.60 eV) in the double core QDs. It is shown that the essential transformation of PL spectra is useful for the study of QD bioconjugation with specific antibodies and can be a powerful technique in early medical diagnostics.

Nonradiative recombination in GaN quantum dots formed in the AlN matrix

International Nuclear Information System (INIS)

Aleksandrov, I. A.; Zhuravlev, K. S.; Mansurov, V. G.

2009-01-01

The mechanisms of temperature quenching of steady-state photoluminescence are studied for structures with hexagonal GaN quantum dots embedded in the AlN matrix. The structures are grown by molecular beam epitaxy. The study is conducted for structures with differently sized quantum dots, for which the peak of the photoluminescence band is in the range from 2.5 to 4.0 eV. It is found that the activation energy of thermal quenching of photoluminescence varies from 27 to 110 meV, as the quantum-dot height is decreased from 5 to 2 nm. A model is suggested to interpret the results. According to the model, the photo-luminescence signal is quenched because of the transfer of charge carriers from energy levels in the quantum dots to defect levels in the matrix.

Exciton-related nonlinear optical response and photoluminescence in dilute nitrogen In{sub x}Ga{sub 1−x}N{sub y}As{sub 1−y}/GaAs cylindrically shaped quantum dots

Energy Technology Data Exchange (ETDEWEB)

Duque, C.M.; Morales, A.L. [Grupo de Materia Condensada-UdeA, Instituto de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquia UdeA, Calle 70 No. 52-21, Medellín (Colombia); Mora-Ramos, M.E. [Grupo de Materia Condensada-UdeA, Instituto de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquia UdeA, Calle 70 No. 52-21, Medellín (Colombia); Facultad de Ciencias, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, CP 62209 Cuernavaca, Morelos (Mexico); Duque, C.A. [Grupo de Materia Condensada-UdeA, Instituto de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquia UdeA, Calle 70 No. 52-21, Medellín (Colombia)

2014-10-15

An investigation of the effects of the dilute nitrogen contents in the exciton states of cylindrical In{sub x}Ga{sub 1−x}N{sub y}As{sub 1−y}/GaAs quantum dots is presented. The exciton states in the system are obtained within the effective mass theory and the band anti-crossing model. Exciton-related nonlinear optical absorption and refractive index change, as well as excitonic photoluminescence are studied with the help of the calculated exciton states. - Highlights: • Theoretical study of excitons in cylindrical In{sub x}Ga{sub 1−x}N{sub y}As{sub 1−y}/GaAs quantum dots. • Calculations of binding energy for different configurations of electron-hole pairs. • Nonlinear optical absorption and refractive index changes. • Dependence of photoluminescence energy transitions with several inputs.

InP quantum dots embedded in GaP: Optical properties and carrier dynamics

International Nuclear Information System (INIS)

Hatami, F.; Masselink, W.T.; Schrottke, L.; Tomm, J.W.; Talalaev, V.; Kristukat, C.; Goni, A.R.

2003-01-01

The optical emission and dynamics of carriers in Stranski-Krastanow self-organized InP quantum dots embedded in a GaP matrix are studied. InP deposited on GaP (001) using gas-source molecular-beam epitaxy forms quantum dots for InP coverage greater than 1.8 monolayers. Strong photoluminescence from the quantum dots is observed up to room temperature at about 2 eV; photoluminescence from the two-dimensional InP wetting layer is measured at about 2.2 eV. Modeling based on the 'model-solid theory' indicates that the band alignment for the InP quantum dots is direct and type I. Furthermore, low-temperature time-resolved photoluminescence measurements indicate that the carrier lifetime in the quantum dots is about 2 ns, typical for type-I quantum dots. Pressure-dependent photoluminescence measurements provide further evidence for a type-I band alignment for InP/GaP quantum dots at normal pressure with the GaP X states lying about 30 meV higher than the Γ states in the InP quantum dots, but indicate that they become type II under hydrostatic pressures of about 1.2 GPa

Tunable photoluminescence of CsPbBr3 perovskite quantum dots for light emitting diodes application

Science.gov (United States)

Chen, Weiwei; Xin, Xing; Zang, Zhigang; Tang, Xiaosheng; Li, Cunlong; Hu, Wei; Zhou, Miao; Du, Juan

2017-11-01

All-inorganic cesium lead halide (CsPbBr3) perovskite quantum dots (QDs), as one kind of promising materials, have attracted considerable attention in optoelectronic applications. Herein, we synthesized the colloidal CsPbBr3 QDs with tunable photoluminescence (PL) (493-531 nm) by adjusting the reaction temperatures, which revealed narrow emission bandwidths of about 25 nm. The average diameters of the QDs could be adjusted from 7.1 to 12.3 nm as the temperature increased from 100 °C to 180 °C. Moreover, the radiative lifetimes of CsPbBr3 QDs were measured to be 2 ns, and the single QD fluorescence intensity time trace results demonstrated its suppressed blinking emission. Moreover, green light emitting diodes by using CsPbBr3 QDs casted on blue LED chips were further fabricated, which provided potential applications in the field of display and lighting technology.

Photoluminescence energy transitions in GaAs-Ga1-xAlxAs double quantum wells: Electric and magnetic fields and hydrostatic pressure effects

International Nuclear Information System (INIS)

Lopez, S.Y.; Mora-Ramos, M.E.; Duque, C.A.

2009-01-01

The photoluminescence energy transitions in GaAs-Ga 1-x Al x As coupled double quantum wells are presented by considering the simultaneous effects of applied electric and magnetic fields and hydrostatic pressure. Calculations have been made in the framework of the effective mass and parabolic band approximations and using a variational procedure. The electric field is taken to be oriented along the growth direction of the heterostructure whereas for the magnetic field both in-plane and in-growth directions have been considered. The results show that the hydrostatic pressure and the applied electric field are two useful tools to tune the direct and indirect exciton transitions in such heterostructures. Our results are in good agreement with previous experimental findings in double quantum wells under applied electric field and hydrostatic pressure.

Effects of low charge carrier wave function overlap on internal quantum efficiency in GaInN quantum wells

Energy Technology Data Exchange (ETDEWEB)

Netzel, Carsten; Hoffmann, Veit; Wernicke, Tim; Knauer, Arne; Weyers, Markus [Ferdinand-Braun-Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Strasse 4, 12489 Berlin (Germany); Kneissl, Michael [Ferdinand-Braun-Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Strasse 4, 12489 Berlin (Germany); Institut fuer Festkoerperphysik, Technische Universitaet Berlin, Hardenbergstrasse 36, 10623 Berlin (Germany)

2010-07-15

To determine relevant processes affecting the internal quantum efficiency in GaInN quantum well structures, we have studied the temperature and excitation power dependent photoluminescence intensity for quantum wells with different well widths on (0001) c-plane GaN and for quantum wells on nonpolar (11-20) a-plane GaN. In thick polar quantum wells, the quantum confined Stark effect (QCSE) causes a stronger intensity decrease with increasing temperature as long as the radiative recombination dominates. At higher temperatures, when the nonradiative recombination becomes more important, thick polar quantum wells feature a lower relative intensity decrease than thinner polar or nonpolar quantum wells. Excitation power dependent photoluminescence points to a transition from a recombination of excitons to a bimolecular recombination of uncorrelated charge carriers for thick polar quantum wells in the same temperature range. This transition might contribute to the limitation of nonradiative recombination by a reduced diffusivity of charge carriers. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Narrow photoluminescence peak from Ge(Si) islands embedded between tensile-strained Si layers

Energy Technology Data Exchange (ETDEWEB)

Shaleev, Mikhail; Novikov, Alexey; Baydakova, Nataliya; Yablonskiy, Artem; Drozdov, Yuriy; Lobanov, Dmitriy; Krasilnik, Zakhary [Institute for Physics of Microstructures, Russian Academy of Sciences, GSP-105, 603950 Nizhny Novgorod (Russian Federation); Kuznetsov, Oleg [Physical-Technical Research Institute, Nizhny Novgorod State University, pr. Gagarina 23, 603950 Nizhny Novgorod (Russian Federation)

2011-03-15

The influence of thickness of the strained Si layers, measurement temperature and optical pumping power on width of the photoluminescence line from Ge(Si) self-assembled nanoislands grown on relaxed SiGe/Si(001) buffer layers and embedded between tensile-stained Si layers was studied. This line appears due to the II-type optical transition between the holes localized in islands and the electrons confined in tensile-strained Si layers under and above the islands. The possibility of tuning the photoluminescence line width by changing the strained Si layer thicknesses under and above the islands is showed. The decrease of the photoluminescence line width from Ge(Si) islands down to values comparable with width of the PL line from InAs/GaAs quantum dots was achieved due to the quantum confinement of electrons in thin strained Si layers and taking into account of the higher diffusion-induced smearing of strained Si layer above the islands. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Composition-dependent photoluminescence properties of CuInS_2/ZnS core/shell quantum dots

International Nuclear Information System (INIS)

Hua, Jie; Du, Yuwei; Wei, Qi; Yuan, Xi; Wang, Jin; Zhao, Jialong; Li, Haibo

2016-01-01

CuInS_2/ZnS (CIS/ZnS) core/shell quantum dots (QDs) with various Cu/In ratios were synthesized using the hot-injection method, and their photoluminescence (PL) properties were investigated by measuring steady-state and time-resolved PL spectroscopy. The emission peak of the CIS/ZnS QDs were tuned from 680 to 580 nm by decreasing the Cu/In precursor ratio from 1/1 to 1/9. As the Cu/In ratio decreases, the PL lifetimes and PL quantum yields (QYs) of CIS/ZnS core/shell QDs increased firstly and then decreased. Two dominant radiative recombination processes were postulated to analyze composition-dependent PL properties, including the recombination from a quantized conduction band to deep defects state and donor-acceptor pair (DAP) recombination. The decrease of PL efficiency resulted from high density defects and traps, which formed at the interface between CIS core and ZnS shell due to the large off-stoichiometry composition. The PL intensity and peak energy for CIS/ZnS core/shell QDs as a function of temperature were also provided. The thermal quenching further confirmed that the PL emission of CIS/ZnS QDs did not come from the recombination of excitons but from the recombination of many kinds of intrinsic defects inside the QDs as emission centers.

High quantum yield ZnO quantum dots synthesizing via an ultrasonication microreactor method.

Science.gov (United States)

Yang, Weimin; Yang, Huafang; Ding, Wenhao; Zhang, Bing; Zhang, Le; Wang, Lixi; Yu, Mingxun; Zhang, Qitu

2016-11-01

Green emission ZnO quantum dots were synthesized by an ultrasonic microreactor. Ultrasonic radiation brought bubbles through ultrasonic cavitation. These bubbles built microreactor inside the microreactor. The photoluminescence properties of ZnO quantum dots synthesized with different flow rate, ultrasonic power and temperature were discussed. Flow rate, ultrasonic power and temperature would influence the type and quantity of defects in ZnO quantum dots. The sizes of ZnO quantum dots would be controlled by those conditions as well. Flow rate affected the reaction time. With the increasing of flow rate, the sizes of ZnO quantum dots decreased and the quantum yields first increased then decreased. Ultrasonic power changed the ultrasonic cavitation intensity, which affected the reaction energy and the separation of the solution. With the increasing of ultrasonic power, sizes of ZnO quantum dots first decreased then increased, while the quantum yields kept increasing. The effect of ultrasonic temperature on the photoluminescence properties of ZnO quantum dots was influenced by the flow rate. Different flow rate related to opposite changing trend. Moreover, the quantum yields of ZnO QDs synthesized by ultrasonic microreactor could reach 64.7%, which is higher than those synthesized only under ultrasonic radiation or only by microreactor. Copyright © 2016 Elsevier B.V. All rights reserved.

Photoluminescence and applications of Ni:ZnS in photovoltaic cells

Science.gov (United States)

Kalya Tulasidas, Vadiraj; Belagali, Shiddappa L.; Palakkandy, Arun; Kumar, Kuldeep

2018-05-01

An enormous amount of development has been made in the field of photovoltaics in the last 50 odd years. In recent years, the uses of semiconductor nanoparticles have given a new impetus and direction to research in the field of solar cells. This is due to the excellent photoemission properties shown by semiconductors in the quantum dot (QD) state. ZnS QDs show a further interesting feature where their photoemission properties show perceivable changes on adding dopants such as nickel. In the present work, we describe the characterization studies made on Ni:ZnS thin films using photoluminescence (PL), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), and further reports their performance as an absorbing layer in a hybrid solar cell along with poly(3-hexylthiophene) (P3HT). Fabricated Ni:ZnS cell showed a conversion efficiency of 0.25 ± 0.05% with V OC and J SC of 560 mV and 0.11 mA/cm2, respectively. Although the absolute conversion efficiency appears low (only 0.25%), the addition of nickel was found to have improved the efficiency by a hundredfold compared with undoped ZnS.

The effect of ultraviolet irradiation on the photothermal, photoluminescence and photoluminescence excitation spectra of Mn-doped ZnS nanoparticles

International Nuclear Information System (INIS)

Briones Cruz, Almira; Shen Qing; Toyoda, Taro

2006-01-01

Research involving Mn doped nanocrystalline ZnS (ZnS:Mn) has grown in recent years, partly due to the high quantum luminescence efficiencies that have been reported. We measured the photoacoustic (PA), the photoluminescence (PL) and the photoluminescence excitation (PLE) spectra of surface-passivated and unpassivated ZnS:Mn. The effects of UV irradiation on the PL and PLE spectra were also studied. A decrease in the PA intensity after UV exposure was observed for the ZnS:Mn, indicating a decrease in the nonradiative relaxation probability. The observed increase in PL intensity indicates a corresponding increase in the radiative transition probability. For the PLE spectra, possible aggregation of the primary particles could have resulted in the lower measured energy of the PLE peak compared to the value predicted by the effective mass approximation theory

Polarized electrons, trions, and nuclei in charged quantum dots

Science.gov (United States)

Bracker, A. S.; Tischler, J. G.; Korenev, V. L.; Gammon, D.

2003-07-01

We have investigated spin polarization in GaAs quantum dots. Excitons and trions are polarized directly by optical excitation and studied through polarization of photoluminescence. Electrons and nuclei are polarized indirectly through subsequent relaxation processes. Polarized electrons are identified by the Hanle effect for exciton and trion photoluminescence, while polarized nuclei are identified through the Overhauser effect in individual charged quantum dots.

(110) oriented GaAs/Al0.3Ga0.7As quantum wells for optimized T-shaped quantum wires

DEFF Research Database (Denmark)

Gislason, Hannes; Sørensen, Claus Birger; Hvam, Jørn Märcher

1996-01-01

High control of (110) oriented GaAs/Al0.3Ga0.7As quantum wells is very important for the growth of optimized T-shaped GaAs/AlGaAs quantum wires, We investigate theoretically and experimentally 20-200 Angstrom wide (110) oriented GaAs quantum wells grown on (110) oriented substrates and cleaved...... edges. Photoluminescence transition energies are found to be in good agreement with theory for all well widths. The mean well width is controllable to 1 monolayer accuracy and an effective well width fluctuation of 3.7 Angstrom is derived from the photoluminescence linewidths. The growth rate...

Effects of post-growth annealing on InGaAs quantum posts embedded in Schottky diodes

International Nuclear Information System (INIS)

Schramm, A; Polojärvi, V; Hakkarainen, T V; Tukiainen, A; Guina, M

2011-01-01

We study effects of rapid thermal annealing on photoluminescence and electron confinement of InGaAs quantum posts by means of photoluminescence experiments and capacitance–voltage spectroscopy. The quantum posts are embedded in n-type Schottky diodes grown by molecular beam epitaxy on GaAs(1 0 0). The observed photoluminescence spectra arise from the quantum posts as well as from a contribution of a wetting-layer superlattice. With increasing annealing temperatures, the quantum-post photoluminescence blueshifts toward the wetting-layer superlattice, and upon the highest annealing step, the wetting-layer superlattice luminescence dominates. In capacitance–voltage experiments, we clearly observe a charge accumulation in the quantum-post layer as well as from the wetting-layer superlattice. Capacitance–voltage spectra and carrier-density profiles only experience slight changes upon annealing treatments. We suggest that the main electron accumulation takes place in the wetting-layer superlattice

Photoluminescence of 1,3-dimethyl pyrazoloquinoline derivatives

Energy Technology Data Exchange (ETDEWEB)

Koscien, E. [1st Liceum, Sobieskiego 22, 42-700 Lubliniec (Poland); Gondek, E.; Pokladko, M. [Institute of Physics, Technical University of Krakow, Podhorazych 1, 30-084 Krakow (Poland); Jarosz, B. [Department of Chemistry, Hugon Kollotaj Agricultural University, Al. Mickiewicza 24/28, 30-059 Krakow (Poland); Vlokh, R.O. [Institute of Physical Optics, Dragomanova 23, 79005 Lviv (Ukraine); Kityk, A.V. [Department of Electrical Engineering, Czestochowa University of Technology, Al. Armii Krajowej 17, 42-200 Czestochowa (Poland)], E-mail: kityk@ap.univie.ac.at

2009-04-15

This paper presents absorption and photoluminescence of 6-F, 6-Br, 6-Cl, 7-TFM and 6-COOEt derivatives of 1,3-dimethyl-1H-Pyrazolo[3,4-b]quinoline (DMPQ). The measured absorption and emission spectra are compared with the quantum chemical calculations performed by means of the semi-empirical methods (AM1 or PM3) that are applied either to the equilibrium conformations in vacuo (T = 0 K) or combined with the molecular dynamics simulations (T = 300 K). The spectra calculated by the AM1 method appear to be for all dyes in practically excellent agreement with the measured ones. In particular, the position of the first absorption band is obtained with the accuracy up to a few nanometers, whereas the calculated photoluminescence spectra predict the positions of the emission maxima for a gas phase with the accuracy up to 10-18 nm. The photoemission spectra of DMPQ dyes are considerably less solvatochromic comparing to phenyl-containing pyrazoloquinoline derivatives. According to the quantum chemical analysis the reason for such behaviour lies in a local character of the electronic transitions of DMPQ dyes which are characterized by a relatively small difference between the excited state and ground state dipole moments. Importantly that the rotational dynamics of both methyl subunits does not change this situation.

Changes in luminescence emission induced by proton irradiation: InGaAs/GaAs quantum wells and quantum dots

Science.gov (United States)

Leon, R.; Swift, G. M.; Magness, B.; Taylor, W. A.; Tang, Y. S.; Wang, K. L.; Dowd, P.; Zhang, Y. H.

2000-01-01

The photoluminescence emission from InGaAs/GaAs quantum-well and quantum-dot (QD) structures are compared after controlled irradiation with 1.5 MeV proton fluxes. Results presented here show a significant enhancement in radiation tolerance with three-dimensional quantum confinement.

Longer than 1.9 μm photoluminescence emission from InAs quantum structure on GaAs (001) substrate

Energy Technology Data Exchange (ETDEWEB)

Liu, Ke; Ma, Wenquan, E-mail: wqma@semi.ac.cn; Huang, Jianliang; Zhang, Yanhua; Cao, Yulian; Huang, Wenjun; Luo, Shuai; Yang, Tao [Institute of Semiconductors, Chinese Academy of Sciences, Qinghua East Road A 35, Beijing 100083 (China)

2015-07-27

We report on photoluminescence (PL) emission with long wavelength for quantum structure by the sub-monolayer (SML) growth technique on GaAs (001) substrate. It is found that the PL emission wavelength can be controlled by controlling the SML InAs deposition amount. At 12 K, the PL peak position of the grown samples changes from about 1.66 to 1.78 μm. At 120 K, the PL emission of a sample reaches 1.91 μm. The physical mechanism responsible for the measured long wavelength PL emission may be related to strong In segregation and intermixing effects occurred in the structure grown by SML growth technique.

Polarization-dependent photoluminescence studies of semipolar and nonpolar InGaN quantum wells

Energy Technology Data Exchange (ETDEWEB)

Schade, Lukas; Schwarz, Ulrich [IAF, Freiburg (Germany); Wernicke, Tim; Weyers, Markus [FBH, Berlin (Germany); Kneissl, Michael [FBH, Berlin (Germany); Institute of Solid State Physics, TU Berlin (Germany)

2010-07-01

Light emitted from optical devices based on semi- and nonpolar GaN quantum well (QW) structures is partially or totally polarized, as a consequence of crystal symmetry and band structure. This can be an additional advantage over polar (0001)GaN in specific applications, e.g. in LED backlighting. Fundamentally, the polarized emission stems from breaking the isotropic symmetry of the hexagonal c-plane, resulting in two discrete semi- and nonpolar directions (parallel and normal to the projection of (0001)). We use the k.p method to simulate the crystal-direction dependent emission. The resulting transition matrix elements assign a specific (partial) polarization for each subband. The thermal occupation of the subbands results in a temperature dependent effective polarization of the light emission. We study MOVPE grown homoepitactical polar, semi- and nonpolar samples, measuring the polarization properties of the resonantly excited photoluminescence from the QW. With the complete polarization of the subbands for nonpolar devices it is possible to measure the energetic difference of the first two valence band levels. In contrast to our calculations we find a higher degree of polarization also in semipolar directions. A possible explanation could be a higher energetic subband difference than computed.

Photoluminescence enhancement in nanocomposite thin films of CdS-ZnO

International Nuclear Information System (INIS)

Ayyub, Pushan; Vasa, Parinda; Taneja, Praveen; Banerjee, Rajarshi; Singh, B.P.

2005-01-01

We show that the photoluminescence emitted from a dense, two-component quantum dot ensemble on a thin film is significantly higher and decays much faster than that from quantum dots of either of the two pure systems (CdS and ZnO). The semiconductor nanocomposite, in which the characteristic grain size of each species was 2-3 nm, was deposited directly on Si wafers by high-pressure magnetron sputtering, and exhibits a single, relatively sharp optical absorption edge

Characterisation of multi-layer InAs/InP quantum wires by surface photovoltage and photoluminescence spectroscopies

International Nuclear Information System (INIS)

Ivanov, Ts; Donchev, V; Angelova, T; Cros, A; Cantarero, A; Shtinkov, N; Borissov, K; Fuster, D; Gonzalez, Y; Gonzalez, L

2010-01-01

The optical properties of multi-layer InAs/InP quantum wires (QWRs) with two different spacer thicknesses have been investigated by means of room temperature surface photovoltage (SPV) and photoluminescence (PL) spectroscopies, combined with empirical tight binding electronic structure calculations and structural data. The SPV and PL spectra reveal several features, which energy positions are in good agreement. They have been ascribed to excitonic transitions, which take place in the QWR families with heights differing by an integer number of monolayers. Comparing the experimental results with the theoretical ones, we have estimated the QWR family heights and the average atomic concentration of phosphorus in the QWRs. From the simultaneous analysis of the SPV amplitude and phase spectra, based on our vector model for SPV signal representation, a deeper understanding of the SPV results and of the mechanisms of carrier separation in the sample is obtained.

Characterisation of multi-layer InAs/InP quantum wires by surface photovoltage and photoluminescence spectroscopies

Science.gov (United States)

Ivanov, Ts; Donchev, V.; Angelova, T.; Cros, A.; Cantarero, A.; Shtinkov, N.; Borissov, K.; Fuster, D.; González, Y.; González, L.

2010-11-01

The optical properties of multi-layer InAs/InP quantum wires (QWRs) with two different spacer thicknesses have been investigated by means of room temperature surface photovoltage (SPV) and photoluminescence (PL) spectroscopies, combined with empirical tight binding electronic structure calculations and structural data. The SPV and PL spectra reveal several features, which energy positions are in good agreement. They have been ascribed to excitonic transitions, which take place in the QWR families with heights differing by an integer number of monolayers. Comparing the experimental results with the theoretical ones, we have estimated the QWR family heights and the average atomic concentration of phosphorus in the QWRs. From the simultaneous analysis of the SPV amplitude and phase spectra, based on our vector model for SPV signal representation, a deeper understanding of the SPV results and of the mechanisms of carrier separation in the sample is obtained.

Cavity quantum electrodynamics in the Anderson-localized regime

DEFF Research Database (Denmark)

Sapienza, Luca; Nielsen, Henri Thyrrestrup; Stobbe, Søren

2010-01-01

We experimentally measure, by means of time-resolved photoluminescence spectroscopy, a 15-fold enhancement of the spontaneous emission decay rate of single semiconductor quantum dots coupled to disorder-induced Anderson-localized modes with efficiencies reaching 94%.......We experimentally measure, by means of time-resolved photoluminescence spectroscopy, a 15-fold enhancement of the spontaneous emission decay rate of single semiconductor quantum dots coupled to disorder-induced Anderson-localized modes with efficiencies reaching 94%....

The pH-dependent photoluminescence of colloidal CdSe/ZnS quantum dots with different organic coatings

International Nuclear Information System (INIS)

Debruyne, David; Locquet, Jean-Pierre; Van Bael, Margriet J; Deschaume, Olivier; Bartic, Carmen; Coutiño-Gonzalez, Eduardo; Hofkens, Johan

2015-01-01

The photoluminescence (PL) of colloidal quantum dots (QDs) is known to be sensitive to the solution pH. In this work we investigate the role played by the organic coating in determining the pH-dependent PL. We compare two types of CdSe/ZnS QDs equipped with different organic coatings, namely dihydrolipoic acid (DHLA)-capped QDs and phospholipid micelle-encapsulated QDs. Both QD types have their PL intensity quenched at acidic pH values, but they differ in terms of the reversibility of the quenching process. For DHLA-capped QDs, the quenching is nearly irreversible, with a small reversible component visible only on short time scales. For phospholipid micelle-encapsulated QDs the quenching is notably almost fully reversible. We suggest that the surface passivation by the organic ligands is reversible for the micelle-encapsulated QDs. Additionally, both coatings display pH-dependent spectral shifts. These shifts can be explained by a combination of irreversible processes, such as photo-oxidation and acid etching, and reversible charging of the QD surface, leading to the quantum-confined Stark effect (QCSE), the extent of each effect being coating-dependent. At high ionic strengths, the aggregation of QDs also leads to a spectral (red) shift, which is attributable to the QCSE and/or electronic energy transfer. (paper)

High Photoluminescence Quantum Yields in Organic Semiconductor-Perovskite Composite Thin Films.

Science.gov (United States)

Longo, Giulia; La-Placa, Maria-Grazia; Sessolo, Michele; Bolink, Henk J

2017-10-09

One of the obstacles towards efficient radiative recombination in hybrid perovskites is a low exciton binding energy, typically in the orders of tens of meV. It has been shown that the use of electron-donor additives can lead to a substantial reduction of the non-radiative recombination in perovskite films. Herein, the approach using small molecules with semiconducting properties, which are candidates to be implemented in future optoelectronic devices, is presented. In particular, highly luminescent perovskite-organic semiconductor composite thin films have been developed, which can be processed from solution in a simple coating step. By tuning the relative concentration of methylammonium lead bromide (MAPbBr 3 ) and 9,9spirobifluoren-2-yl-diphenyl-phosphine oxide (SPPO1), it is possible to achieve photoluminescent quantum yields (PLQYs) as high as 85 %. This is attributed to the dual functions of SPPO1 that limit the grain growth while passivating the perovskite surface. The electroluminescence of these materials was investigated by fabricating multilayer LEDs, where charge injection and transport was found to be severely hindered for the perovskite/SPPO1 material. This was alleviated by partially substituting SPPO1 with a hole-transporting material, 1,3-bis(N-carbazolyl)benzene (mCP), leading to bright electroluminescence. The potential of combining perovskite and organic semiconductors to prepare materials with improved properties opens new avenues for the preparation of simple lightemitting devices using perovskites as the emitter. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Observation of many-body Coulomb interaction effects on the photoluminescence spectra of InAs/GaAs quantum dots

International Nuclear Information System (INIS)

Rihani, J.; Sedrine, N.B.; Sallet, V.; Oueslati, M.; Chtourou, R.

2008-01-01

InAs quantum dots (QDs) on GaAs (0 0 1) substrates were grown by Molecular Beam Epitaxy (MBE) using two growth temperatures. Photoluminescence (PL) pump power dependence measurements at low temperature were carried out for sample grown at higher temperature (520 deg. C). With increasing excitation density, the ground-state transition energy is found to decrease by 8 meV, while the excited-state transition energies exhibit resonance behaviour. The redshift of the ground-state emission was related to the band-gap renomalization (BGR) effect whereas the blueshift of the excited-state emissions was assigned to the compensation between filling of fine structure states and BGR effects. Using a quasi-resonant PL measurement, we have shown that the renormalization of the band-gap had to occur in the QD barrier

Rhodamine 6G impregnated porous silica: A photoluminescence study

Energy Technology Data Exchange (ETDEWEB)

Anedda, A. [Dipartimento di Fisica, Universita degli Studi di Cagliari and INMF UdR Cagliari, SP no8, Km 0700, 09042, Monserrato (Canada) (Italy); Carbonaro, C.M. [Dipartimento di Fisica, Universita degli Studi di Cagliari and INMF UdR Cagliari, SP no8, Km 0700, 09042, Monserrato (Canada) (Italy)]. E-mail: cm.carbonaro@dsf.unica.it; Clemente, F. [Dipartimento di Fisica, Universita degli Studi di Cagliari and INMF UdR Cagliari, SP no8, Km 0700, 09042, Monserrato (Ca) (Italy); Corpino, R. [Dipartimento di Fisica, Universita degli Studi di Cagliari and INMF UdR Cagliari, SP no8, Km 0700, 09042, Monserrato (Ca) (Italy); Ricci, P.C. [Dipartimento di Fisica, Universita degli Studi di Cagliari and INMF UdR Cagliari, SP no8, Km 0700, 09042, Monserrato (Ca) (Italy); Rossini, S. [Dipartimento di Fisica, Universita degli Studi di Cagliari and INMF UdR Cagliari, SP no8, Km 0700, 09042, Monserrato (Ca) (Italy)

2005-12-15

The optical properties of rhodamine 6G dye confined in porous silica are reported. Photoluminescence properties of embedded chromophores in mesoporous hosts can be affected by the surrounding matrices: shifts in emission spectra and variations of photoluminescence quantum yield are found as compared to dye solutions. Host-guest interactions are studied here by varying both SiO{sub 2} xerogels porosity and the dye concentration. Comparing samples obtained by impregnating matrices with 5.4 and 18.2 nm pores with solutions having concentrations in the rhodamine 6G high laser gain, matrices with 5.4 nm pores impregnated with a dye concentration of 5 x 10{sup -4} M are found to be the most stable and efficient in the examined range.

Polytypism and band alignment in ZnSe nanowires revealed by photoluminescence spectroscopy of embedded (Zn,Cd)Se quantum dots

Science.gov (United States)

Bieker, S.; Pfeuffer, R.; Kiessling, T.; Tarakina, N.; Schumacher, C.; Ossau, W.; Molenkamp, L. W.; Karczewski, G.

2015-03-01

We report on the optical characterization of single (Zn,Cd)Se quantum dots (QDs) embedded in vapor-liquid-solid-grown ZnSe nanowires (NWs). The temperature dependent quenching of the QD luminescence demonstrates that their electronic structure is comparable to that of self-assembled (Zn,Cd)Se QDs in ZnSe matrices. The photoluminescence excitation (PLE) spectrum of single nanowire QDs reveals the presence of both zinc blende (ZB) and wurtzite (WZ) crystal modifications of ZnSe in the NW shafts. PLE provides, therefore, a complementary technique to transmission electron microscopy imaging to reveal polytypism in ZnSe NWs. A transient quenching of the PL emission suggests a type II staggered band alignment at the ZB/WZ interface in our ZnSe NWs.

Carrier redistribution between different potential sites in semipolar (202¯1) InGaN quantum wells studied by near-field photoluminescence

KAUST Repository

Marcinkevičius, S.

2014-09-15

© 2014 AIP Publishing LLC. Scanning near-field photoluminescence (PL) spectroscopy at different excitation powers was applied to study nanoscale properties of carrier localization and recombination in semipolar (202¯1) InGaN quantum wells (QWs) emitting in violet, blue, and green-yellow spectral regions. With increased excitation power, an untypical PL peak energy shift to lower energies was observed. The shift was attributed to carrier density dependent carrier redistribution between nm-scale sites of different potentials. Near-field PL scans showed that in (202¯1) QWs the in-plane carrier diffusion is modest, and the recombination properties are uniform, which is advantageous for photonic applications.

Effect of graphene on photoluminescence properties of graphene/GeSi quantum dot hybrid structures

International Nuclear Information System (INIS)

Chen, Y. L.; Ma, Y. J.; Wang, W. Q.; Ding, K.; Wu, Q.; Fan, Y. L.; Yang, X. J.; Zhong, Z. Y.; Jiang, Z. M.; Chen, D. D.; Xu, F.

2014-01-01

Graphene has been discovered to have two effects on the photoluminescence (PL) properties of graphene/GeSi quantum dot (QD) hybrid structures, which were formed by covering monolayer graphene sheet on the multilayer ordered GeSi QDs sample surfaces. At the excitation of 488 nm laser line, the hybrid structure had a reduced PL intensity, while at the excitation of 325 nm, it had an enhanced PL intensity. The attenuation in PL intensity can be attributed to the transferring of electrons from the conducting band of GeSi QDs to the graphene sheet. The electron transfer mechanism was confirmed by the time resolved PL measurements. For the PL enhancement, a mechanism called surface-plasmon-polariton (SPP) enhanced absorption mechanism is proposed, in which the excitation of SPP in the graphene is suggested. Due to the resonant excitation of SPP by incident light, the absorption of incident light is much enhanced at the surface region, thus leading to more exciton generation and a PL enhancement in the region. The results may be helpful to provide us a way to improve optical properties of low dimensional surface structures.

Effect of band alignment on photoluminescence and carrier escape from InP surface quantum dots grown by metalorganic chemical vapor deposition on Si

Energy Technology Data Exchange (ETDEWEB)

Halder, Nripendra N. [Advanced Technology Development Centre, Indian Institute of Technology, Kharagpur 721 302 (India); Biswas, Pranab; Banerji, P., E-mail: pallab@matsc.iitkgp.ernet.in [Materials Science Centre, Indian Institute of Technology, Kharagpur 721 302 (India); Dhabal Das, Tushar; Das, Sanat Kr.; Chattopadhyay, S. [Department of Electronic Science, University of Calcutta, 92 Acharya Prafulla Chandra Road, Kolkata 700 009 (India); Biswas, D. [Department of Electronics and Electrical Communication Engineering, Indian Institute of Technology, Kharagpur 721 302 (India)

2014-01-28

A detailed analysis of photoluminescence (PL) from InP quantum dots (QDs) grown on Si has been carried out to understand the effect of substrate/host material in the luminescence and carrier escape process from the surface quantum dots. Such studies are required for the development of monolithically integrated next generation III-V QD based optoelectronics with fully developed Si microelectronics. The samples were grown by atmospheric pressure metalorganic chemical vapor deposition technique, and the PL measurements were made in the temperature range 10–80 K. The distribution of the dot diameter as well as the dot height has been investigated from atomic force microscopy. The origin of the photoluminescence has been explained theoretically. The band alignment of InP/Si heterostructure has been determined, and it is found be type II in nature. The positions of the conduction band minimum of Si and the 1st excited state in the conduction band of InP QDs have been estimated to understand the carrier escape phenomenon. A blue shift with a temperature co-efficient of 0.19 meV/K of the PL emission peak has been found as a result of competitive effect of different physical processes like quantum confinement, strain, and surface states. The corresponding effect of blue shift by quantum confinement and strain as well as the red shift by the surface states in the PL peaks has been studied. The origin of the luminescence in this heterojunction is found to be due to the recombination of free excitons, bound excitons, and a transition from the 1st electron excited state in the conduction band (e{sub 1}) to the heavy hole band (hh{sub 1}). Monotonic decrease in the PL intensity due to increase of thermally escaped carriers with temperature has been observed. The change in barrier height by the photogenerated electric-field enhanced the capture of the carriers by the surface states rather than their accumulation in the QD excited state. From an analysis of the dependence of

A job for quantum dots: use of a smartphone and 3D-printed accessory for all-in-one excitation and imaging of photoluminescence.

Science.gov (United States)

Petryayeva, Eleonora; Algar, W Russ

2016-04-01

Point-of-care (POC) diagnostic technologies are needed to improve global health and smartphones are a prospective platform for these technologies. While many fluorescence or photoluminescence-based smartphone assays have been reported in the literature, common shortcomings are the requirement of an excitation light source external to the smartphone and complicated integration of that excitation source with the smartphone. Here, we show that the photographic flash associated with the smartphone camera can be utilized to enable all-in-one excitation and imaging of photoluminescence (PL), thus eliminating the need for an excitation light source external to the smartphone. A simple and low-cost 3D-printed accessory was designed to create a dark environment and direct excitation light from the smartphone flash onto a sample. Multiple colors and compositions of semiconductor quantum dot (QD) were evaluated as photoluminescent materials for all-in-one smartphone excitation and imaging of PL, and these were compared with fluorescein and R-phycoerythrin (R-PE), which are widely utilized molecular and protein materials for fluorescence-based bioanalysis. The QDs were found to exhibit much better brightness and have the best potential for two-color detection. A model protein binding assay with a sub-microgram per milliliter detection limit and a Förster resonance energy transfer (FRET) assay for proteolytic activity were demonstrated, including imaging with serum as a sample matrix. In addition, FRET within tandem conjugates of a QD donor and fluorescent dye acceptor enabled smartphone detection of dye fluorescence that was otherwise unobservable without the QD to enhance its brightness. The ideal properties of photoluminescent materials for all-in-one smartphone excitation and imaging are discussed in the context of several different materials, where QDs appear to be the best overall material for this application.

Transmission electron microscopy and photoluminescence characterization of InGaAs strained quantum wires on GaAs vicinal (110) substrates

CERN Document Server

Shim, B R; Ota, T; Kobayashi, K; Maehashi, K; Nakashima, H; Lee, S Y

1999-01-01

We have used transmission electron microscopy (TEM) and photoluminescence (PL) to study InGaAs/AlGaAs strained quantum wires (QWRs) grown by molecular beam epitaxy (MBE) on GaAs vicinal (110) substrates. The cross-sectional TEM image reveals that InGaAs QWRs structures are naturally formed on AlGaAs giant steps. In the plan-view TEM images, the fringe pattern in the giant-step region is observed for In sub x Ga sub 1 sub - sub x As layers with x<= 0.4 We measured the separation of the fringe in the plan-view TEM images and compared the result with the calculated fringe separation. From this result, we conclude that the fringes observed in the plan-view TEM images are moire fringes. PL spectra of the InGaAs QWRs samples reveal 80-meV shifts to lower energy with respect to the spectrum of a quantum well (QWL) grown on a (001) substrate under the same conditions. We also measured the polarization anisotropy of the PL spectra from the QWRs. The PL peak shifts systematically toward higher energy with decreasing...

Photoluminescence and structural properties of unintentional single and double InGaSb/GaSb quantum wells grown by MOVPE

Science.gov (United States)

Ahia, Chinedu Christian; Tile, Ngcali; Botha, Johannes R.; Olivier, E. J.

2018-04-01

The structural and photoluminescence (PL) characterization of InGaSb quantum well (QW) structures grown on GaSb substrate (100) using atmospheric pressure Metalorganic Vapor Phase Epitaxy (MOVPE) is presented. Both structures (single and double-InGaSb QWs) were inadvertently formed during an attempt to grow capped InSb/GaSb quantum dots (QDs). In this work, 10 K PL peak energies at 735 meV and 740 meV are suggested to be emissions from the single and double QWs, respectively. These lines exhibit red shifts, accompanied by a reduction in their full-widths at half-maximum (FWHM) as the excitation power decreases. The presence of a GaSb spacer in the double QW was found to increase the strength of the PL emission, which consequently gives rise to a reduced blue-shift and broadening of the PL emission line observed for the double QW with an increase in laser power, while the low thermal activation energy for the quenching of the PL from the double QW is attributed to the existence of threading dislocations, as seen in the bright field TEM image for this sample.

GaSb quantum rings in GaAs/Al{sub x}Ga{sub 1−x}As quantum wells

Energy Technology Data Exchange (ETDEWEB)

Hodgson, P. D., E-mail: pdhodgson@hotmail.co.uk; Hayne, M.; Robson, A. J.; Zhuang, Q. D. [Department of Physics, Lancaster University, Lancaster LA1 4YB (United Kingdom); Danos, L. [Department of Chemistry, Lancaster University, Lancaster LA1 4YB (United Kingdom)

2016-01-28

We report the results of continuous and time-resolved photoluminescence measurements on type-II GaSb quantum rings embedded within GaAs/Al{sub x}Ga{sub 1−x}As quantum wells. A range of samples were grown with different well widths, compensation-doping concentrations within the wells, and number of quantum-ring layers. We find that each of these variants have no discernible effect on the radiative recombination, except for the very narrowest (5 nm) quantum well. In contrast, single-particle numerical simulations of the sample predict changes in photoluminescence energy of up to 200 meV. This remarkable difference is explained by the strong Coulomb binding of electrons to rings that are multiply charged with holes. The resilience of the emission to compensation doping indicates that multiple hole occupancy of the quantum rings is required for efficient carrier recombination, regardless of whether these holes come from doping or excitation.

Photoluminescence energy transitions in GaAs-Ga{sub 1-x}Al{sub x}As double quantum wells: Electric and magnetic fields and hydrostatic pressure effects

Energy Technology Data Exchange (ETDEWEB)

Lopez, S.Y. [Grupo de Educacion en Ciencias Experimentales y Matematicas-GECEM, Facultad de Educacion, Universidad de Antioquia, AA 1226 Medellin (Colombia); Mora-Ramos, M.E. [Facultad de Ciencias, Universidad Autonoma del Estado de Morelos, Av. Universidad 1001, CP 62209, Cuernavaca, Morelos (Mexico); Duque, C.A., E-mail: cduque@fisica.udea.edu.c [Instituto de Fisica, Universidad de Antioquia, AA 1226 Medellin (Colombia)

2009-12-15

The photoluminescence energy transitions in GaAs-Ga{sub 1-x}Al{sub x}As coupled double quantum wells are presented by considering the simultaneous effects of applied electric and magnetic fields and hydrostatic pressure. Calculations have been made in the framework of the effective mass and parabolic band approximations and using a variational procedure. The electric field is taken to be oriented along the growth direction of the heterostructure whereas for the magnetic field both in-plane and in-growth directions have been considered. The results show that the hydrostatic pressure and the applied electric field are two useful tools to tune the direct and indirect exciton transitions in such heterostructures. Our results are in good agreement with previous experimental findings in double quantum wells under applied electric field and hydrostatic pressure.

Photoconductance-calibrated photoluminescence lifetime imaging of crystalline silicon

International Nuclear Information System (INIS)

Herlufsen, Sandra; Schmidt, Jan; Hinken, David; Bothe, Karsten; Brendel, Rolf

2008-01-01

We use photoluminescence (PL) measurements by a silicon charge-coupled device camera to generate high-resolution lifetime images of multicrystalline silicon wafers. Absolute values of the excess carrier density are determined by calibrating the PL image by means of contactless photoconductance measurements. The photoconductance setup is integrated in the camera-based PL setup and therefore identical measurement conditions are realised. We demonstrate the validity of this method by comparison with microwave-detected photoconductance decay measurements. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (Abstract Copyright [2008], Wiley Periodicals, Inc.)

Strong white photoluminescence from annealed zeolites

International Nuclear Information System (INIS)

Bai, Zhenhua; Fujii, Minoru; Imakita, Kenji; Hayashi, Shinji

2014-01-01

The optical properties of zeolites annealed at various temperatures are investigated for the first time. The annealed zeolites exhibit strong white photoluminescence (PL) under ultraviolet light excitation. With increasing annealing temperature, the emission intensity of annealed zeolites first increases and then decreases. At the same time, the PL peak red-shifts from 495 nm to 530 nm, and then returns to 500 nm. The strongest emission appears when the annealing temperature is 500 °C. The quantum yield of the sample is measured to be ∼10%. The PL lifetime monotonously increases from 223 μs to 251 μs with increasing annealing temperature. The origin of white PL is ascribed to oxygen vacancies formed during the annealing process. -- Highlights: • The optical properties of zeolites annealed at various temperatures are investigated. • The annealed zeolites exhibit strong white photoluminescence. • The maximum PL enhancement reaches as large as 62 times. • The lifetime shows little dependence on annealing temperature. • The origin of white emission is ascribed to the oxygen vacancies

Exciton lifetime and spin dynamics in type-I In1−xAlxAs/Ga0.67Al0.33As quantum dots: Photoluminescence and pump-probe experiments

International Nuclear Information System (INIS)

Ben Daly, A.; Bernardot, F.; Barisien, T.; Galopin, E.; Lemaître, A.; Maaref, M.A.; Testelin, C.

2015-01-01

The exciton lifetime and spin relaxation have been studied in self-assembled In 1−x Al x As/Ga 0.67 Al 0.33 As quantum dots (QDs). Time-resolved photoluminescence and resonant pump-probe measurements were performed, at variable temperature and for different QD aluminium compositions. At low temperature, a long exciton-spin relaxation time has been measured, in agreement with the QD zero-dimensional confinement and the quenching of the relaxation mechanisms. The existence of a quasi-2D regime, in sample with a high QD density, has been observed. The importance of thermally-activated processes toward excited states is also evidenced, for QDs with different compositions and sizes. - Highlights: • The exciton lifetime and spin relaxation have been studied in In 1−x Al x As/Ga 0.67 Al 0.33 As quantum dot (QD). • Time-resolved photoluminescence (TRPL) and pump-probe measurements were performed, at variable temperature and for different QD aluminium compositions. • From the PL decay time, several thermal activation processes, related to 0D or 2D regime, or dependending on collective mechanisms. • The importance of thermal activated processes toward excited states is also evidenced, for QD with different compositions and sizes

Excitation power dependence of photoluminescence spectra of GaSb type-II quantum dots in GaAs grown by droplet epitaxy

Energy Technology Data Exchange (ETDEWEB)

Kawazu, T., E-mail: KAWAZU.Takuya@nims.go.jp; Noda, T.; Sakuma, Y. [National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Sakaki, H. [National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Toyota Technological Institute, 2-12-1 Hisakata, Tempaku-ku, Nagoya 468-8511 (Japan)

2016-04-15

We investigated the excitation power P dependence of photoluminescence (PL) spectra of GaSb type-II quantum dots (QDs) in GaAs grown by droplet epitaxy. We prepared two QD samples annealed at slightly different temperatures (380 {sup o}C and 400 {sup o}C) and carried out PL measurements. The 20 {sup o}C increase of the annealing temperature leads to (1) about 140 and 60 times stronger wetting layer (WL) luminescence at low and high P, (2) about 45% large energy shift of QD luminescence with P, and (3) the different P dependence of the PL intensity ratio between the QD and the WL. These differences of the PL characteristics are explained by the effects of the WL.

Photoluminescence spectral study of single cadmium selenide/zinc sulfide colloidal nanocrystals in poly(methyl methacrylate) and quantum dots molecules

Science.gov (United States)

Shen, Yaoming

Quantum dots (QDs)and Nano-crystals (NCs) have been studies for decades. Because of the nanoscale quantum confinement, delta shape like energy density states and narrowband emitters properties, they hold great promise for numerous optoelectronics and photonics applications. They could be used for tunable lasers, white LED, Nano-OLED, non-volatile memory and solar cells. They are also the most promising candidates for the quantum computing. The benefits for NCs over QDs is that NCs can be incorporated into a variety of polymers as well as thin films of bulk semiconductors. These exceptional flexibility and structural control distinguish NCs from the more traditional QD structures fabricated using epitaxial growth techniques. In my research of work, I studied the photoluminescence (PL) and absorption character of ensemble NCs incorporated in Polymethyl methacrylate (PMMA). To understand the behavior of the NCs in PMMA, it is important to measure a singe NC to avoid the inhomogenous broading of many NCs. So I particularly studied the behavior of a single NC in PMMA matrix. A microphotoluminescence setup to optically isolate a single nanocrystal is used. Random spectral shift and blinking behavior (on and off) are found. Addition to that, two color spectral shifting, is a major phenomena found in the system. Other interesting results such as PL intensity changes (decreasing or increasing with time) and quenching effect are observed and explained too. From the correlation function, we can distinguish the phonon replicas. The energy of these phonons can be calculated very accurately from the experiment result. The Huang-Rhys factors can be estimated too. Self-assembled semiconductor quantum dots (QDs), from highly strained-layer heteroepitaxy in the Stranski-Krastanow (S-K) growth mode, have been intensively studied because of the delta-function-like density of states, which is significant for optoelectronic applications. Spontaneous formation of semiconductor quantum

Lensless Photoluminescence Hyperspectral Camera Employing Random Speckle Patterns.

Czech Academy of Sciences Publication Activity Database

Žídek, Karel; Denk, Ondřej; Hlubuček, Jiří

2017-01-01

Roč. 7, č. 1 (2017), č. článku 15309. ISSN 2045-2322 R&D Projects: GA MŠk(CZ) LO1206; GA ČR(CZ) GJ17-26284Y Institutional support: RVO:61389021 Keywords : compressed sensing * photoluminescence imaging * laser speckles * single-pixel camera Subject RIV: BH - Optics, Masers, Lasers OBOR OECD: Optics (including laser optics and quantum optics) Impact factor: 4.259, year: 2016 https://www.nature.com/articles/s41598-017-14443-4

Nanomedicine photoluminescence crystal-inspired brain sensing approach

Science.gov (United States)

Fang, Yan; Wang, Fangzhen; Wu, Rong

2018-02-01

Precision sensing needs to overcome a gap of a single atomic step height standard. In response to the cutting-edge challenge, a heterosingle molecular nanomedicine crystal was developed wherein a nanomedicine crystal height less than 1 nm was designed and selfassembled on a substrate of either a highly ordered and freshly separated graphite or a N-doped silicon with hydrogen bonding by a home-made hybrid system of interacting single bioelectron donor-acceptor and a single biophoton donor-acceptor according to orthogonal mathematical optimization scheme, and an atomic spatial resolution conducting atomic force microscopy (C-AFM) with MHz signal processing by a special transformation of an atomic force microscopy (AFM) and a scanning tunneling microscopy (STM) were employed, wherein a z axis direction UV-VIS laser interferometer and a feedback circuit were used to achieve the minimized uncertainty of a micro-regional structure height and its corresponding local differential conductance quantization (spin state) process was repeatedly measured with a highly time resolution, as well as a pulsed UV-VIS laser micro-photoluminescence (PL) spectrum with a single photon resolution was set up by traceable quantum sensing and metrology relied up a quantum electrical triangle principle. The coupling of a single bioelectron conducting, a single biophoton photoluminescence, a frequency domain temporal spin phase in nanomedicine crystal-inspired sensing methods and sensor technologies were revealed by a combination of C-AFM and PL measurement data-based mathematic analyses1-3, as depicted in Figure 1 and repeated in nanomedicine crystals with a single atomic height. It is concluded that height-current-phase uncertainty correlation pave a way to develop a brain imaging and a single atomic height standard, quantum sensing, national security, worldwide impact1-3 technology and beyond.

High-resolution dynamic pressure sensor array based on piezo-phototronic effect tuned photoluminescence imaging.

Science.gov (United States)

Peng, Mingzeng; Li, Zhou; Liu, Caihong; Zheng, Qiang; Shi, Xieqing; Song, Ming; Zhang, Yang; Du, Shiyu; Zhai, Junyi; Wang, Zhong Lin

2015-03-24

A high-resolution dynamic tactile/pressure display is indispensable to the comprehensive perception of force/mechanical stimulations such as electronic skin, biomechanical imaging/analysis, or personalized signatures. Here, we present a dynamic pressure sensor array based on pressure/strain tuned photoluminescence imaging without the need for electricity. Each sensor is a nanopillar that consists of InGaN/GaN multiple quantum wells. Its photoluminescence intensity can be modulated dramatically and linearly by small strain (0-0.15%) owing to the piezo-phototronic effect. The sensor array has a high pixel density of 6350 dpi and exceptional small standard deviation of photoluminescence. High-quality tactile/pressure sensing distribution can be real-time recorded by parallel photoluminescence imaging without any cross-talk. The sensor array can be inexpensively fabricated over large areas by semiconductor product lines. The proposed dynamic all-optical pressure imaging with excellent resolution, high sensitivity, good uniformity, and ultrafast response time offers a suitable way for smart sensing, micro/nano-opto-electromechanical systems.

Optical pumping and negative luminescence polarization in charged GaAs quantum dots

Science.gov (United States)

Shabaev, Andrew; Stinaff, Eric A.; Bracker, Allan S.; Gammon, Daniel; Efros, Alexander L.; Korenev, Vladimir L.; Merkulov, Igor

2009-01-01

Optical pumping of electron spins and negative photoluminescence polarization are observed when interface quantum dots in a GaAs quantum well are excited nonresonantly by circularly polarized light. Both observations can be explained by the formation of long-lived dark excitons through hole spin relaxation in the GaAs quantum well prior to exciton capture. In this model, optical pumping of resident electron spins is caused by capture of dark excitons and recombination in charged quantum dots. Negative polarization results from accumulation of dark excitons in the quantum well and is enhanced by optical pumping. The dark exciton model describes the experimental results very well, including intensity and bias dependence of the photoluminescence polarization and the Hanle effect.

Origin of photoluminescence from silicon nanowires prepared by metal induced etching (MIE)

International Nuclear Information System (INIS)

Saxena, Shailendra K.; Rai, Hari. M.; Late, Ravikiran; Sagdeo, Pankaj R.; Kumar, Rajesh

2015-01-01

In this present study the origin of luminescence from silicon nanowires (SiNws) has been studied. SiNWs are fabricated on Si substrate by metal induced chemical etching (MIE). Here it is found that the band gap of SiNWs is higher than the gap of luminescent states in SiNWs which leads to the effect of Si=O bond. The band gap is estimated from diffuse reflectance analysis. Here we observe that band gap can be tailored depending on size (quantum confinement) but photoluminescence (PL) from all the sample is found to be fixed at 1.91 eV. This study is important for the understanding of origin of photoluminescence

Resonant photoluminescence studies of carrier localisation in c-plane InGaN/GaN quantum well structures

Science.gov (United States)

Blenkhorn, W. E.; Schulz, S.; Tanner, D. S. P.; Oliver, R. A.; Kappers, M. J.; Humphreys, C. J.; Dawson, P.

2018-05-01

In this paper we report on changes in the form of the low temperature (12 K) photoluminescence spectra of an InGaN/GaN quantum well structure as a function of excitation photon energy. As the photon energy is progressively reduced we observe at a critical energy a change in the form of the spectra from one which is determined by the occupation of the complete distribution of hole localisation centres to one which is determined by the resonant excitation of specific localisation sites. This change is governed by an effective mobility edge whereby the photo-excited holes remain localised at their initial energy and are prevented from scattering to other localisation sites. This assignment is confirmed by the results of atomistic tight binding calculations which show that the wave function overlap of the lowest lying localised holes with other hole states is low compared with the overlap of higher lying hole states with other higher lying hole states.

Photoluminescence of hybrid quantum dot systems

Czech Academy of Sciences Publication Activity Database

Král, Karel; Menšík, Miroslav

2015-01-01

Roč. 7, č. 4 (2015), 347-349 ISSN 2164-6627 R&D Projects: GA MŠk LH12236; GA MŠk LH12186 Institutional support: RVO:68378271 ; RVO:61389013 Keywords : quantum dots * energy transfer * electron-phonon interaction Subject RIV: BM - Solid Matter Physics ; Magnetism

Defect-mediated photoluminescence up-conversion in cadmium sulfide nanobelts (Conference Presentation)

Science.gov (United States)

Morozov, Yurii; Kuno, Masaru K.

2017-02-01

The concept of optical cooling of solids has existed for nearly 90 years ever since Pringsheim proposed a way to cool solids through the annihilation of phonons via phonon-assisted photoluminescence (PL) up-conversion. In this process, energy is removed from the solid by the emission of photons with energies larger than those of incident photons. However, actually realizing optical cooling requires exacting parameters from the condensed phase medium such as near unity external quantum efficiencies as well as existence of a low background absorption. Until recently, laser cooling has only been successfully realized in rare earth doped solids. In semiconductors, optical cooling has very recently been demonstrated in cadmium sulfide (CdS) nanobelts as well as in hybrid lead halide perovskites. For the former, large internal quantum efficiencies, sub-wavelength thicknesses, which decrease light trapping, and low background absorption, all make near unity external quantum yields possible. Net cooling by as much as 40 K has therefore been possible with CdS nanobelts. In this study, we describe a detailed investigation of the nature of efficient anti-Stokes photoluminescence (ASPL) in CdS nanobelts. Temperature-dependent PL up-conversion and optical absorption studies on individual NBs together with frequency-dependent up-converted PL intensity spectroscopies suggest that ASPL in CdS nanobelts is defect-mediated through involvement of defect levels below the band gap.

Photoluminescence of colloidal CdSe nano-tetrapods and quantum dots in oxygenic and oxygen-free environments

Energy Technology Data Exchange (ETDEWEB)

Zhao, Lijuan [Donghua University, Applied Physics Department, Shanghai (China); Hong Kong University of Science and Technology, Physics Department and the Institute of Nano-Science and Technology, Hong Kong (China); Pang, Qi; Ge, Weikun; Wang, Jiannong [Hong Kong University of Science and Technology, Physics Department and the Institute of Nano-Science and Technology, Hong Kong (China); Yang, Shihe [Hong Kong University of Science and Technology, Chemistry Department and the Institute of Nano-Science and Technology, Hong Kong (China)

2011-05-15

The effects of oxygenic versus oxygen-free environments on colloidal CdSe nano-tetrapods and quantum dots (QDs) were studied using both continuous and time-resolved photoluminescence (PL) measurements. The decays of PL intensities for tetrapods and QDs in oxygen-free solution (chloroform) and in air (on silicon) can be well fitted by a bi-exponential function. Based on the emission-energy dependence of carrier lifetimes and the amplitude ratio of the fast-decay component to the slow-decay component, the fast and slow PL decays of CdSe nanocrystals are attributed to the recombination of delocalized carriers in the core states and localized carriers in the surface states, respectively. The PL intensities of CdSe nano-tetrapods and QDs were found to be five times and an order of magnitude higher in air than in vacuum, respectively, which is explained by the passivation of surface defects by the polar gas (oxygen) absorption. The lower enhancement in PL intensities of CdSe nano-tetrapods is explained by the special morphology of the tetrapods. (orig.)

The influence of post-growth annealing on the optical properties of InAs quantum dot chains grown on pre-patterned GaAs(100)

International Nuclear Information System (INIS)

Hakkarainen, T V; Polojärvi, V; Schramm, A; Tommila, J; Guina, M

2012-01-01

We report on the effect of post-growth thermal annealing of [011]-, [01 1-bar ]-, and [010]-oriented quantum dot chains grown by molecular beam epitaxy on GaAs(100) substrates patterned by UV-nanoimprint lithography. We show that the quantum dot chains experience a blueshift of the photoluminescence energy, spectral narrowing, and a reduction of the intersubband energy separation during annealing. The photoluminescence blueshift is more rapid for the quantum dot chains than for self-assembled quantum dots that were used as a reference. Furthermore, we studied polarization resolved photoluminescence and observed that annealing reduces the intrinsic optical anisotropy of the quantum dot chains and the self-assembled quantum dots. (paper)

Optical Spectroscopy Of Charged Quantum Dot Molecules

Science.gov (United States)

Scheibner, M.; Bracker, A. S.; Stinaff, E. A.; Doty, M. F.; Gammon, D.; Ponomarev, I. V.; Reinecke, T. L.; Korenev, V. L.

2007-04-01

Coupling between two closely spaced quantum dots is observed by means of photoluminescence spectroscopy. Hole coupling is realized by rational crystal growth and heterostructure design. We identify molecular resonances of different excitonic charge states, including the important case of a doubly charged quantum dot molecule.

Photoluminescence excitation measurements using pressure-tuned laser diodes

Science.gov (United States)

Bercha, Artem; Ivonyak, Yurii; Medryk, Radosław; Trzeciakowski, Witold A.; Dybała, Filip; Piechal, Bernard

2015-06-01

Pressure-tuned laser diodes in external cavity were used as tunable sources for photoluminescence excitation (PLE) spectroscopy. The method was demonstrated in the 720 nm-1070 nm spectral range using a few commercial laser diodes. The samples for PLE measurements were quantum-well structures grown on GaAs and on InP. The method is superior to standard PLE measurements using titanium sapphire laser because it can be extended to any spectral range where anti-reflection coated laser diodes are available.

Photoluminescence excitation measurements using pressure-tuned laser diodes

International Nuclear Information System (INIS)

Bercha, Artem; Ivonyak, Yurii; Mędryk, Radosław; Trzeciakowski, Witold A.; Dybała, Filip; Piechal, Bernard

2015-01-01

Pressure-tuned laser diodes in external cavity were used as tunable sources for photoluminescence excitation (PLE) spectroscopy. The method was demonstrated in the 720 nm-1070 nm spectral range using a few commercial laser diodes. The samples for PLE measurements were quantum-well structures grown on GaAs and on InP. The method is superior to standard PLE measurements using titanium sapphire laser because it can be extended to any spectral range where anti-reflection coated laser diodes are available

Quantum well effect in bulk PbI(2) crystals revealed by the anisotropy of photoluminescence and Raman spectra.

Science.gov (United States)

Baltog, I; Baibarac, M; Lefrant, S

2009-01-14

On subjecting a bulk 2H-PbI(2) crystal to vacuum annealing at 500 K followed by a sudden cooling at liquid nitrogen temperature stacking faults are generated that separate distinct layers of nanometric thickness in which different numbers of I-Pb-I atomic layers are bundled together. Such structures, containing two, three, four, five etc I-Pb-I atomic layers, behave as quantum wells of different widths. The signature of such a transformation is given by a shift towards higher energies of the fundamental absorption edge, which is experimentally revealed by specific anisotropies in the photoluminescence and Raman spectra. The quantum confining effect is made visible by specific variations of a wide extra-excitonic band (G) at 2.06 eV that originates in the radiative recombination of carriers (electrons and holes), trapped on the surface defects. The excitation spectrum of the G band, with p polarized exciting light, reveals a fine structure comprised of narrow bands at 2.75, 2.64, 2.59 and 2.56 eV, which are associated with the PbI(2) quantum wells formed from two, three, four and five I-Pb-I atomic layers of 0.7 nm thickness. Regardless of the polarization state of the laser exciting light of 514.5 nm (2.41 eV), which is close to the band gap energy of PbI(2) (2.52 eV), the Raman scattering on bulk as-grown PbI(2) crystals has the character of a resonant process. For p polarized exciting light, the Raman scattering process on vacuum annealed PbI(2) becomes non-resonant. This originates from the quantum well structures generated inside the crystal, whose band gap energies are higher than the energy of the exciting light.

Growth and optical characteristics of InAs quantum dot structures with tunnel injection quantum wells for 1.55 μ m high-speed lasers

Science.gov (United States)

Bauer, Sven; Sichkovskyi, Vitalii; Reithmaier, Johann Peter

2018-06-01

InP based lattice matched tunnel injection structures consisting of a InGaAs quantum well, InAlGaAs barrier and InAs quantum dots designed to emit at 1.55 μ m were grown by molecular beam epitaxy and investigated by photoluminescence spectroscopy and atomic force microscopy. The strong influence of quantum well and barrier thicknesses on the samples emission properties at low and room temperatures was investigated. The phenomenon of a decreased photoluminescence linewidth of tunnel injection structures compared to a reference InAs quantum dots sample could be explained by the selection of the emitting dots through the tunneling process. Morphological investigations have not revealed any effect of the injector well on the dot formation and their size distribution. The optimum TI structure design could be defined.

Quantum Electrodynamics with Semiconductor Quantum Dots Coupled to Anderson‐localized Random Cavities

DEFF Research Database (Denmark)

Sapienza, Luca; Nielsen, Henri Thyrrestrup; Stobbe, Søren

2011-01-01

of the spontaneous emission decay rate by up to a factor 15 and an efficiency of channeling single photons into Anderson-localized modes reaching values as high as 94%. These results prove that disordered photonic media provide an efficient platform for quantum electrodynamics, offering a novel route to quantum......We demonstrate that the spontaneous emission decay rate of semiconductor quantum dots can be strongly modified by the coupling to disorder-induced Anderson-localized photonic modes. We experimentally measure, by means of time-resolved photoluminescence spectroscopy, the enhancement...

Carrier dynamics in submonolayer InGaAs/GaAs quantum dots

DEFF Research Database (Denmark)

Xu, Zhangcheng; Zhang, Yating; Hvam, Jørn Märcher

2006-01-01

Carrier dynamics of submonolayer InGaAs/GaAs quantum dots (QDs) were studied by microphotoluminecence (MPL), selectively excited photoluminescence (SEPL), and time-resolved photoluminescence (TRPL). MPL and SEPL show the coexistence of localized and delocalized states, and different local phonon...

Fabrication of GaAs concentric multiple quantum rings by droplet epitaxy

International Nuclear Information System (INIS)

Somaschini, C; Bietti, S; Sanguinetti, S; Koguchi, N; Fedorov, A; Abbarchi, M; Gurioli, M

2009-01-01

We present the fabrication of a novel quantum nanostructure, constituted by three concentric quantum rings by droplet epitaxy. Atomic Force Microscopy and photoluminescence characterization of these nanostructures is reported.

Photoluminescence and structural properties of CdSe quantum dot–gelatin composite films

Energy Technology Data Exchange (ETDEWEB)

Borkovska, L., E-mail: bork@isp.kiev.ua [V. Lashkaryov Institute of Semiconductor Physics of NAS of Ukraine, Pr. Nauky 41, 03028 Kyiv (Ukraine); Korsunska, N.; Stara, T.; Gudymenko, O.; Kladko, V. [V. Lashkaryov Institute of Semiconductor Physics of NAS of Ukraine, Pr. Nauky 41, 03028 Kyiv (Ukraine); Stroyuk, O.; Raevskaya, A. [L. Pysarzhevsky Institute of Physical Chemistry of NAS of Ukraine, Pr. Nauky 31, 03028 Kyiv (Ukraine); Kryshtab, T. [Instituto Politécnico Nacional – ESFM, Av. IPN, Ed.9 U.P.A.L.M., 07738 Mexico D.F. (Mexico)

2014-11-15

Optical and structural properties of composite films of CdSe quantum dots (QDs) embedded in gelatin matrix have been investigated by photoluminescence (PL), optical absorption and X-ray diffraction (XRD) methods. The optical absorption of the composite in the visible spectral range is found to be determined mainly by light absorption in the QDs. The decrease of the film transparency and the shift of the absorption edge to lower energies observed upon thermal annealing of the films at 140–160 °C are ascribed to the formation of chromophore groups in gelatin matrix. XRD patterns of the composite revealed helix to coil transition in gelatin matrix under thermal annealing of the composite at 100–160 °C. It is found that PL spectra of the composite are dominated by exciton and defect-related emission of the QDs and also contain weak emission of gelatin matrix. It is found that thermal annealing of the composite at 100–160 °C changes PL intensity and produces the shift of the PL bands to lower energies. As the annealed composite was kept in air for several months, the shift of exciton-related PL band position restored partially and the PL intensity increased. It is proposed that the increase of the PL intensity upon the thermal annealing of composite at 140 °C can be used for enhancement of the QD-related PL. Changes that occurred in the PL spectra of composite are ascribed to structural and chemical transformations in gelatin matrix and at the QD/gelatin interface.

Enhanced quantum yield of photoluminescent porous silicon prepared by supercritical drying

International Nuclear Information System (INIS)

Joo, Jinmyoung; Defforge, Thomas; Gautier, Gael; Loni, Armando; Kim, Dokyoung; Sailor, Michael J.; Li, Z. Y.; Canham, Leigh T.

2016-01-01

The effect of supercritical drying (SCD) on the preparation of porous silicon (pSi) powders has been investigated in terms of photoluminescence (PL) efficiency. Since the pSi contains closely spaced and possibly interconnected Si nanocrystals ( 32% at room temperature) has been achieved, prompting the need for further detailed studies to establish the dominant causes of such an improvement.

Enzyme biosensor systems based on porous silicon photoluminescence for detection of glucose, urea and heavy metals.

Science.gov (United States)

Syshchyk, Olga; Skryshevsky, Valeriy A; Soldatkin, Oleksandr O; Soldatkin, Alexey P

2015-04-15

A phenomenon of changes in photoluminescence of porous silicon at variations in medium pH is proposed to be used as a basis for the biosensor system development. The method of conversion of a biochemical signal into an optical one is applied for direct determination of glucose and urea as well as for inhibitory analysis of heavy metal ions. Changes in the quantum yield of porous silicon photoluminescence occur at varying pH of the tested solution due to the enzyme-substrate reaction. When creating the biosensor systems, the enzymes urease and glucose oxidase (GOD) were used as a bioselective material; their optimal concentrations were experimentally determined. It was shown that the photoluminescence intensity of porous silicon increased by 1.7 times when increasing glucose concentration in the GOD-containing reaction medium from 0 to 3.0mM, and decreased by 1.45 times at the same increase in the urea concentration in the urease-containing reaction medium. The calibration curves of dependence of the biosensor system responses on the substrate concentrations are presented. It is shown that the presence of heavy metal ions (Cu(2+), Pb(2+), and Cd(2+)) in the tested solution causes an inhibition of the enzymatic reactions catalyzed by glucose oxidase and urease, which results in a restoration of the photoluminescence quantum yield of porous silicon. It is proposed to use this effect for the inhibitory analysis of heavy metal ions. Copyright © 2014 Elsevier B.V. All rights reserved.

Impact of band structure and transition matrix elements on polarization properties of the photoluminescence of semipolar and nonpolar InGaN quantum wells

Energy Technology Data Exchange (ETDEWEB)

Schade, L.; Schwarz, U.T. [Department of Microsystems Engineering, University of Freiburg, Georges-Koehler-Allee 103, 79108 Freiburg (Germany); Fraunhofer Institute for Applied Solid State Physics (IAF), Tullastrasse 72, 79108 Freiburg (Germany); Wernicke, T. [Institute of Solid State Physics, Technical University, Hardenbergstrasse 36, 10623 Berlin (Germany); Weyers, M. [Ferdinand-Braun-Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Strasse 4, 12489 Berlin (Germany); Kneissl, M. [Institute of Solid State Physics, Technical University, Hardenbergstrasse 36, 10623 Berlin (Germany); Ferdinand-Braun-Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Strasse 4, 12489 Berlin (Germany)

2011-03-15

Partial or full linear polarization is characteristic for the spontaneous emission of light from semipolar and nonpolar InGaN quantum wells. This property is an implication of the crystalline anisotropy as a basic property of the wurtzite structure. The influence of this anisotropy on the band structure and the transition matrix elements was calculated by a k.p-method for arbitrary quantum well orientations with respect to the c-axis; results are shown here in detail. Optical polarization is a direct consequence of a broken symmetry, mainly affecting the transition matrix elements from the conduction to the valence bands. Furthermore, the strain of the InGaN quantum well strongly depends on the crystal orientation of the substrate, resulting in a valence band mixing. The composition of the eigenfunctions has emerged to be most important for the polarization dependence of strained semipolar and nonpolar InGaN QW. The matrix elements, in combination with the thermal occupation of the bands, determine the polarization of the spontaneously emitted light. Our photoluminescence measurements of nonpolar QW match well with this model. However, in contrast to calculations with standard band parameters, the two topmost subbands show a larger separation in the emitted energy. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Shape-engineered epitaxial InGaAs quantum rods for laser applications

International Nuclear Information System (INIS)

Li, L. H.; Ridha, P.; Chauvin, N.; Fiore, A.; Patriarche, G.

2008-01-01

We apply artificial shape engineering of epitaxial semiconductor nanostructures to demonstrate InGaAs quantum rods (QRs), nanocandles, and quantum dots-in-rods on a GaAs substrate. The evolution of the QRs from a zero-dimensional to one-dimensional confinement is evidenced by systematically measuring the photoluminescence and photoluminescence decay as a function of the rod length. Lasers based on a three-stack QR active region are demonstrated at room temperature, validating the applicability of the QRs in the real devices

Evidence for possible quantum dot interdiffusion induced by cap layer growth

International Nuclear Information System (INIS)

Jasinski, J.; Czeczott, M.; Gladysz, A.; Babinski, A.; Kozubowski, J.

1999-01-01

Self-organised InGaAs quantum dots were grown on (001) GaAs substrates and covered with two different types of cap layers grown at significantly different temperatures. In order to determine quantum dot emission energy and dot size distribution, photoluminescence and transmission electron microscopy studies were carried out on such samples. Simple theoretical model neglecting effect of interdiffusion allowed for correlation between quantum dot size and photoluminescence emission energy only in the case of dots covered by cap layers grown at the lower temperature. For dots covered by layers grown at the higher temperature such correlation was possible only when strong interdiffusion was assumed. (author)

Spin interactions in InAs quantum dots

Science.gov (United States)

Doty, M. F.; Ware, M. E.; Stinaff, E. A.; Scheibner, M.; Bracker, A. S.; Gammon, D.; Ponomarev, I. V.; Reinecke, T. L.; Korenev, V. L.

2006-03-01

Fine structure splittings in optical spectra of self-assembled InAs quantum dots (QDs) generally arise from spin interactions between particles confined in the dots. We present experimental studies of the fine structure that arises from multiple charges confined in a single dot [1] or in molecular orbitals of coupled pairs of dots. To probe the underlying spin interactions we inject particles with a known spin orientation (by using polarized light to perform photoluminescence excitation spectroscopy experiments) or use a magnetic field to orient and/or mix the spin states. We develop a model of the spin interactions that aids in the development of quantum information processing applications based on controllable interactions between spins confined to QDs. [1] Polarized Fine Structure in the Photoluminescence Excitation Spectrum of a Negatively Charged Quantum Dot, Phys. Rev. Lett. 95, 177403 (2005)

Assessment of quantum dots concentrators for photovoltaic electricity production; Evaluation du potentiel de concentrateurs a quantum dots pour la production d'electricite photovoltaique. Rapport final

Energy Technology Data Exchange (ETDEWEB)

Schueler, A; Kostro, A; Huriet, B

2006-07-01

One of the most promising application of semiconductor nanostructures in the field of photovoltaics might be planar photoluminescent concentrators. Even for diffuse solar radiation, considerable concentration factors might be achieved. Such devices have originally been designed on the basis of organic dyes and might benefit from a considerably improved lifetime when replacing the organic fluorescent substances by inorganic semiconductor nanocrystals, so-called quantum dots. Quantum dot containing nanocomposite thin films are synthesized at EPFL-LESO by a low cost sol-gel process. In order to study the potential of the use of quantum dot solar concentrators in photovoltaic solar energy conversion, reliable computer simulations are needed. A tool for ray tracing simulations of quantum dot solar concentrators has been developed at EPFL-LESO on the basis of Monte-Carlo methods that are applied to polarization-dependent reflection/transmission at interfaces, photon absorption by the semiconductor nanocrystals and photoluminescent re-emission. Together with the knowledge on the optoelectronical properties of suitable photovoltaic cells, such simulations allow to predict the total efficiency of the envisaged concentrating PV systems, and to optimize pane dimensions, photoluminescent emission frequencies, and choice of PV cell types. (author)

A Review of the Synthesis and Photoluminescence Properties of Hybrid ZnO and Carbon Nanomaterials

Directory of Open Access Journals (Sweden)

Protima Rauwel

2016-01-01

Full Text Available Photoluminescent ZnO carbon nanomaterials are an emerging class of nanomaterials with unique optical properties. They each, ZnO and carbon nanomaterials, have an advantage of being nontoxic and environmentally friendly. Their cost-effective production methods along with simple synthesis routes are also of interest. Moreover, ZnO presents photoluminescence emission in the UV and visible region depending on the synthesis routes, shape, size, deep level, and surface defects. When combined with carbon nanomaterials, modification of surface defects in ZnO allows tuning of these photoluminescence properties to produce, for example, white light. Moreover, efficient energy transfer from the ZnO to carbon nanostructures makes them suitable candidates not only in energy harvesting applications but also in biosensors, photodetectors, and low temperature thermal imaging. This work reviews the synthesis and photoluminescence properties of 3 carbon allotropes: carbon quantum or nanodots, graphene, and carbon nanotubes when hybridized with ZnO nanostructures. Various synthesis routes for the hybrid materials with different morphologies of ZnO are presented. Moreover, differences in photoluminescence emission when combining ZnO with each of the three different allotropes are analysed.

Fast synthesize ZnO quantum dots via ultrasonic method.

Science.gov (United States)

Yang, Weimin; Zhang, Bing; Ding, Nan; Ding, Wenhao; Wang, Lixi; Yu, Mingxun; Zhang, Qitu

2016-05-01

Green emission ZnO quantum dots were synthesized by an ultrasonic sol-gel method. The ZnO quantum dots were synthesized in various ultrasonic temperature and time. Photoluminescence properties of these ZnO quantum dots were measured. Time-resolved photoluminescence decay spectra were also taken to discover the change of defects amount during the reaction. Both ultrasonic temperature and time could affect the type and amount of defects in ZnO quantum dots. Total defects of ZnO quantum dots decreased with the increasing of ultrasonic temperature and time. The dangling bonds defects disappeared faster than the optical defects. Types of optical defects first changed from oxygen interstitial defects to oxygen vacancy and zinc interstitial defects. Then transformed back to oxygen interstitial defects again. The sizes of ZnO quantum dots would be controlled by both ultrasonic temperature and time as well. That is, with the increasing of ultrasonic temperature and time, the sizes of ZnO quantum dots first decreased then increased. Moreover, concentrated raw materials solution brought larger sizes and more optical defects of ZnO quantum dots. Copyright © 2015 Elsevier B.V. All rights reserved.

High-resolution photoluminescence studies of single semiconductor quantum dots

DEFF Research Database (Denmark)

Leosson, Kristjan; Østergaard, John Erland; Jensen, Jacob Riis

2000-01-01

Semiconductor quantum dots, especially those formed by self-organized growth, are considered a promising material system for future optical devices [1] and the optical properties of quantum dot ensembles have been investigated in detail over the past years. Recently, considerable interest has...

Photoconductivity, photoluminescence and optical Kerr nonlinear effects in zinc oxide films containing chromium nanoclusters

International Nuclear Information System (INIS)

Torres-Torres, C.; García-Cruz, M.L.; Castañeda, L.; Rangel Rojo, R.; Tamayo-Rivera, L.; Maldonado, A.; Avendaño-Alejo, M.

2012-01-01

Chromium doped zinc oxide thin solid films were deposited on soda–lime glass substrates. The photoconductivity of the material and its influence on the optical behavior was evaluated. A non-alkoxide sol–gel synthesis approach was used for the preparation of the samples. An enhancement of the photoluminescence response exhibited by the resulting photoconductive films with embedded chromium nanoclusters is presented. The modification in the photoconduction induced by a 445 nm wavelength was measured and then associated with the participation of the optical absorptive response. In order to investigate the third order optical nonlinearities of the samples, a standard time-resolved Optical Kerr Gate configuration with 80 fs pulses at 830 nm was used and a quasi-instantaneous pure electronic nonlinearity without the contribution of nonlinear optical absorption was observed. We estimate that from the inclusion of Cr nanoclusters into the sample results a strong optical Kerr effect originated by quantum confinement. The large photoluminescence response and the important refractive nonlinearity of the photoconductive samples seem to promise potential applications for the development of multifunctional all-optical nanodevices. - Highlights: ► Enhancement in photoluminescence for chromium doped zinc oxide films is presented. ► A strong and ultrafast optical Kerr effect seems to result from quantum confinement. ► Photoconductive properties for optical and optoelectronic functions were observed.

Photoconductivity, photoluminescence and optical Kerr nonlinear effects in zinc oxide films containing chromium nanoclusters

Energy Technology Data Exchange (ETDEWEB)

Torres-Torres, C., E-mail: crstorres@yahoo.com.mx [Seccion de Estudios de Posgrado e Investigacion, ESIME-Z, Instituto Politecnico Nacional, Mexico, DF 07738 (Mexico); Garcia-Cruz, M.L. [Centro de Investigacion en Dispositivos Semiconductores, Benemerita Universidad Autonoma de Puebla, A. P. J-48, Puebla 72570, Mexico (Mexico); Castaneda, L., E-mail: luisca@sirio.ifuap.buap.mx [Instituto de Fisica, Benemerita Universidad Autonoma de Puebla, A. P. J-48, Puebla 72570, Mexico (Mexico); Rangel Rojo, R. [CICESE/Depto. de Optica, A. P. 360, Ensenada, BC 22860 (Mexico); Tamayo-Rivera, L. [Instituto de Fisica, Universidad Nacional Autonoma de Mexico, Mexico, DF 01000 (Mexico); Maldonado, A. [Depto. de Ing. Electrica, CINVESTAV IPN-SEES, A. P. 14740, Mexico DF 07000 (Mexico); Avendano-Alejo, M., E-mail: imax_aa@yahoo.com.mx [Centro de Ciencias Aplicadas y Desarrollo Tecnologico, Universidad Nacional Autonoma de Mexico, A. P. 70-186, 04510, DF (Mexico); and others

2012-04-15

Chromium doped zinc oxide thin solid films were deposited on soda-lime glass substrates. The photoconductivity of the material and its influence on the optical behavior was evaluated. A non-alkoxide sol-gel synthesis approach was used for the preparation of the samples. An enhancement of the photoluminescence response exhibited by the resulting photoconductive films with embedded chromium nanoclusters is presented. The modification in the photoconduction induced by a 445 nm wavelength was measured and then associated with the participation of the optical absorptive response. In order to investigate the third order optical nonlinearities of the samples, a standard time-resolved Optical Kerr Gate configuration with 80 fs pulses at 830 nm was used and a quasi-instantaneous pure electronic nonlinearity without the contribution of nonlinear optical absorption was observed. We estimate that from the inclusion of Cr nanoclusters into the sample results a strong optical Kerr effect originated by quantum confinement. The large photoluminescence response and the important refractive nonlinearity of the photoconductive samples seem to promise potential applications for the development of multifunctional all-optical nanodevices. - Highlights: Black-Right-Pointing-Pointer Enhancement in photoluminescence for chromium doped zinc oxide films is presented. Black-Right-Pointing-Pointer A strong and ultrafast optical Kerr effect seems to result from quantum confinement. Black-Right-Pointing-Pointer Photoconductive properties for optical and optoelectronic functions were observed.

Assessment of quantum dots concentrators for photovoltaic electricity production; Evaluation du potentiel de concentrateurs a quantum dots pour la production d'electricite photovoltaique. Rapport final

Energy Technology Data Exchange (ETDEWEB)

Schueler, A.; Kostro, A.; Huriet, B.

2006-07-01

One of the most promising application of semiconductor nanostructures in the field of photovoltaics might be planar photoluminescent concentrators. Even for diffuse solar radiation, considerable concentration factors might be achieved. Such devices have originally been designed on the basis of organic dyes and might benefit from a considerably improved lifetime when replacing the organic fluorescent substances by inorganic semiconductor nanocrystals, so-called quantum dots. Quantum dot containing nanocomposite thin films are synthesized at EPFL-LESO by a low cost sol-gel process. In order to study the potential of the use of quantum dot solar concentrators in photovoltaic solar energy conversion, reliable computer simulations are needed. A tool for ray tracing simulations of quantum dot solar concentrators has been developed at EPFL-LESO on the basis of Monte-Carlo methods that are applied to polarization-dependent reflection/transmission at interfaces, photon absorption by the semiconductor nanocrystals and photoluminescent re-emission. Together with the knowledge on the optoelectronical properties of suitable photovoltaic cells, such simulations allow to predict the total efficiency of the envisaged concentrating PV systems, and to optimize pane dimensions, photoluminescent emission frequencies, and choice of PV cell types. (author)

Active region dimensionality and quantum efficiencies of InGaN LEDs from temperature dependent photoluminescence transients

Science.gov (United States)

Can, Nuri; Okur, Serdal; Monavarian, Morteza; Zhang, Fan; Avrutin, Vitaliy; Morkoç, Hadis; Teke, Ali; Özgür, Ümit

2015-03-01

Temperature dependent recombination dynamics in c-plane InGaN light emitting diodes (LEDs) with different well thicknesses, 1.5, 2, and 3 nm, were investigated to determine the active region dimensionality and its effect on the internal quantum efficiencies. It was confirmed for all LEDs that the photoluminescence (PL) transients are governed by radiative recombination at low temperatures while nonradiative recombination dominates at room temperature. At photoexcited carrier densities of 3 - 4.5 x 1016 cm-3 , the room-temperature Shockley-Read-Hall (A) and the bimolecular (B) recombination coefficients (A, B) were deduced to be (9.2x107 s-1, 8.8x10-10 cm3s-1), (8.5x107 s-1, 6.6x10-10 cm3s-1), and (6.5x107 s-1, 1.4x10-10 cm3s-1) for the six period 1.5, 2, and 3 nm well-width LEDs, respectively. From the temperature dependence of the radiative lifetimes, τrad α Tn/2, the dimensionality n of the active region was found to decrease consistently with decreasing well width. The 3 nm wide wells exhibited ~T1.5 dependence, suggesting a three-dimensional nature, whereas the 1.5 nm wells were confirmed to be two-dimensional (~T1) and the 2 nm wells close to being two-dimensional. We demonstrate that a combination of temperature dependent PL and time-resolved PL techniques can be used to evaluate the dimensionality as well as the quantum efficiencies of the LED active regions for a better understanding of the relationship between active-region design and the efficiency limiting processes in InGaN LEDs.

Temperature-dependent photoluminescence and contactless electroreflectance characterization of a ZnxCd1-xSe/Znx'Cdy'Mg1-x'-y'Se asymmetric coupled quantum well structure

International Nuclear Information System (INIS)

Wu, J.D.; Huang, Y.S.; Lin, D.Y.; Charles, W.O.; Shen, A.; Tamargo, M.C.; Tiong, K.K.

2011-01-01

Research highlights: → We report a detailed study of a ZnxCd 1-x Se/Znx'Cdy'Mg 1-x '-y'Se asymmetric coupled quantum well structure by using temperature-dependent photoluminescence (PL) and contactless electroreflectance (CER) techniques. → The PL peak position yielded information of the fundamental excitonic recombinations. → Analysis of the CER spectra led to the identification of various interband transitions. →Study of the temperature dependence of the excitonic transition energies indicated that main influence of temperature on the quantized transitions is through temperature dependence of the constituent material band gap in the well. - Abstract: Temperature-dependent photoluminescence (PL) and contactless electroreflectance (CER) were used to characterize a Zn x Cd 1-x Se/Zn x' Cd y' Mg 1-x'-y' Se asymmetric coupled quantum well (ACQW) structure in the range of 10-300 K. The PL peak position yielded information of the fundamental excitonic recombinations. A detailed analysis of the CER spectra led to the identification of various interband transitions. The intersubband transitions were then estimated and found to be in a good agreement with the previous report of Fourier-transform infrared absorption measurements. At low temperature, the PL spectra of the sample showed an asymmetric behavior with an exponential tail at the lower-energy side and were attributed to the localized excitonic recombinations due to potential fluctuations. Detailed study of the temperature dependence of the excitonic transition energies indicated that the main influence of temperature on the quantized transitions is through the temperature dependence of the band gap of the constituent material in the well.

Photoluminescence and electrical properties of silicon oxide and silicon nitride superlattices containing silicon nanocrystals

International Nuclear Information System (INIS)

Shuleiko, D V; Ilin, A S

2016-01-01

Photoluminescence and electrical properties of superlattices with thin (1 to 5 nm) alternating silicon-rich silicon oxide or silicon-rich silicon nitride, and silicon oxide or silicon nitride layers containing silicon nanocrystals prepared by plasma-enhanced chemical vapor deposition with subsequent annealing were investigated. The entirely silicon oxide based superlattices demonstrated photoluminescence peak shift due to quantum confinement effect. Electrical measurements showed the hysteresis effect in the vicinity of zero voltage due to structural features of the superlattices from SiOa 93 /Si 3 N 4 and SiN 0 . 8 /Si 3 N 4 layers. The entirely silicon nitride based samples demonstrated resistive switching effect, comprising an abrupt conductivity change at about 5 to 6 V with current-voltage characteristic hysteresis. The samples also demonstrated efficient photoluminescence with maximum at ∼1.4 eV, due to exiton recombination in silicon nanocrystals. (paper)

Ion-beam synthesis and photoluminescence of SiC nanocrystals assisted by MeV-heavy-ion-beam annealing

International Nuclear Information System (INIS)

Khamsuwan, J.; Intarasiri, S.; Kirkby, K.; Chu, P.K.; Singkarat, S.; Yu, L.D.

2012-01-01

This work explored a novel way to synthesize silicon carbide (SiC) nanocrystals for photoluminescence. Carbon ions at 90 keV were implanted in single crystalline silicon wafers at elevated temperature, followed by irradiation using xenon ion beams at an energy of 4 MeV with two low fluences of 5 × 10 13 and 1 × 10 14 ions/cm 2 at elevated temperatures for annealing. X-ray diffraction, Raman scattering, infrared spectroscopy and transmission electron microscopy were used to characterize the formation of nanocrystalline SiC. Photoluminescence was measured from the samples. The results demonstrated that MeV-heavy-ion-beam annealing could indeed induce crystallization of SiC nanocrystals and enhance emission of photoluminescence with violet bands dominance due to the quantum confinement effect.

The mechanism of the photoluminescence changes in bio-conjugated CdSe/ZnS quantum dots

Science.gov (United States)

Borkovska, L.; Korsunska, N.; Stara, T.; Kolomys, O.; Strelchuk, V.; Rachkov, O.; Kryshtab, T.

2013-09-01

The change of the photoluminescence (PL) and optical characteristics in non-conjugated and conjugated with S6K2 antibody CdSe/ZnS core/shell quantum dots (QDs) during storage in air has been studied by the conventional PL, micro-PL and micro-Raman techniques. The QDs dried on a crystalline Si substrate were kept in the darkness and under illumination. In the PL spectra, the storage resulted in a blue shift of PL peak position, in the increasing of the full width at a half maximum (FWHM) of the PL band and in the decreasing of the PL intensity. In the Raman spectra, the shift of the CdSe LO peak position to the low frequency region and the increasing of its FWHM were observed. The transformations in the PL and optical characteristics correlate with each other and are found to be the largest in bio-conjugated QDs stored under illumination. The increase of the light intensity accelerated the changes occurred during storage. An oxidation of the QD core, which decreases the QD size, is supposed to be responsible for observed transformations. The bio-conjugation is assumed to promote QD oxidation that results in different PL peak position in stored non-conjugated and bio-conjugated QDs. The mechanism of the effect is discussed.

Comparison of the Optical Properties of Graphene and Alkyl-terminated Si and Ge Quantum Dots.

Science.gov (United States)

de Weerd, Chris; Shin, Yonghun; Marino, Emanuele; Kim, Joosung; Lee, Hyoyoung; Saeed, Saba; Gregorkiewicz, Tom

2017-10-31

Semiconductor quantum dots are widely investigated due to their size dependent energy structure. In particular, colloidal quantum dots represent a promising nanomaterial for optoelectronic devices, such as photodetectors and solar cells, but also luminescent markers for biotechnology, among other applications. Ideal materials for these applications should feature efficient radiative recombination and absorption transitions, altogether with spectral tunability over a wide range. Group IV semiconductor quantum dots can fulfill these requirements and serve as an alternative to the commonly used direct bandgap materials containing toxic and/or rare elements. Here, we present optical properties of butyl-terminated Si and Ge quantum dots and compare them to those of graphene quantum dots, finding them remarkably similar. We investigate their time-resolved photoluminescence emission as well as the photoluminescence excitation and linear absorption spectra. We contemplate that their emission characteristics indicate a (semi-) resonant activation of the emitting channel; the photoluminescence excitation shows characteristics similar to those of a molecule. The optical density is consistent with band-to-band absorption processes originating from core-related states. Hence, these observations strongly indicate a different microscopic origin for absorption and radiative recombination in the three investigated quantum dot systems.

Investigation of the non-square InGaAsP/InP quantum wells in the electric field by photoreflectance

International Nuclear Information System (INIS)

Kudrawiec, R.; Sek, G.; Rudno-Rudzinski, W.; Misiewicz, J.; Wojcik, J.; Robinson, B.J.; Thompson, D.A.; Mascher, P.

2002-01-01

Non-square quantum wells in electric field have been investigated by photoreflectance and photoluminescence spectroscopies. The structures have been obtained by a post-growth modification (rapid thermal annealing) of standard 1.55 μm InGaAsP-based laser structures that have grown by gas molecular beam epitaxy. During rapid thermal annealing a migration of semiconductor atoms across quantum well interfaces changes the quantum well profile from a square well to rounded well. The modification of the profile changes energy levels in the quantum wells and in consequence a blue shift of the quantum well emission peak is observed in photoluminescence. In this paper the blue shift of the ground state transition of post-growth modified quantum well structures has been investigated by both photoluminescence and photoreflectance techniques. Also a blue shift of excited state transitions has been observed in photoreflectance spectra. Generally, a stronger blue shift for the ground state transition than for excited state transitions has been observed. Additionally, oscillator strengths for all quantum well transitions have been determined from photoreflectance spectra. It has been found that the oscillator strength is constant for all quantum well transitions despite of modification of the quantum well profile. (author)

Colloidal Photoluminescent Amorphous Porous Silicon, Methods Of Making Colloidal Photoluminescent Amorphous Porous Silicon, And Methods Of Using Colloidal Photoluminescent Amorphous Porous Silicon

KAUST Repository

Chaieb, Sahraoui

2015-04-09

Embodiments of the present disclosure provide for a colloidal photoluminescent amorphous porous silicon particle suspension, methods of making a colloidal photoluminescent amorphous porous silicon particle suspension, methods of using a colloidal photoluminescent amorphous porous silicon particle suspension, and the like.

Colloidal Photoluminescent Amorphous Porous Silicon, Methods Of Making Colloidal Photoluminescent Amorphous Porous Silicon, And Methods Of Using Colloidal Photoluminescent Amorphous Porous Silicon

KAUST Repository

Chaieb, Saharoui; Mughal, Asad Jahangir

2015-01-01

Embodiments of the present disclosure provide for a colloidal photoluminescent amorphous porous silicon particle suspension, methods of making a colloidal photoluminescent amorphous porous silicon particle suspension, methods of using a colloidal photoluminescent amorphous porous silicon particle suspension, and the like.

Self-assembly of concentric quantum double rings.

Science.gov (United States)

Mano, Takaaki; Kuroda, Takashi; Sanguinetti, Stefano; Ochiai, Tetsuyuki; Tateno, Takahiro; Kim, Jongsu; Noda, Takeshi; Kawabe, Mitsuo; Sakoda, Kazuaki; Kido, Giyuu; Koguchi, Nobuyuki

2005-03-01

We demonstrate the self-assembled formation of concentric quantum double rings with high uniformity and excellent rotational symmetry using the droplet epitaxy technique. Varying the growth process conditions can control each ring's size. Photoluminescence spectra emitted from an individual quantum ring complex show peculiar quantized levels that are specified by the carriers' orbital trajectories.

Influence of hydrogen peroxide on the stability and optical properties of CdS quantum dots in gelatin

Energy Technology Data Exchange (ETDEWEB)

Klyuev, V.G.; Volykhin, D.V., E-mail: volykhin.d@ya.ru; Ivanova, A.A.

2017-03-15

Influence of hydrogen peroxide on the stability and optical characteristics of CdS quantum dots obtained by aqueous synthesis in gelatin is investigated. It is shown that the action of hydrogen peroxide on the CdS quantum dots reduces the average particle size, increases monodispersity of particle size distribution, and also increases the photoluminescence intensity. A model that explains the behavior of CdS quantum dots photoluminescence with a decrease of particle size as a result of treatment with hydrogen peroxide is presented.

Photoluminescence from CdxHg1-xTe

International Nuclear Information System (INIS)

Breivik, M; Selvig, E; Tonheim, C R; Brendhagen, E; Brudevoll, T; Rheenen, A D van; Steen, H; Nicolas, S; Lorentzen, T; Haakenaasen, R

2008-01-01

We present important aspects of photoluminescence (PL) of Cd x Hg 1-x Te in the infrared part of the spectrum where background thermal radiation significantly affects the PL spectrum. We show how the background spectrum can be removed from the data. We also show how the wavelength of the excitation laser affects the relative intensity of the PL peaks from a multi-layer structure. Finally, we present temperature dependent PL of a Cd 0.36 Hg 0.64 Te/Cd 0.61 Hg 0.39 Te multiple quantum well structure grown on a 4 μm thick Cd 0.36 Hg 0.64 Te buffer layer. We attribute the low temperature peak from the buffer layer to impurities. The impurity levels are depopulated as the temperature increases, resulting in a decreased PL peak intensity. Above ∼200 K a band-to-band peak from the buffer layer is observed. The quantum well peak persists up to ∼200 K

Photoluminescence spectra of n-doped double quantum wells in a parallel magnetic field

International Nuclear Information System (INIS)

Huang, D.; Lyo, S.K.

1999-01-01

We show that the photoluminescence (PL) line shapes from tunnel-split ground sublevels of n-doped thin double quantum wells (DQW close-quote s) are sensitively modulated by an in-plane magnetic field B parallel at low temperatures (T). The modulation is caused by the B parallel -induced distortion of the electronic structure. The latter arises from the relative shift of the energy-dispersion parabolas of the two quantum wells (QW close-quote s) in rvec k space, both in the conduction and valence bands, and formation of an anticrossing gap in the conduction band. Using a self-consistent density-functional theory, the PL spectra and the band-gap narrowing are calculated as a function of B parallel , T, and the homogeneous linewidths. The PL spectra from symmetric and asymmetric DQW close-quote s are found to show strikingly different behavior. In symmetric DQW close-quote s with a high density of electrons, two PL peaks are obtained at B parallel =0, representing the interband transitions between the pair of the upper (i.e., antisymmetric) levels and that of the lower (i.e., symmetric) levels of the ground doublets. As B parallel increases, the upper PL peak develops an N-type kink, namely a maximum followed by a minimum, and merges with the lower peak, which rises monotonically as a function of B parallel due to the diamagnetic energy. When the electron density is low, however, only a single PL peak, arising from the transitions between the lower levels, is obtained. In asymmetric DQW close-quote s, the PL spectra show mainly one dominant peak at all B parallel close-quote s. In this case, the holes are localized in one of the QW close-quote s at low T and recombine only with the electrons in the same QW. At high electron densities, the upper PL peak shows an N-type kink like in symmetric DQW close-quote s. However, the lower peak is absent at low B parallel close-quote s because it arises from the inter-QW transitions. Reasonable agreement is obtained with recent

The synthesis of CdSe quantum dots with carboxyl group and study on their optical characteristics

International Nuclear Information System (INIS)

Ye, Chen; Park, Sangjoon; Kim, Jongsung

2009-01-01

Quantum dots are nanocrystal semiconductors which attract lots of research interests due to their peculiar optical properties. CdSe/ZnS quantum dots have been synthesized via pyrolysis of organometallic reagents. The color of the quantum dot changes from yellow-green to red as their size increases with reaction time. Photoluminescence quantum efficiency of CdSe quantum dots have been enhanced by passivating the surface of CdSe quantum dots with ZnS layers. Quantum dots are nanocrystal semiconductors which attract lots of research interests due to their peculiar optical properties. CdSe/ZnS quantum dots have been synthesized via pyrolysis of organometallic reagents. The color of the quantum dot changes from yellow-green to red as their size increases with reaction time. Photoluminescence quantum efficiency of CdSe quantum dots have been enhanced by passivating the surface of CdSe quantum dots with ZnS layers. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

High-amplitude THz and GHz strain waves, generated by ultrafast screening of piezoelectric fields in InGaN/GaN multiple quantum wells

DEFF Research Database (Denmark)

Porte, Henrik; van Capel, P.J.S.; Turchinovich, Dmitry

2010-01-01

Screening of large built-in piezoelectric fields in InGaN/GaN quantum wells leads to high-amplitude acoustic emission. We will compare acoustic emission by quantum wells with different thicknesses with photoluminescence; indicating screening.......Screening of large built-in piezoelectric fields in InGaN/GaN quantum wells leads to high-amplitude acoustic emission. We will compare acoustic emission by quantum wells with different thicknesses with photoluminescence; indicating screening....

The world of quantum matter

CERN Multimedia

CERN. Geneva

2006-01-01

In my lecture series, I will present the recent spectacular advances in the field of quantum gases and macroscopic quantum physics. A variety of subjects will be covered including Bose condensates and degenerate Fermi gases, ultracold molecules and chemistry near absolute zero, Rydberg gases, single-atom manipulation, quantum information processing, as well as applications of cold atoms as precision targets. The topics of the lectures are: I. Physics near absolute zero II. Bose condensation and Fermi degeneracy III. Molecules, Rydberg gases and other exotic species IV. Single-atom manipulation, quantum information processing and ultracold atoms as targets in storage rings

Phosphorene quantum dots

Science.gov (United States)

Vishnoi, Pratap; Mazumder, Madhulika; Barua, Manaswee; Pati, Swapan K.; Rao, C. N. R.

2018-05-01

Phosphorene, a two-dimensional material, has been a subject of recent investigations. In the present study, we have prepared blue fluorescent phosphorene quantum dots (PQDs) by liquid phase exfoliation of black phosphorus in two non-polar solvents, toluene and mesitylene. The average particle sizes of PQDs decrease from 5.0 to 1.0 nm on increasing the sonicator power from 150 to 225 W. The photoluminescence spectrum of the PQDs is red-shifted in the 395-470 nm range on increasing the excitation-wavelength from 300 to 480 nm. Electron donor and acceptor molecules quench the photoluminescence, with the acceptors showing more marked effects.

Investigation of In0.7Ga0.3As/In0.7Al0.3As metamorphic HEMT- heterostructures by photoluminescence spectroscopy

International Nuclear Information System (INIS)

LETT', Prof. Popova 5, St. Petersburg 197376 (Russian Federation))" data-affiliation=" (Saint-Petersburg Electrotechnical University LETT', Prof. Popova 5, St. Petersburg 197376 (Russian Federation))" >Romanovskiy, D S; LETT', Prof. Popova 5, St. Petersburg 197376 (Russian Federation))" data-affiliation=" (Saint-Petersburg Electrotechnical University LETT', Prof. Popova 5, St. Petersburg 197376 (Russian Federation))" >Tarasov, S A; Galiev, G B; Pushkarev, S S

2014-01-01

Low-temperature photoluminescence and photoreflectance have been studied in several metamorphic HEMT- (MHEMT-) heterostructures with the same active regions and different buffer layer designs grown by solid-source molecular beam epitaxy. The indium mole fraction in InAlAs/InGaAs/InAlAs single quantum well (QW) is 0.7. It was found that structures with step-graded metamorphic buffer have better quality. Also it was shown that mismatched superlattices in metamorphic buffer can influence on the half-width of photoluminescence spectra. The possible attribution of photoluminescence and photoreflectance spectral lines and their thermal behaviour are critically discussed

Characterization of interfaces in semimagnetic quantum wells

International Nuclear Information System (INIS)

Schmitt, G.; Kuhn-Heinrich, B.; Zehnder, U.; Ossau, W.; Litz, T.; Waag, A.; Landwehr, G.

1995-01-01

The interfaces between nonmagnetic CdTe quantum wells and semimagnetic barriers of Cd 1-x Mn x Te were investigated for several well widths by low temperature photoluminescence and photoluminescence excitation spectroscopy. Specially designed Cd 1-x Mn x /CdTe/Cd 1-y Mg y Te structures enable us to distinguish the quality of semimagnetic normal and inverted interfaces. The normal interface shows to better structural quality than the inverted interface. (author)

Effects of rapid thermal annealing on the optical properties of strain-free quantum ring solar cells

Science.gov (United States)

2013-01-01

Strain-free GaAs/Al0.33Ga0.67As quantum rings are fabricated by droplet epitaxy. Both photoresponse and photoluminescence spectra confirm optical transitions in quantum rings, suggesting that droplet epitaxial nanomaterials are applicable to intermediate band solar cells. The effects of post-growth annealing on the quantum ring solar cells are investigated, and the optical properties of the solar cells with and without thermal treatment are characterized by photoluminescence technique. Rapid thermal annealing treatment has resulted in the significant improvement of material quality, which can be served as a standard process for quantum structure solar cells grown by droplet epitaxy. PMID:23281811

Effect of boron incorporation on the structural and photoluminescence properties of highly-strained InxGa1-xAs/GaAs multiple quantum wells

Directory of Open Access Journals (Sweden)

Qi Wang

2013-07-01

Full Text Available In this research, 5-period highly-strained BInGaAs/GaAs multiple quantum wells (MQWs have been successfully grown at 480-510ºC by LP-MOCVD. Room-temperature photoluminescence (RT-PL measurements of BInGaAs/GaAs MQWs showed the peak wavelength as long as 1.17 μm with full-width at half maximum (FWHM of only 29.5 meV. In addition, a slight blue-shift (∼18 meV of PL peak energy of InxGa1-xAs/GaAs MQWs was observed after boron incorporation. It has been found boron incorporation ( 40%, the positive effect of boron incorporation prevailed, i.e., boron incorporation completely suppressed the thickness undulation and lead to the improvement of PL properties.

Improved photoluminescence quantum yield and stability of CdSe-TOP, CdSe-ODA-TOPO, CdSe/CdS and CdSe/EP nanocomposites

Science.gov (United States)

Wei, Shutian; Zhu, Zhilin; Wang, Zhixiao; Wei, Gugangfen; Wang, Pingjian; Li, Hai; Hua, Zhen; Lin, Zhonghai

2016-07-01

Size-controllable monodisperse CdSe nanocrystals with different organic capping were prepared based on the hot-injection method. The effective separation of nucleation and growth was achieved by rapidly mixing two highly reactive precursors. As a contrast, we prepared CdSe/CdS nanocrystals (NCs) successfully based on the selective ion layer adsorption and reaction (SILAR) technique. This inorganic capping obtained higher photoluminescence quantum yield (PLQY) of 59.3% compared with organic capping of 40.8%. Furthermore, the CdSe-epoxy resin (EP) composites were prepared by adopting a flexible ex situ method, and showed excellent stability in the ambient environment for one year. So the composites with both high PLQY of nanocrystals and excellent stability are very promising to device application.

Carrier-density dependence of photoluminescence from localized states in InGaN/GaN quantum wells in nanocolumns and a thin film

Energy Technology Data Exchange (ETDEWEB)

Shimosako, N., E-mail: n-shimosako@sophia.jp; Inose, Y.; Satoh, H.; Kinjo, K.; Nakaoka, T.; Oto, T. [Department of Engineering and Applied Sciences, Sophia University, 7-1 Kioi-cho, Chiyoda-ku, Tokyo 102-8554 (Japan); Kishino, K.; Ema, K. [Department of Engineering and Applied Sciences, Sophia University, 7-1 Kioi-cho, Chiyoda-ku, Tokyo 102-8554 (Japan); Sophia Nanotechnology Research Center, Sophia University, 7-1 Kioi-cho, Chiyoda-ku, Tokyo 102-8554 (Japan)

2015-11-07

We have measured and analyzed the carrier-density dependence of photoluminescence (PL) spectra and the PL efficiency of InGaN/GaN multiple quantum wells in nanocolumns and in a thin film over a wide excitation range. The localized states parameters, such as the tailing parameter, density and size of the localized states, and the mobility edge density are estimated. The spectral change and reduction of PL efficiency are explained by filling of the localized states and population into the extended states around the mobility edge density. We have also found that the nanocolumns have a narrower distribution of the localized states and a higher PL efficiency than those of the film sample although the In composition of the nanocolumns is higher than that of the film.

Absolute continuity for operator valued completely positive maps on C∗-algebras

Science.gov (United States)

Gheondea, Aurelian; Kavruk, Ali Şamil

2009-02-01

Motivated by applicability to quantum operations, quantum information, and quantum probability, we investigate the notion of absolute continuity for operator valued completely positive maps on C∗-algebras, previously introduced by Parthasarathy [in Athens Conference on Applied Probability and Time Series Analysis I (Springer-Verlag, Berlin, 1996), pp. 34-54]. We obtain an intrinsic definition of absolute continuity, we show that the Lebesgue decomposition defined by Parthasarathy is the maximal one among all other Lebesgue-type decompositions and that this maximal Lebesgue decomposition does not depend on the jointly dominating completely positive map, we obtain more flexible formulas for calculating the maximal Lebesgue decomposition, and we point out the nonuniqueness of the Lebesgue decomposition as well as a sufficient condition for uniqueness. In addition, we consider Radon-Nikodym derivatives for absolutely continuous completely positive maps that, in general, are unbounded positive self-adjoint operators affiliated to a certain von Neumann algebra, and we obtain a spectral approximation by bounded Radon-Nikodym derivatives. An application to the existence of the infimum of two completely positive maps is indicated, and formulas in terms of Choi's matrices for the Lebesgue decomposition of completely positive maps in matrix algebras are obtained.

Integrated smartphone imaging of quantum dot photoluminescence and Förster resonance energy transfer

Science.gov (United States)

Petryayeva, Eleonora; Algar, W. Russ

2015-06-01

Smartphones and other mobile devices are emerging as promising analytical platforms for point-of-care diagnostics, particularly when combined with nanotechnology. For example, we have shown that the optical properties of semiconductor quantum dots (QDs) are well suited to photoluminescence (PL) detection with a smartphone camera. However, this previous work has utilized an external excitation source for interrogation of QD PL. In this proceeding, we demonstrate that the white-light LED photographic flashes built into smartphones can be optically filtered to yield blue light suitable for excitation of QD PL. Measurements were made by recording video with filtered flash illumination and averaging the frames of the video to obtain images with good signal-to-background ratios. These images permitted detection of green-emitting and red-emitting QDs at levels comparable to those possible with excitation using an external long-wave UV lamp. The optical properties of QDs proved to be uniquely suited to smartphone PL imaging, exhibiting emission that was 1-2 orders magnitude brighter than that of common fluorescent dyes under the same conditions. Excitation with the smartphone flash was also suitable for imaging of FRET between green-emitting QD donors and Alexa Fluor 555 (A555) fluorescent dye acceptors. No significant difference in FRET imaging capability was observed between excitation with the smartphone flash and a long-wave UV lamp. Although the smartphone flash did have some disadvantages compared to an external UV lamp, these disadvantages are potentially offset by the benefit of having excitation and detection integrated into the smartphone.

Strain engineering of quantum dots for long wavelength emission: Photoluminescence from self-assembled InAs quantum dots grown on GaAs(001) at wavelengths over 1.55 μm

International Nuclear Information System (INIS)

Shimomura, K.; Kamiya, I.

2015-01-01

Photoluminescence (PL) at wavelengths over 1.55 μm from self-assembled InAs quantum dots (QDs) grown on GaAs(001) is observed at room temperature (RT) and 4 K using a bilayer structure with thin cap. The PL peak has been known to redshift with decreasing cap layer thickness, although accompanying intensity decrease and peak broadening. With our strain-controlled bilayer structure, the PL intensity can be comparable to the ordinary QDs while realizing peak emission wavelength of 1.61 μm at 4 K and 1.73 μm at RT. The key issue lies in the control of strain not only in the QDs but also in the cap layer. By combining with underlying seed QD layer, we realize strain-driven bandgap engineering through control of strain in the QD and cap layers

Strain engineering of quantum dots for long wavelength emission: Photoluminescence from self-assembled InAs quantum dots grown on GaAs(001) at wavelengths over 1.55 μm

Energy Technology Data Exchange (ETDEWEB)

Shimomura, K., E-mail: sd12502@toyota-ti.ac.jp; Kamiya, I., E-mail: kamiya@toyota-ti.ac.jp [Toyota Technological Institute 2-12-1 Hisakata, Tempaku, Nagoya 468-8511 (Japan)

2015-02-23

Photoluminescence (PL) at wavelengths over 1.55 μm from self-assembled InAs quantum dots (QDs) grown on GaAs(001) is observed at room temperature (RT) and 4 K using a bilayer structure with thin cap. The PL peak has been known to redshift with decreasing cap layer thickness, although accompanying intensity decrease and peak broadening. With our strain-controlled bilayer structure, the PL intensity can be comparable to the ordinary QDs while realizing peak emission wavelength of 1.61 μm at 4 K and 1.73 μm at RT. The key issue lies in the control of strain not only in the QDs but also in the cap layer. By combining with underlying seed QD layer, we realize strain-driven bandgap engineering through control of strain in the QD and cap layers.

Core–shell quantum dots: Properties and applications

Energy Technology Data Exchange (ETDEWEB)

Vasudevan, D., E-mail: vasudevand@rediffmail.com [Electrodics and electrocatalysis division, CSIR-CECRI, Karaikudi 630006 (India); Gaddam, Rohit Ranganathan [Amity Institute of Nanotechnology, Amity University, Noida 201301 (India); Trinchi, Adrian; Cole, Ivan [CSIRO Materials Science and Engineering, Clayton South MDC, 3169 (Australia)

2015-07-05

Fluorescent quantum dots (QDs) are semiconducting nanocrystals (NCs) that find numerous applications in areas, such as bio labelling, sensors, lasers, light emitting diodes and medicine. Core–shell quantum dots were developed to improve the photoluminescence efficiency of single quantum dots. Capping their surface with organic ligands as well as their extraction into aqueous media enables their use in sensing applications. The current review highlights the importance and applications of core shell quantum dots as well as their surface modifications and applications in the field of medicine and as sensors for chemical and biochemical analysis.

Core–shell quantum dots: Properties and applications

International Nuclear Information System (INIS)

Vasudevan, D.; Gaddam, Rohit Ranganathan; Trinchi, Adrian; Cole, Ivan

2015-01-01

Fluorescent quantum dots (QDs) are semiconducting nanocrystals (NCs) that find numerous applications in areas, such as bio labelling, sensors, lasers, light emitting diodes and medicine. Core–shell quantum dots were developed to improve the photoluminescence efficiency of single quantum dots. Capping their surface with organic ligands as well as their extraction into aqueous media enables their use in sensing applications. The current review highlights the importance and applications of core shell quantum dots as well as their surface modifications and applications in the field of medicine and as sensors for chemical and biochemical analysis

Transmission electron microscopy and photoluminescence characterization of InGaAs strained quantum wires on GaAs vicinal (110) substrates

International Nuclear Information System (INIS)

Shim, Byoung Rho; Torii, Satoshi; Ota, Takeshi; Kobayashi, Keisuke; Maehashi, Kenzo; Nakashima, Hisao; Lee, Sang Yun

1999-01-01

We have used transmission electron microscopy (TEM) and photoluminescence (PL) to study InGaAs/AlGaAs strained quantum wires (QWRs) grown by molecular beam epitaxy (MBE) on GaAs vicinal (110) substrates. The cross-sectional TEM image reveals that InGaAs QWRs structures are naturally formed on AlGaAs giant steps. In the plan-view TEM images, the fringe pattern in the giant-step region is observed for In x Ga 1-x As layers with x≤ 0.4 We measured the separation of the fringe in the plan-view TEM images and compared the result with the calculated fringe separation. From this result, we conclude that the fringes observed in the plan-view TEM images are moire fringes. PL spectra of the InGaAs QWRs samples reveal 80-meV shifts to lower energy with respect to the spectrum of a quantum well (QWL) grown on a (001) substrate under the same conditions. We also measured the polarization anisotropy of the PL spectra from the QWRs. The PL peak shifts systematically toward higher energy with decreasing InGaAs thickness. The degree of polarization for the InGaAs QWRs was about 0.29. The PL observation evidences the carrier confinement in the QWRs. These results indicate that locally thick InGaAs strained QWRs were successfully formed at the edge of AlGaAs giant steps

Photoluminescent enhancement of CdSe/Cd(1-x) Zn(x)S quantum dots by hexadecylamine at room temperature.

Science.gov (United States)

Yang, Jie; Yang, Ping

2012-09-01

CdSe/Cd(1-x) Zn(x)S core/shell quantum dots (QDs) were fabricated in 1-octadecene via a two step synthesis. CdSe cores were first prepared using CdO, trioctylphosphine (TOP) selenium, and stearic acid. Subsquently, a Cd(1-x) Zn(x)S shell coating was carried out using zinc acetate dihydrate, cadmium acetate dihydrate, TOPS, and hexadecylamine (HDA) starting materials in the friendly organic system under relatively low temperature. The absorption and photoluminescence (PL) spectra have a significant red shift after the coverage of Cd(1-x)Zn(x)S shell on CdSe cores. The X-ray diffraction analysis of samples confirmed the formation of core/shell structure. The PL quantum yields (QYs) of CdSe/Cd(1-x)Zn(x)S QDs were improved gradually with time at room temperature. This is ascribed to the surface passivation of HDA to the QDs during store. This phenomenon was confirmed by the Fourier transform infrared spectrum of samples. Namely, HDA does not capped on the surface of as-prepared QDs, in which a low PL QYs was observed (less than 10%). Being storing for certain time, HDA attached to the surface of the QDs, in which the PL QYs increased (up to 31%) and the full width at half maximum of PL spectra decreased. Moreover, the fluorescence decay curve of the core/shell QDs is closer to a biexponential decay profile and has a longer average PL lifetime. The variation of average PL lifetime also indicated the influence of HDA during store.

Quantum gravity and quantum nondemolition measurements

International Nuclear Information System (INIS)

Borzeszkowski, H.H. von; Treder, H.J.

1984-01-01

It is shown that in Quantum Gravity, and more general: in Grand Unified Theory incorporating General Relativity on a basic level, there arise necessarily absolute limitations on measurement which one cannot evade by any 'quantum nondemolition measurements'. This fact is demonstrated not to oppose the existence of certain approximations to the full theory where these limitations do not arise. (author)

Enhancement of the photoluminescence in CdSe quantum dot–polyvinyl alcohol composite by light irradiation

Energy Technology Data Exchange (ETDEWEB)

Borkovska, L., E-mail: bork@isp.kiev.ua [V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine, pr. Nauky 41, 03028 Kyiv (Ukraine); Korsunska, N.; Stara, T.; Gudymenko, O.; Venger, Ye. [V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine, pr. Nauky 41, 03028 Kyiv (Ukraine); Stroyuk, O.; Raevska, O. [L. Pysarzhevsky Institute of Physical Chemistry, NAS of Ukraine, pr. Nauky 31, 03028 Kyiv (Ukraine); Kryshtab, T., E-mail: kryshtab@gmail.com [Instituto Politécnico Nacional – ESFM, Av. IPN, Ed.9 U.P.A.L.M., 07738 Mexico D.F. (Mexico)

2013-09-15

The effect of photo-induced enhancement (more than a tenfold) of room temperature deep-trap photoluminescence (PL) in CdSe quantum dots (QDs) embedded in polyvinyl alcohol (PVA) film has been found and investigated by the PL and X-ray diffraction methods. The effect is observed under illumination of the QD/PVA composite with LED's light of 409 or 470 nm at elevated temperatures and is shown to be caused by an increase of the activation energy of thermal quenching of defect-related PL. It is shown that thermal annealing of the composite by itself stimulates polymer crystallization and produces a small increase in the intensity of both the band-edge and defect-related PL bands of CdSe QDs. It is found that the effect of illumination decreases when the annealing temperature increases from 90 °C to 120 °C because thermal annealing at 120 °C per se results in strong enhancement of room temperature deep-trap PL. The effect of photo-induced enhancement of defect-related PL is found to be irreversible and is assumed to be related to the change of QD surface defect passivation or surface defect rearrangement. This is ascribed to partial destruction of PVA matrix as a result of interaction of QD/PVA interface with photocarriers generated in the QDs due to LED's light absorption.

Reversible Concentration-Dependent Photoluminescence Quenching and Change of Emission Color in CsPbBr3 Nanowires and Nanoplatelets.

Science.gov (United States)

Di Stasio, Francesco; Imran, Muhammad; Akkerman, Quinten A; Prato, Mirko; Manna, Liberato; Krahne, Roman

2017-06-15

We discuss the photoluminescence (PL) of quantum-confined CsPbBr 3 colloidal nanocrystals of two different shapes (nanowires and nanoplatelets) at different concentrations in solution and in solid-state films. Upon increasing the nanocrystal concentration in solution, a constant drop in photoluminescence quantum yield is observed, accompanied by a significant PL red shift. This effect is reversible, and the original PL can be restored by diluting to the original concentration. We show that this effect can be in part attributed to self-absorption and partly to aggregation. In particular, for nanoplatelets, where the aggregation is mostly irreversible, while the self-absorption effect is reversible, the two contributions can be well separated. Finally, when dry solid-state films are prepared, the emission band is shifted into the green spectral region, close to the bulk CsPbBr 3 band gap, thus preventing blue emission from such films.

Absolute spectroscopy near 7.8 {\\mu} m with a comb-locked extended-cavity quantum-cascade-laser

KAUST Repository

Lamperti, Marco

2017-07-31

We report the first experimental demonstration of frequency-locking of an extended-cavity quantum-cascade-laser (EC-QCL) to a near-infrared frequency comb. The locking scheme is applied to carry out absolute spectroscopy of N2O lines near 7.87 {\\\\mu}m with an accuracy of ~60 kHz. Thanks to a single mode operation over more than 100 cm^{-1}, the comb-locked EC-QCL shows great potential for the accurate retrieval of line center frequencies in a spectral region that is currently outside the reach of broadly tunable cw sources, either based on difference frequency generation or optical parametric oscillation. The approach described here can be straightforwardly extended up to 12 {\\\\mu}m, which is the current wavelength limit for commercial cw EC-QCLs.

Transformation of photoluminescence spectra at the bioconjugation of core-shell CdSe/ZnS quantum dots

Energy Technology Data Exchange (ETDEWEB)

Macotela, L.G.V.; Douda, J. [UPIITA - Instituto Politecnico Nacional, Mexico (Mexico); Torchynska, T.V. [ESFM- Instituto Politecnico Nacional, Mexico (Mexico); Sierra, R.P. [CINVESTAV del IPN, Mexico (Mexico); Shcherbyna, L. [V. Lashkarev Institute of Semiconductor Physics at NASU, Kiev (Ukraine)

2010-04-15

The photoluminescence (PL) of nonconjugated and bioconjugated core-shell CdSe/ZnS quantum dots (QDs) has been discussed in this paper. Commercial CdSe/ZnS QDs with the size of 3.6-4.0 nm covered by polymer with emission at 560-565 nm (2.19-2.22 eV) have been used. The QD bioconjugation is performed with the mouse anti PSA (Prostate-Specific Antigen) antibody (mab). PL spectra of nonconjugated QDs are characterized by a superposition of PL bands related to exciton emission in the CdSe core (2.19-2.22 eV) and to hot electron-hole emission via surface states (2.37, 2.73 and 3.06 eV) at the CdSe/ZnS or ZnS/polymer interfaces. The PL spectrum of bioconjugated QDs has changed dramatically, with essential decreasing of the hot electron-hole recombination flow via interface states. This effect is explained on the base of re-charging of QD interface states at the bioconjugation. It is shown that the CdSe/ZnS QDs with interface states are very promising for the study of bioconjugation effects to antibodies (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Hydrothermal synthesis, crystal structures and photoluminescence properties of mixed europium–yttrium organic frameworks

International Nuclear Information System (INIS)

Han Yinfeng; Fu Lianshe; Mafra, Luís; Shi, Fa-Nian

2012-01-01

Three mixed europium–yttrium organic frameworks: Eu 2−x Y x (Mel)(H 2 O) 6 (Mel=mellitic acid or benzene-1,2,3,4,5,6-hexacarboxylic acid, x=0.38 1, 0.74 2, and 0.86 3) have been synthesized and characterized. All the compounds contain a 3-D net with (4, 8)-flu topology. The study indicates that the photoluminescence properties are effectively affected by the different ratios of europium and yttrium ions, the quantum efficiency is increased and the Eu 3+ lifetime becomes longer in these MOFs than those of the Eu analog. - Graphical abstract: Three mixed europium and yttrium organic frameworks: Eu 2−x Y x (Mel)(H 2 O) 6 (Mel=mellitic acid) have been synthesized and characterized. All the compounds contain a 3-D net with (4, 8)-flu topology. The study indicates that the photoluminescence properties are effectively affected by the different ratios of europium and yttrium ions, the quantum efficiency is increased and the Eu 3+ lifetime becomes longer in these MOFs than those of the Eu analog. Highlights: ► Three (4, 8)-flu topological mixed Eu and Y MOFs were synthesized under mild conditions. ► Metal ratios were refined by the single crystal data consistent with the EDS analysis. ► Mixed Eu and Y MOFs show longer lifetime and higher quantum efficiency than the Eu analog. ► Adding inert lanthanide into luminescent MOFs enlarges the field of luminescent MOFs.

Stretched exponential profiles of photoluminescence decays related to localized states in InGaAsN/GaAs single-quantum wells

International Nuclear Information System (INIS)

Nakayama, M.; Iguchi, Y.; Nomura, K.; Hashimoto, J.; Yamada, T.; Takagishi, S.

2007-01-01

We have investigated photoluminescence (PL) dynamics related to localized states in In x Ga 1-x As 1-y N y /GaAs single-quantum wells (SQWs) with the constant In content of x=0.32 and various N contents of y=0,0.004,and0.008. In order to determine the intrinsic band-edge energy, we used photoreflectance (PR) spectroscopy that is sensitive to the optical transitions at critical points. From systematic measurements of the PL and PR spectra, it is demonstrated that the slight incorporation of nitrogen considerably disorders the band-edge states of the InGaAsN SQWs, resulting from formation of localized states, so-called band-tail states. We find that the PL-decay profile related to the localized states generally exhibits a stretched exponential behavior peculiar to a disordered system at low temperatures, which means that randomness of alloy potential fluctuations including nitrogen dominates the PL dynamics

Carrier transfer and magneto-transport in single modulation-doped V-grooved quantum wire modified by ion implantation

International Nuclear Information System (INIS)

Huang, S.H.; Chen Zhanghai; Wang, F.Z.; Shen, S.C.; Tan, H.H.; Fu, L.; Fraser, M.; Jagadish, C.

2006-01-01

A single Al 0.5 Ga 0.5 As/GaAs V-grooved quantum wire modified by selective ion implantation and rapid thermal annealing was investigated by using spatially resolved micro-photoluminescence spectroscopy and magneto-resistance measurements. The results of spatially resolved photoluminescence indicate that the ion-implantation-induced quantum well intermixing significantly raises the electronic sub-band energies in the side quantum wells (SQWs) and vertical quantum wells, and a more efficient accumulation of electrons in the quantum wires is achieved. Processes of real space carrier transfer from the SQW to the quantum wire was experimentally observed, and showed the blocking effect of carrier transfer due to the existence of the necking quantum well region. Furthermore, magneto-transport investigation on the ion-implanted quantum wire samples shows the quasi-one-dimensional intrinsic motion of electrons, which is important for the design and the optimization of one-dimensional electronic devices

Relative and absolute level populations in beam-foil--excited neutral helium

International Nuclear Information System (INIS)

Davidson, J.

1975-01-01

Relative and absolute populations of 19 levels in beam-foil--excited neutral helium at 0.275 MeV have been measured. The singlet angular-momentum sequences show dependences on principal quantum number consistent with n -3 , but the triplet sequences do not. Singlet and triplet angular-momentum sequences show similar dependences on level excitation energy. Excitation functions for six representative levels were measured in the range 0.160 to 0.500 MeV. The absolute level populations increase with energy, whereas the neutral fraction of the beam decreases with energy. Further, the P angular-momentum levels are found to be overpopulated with respect to the S and D levels. The overpopulation decreases with increasing principal quantum number

A novel one-pot room-temperature synthesis route to produce very small photoluminescent silicon nanocrystals

Science.gov (United States)

Douglas-Gallardo, Oscar A.; Burgos-Paci, Maxi A.; Mendoza-Cruz, Rubén; Putnam, Karl G.; Josefina Arellano-Jiménez, M.; José-Yacamán, Miguel; Mariscal, Marcelo M.; Macagno, Vicente A.; Sánchez, Cristián G.; Pérez, Manuel A.

2018-03-01

A novel strategy to synthesize photoluminescent silicon nanocrystals (SiNCs) from a reaction between tetraethylorthosilicate (TEOS) and trimethyl-hexadecyl-ammonium borohydride (CTABH4) in organic solvent is presented. The formation reaction occurs spontaneously at room temperature in homogeneous phase. The produced silicon nanocrystals are characterized by using their photoluminescent properties and via HRTEM. In addition, theoretical calculations of the optical absorption spectrum of silicon quantum dots in vacuum with different sizes and surface moieties were performed in order to compare with the experimental findings. The new chemical reaction is simple and can be implemented to produce silicon nanocrystal with regular laboratory materials by performing easy and safe procedures. [Figure not available: see fulltext.

Multi-Excitonic Quantum Dot Molecules

Science.gov (United States)

Scheibner, M.; Stinaff, E. A.; Doty, M. F.; Ware, M. E.; Bracker, A. S.; Gammon, D.; Ponomarev, I. V.; Reinecke, T. L.; Korenev, V. L.

2006-03-01

With the ability to create coupled pairs of quantum dots, the next step towards the realization of semiconductor based quantum information processing devices can be taken. However, so far little knowledge has been gained on these artificial molecules. Our photoluminescence experiments on single InAs/GaAs quantum dot molecules provide the systematics of coupled quantum dots by delineating the spectroscopic features of several key charge configurations in such quantum systems, including X, X^+,X^2+, XX, XX^+ (with X being the neutral exciton). We extract general rules which determine the formation of molecular states of coupled quantum dots. These include the fact that quantum dot molecules provide the possibility to realize various spin configurations and to switch the electron hole exchange interaction on and off by shifting charges inside the molecule. This knowledge will be valuable in developing implementations for quantum information processing.

Synthetic Control of Exciton Behavior in Colloidal Quantum Dots.

Science.gov (United States)

Pu, Chaodan; Qin, Haiyan; Gao, Yuan; Zhou, Jianhai; Wang, Peng; Peng, Xiaogang

2017-03-08

Colloidal quantum dots are promising optical and optoelectronic materials for various applications, whose performance is dominated by their excited-state properties. This article illustrates synthetic control of their excited states. Description of the excited states of quantum-dot emitters can be centered around exciton. We shall discuss that, different from conventional molecular emitters, ground-state structures of quantum dots are not necessarily correlated with their excited states. Synthetic control of exciton behavior heavily relies on convenient and affordable monitoring tools. For synthetic development of ideal optical and optoelectronic emitters, the key process is decay of band-edge excitons, which renders transient photoluminescence as important monitoring tool. On the basis of extensive synthetic developments in the past 20-30 years, synthetic control of exciton behavior implies surface engineering of quantum dots, including surface cation/anion stoichiometry, organic ligands, inorganic epitaxial shells, etc. For phosphors based on quantum dots doped with transition metal ions, concentration and location of the dopant ions within a nanocrystal lattice are found to be as important as control of the surface states in order to obtain bright dopant emission with monoexponential yet tunable photoluminescence decay dynamics.

Hydrophobic perfluoro-silane functionalization of porous silicon photoluminescent films and particles

Energy Technology Data Exchange (ETDEWEB)

Rodriguez, C.; Laplace, P.; Gallach-Pérez, D.; Pellacani, P.; Martín-Palma, R.J. [Departamento de Física Aplicada e Instituto de Ciencia de Materiales Nicolás Cabrera, Universidad Autónoma de Madrid, 28049, Madrid (Spain); Torres-Costa, V. [Departamento de Física Aplicada e Instituto de Ciencia de Materiales Nicolás Cabrera, Universidad Autónoma de Madrid, 28049, Madrid (Spain); Centro de Microanálisis de Materiales, Universidad Autónoma de Madrid, 28049, Madrid (Spain); Ceccone, G. [European Commission, Joint Research Centre, Institute for Health and Consumer Protection, 21020, Ispra (Italy); Manso Silván, M., E-mail: miguel.manso@uam.es [Departamento de Física Aplicada e Instituto de Ciencia de Materiales Nicolás Cabrera, Universidad Autónoma de Madrid, 28049, Madrid (Spain)

2016-09-01

Highlights: • Hydrophobic functionalization of porous silicon structures. • Perfluorooctyl group binding confirmed by XPS. • Improved stability face to extreme oxidation conditions. • Perfluorooctyl functionalization compatible with photoluminescence of porous silicon particles. - Abstract: Luminescent structures based on semiconductor quantum dots (QDs) are increasingly used in biomolecular assays, cell tracking systems, and in-vivo diagnostics devices. In this work we have carried out the functionalization of porous silicon (PSi) luminescent structures by a perfluorosilane (Perfluoro-octyltriethoxysilane, PFOS) self assembly. The PFOS surface binding (traced by X-ray photoelectron spectroscopy) and photoluminescence efficiency were analyzed on flat model PSi. Maximal photoluminescence intensity was obtained from PSi layers anodized at 110 mA/cm{sup 2}. Resistance to hydroxylation was assayed in H{sub 2}O{sub 2}:ethanol solutions and evidenced by water contact angle (WCA) measurements. PFOS-functionalized PSi presented systematically higher WCA than untreated PSi. The PFOS functionalization was found to slightly improve the aging of the PSi particles in water giving rise to particles with longer luminescent life. Confirmation of PFOS binding to PSi particles was derived from FTIR spectra and the preservation of luminescence was observed by fluorescence microscopy. Such functionalization opens the possibility of promoting hydrophobic-hydrophobic interactions between biomolecules and fluorescent QD structures, which may enlarge their biomedical applications catalogue.

Facile synthetic method for pristine graphene quantum dots and graphene oxide quantum dots: origin of blue and green luminescence.

Science.gov (United States)

Liu, Fei; Jang, Min-Ho; Ha, Hyun Dong; Kim, Je-Hyung; Cho, Yong-Hoon; Seo, Tae Seok

2013-07-19

Pristine graphene quantum dots and graphene oxide quantum dots are synthesized by chemical exfoliation from the graphite nanoparticles with high uniformity in terms of shape (circle), size (less than 4 nm), and thickness (monolayer). The origin of the blue and green photoluminescence of GQDs and GOQDs is attributed to intrinsic and extrinsic energy states, respectively. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Emergence of localized states in narrow GaAs/AlGaAs nanowire quantum well tubes.

Science.gov (United States)

Shi, Teng; Jackson, Howard E; Smith, Leigh M; Jiang, Nian; Gao, Qiang; Tan, H Hoe; Jagadish, Chennupati; Zheng, Changlin; Etheridge, Joanne

2015-03-11

We use low-temperature photoluminescence, photoluminescence excitation, and photoluminescence imaging spectroscopy to explore the optical and electronic properties of GaAs/AlGaAs quantum well tube (QWT) heterostructured nanowires (NWs). We find that GaAs QWTs with widths >5 nm have electronic states which are delocalized and continuous along the length of the NW. As the NW QWT width decreases from 5 to 1.5 nm, only a single electron state is bound to the well, and no optical excitations to a confined excited state are present. Simultaneously, narrow emission lines (fwhm points along the length of the NW. We find that these quantum-dot-like states broaden at higher temperatures and quench at temperatures above 80 K. The lifetimes of these localized states are observed to vary from dot to dot from 160 to 400 ps. The presence of delocalized states and then localized states as the QWTs become more confined suggests both opportunities and challenges for possible incorporation into quantum-confined device structures.

Utilizing a CdTe quantum dots-enzyme hybrid system for the determination of both phenolic compounds and hydrogen peroxide.

Science.gov (United States)

Yuan, Jipei; Guo, Weiwei; Wang, Erkang

2008-02-15

In this paper, we attempt to construct a simple and sensitive detection method for both phenolic compounds and hydrogen peroxide, with the successful combination of the unique property of quantum dots and the specificity of enzymatic reactions. In the presence of H2O2 and horseradish peroxidase, phenolic compounds can quench quantum dots' photoluminescence efficiently, and the extent of quenching is severalfold to more than 100-fold increase. Quinone intermediates produced from the enzymatic catalyzed oxidation of phenolic compounds were believed to play the main role in the photoluminescence quenching. Using a quantum dots-enzyme system, the detection limits for phenolic compounds and hydrogen peroxide were detected to be approximately 10(-7) mol L(-1). The coupling of efficient quenching of quantum dot photoluminescence by quinone and the effective enzymatic reactions make this a simple and sensitive method for phenolic compound detection and great potential in the development of H2O2 biosensors for various analytes.

Energy transfer and visible-infrared quantum cutting photoluminescence modification in Tm-Yb codoped YPO(4) inverse opal photonic crystals.

Science.gov (United States)

Wang, Siqin; Qiu, Jianbei; Wang, Qi; Zhou, Dacheng; Yang, Zhengwen

2015-08-01

YPO4:  Tm, Yb inverse opal photonic crystals were successfully synthesized by the colloidal crystal templates method, and the visible-infrared quantum cutting (QC) photoluminescence properties of YPO4:  Tm, Yb inverse opal photonic crystals were investigated. We obtained tetragonal phase YPO4 in all the samples when the samples sintered at 950°C for 5 h. The visible emission intensity of Tm3+ decreased significantly when the photonic bandgap was located at 650 nm under 480 nm excitation. On the contrary, the QC emission intensity of Yb3+ was enhanced as compared with the no photonic bandgap sample. When the photonic bandgap was located at 480 nm, the Yb3+ and Tm3+ light-emitting intensity weakened at the same time. We demonstrated that the energy transfer between Tm3+ and Yb3+ is enhanced by the suppression of the red emission of Tm3+. Additionally, the mechanisms for the influence of the photonic bandgap on the energy transfer process of the Tm3+, Yb3+ codoped YPO4 inverse opal are discussed.

Contactless electroreflectance and photoluminescence of InAs quantum dots with GaInNAs barriers grown on GaAs substrate

International Nuclear Information System (INIS)

Motyka, M.; Kudrawiec, R.; Misiewicz, J.; Pucicki, D.; Tlaczala, M.; Fischer, M.; Marquardt, B.; Forchel, A.

2007-01-01

InAs quantum dots (QDs) with GaInNAs barriers grown on (001) GaAs substrate by molecular beam epitaxy have been studied by contactless electroreflectance (CER) and photoluminescence (PL) spectroscopies. It has been observed that the overgrowth of self-organized InAs QDs with GaInNAs layers effectively tunes the QD emission to the 1.3 μm spectral region. In case of PL spectra only one peak related to QD emission has been observed. In the case of CER spectra, in addition to a CER feature corresponding to the QD ground state, a rich spectrum of CER resonances related to optical transitions in InAs/GaInNAs/GaAs QW has been observed. It has been concluded that the application of GaInNAs instead InGaAs leads to better control of emission wavelength from InAs QDs since strains in GaInNAs can be tuned from compressive to tensile. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Quantum-size-controlled photoelectrochemical etching of semiconductor nanostructures

Science.gov (United States)

Fischer, Arthur J.; Tsao, Jeffrey Y.; Wierer, Jr., Jonathan J.; Xiao, Xiaoyin; Wang, George T.

2016-03-01

Quantum-size-controlled photoelectrochemical (QSC-PEC) etching provides a new route to the precision fabrication of epitaxial semiconductor nanostructures in the sub-10-nm size regime. For example, quantum dots (QDs) can be QSC-PEC-etched from epitaxial InGaN thin films using narrowband laser photoexcitation, and the QD sizes (and hence bandgaps and photoluminescence wavelengths) are determined by the photoexcitation wavelength.

Optical spectroscopy of GaAs in the extreme quantum limit: Integer and fractional quantum Hall effect, and onset of the electron solid

Energy Technology Data Exchange (ETDEWEB)

Clark, R.G.; Ford, R.A.; Haynes, S.R.; Ryan, J.F.; Turberfield, A.J.; Wright, P.A. (Clarendon Lab., Univ. of Oxford (UK)); Williams, F.I.B.; Deville, G.; Glattli, D.C. (CEN de Saclay, 91 - Gif-sur-Yvette (France)); Mallett, J.R.; Oswald, P.M.W. (Clarendon Lab., Univ. of Oxford (UK) Katholieke Univ. Leuven (Belgium)); Burgt, M. van der; Herlach, F. (Katholieke Univ. Leuven (Belgium)); Foxon, C.T.; Harris, J.J. (Philips Research Labs., Redhill (UK))

1991-02-01

Our recent optical detection of the integer and fractional quantum Hall effects in GaAs, by intrinsic band-gap photoluminescence at dilution refrigerator temperatures, is reviewed. This work has been extended to the extreme quantum limit where a photoluminescence peak develops close to Landau level filling factor {nu}=1/5 which correlates both with the onset of threshold behaviour in current-voltage characteristics of the two-dimensional electron system and a resonant radio-frequency absorption; the latter are quantitatively accounted for by a model of crystalline electronic structure broken up into domains. Preliminary mK transport experiments in intense, pulsed magnetic fields are also described, which establish a basis to access the electron solid phase transition in a hitherto unattainable region of the (B,T) plane. (orig.).

Photoluminescence Detected Doublet Structure in the Integer and Fractional Quantum Hall Regime

International Nuclear Information System (INIS)

Kim, Yongmin; Munteanu, F.M.; Perry, C.H.; Reno, J.L.; Rickel, D.G.; Simmons, J.A.

1999-01-01

We present here the results of polarized magneto-photoluminescence measurements on a high mobility single-heterojunction. The presence of a doublet structure over a large magnetic field range (2>v>l/6) is interpreted as possible evidence for the existence of a magneto-roton minima of the charged density waves. This is understood as an indication of strong electronic correlation even in the case of the IQHE limit

The influence of nitrogen on the photoluminescence of metastable III-V nitrides

International Nuclear Information System (INIS)

Hantke, K.

2005-01-01

The work presented here mainly summarizes experimental and theoretical results enlightening the material-specific, optical properties of (GaIn)(NAs). The primarily used experiment is the time-resolved photoluminescence spectroscopy. The comparison of experiment and theory yields a simple exponential form for the density of localized states. Furthermore it can be confirmed that the typical energy scale of the localization is diminished by the annealing step as well as by the hydrogenation process. In a next step, the investigation of (GaIn)(NAs) epitactical layers, that were optimized for solar cell application, reveals astonishing features: The minority-carrier diffusion-length of the p-doped layers is found to be slightly higher than for the n-doped material implying that (GaIn)(NAs) solar cells with a p-on-n structure should be preferred in terms of higher quantum efficiency. A new effect found during the investigations is the optimization of the internal quantum efficiency of the (GaIn)(NAs) structures after irradiation with intensive laser light attributed to the laser-induced annealing of defects. The final paragraph concentrates on the successful comparison of time-resolved photoluminescence, photo-modulated reflection measurements and a microscopic many-body theory. A profound understanding of the type-I type-II transition in (GaIn)As/Ga(NAs) heterostructures is achieved resulting in material-specific information as e.g. the temperature-dependent bandgap energies, the band offsets in Ga(NAs)/GaAs and (GaIn)As/Ga(NAs) respectively, as well as the interaction potential VN dependent on the nitrogen content. Finally, the fundamental dependence on excitation density investigated in the experiment is theoretically quantified not only for the photoluminescence intensity and but for the lifetimes, too. (orig.)

Suppression of the internal electric field effects in ZnO/Zn0.7Mg0.3O quantum wells by ion-implantation induced intermixing

International Nuclear Information System (INIS)

Davis, J A; Dao, L V; Wen, X; Ticknor, C; Hannaford, P; Coleman, V A; Tan, H H; Jagadish, C; Koike, K; Sasa, S; Inoue, M; Yano, M

2008-01-01

Strong suppression of the effects caused by the internal electric field in ZnO/ZnMgO quantum wells following ion-implantation and rapid thermal annealing, is revealed by photoluminescence, time-resolved photoluminescence, and band structure calculations. The implantation and annealing induces Zn/Mg intermixing, resulting in graded quantum well interfaces. This reduces the quantum-confined Stark shift and increases electron-hole wavefunction overlap, which significantly reduces the exciton lifetime and increases the oscillator strength

InGaAs/GaAs quantum-dot-quantum-well heterostructure formed by submonolayer deposition

DEFF Research Database (Denmark)

Xu, Zhangcheng; Leosson, K.; Birkedal, Dan

2003-01-01

-dot-quantum-well (QDQW) structure, by using high power PL and selective PL with excitation energies below the band gap of the GaAs barriers and temperature dependent PL. As the temperature is increased from 10 to 300 K, a narrowing of the full width at half-maximum at intermediate temperatures and a sigmoidal behaviour......Discrete emission lines from self-assembled InGaAs quantum dots (QDs) grown in the submonolayer (SML) deposition mode have been observed in micro-photoluminescence (PL) spectra at 10 K. For the first time, the SML-grown InGaAs/GaAs QD heterostructure is verified to be a quantum...

InAs quantum wires on InP substrate for VCSEL applications

OpenAIRE

Lamy , Jean-Michel; Paranthoën , Cyril; Levallois , Christophe; Nakkar , Abdulhadi; Folliot , Hervé; Dehaese , Olivier; Le Corre , Alain; Loualiche , Slimane; Castany , Olivier; Dupont , Laurent

2008-01-01

International audience; Quantum dash based vertical cavity surface emitting lasers (VCSEL) on InP substrate are presented. Single and close stacking layers were successfully grown with molecular beam epitaxy. Optimized quantum dash layers exhibit a strong polarized 1.55 µm photoluminescence along the [1-10] crystallographic axis. Continuous wave laser emission is demonstrated at room temperature for the first time on a quantum dash VCSEL structure on InP susbtrate. The quantum dash VCSEL lase...

Characterization of interfaces in semimagnetic quantum wells

Energy Technology Data Exchange (ETDEWEB)

Schmitt, G.; Kuhn-Heinrich, B.; Zehnder, U.; Ossau, W.; Litz, T.; Waag, A.; Landwehr, G. [Physikalishes Institut der Universitaet Wuerzburg am Hubland, Wuerzburg (Germany)

1995-12-31

The interfaces between nonmagnetic CdTe quantum wells and semimagnetic barriers of Cd{sub 1-x}Mn{sub x}Te were investigated for several well widths by low temperature photoluminescence and photoluminescence excitation spectroscopy. Specially designed Cd{sub 1-x}Mn{sub x}/CdTe/Cd{sub 1-y} Mg{sub y}Te structures enable us to distinguish the quality of semimagnetic normal and inverted interfaces. The normal interface shows to better structural quality than the inverted interface. (author). 5 refs, 2 figs, 1 tab.

A label-free silicon quantum dots-based photoluminescence sensor for ultrasensitive detection of pesticides.

Science.gov (United States)

Yi, Yinhui; Zhu, Gangbing; Liu, Chang; Huang, Yan; Zhang, Youyu; Li, Haitao; Zhao, Jiangna; Yao, Shouzhuo

2013-12-03

Sensitive, rapid, and simple detection methods for the screening of extensively used organophosphorus pesticides and highly toxic nerve agents are in urgent demand. A novel label-free silicon quantum dots (SiQDs)-based sensor was designed for ultrasensitive detection of pesticides. This sensing strategy involves the reaction of acetylcholine chloride (ACh) with acetylcholinesterase (AChE) to form choline that is in turn catalytically oxidized by choline oxidase (ChOx) to produce betaine and H2O2 which can quench the photoluminescence (PL) of SiQDs. Upon the addition of pesticides, the activity of AChE is inhibited, leading to the decrease of the generated H2O2, and hence the PL of SiQDs increases. By measuring the increase in SiQDs PL, the inhibition efficiency of pesticide to AChE activity was evaluated. It was found that the inhibition efficiency was linearly dependent on the logarithm of the pesticides concentration. Consequently, pesticides, such as carbaryl, parathion, diazinon, and phorate, were determined with the SiQDs PL sensing method. The lowest detectable concentrations for carbaryl, parathion, diazinon, and phorate reached 7.25 × 10(-9), 3.25 × 10(-8), 6.76 × 10(-8), and 1.9 × 10(-7) g/L, respectively, which were much lower than those previously reported. The detecting results of pesticide residues in food samples via this method agree well with those from high-performance liquid chromatography. The simple strategy reported here should be suitable for on-site pesticides detection, especially in combination with other portable platforms.

Lyman alpha SMM/UVSP absolute calibration and geocoronal correction

Science.gov (United States)

Fontenla, Juan M.; Reichmann, Edwin J.

1987-01-01

Lyman alpha observations from the Ultraviolet Spectrometer Polarimeter (UVSP) instrument of the Solar Maximum Mission (SMM) spacecraft were analyzed and provide instrumental calibration details. Specific values of the instrument quantum efficiency, Lyman alpha absolute intensity, and correction for geocoronal absorption are presented.

Relative and absolute level populations in beam-foil-excited neutral helium

Science.gov (United States)

Davidson, J.

1975-01-01

Relative and absolute populations of 19 levels in beam-foil-excited neutral helium at 0.275 MeV have been measured. The singlet angular-momentum sequences show dependences on principal quantum number consistent with n to the -3rd power, but the triplet sequences do not. Singlet and triplet angular-momentum sequences show similar dependences on level excitation energy. Excitation functions for six representative levels were measured in the range from 0.160 to 0.500 MeV. The absolute level populations increase with energy, whereas the neutral fraction of the beam decreases with energy. Further, the P angular-momentum levels are found to be overpopulated with respect to the S and D levels. The overpopulation decreases with increasing principal quantum number.

Electroluminescence of colloidal ZnSe quantum dots

International Nuclear Information System (INIS)

Dey, S.C.; Nath, S.S.

2011-01-01

The article reports a green chemical synthesis of colloidal ZnSe quantum dots at a moderate temperature. The prepared colloid sample is characterised by UV-vis absorption spectroscopy and transmission electron microscopy. UV-vis spectroscopy reveals as-expected blue-shift with strong absorption edge at 400 nm and micrographs show a non-uniform size distribution of ZnSe quantum dots in the range 1-4 nm. Further, photoluminescence and electroluminescence spectroscopies are carried out to study optical emission. Each of the spectroscopies reveals two emission peaks, indicating band-to-band transition and defect related transition. From the luminescence studies, it can be inferred that the recombination of electrons and holes resulting from interband transition causes violet emission and the recombination of a photon generated hole with a charged state of Zn-vacancy gives blue emission. Meanwhile electroluminescence study suggests the application of ZnSe quantum dots as an efficient light emitting device with the advantage of colour tuning (violet-blue-violet). - Highlights: → Synthesis of ZnSe quantum dots by a green chemical route. → Characterisation: UV-vis absorption spectroscopy and transmission electron microscopy. → Analysis of UV-vis absorption spectrum and transmission electron micrographs. → Study of electro-optical properties by photoluminescence and electroluminescence. → Conclusion: ZnSe quantum dots can be used as LED with dual colour emission.

Optical excitation and external photoluminescence quantum efficiency of Eu3+ in GaN

NARCIS (Netherlands)

de Boer, W.D.A.M.; McGonigle, C.; Gregorkiewicz, T.; Fujiwara, Y.; Stallinga, P.

2014-01-01

We investigate photoluminescence of Eu-related emission in a GaN host consisting of thin layers grown by organometallic vapor-phase epitaxy. By comparing it with a reference sample of Eu-doped Y2O3, we find that the fraction of Eu3+ ions that can emit light upon optical excitation is of the order of

Optical transitions in Ge/SiGe multiple quantum wells with Ge-rich barriers

Science.gov (United States)

Bonfanti, M.; Grilli, E.; Guzzi, M.; Virgilio, M.; Grosso, G.; Chrastina, D.; Isella, G.; von Känel, H.; Neels, A.

2008-07-01

Direct-gap and indirect-gap transitions in strain-compensated Ge/SiGe multiple quantum wells with Ge-rich SiGe barriers have been studied by optical transmission spectroscopy and photoluminescence experiments. An sp3d5s∗ tight-binding model has been adopted to interpret the experimental results. Photoluminescence spectra and their comparison with theoretical calculations prove the existence of type-I band alignment in compressively strained Ge quantum wells grown on relaxed Ge-rich SiGe buffers. The high quality of the transmission spectra opens up other perspectives for application of these structures in near-infrared optical modulators.

Electronic properties of excited states in single InAs quantum dots

International Nuclear Information System (INIS)

Warming, Till

2009-01-01

The application of quantum-mechanical effects in semiconductor nanostructures enables the realization of novel opto-electronic devices. Examples are given by single-photon emitters and emitters of entangled photon pairs, both being essential for quantum cryptography, or for qubit systems as needed for quantum computing. InAs/GaAs quantum dots are one of the most promising candidates for such applications. A detailed knowledge of the electronic properties of quantum dots is a prerequisite for this development. The aim of this work is an experimental access to the detailed electronic structure of the excited states in single InAs/GaAs quantum dots including few-particle effects and in particular exchange interaction. The experimental approach is micro photoluminescence excitation spectroscopy (μPLE). One of the main difficulties using μPLE to probe single QDs is the unambiguous assignment of the observed resonances in the spectrum to specific transitions. By comparing micro photoluminescence (μPL) and μPLE spectra, the identification of the main resonances becomes possible. The key is given by the fine structure of the hot trion. Excitation spectroscopy on single charged QDs enables for the first time the complete observation of a non-trivial fine structure of an excitonic complex in a QD, the hot trion. Modelling based on eight-band k.p theory in combination with a configuration interaction scheme is in excellent agreement. Therewith the simulation also enables realistic predictions on the fine structure of the ground-state exciton which is of large importance for single quantum dot devices. Theory concludes from the observed transitions that the structural symmetry of the QDs is broken. Micro photoluminescence excitation spectroscopy combined with resonantly excited micro photoluminescence enables an optical access to the single particle states of the hole without the influence of few-particle coulomb interactions. Based on this knowledge the exciton binding

Comparative investigation of photoluminescence of In- and Si- doped GaN/AlGaN multi-quantum wells

International Nuclear Information System (INIS)

Wang, L.S.; Sun, W.H.; Chua, S.J.; Johnson, Mark

2003-01-01

The GaN/AlGaN multi-quantum-wells (MQWs) have been grown via metalorganic chemical vapor deposition (MOCVD). Micro-photoluminescence (PL) measurement has been performed on non-, In- and Si- doped GaN/AlGaN MQW samples in the temperature ranges of 90-300 K. In the non-doped GaN/AlGaN MQWs we observed the free exciton peak at 3.4587 eV at 90 K. Other exciton related peaks are located at 3.4346, 3.4177, 3.394 and 3.3129 eV, which are probably associated with the strongly localized excitons involving the defects. In In-doped GaN/AlGaN MQWs, the free exciton peaks have a slight red-shift from 3.4712 to 3.4629 eV, but the PL intensities become stronger with increasing trimethylindium (TMIn) flow from 10.6 to 42.6 μmol min -1 . With Si-doping in the well layers, PL exhibits an envelope of exciton bands ranged from 3.4796 (free exciton) to 3.43915 eV. The excitonic peaks in the bands vary in intensity and position with sample temperature. In addition, we have also observed the LO phonon replica of AlGaN interacted by the laser line due to the resonance effect

Composition-dependent trap distributions in CdSe and InP quantum dots probed using photoluminescence blinking dynamics.

Science.gov (United States)

Chung, Heejae; Cho, Kyung-Sang; Koh, Weon-Kyu; Kim, Dongho; Kim, Jiwon

2016-07-21

Although Group II-VI quantum dots (QDs) have attracted much attention due to their wide range of applications in QD-based devices, the presence of toxic ions in II-VI QDs raises environmental concerns. To fulfill the demands of nontoxic QDs, synthetic routes for III-V QDs have been developed. However, only a few comparative analyses on optical properties of III-V QDs have been performed. In this study, the composition-related energetic trap distributions have been explored by using three different types of core/multishell QDs: CdSe-CdS (CdSe/CdS/ZnS), InP-ZnSe (InP/ZnSe/ZnS), and InP-GaP (InP/GaP/ZnS). It was shown that CdSe-CdS QDs have much larger trap densities than InP-shell QDs at higher energy states (at least 1Eg (band gap energy) above the lowest conduction band edge) based on probability density plots and Auger ionization efficiencies which are determined by analyses of photoluminescence blinking dynamics. This result suggests that the composition of encapsulated QDs is closely associated with the charge trapping processes, and also provides an insight into the development of more environmentally friendly QD-based devices.

Temporal evolution of multi-carrier complexes in single GaN/AlGaN quantum dots

International Nuclear Information System (INIS)

Surowiecka, K.; Wysmolek, A.; Stepniewski, R.; Bozek, R.; Pakula, K.; Baranowski, J.M.

2005-01-01

Micro photoluminescence of low-density GaN/Al x Ga 1-x N quantum dots grown by metal-organic vapor phase epitaxy using in situ etching of AlGaN is presented. The narrow lines in the micro photoluminescence spectra due to the single quantum dots are observed. Both energy and intensity of these lines show temporal fluctuations. Statistical analysis based on the correlation matrix allowed us to identify objects, which are affected by photo-induced electric field fluctuations. Relations between emission lines participating in the spectrum are discussed. (author)

Effect of the nitrogen incorporation and fast carrier dynamics in (In,Ga)AsN/GaP self-assembled quantum dots

Energy Technology Data Exchange (ETDEWEB)

Gauthier, J.-P.; Almosni, S.; Léger, Y.; Perrin, M.; Even, J.; Cornet, C., E-mail: charles.cornet@insa-rennes.fr; Durand, O. [UMR FOTON, CNRS, INSA-Rennes, F-35708 Rennes (France); Robert, C. [Tyndall National Institute, University College Cork, Lee Maltings, Cork (Ireland); Balocchi, A.; Carrère, H.; Marie, X. [Université de Toulouse, INSA-CNRS-UPS, LPCNO, F-31077 Toulouse (France)

2014-12-15

We report on the structural and optical properties of (In,Ga)AsN self-assembled quantum dots grown on GaP (001) substrate. A comparison with nitrogen free (In,Ga)As system is presented, showing a clear modification of growth mechanisms and a significant shift of the photoluminescence spectrum. Low temperature carrier recombination dynamics is studied by time-resolved photoluminescence, highlighting a drastic reduction of the characteristic decay-time when nitrogen is incorporated in the quantum dots. Room temperature photoluminescence is observed at 840 nm. These results reveal the potential of (In,Ga)AsN as an efficient active medium monolithically integrated on Si for laser applications.

Photo-stability of CsPbBr3 perovskite quantum dots for optoelectronic application

NARCIS (Netherlands)

Chen, Junsheng; Liu, Dongzhou; Al-Marri, Mohammed J.; Nuuttila, Lauri; Lehtivuori, Heli; Zheng, Kaibo

Due to their superior photoluminescence (PL) quantum yield (QY) and tunable optical band gap, all-inorganic CsPbBr3 perovskite quantum dots (QDs) have attracted intensive attention for the application in solar cells, light emitting diodes (LED), photodetectors and laser devices. In this scenario,

Quantum Secure Direct Communication with Quantum Memory.

Science.gov (United States)

Zhang, Wei; Ding, Dong-Sheng; Sheng, Yu-Bo; Zhou, Lan; Shi, Bao-Sen; Guo, Guang-Can

2017-06-02

Quantum communication provides an absolute security advantage, and it has been widely developed over the past 30 years. As an important branch of quantum communication, quantum secure direct communication (QSDC) promotes high security and instantaneousness in communication through directly transmitting messages over a quantum channel. The full implementation of a quantum protocol always requires the ability to control the transfer of a message effectively in the time domain; thus, it is essential to combine QSDC with quantum memory to accomplish the communication task. In this Letter, we report the experimental demonstration of QSDC with state-of-the-art atomic quantum memory for the first time in principle. We use the polarization degrees of freedom of photons as the information carrier, and the fidelity of entanglement decoding is verified as approximately 90%. Our work completes a fundamental step toward practical QSDC and demonstrates a potential application for long-distance quantum communication in a quantum network.

Conditions giving rise to intense visible room temperature photoluminescence in SrWO4 thin films: the role of disorder

International Nuclear Information System (INIS)

Orhan, E.; Anicete-Santos, M.; Maurera, M.A.M.A.; Pontes, F.M.; Paiva-Santos, C.O.; Souza, A.G.; Varela, J.A.; Pizani, P.S.; Longo, E.

2005-01-01

The nature of intense visible photoluminescence at room temperature of SrWO 4 (SWO) non-crystalline thin films is discussed in the light of experimental results and theoretical calculations. The SWO thin films were synthesized by the polymeric precursors method. Their structural properties have been obtained by X-ray diffraction data and the corresponding photoluminescence (PL) spectra have been measured. The UV-vis optical spectra measurements suggest the creation of localized states in the disordered structure. The photoluminescence measurements reveal that the PL changes with the degree of disorder in the SWO thin film. To understand the origin of visible PL at room temperature in disordered SWO, we performed quantum-mechanical calculations on crystalline and disordered SWO periodic models. Their electronic structures are analyzed in terms of DOS, band dispersion and charge densities. We used DFT method with the hybrid non-local B3LYP approximation. The polarization induced by the symmetry break and the existence of localized levels favors the creation of trapped holes and electrons, giving origin to the room temperature photoluminescence phenomenon in the SWO thin films

Excitonic effects in the luminescence of quantum wells

International Nuclear Information System (INIS)

Deveaud, B.; Kappei, L.; Berney, J.; Morier-Genoud, F.; Portella-Oberli, M.T.; Szczytko, J.; Piermarocchi, C.

2005-01-01

We report on the origin of the excitonic luminescence in quantum wells. This study is carried out by time-resolved photoluminescence experiments performed on a very high-quality InGaAs quantum well sample in which the photoluminescence contributions at the energy of the exciton and at the band edge can be clearly separated and traced over a broad range of times and densities. This allows us to compare the two conflicting theoretical approaches to the question of the origin of the excitonic luminescence in quantum wells: the model of the exciton population and the model of the Coulomb correlated plasma. We measure the exciton formation time and we show the fast exciton formation and its dependence with carrier density. We are also able to give the boundaries of the Mott transition in our system, and to show the absence of observable renormalization of the gap below the onset of this transition. We detail the characteristics of the trion formation and evidence the possible formation of both positive and negative trions in the absence of any resident free carrier populations

Colloidal quantum dot photovoltaics: The effect of polydispersity

KAUST Repository

Zhitomirsky, David; Kramer, Illan J.; Labelle, André J.; Fischer, Armin H.; Debnath, Ratan K.; Pan, Jun; Bakr, Osman; Sargent, E. H.

2012-01-01

, the dependence of both open-circuit voltage and photoluminescence behavior on the density of small-bandgap (large-diameter) quantum dot inclusions. The model requires inclusion of trap states to explain the experimental data quantitatively. We then explore using

GaAsSb-capped InAs quantum dots: From enlarged quantum dot height to alloy fluctuations

NARCIS (Netherlands)

Ulloa Herrero, J.M.; Gargallo-Caballero, R.; Bozkurt, M.; Moral, del M.; Guzman, A.; Koenraad, P.M.; Hierro, A.

2010-01-01

The Sb-induced changes in the optical properties of GaAsSb-capped InAs/GaAs quantum dots (QDs) are shown to be strongly correlated with structural changes. The observed redshift of the photoluminescence emission is shown to follow two different regimes. In the first regime, with Sb concentrations up

Optically detected SdH oscillations in CdTe/(CdMg)Te and CdTe/(CdMnMg)Te modulation doped quantum wells

International Nuclear Information System (INIS)

Shen, J.X.; Ossau, W.; Fischer, F.; Waag, A.; Landwehr, G.

1995-01-01

Oscillations of photoluminescence properties in external magnetic fields are investigated in CdTe modulation doped quantum wells. The oscillatory behaviour of the luminescence intensity, the line width and the g factor is due to many-body effects in the 2-dimensional electron gas. The oscillation of photoluminescence intensity can be easily used as optically detected Shubnikov de Haas effect to determine the electron concentration in quantum wells without contacts. (author)

Microwave Synthesis of Nearly Monodisperse Core/Multishell Quantum Dots with Cell Imaging Applications

Directory of Open Access Journals (Sweden)

Xu Hengyi

2010-01-01

Full Text Available Abstract We report in this article the microwave synthesis of relatively monodisperse, highly crystalline CdSe quantum dots (QDs overcoated with Cd0.5Zn0.5S/ZnS multishells. The as-prepared QDs exhibited narrow photoluminescence bandwidth as the consequence of homogeneous size distribution and uniform crystallinity, which was confirmed by transmission electron microscopy. A high photoluminescence quantum yield up to 80% was measured for the core/multishell nanocrystals. Finally, the resulting CdSe/Cd0.5Zn0.5S/ZnS core/multishell QDs have been successfully applied to the labeling and imaging of breast cancer cells (SK-BR3.

Optimization of InAs/GaAs quantum-dot structures and application to 1.3-μm mode-locked laser diodes

International Nuclear Information System (INIS)

Li Mi-Feng; Ni Hai-Qiao; Niu Zhi-Chuan; Ding Ying; David Bajek; Liang Kong; Ana Cataluna Maria

2014-01-01

The self-assembled growth of InAs/GaAs quantum dots by molecular beam epitaxy is conducted by optimizing several growth parameters, using a one-step interruption method after island formation. The dependence of photoluminescence on areal quantum-dot density is systematically investigated as a function of InAs deposition, growth temperature and arsenic pressure. The results of this investigation along with time-resolved photoluminescence measurements show that the combination of a growth temperature of 490 °C, with a deposition rate of 0.02 ML/s, under an arsenic pressure of 1 × 10 −6 Torr (1 Torr = 1.33322 × 10 2 Pa), provides the best compromise between high density and the photoluminescence of quantum dot structure, with a radiative lifetime of 780 ps. The applicability of this 5-layer quantum dot structure to high-repetition-rate pulsed lasers is demonstrated with the fabrication and characterization of a monolithic InAs/GaAs quantum-dot passively mode-locked laser operating at nearly 1300 nm. Picosecond pulse generation is achieved from a two-section laser, with a ∼ 19.7-GHz repetition rate. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

KYW{sub 2}O{sub 8}:Eu{sup 3+} – A closer look on its photoluminescence and structure

Energy Technology Data Exchange (ETDEWEB)

Schwung, Sebastian; Enseling, David [Fachbereich Chemieingenieurwesen, Fachhochschule Münster, Stegerwaldstrasse 39, 48565 Steinfurt (Germany); Wesemann, Volker [Forschungsinstitut für mineralische und metallische Werkstoffe-Edelsteine/Edelmetalle-GmbH (FEE), Struthstrasse 2, 55743 Idar-Oberstein (Germany); Rytz, Daniel, E-mail: rytz@fee-io.de [Forschungsinstitut für mineralische und metallische Werkstoffe-Edelsteine/Edelmetalle-GmbH (FEE), Struthstrasse 2, 55743 Idar-Oberstein (Germany); Heying, Birgit; Rodewald, Ute Ch.; Gerke, Birgit; Niehaus, Oliver [Institut für Anorganische und Analytische Chemie, Universität Münster, Corrensstrasse 30, D-48149 Münster (Germany); Pöttgen, Rainer, E-mail: pottgen@uni-muenster.de [Institut für Anorganische und Analytische Chemie, Universität Münster, Corrensstrasse 30, D-48149 Münster (Germany); Jüstel, Thomas, E-mail: tj@fh-muenster.de [Fachbereich Chemieingenieurwesen, Fachhochschule Münster, Stegerwaldstrasse 39, 48565 Steinfurt (Germany)

2015-03-15

High-quality single crystals of partially europium-substituted KYW{sub 2}O{sub 8} (KYW) were grown by the top-seeded solution growth technique. The structures of four crystals with different europium content were refined on the basis of single crystal X-ray diffractometer data. The trivalent character of europium in these crystals was manifested through {sup 151}Eu Mössbauer spectra and magnetic susceptibility measurements. Moreover, reflection and photoluminescence spectra were recorded and from these spectra the quantum efficiency, lumen equivalent, and CIE1931 color point were calculated. It turned out that Eu{sup 3+} doped KYW is an efficient photoluminescent material at room temperature, while the thermal quenching temperature T{sub 1/2} is at about 633 K (360 °C), thus making the material a potential radiation converter for light emitting diodes. - Highlights: • Single crystalline K(Y,Eu)W{sub 2}O{sub 8} with different dopant levels. • Refined XRD data shows identical crystal structure for both types. • Thermal quenching behavior up to 800 K is measured. • Crystals show a high quantum efficiency.

Second-harmonic imaging of semiconductor quantum dots

DEFF Research Database (Denmark)

Østergaard, John Erland; Bozhevolnyi, Sergey I.; Pedersen, Kjeld

2000-01-01

Resonant second-harmonic generation is observed at room temperature in reflection from self-assembled InAlGaAs quantum dots grown on a GaAs (001) substrate. The detected second-harmonic signal peaks at a pump wavelength of similar to 885 nm corresponding to the quantum-dot photoluminescence maximum....... In addition, the second-harmonic spectrum exhibits another smaller but well-pronounced peak at 765 nm not found in the linear experiments. We attribute this peak to the generation of second-harmonic radiation in the AlGaAs spacer layer enhanced by the local symmetry at the quantum-dot interface. We further...

Conductive properties of switchable photoluminescence thermosetting systems based on liquid crystals.

Science.gov (United States)

Tercjak, Agnieszka; Gutierrez, Junkal; Ocando, Connie; Mondragon, Iñaki

2010-03-16

Conductive properties of different thermosetting materials modified with nematic 4'-(hexyl)-4-biphenyl-carbonitrile (HBC) liquid crystal and rutile TiO(2) nanoparticles were successfully studied by means of tunneling atomic force miscroscopy (TUNA). Taking into account the liquid crystal state of the HBC at room temperature, depending on both the HBC content and the presence of TiO(2) nanoparticles, designed materials showed different TUNA currents passed through the sample. The addition of TiO(2) nanoparticles into the systems multiply the detected current if compared to the thermosetting systems without TiO(2) nanoparticles and simultaneously stabilized the current passed through the sample, making the process reversible since the absolute current values were almost the same applying both negative and positive voltage. Moreover, thermosetting systems modified with liquid crystals with and without TiO(2) nanoparticles are photoluminescence switchable materials as a function of temperature gradient during repeatable heating/cooling cycle. Conductive properties of switchable photoluminescence thermosetting systems based on liquid crystals can allow them to find potential application in the field of photoresponsive devices, with a high contrast ratio between transparent and opaque states.

Photoluminescence Studies of P-type Modulation Doped GaAs/AlGaAs Quantum Wells in the High Doping Regime

Science.gov (United States)

Wongmanerod, S.; Holtz, P. O.; Reginski, K.; Bugaiski, M.; Monemar, B.

The influence of high Be-acceptor doping on the modulation-doped GaAs/Al0.3Ga0.7As quantum wells structures has been optically studied by using the low-temperature photoluminescence (PL) and photoluminescence excitation (PLE) techniques.The modulation doped samples were grown by the molecular-beam epitaxy technique with a varying Be acceptor concentration ranging from 1×1018 to 8×1018cm-3. Several novels physical effects were observed. The main effect is a significant shift of the main emission towards lower energies as the doping concentrations increase. There are two contradictory mechanisms, which determine the peak energy of the main emission; the shrinkage of the effective bandgap due to many body effects and the reduction of the exciton binding energy due to the carrier screening effect. We conclude that the first one is the dominating effect. At a sufficiently high doping concentration (roughly 2×1018cm-3), the lineshape of the main PL emission is modified, and a new feature, the so called Fermi-edge singularity (FES), appears on the high energy side of the PL emission and exhibits a blue-shift as a function of doping concentration. This feature has been found to be very sensitive to a temperature change, already in the range of 4.4-50K. In addition, PLE spectra with a suitable detection energy show that the absorption edge is blue-shifted with respect to the PL main emission. The resulting Stoke shift is due to phase-space-filling of the carriers, in agreement with the FES interpretation. Finally, we have found from the PLE spectra that the exciton quenching is initiated in the same doping regime. Compared to the exciton quenching in other p-type structures, the critical acceptor concentration required to quench the excitons is significantly lower than in the case of 2D structures with acceptor doping within the well, but larger than in the case of 3D bulk.

Graphene Oxide Quantum Dots Exfoliated From Carbon Fibers by Microwave Irradiation: Two Photoluminescence Centers and Self-Assembly Behavior.

Science.gov (United States)

Yuan, Jian-Min; Zhao, Rui; Wu, Zhen-Jun; Li, Wei; Yang, Xin-Guo

2018-04-17

Graphene oxide quantum dots (GOQDs) attract great attention for their unique properties and promising application potential. The difficulty in the formation of a confined structure, and the numerous and diverse oxygen-containing functional groups results in a low emission yield to GOQDs. Here, GOQDs with a size of about 5 nm, exfoliated from carbon fibers by microwave irradiation, are detected and analyzed. The exfoliated GOQDs are deeply oxidized and induce large numbers of epoxy groups and ether bonds, but only a small amount of carbonyl groups and hydroxyl groups. The subdomains of sp 2 clusters, involving epoxy groups and ether bonds, are responsible for the two strong photoluminescence emissions of GOQDs under different excitation wavelengths. Moreover, GOQDs tend to self-assemble at the edges of their planes to form self-assembly films (SAFs) with the evaporation of water. SAFs can further assemble into different 3D patterns with unique microstructures such as sponge bulk, sponge ball, microsheet, sisal, and schistose coral, which are what applications such as supercapacitors, cells, catalysts, and electrochemical sensors need. This method for preparation of GOQDs is easy, quick, and environmentally friendly, and this work may open up new research interests about GOQDs. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Quantum exam

International Nuclear Information System (INIS)

Nguyen, Ba An

2006-01-01

Absolutely and asymptotically secure protocols for organizing an exam in a quantum way are proposed basing judiciously on multipartite entanglement. The protocols are shown to stand against common types of eavesdropping attack

Theory of Spin States of Quantum Dot Molecules

Science.gov (United States)

Ponomarev, I. V.; Reinecke, T. L.; Scheibner, M.; Stinaff, E. A.; Bracker, A. S.; Doty, M. F.; Gammon, D.; Korenev, V. L.

2007-04-01

The photoluminescence spectrum of an asymmetric pair of coupled InAs quantum dots in an applied electric field shows a rich pattern of level anticrossings, crossings and fine structure that can be understood as a superposition of charge and spin configurations. We present a theoretical model that provides a description of the energy positions and intensities of the optical transitions in exciton, biexciton and charged exciton states of coupled quantum dots molecules.

Investigation of the photoluminescence properties of thermochemically synthesized CdS nanocrystals

Directory of Open Access Journals (Sweden)

M. Molaei

2011-03-01

Full Text Available In this work we have synthesized CdS nanocrystals with thermochemical method. CdSO4 and Na2S2O3 were used as the precursors and thioglycolic acid (TGA was used as capping agent molecule. The structure and optical property of the nanocrystals were characterized by means of XRD, TEM, UV-visible optical spectroscopy and photoluminescence (PL. X-ray diffraction (XRD and TEM analyses demonstrated hexagonal phase CdS nanocrystals with an average size around 2 nm. Synthesized nanocrystals exhibited band gap of about 3.2 eV and showed a broad band emission from 400-750 nm centered at 504 nm with a (0.27, 0.39 CIE coordinate. This emission can be attributed to recombination of an electron in conduction band with a hole trapped in Cd vacancies near to the valance band of CdS. The best attained photoluminescence quantum yield of the nanocrystals was about 12%, this amount is about 20 times higher than that for thioglycerol (TG capped CdS nanocrystals.

Quantum Dots and Their Multimodal Applications: A Review

Directory of Open Access Journals (Sweden)

Paul H. Holloway

2010-03-01

Full Text Available Semiconducting quantum dots, whose particle sizes are in the nanometer range, have very unusual properties. The quantum dots have band gaps that depend in a complicated fashion upon a number of factors, described in the article. Processing-structure-properties-performance relationships are reviewed for compound semiconducting quantum dots. Various methods for synthesizing these quantum dots are discussed, as well as their resulting properties. Quantum states and confinement of their excitons may shift their optical absorption and emission energies. Such effects are important for tuning their luminescence stimulated by photons (photoluminescence or electric field (electroluminescence. In this article, decoupling of quantum effects on excitation and emission are described, along with the use of quantum dots as sensitizers in phosphors. In addition, we reviewed the multimodal applications of quantum dots, including in electroluminescence device, solar cell and biological imaging.

Electrochemical tuning of optical properties of graphitic quantum dots

International Nuclear Information System (INIS)

Ge, Juan; Li, Yan; Zhang, Bo-Ping; Ma, Ning; Wang, Jun; Pu, Chang; Xiang, Ying-Chang

2015-01-01

Graphitic quantum dots (GQDs), as a new class of quantum dots, possess unique properties. Among the various reported approaches for their fabrication, electrochemical method possesses numerous advantages compared with others. In particular, the formation process of the GQDs could be precisely controlled by this method through adjusting the electrochemical parameters and environment. In this study, GQDs with multi-color fluorescence (FL) were obtained by this method through tuning only the applied potential window of cycling voltammetry. The luminescence mechanism of those GQDs was discussed and explained by the ultraviolet (UV)–visible, photoluminescence (PL), and photoluminescence excitation (PLE) spectra. The influence of the applied potential window on the PL properties of GQDs and the relationship between the degree of surface oxidation and PL properties were also investigated. - Highlights: • We produced the graphite quantum dots (GQDs) by an electrochemical method. • We changed the applied potentials of cycling voltammetry (CV). • Varying of applied potentials changed surface oxygen-containing groups of GQDs. • Higher surface oxidation degree resulted in the red-shift of PL spectra

Properties of CdSe quantum dots coated with silica fabricated in a facile way

International Nuclear Information System (INIS)

Liao Yufeng; Li Wenjiang; He Sailing

2007-01-01

High quality quantum dots (QDs) CdSe were prepared using a novel and non-TOP method. Quantum dots of different sizes ranging from 2 to 4 nm could be obtained by removing aliquots of the reaction solution at different time intervals or by adjusting some reaction conditions. The CdSe quantum dots (core) were directly coated with silica (shell) using a microemulsion method. The design and preparation of a model QD/silica was described and characterized using transmission electron microscopy (TEM), UV-vis absorption, photoluminescence and laser confocal scanning microscopy. TEM images confirmed the well-monodispersed QDs and the silica shell around the CdSe core, respectively; laser confocal microscope images, UV-vis absorption and photoluminescence spectra clearly indicated that both the original QDs and the silica-coated QDs had good fluorescence properties. The quantum dots coated with silica shells were stable, water-soluble and less toxic (due to the silica shells), and are anticipated to be used as fluorescent probes for biosensing and imaging applications

Impact of ion-implantation-induced band gap engineering on the temperature-dependent photoluminescence properties of InAs/InP quantum dashes

International Nuclear Information System (INIS)

Hadj Alouane, M. H.; Ilahi, B.; Maaref, H.; Salem, B.; Aimez, V.; Morris, D.; Turala, A.; Regreny, P.; Gendry, M.

2010-01-01

We report on the effects of the As/P intermixing induced by phosphorus ion implantation in InAs/InP quantum dashes (QDas) on their photoluminescence (PL) properties. For nonintermixed QDas, usual temperature-dependent PL properties characterized by a monotonic redshift in the emission band and a continual broadening of the PL linewidth as the temperature increases, are observed. For intermediate ion implantation doses, the inhomogeneous intermixing enhances the QDas size dispersion and the enlarged distribution of carrier confining potential depths strongly affects the temperature-dependent PL properties below 180 K. An important redshift in the PL emission band occurs between 10 and 180 K which is explained by a redistribution of carriers among the different intermixed QDas of the ensemble. For higher implantation doses, the homogeneous intermixing reduces the broadening of the localized QDas state distribution and the measured linewidth temperature behavior matches that of the nonintermixed QDas. An anomalous temperature-dependent emission energy behavior has been observed for extremely high implantation doses, which is interpreted by a possible QDas dissolution.

Cavity quantum electrodynamics studies with site-controlled InGaAs quantum dots integrated into high quality microcavities

DEFF Research Database (Denmark)

Reitzenstein, S.; Schneider, C.; Albert, F.

2011-01-01

Semiconductor quantum dots (QDs) are fascinating nanoscopic structures for photonics and future quantum information technology. However, the random position of self-organized QDs inhibits a deterministic coupling in devices relying on cavity quantum electrodynamics (cQED) effects which complicates......, e.g., the large scale fabrication of quantum light sources. As a result, large efforts focus on the growth and the device integration of site-controlled QDs. We present the growth of low density arrays of site-controlled In(Ga)As QDs where shallow etched nanoholes act as nucleation sites...... linewidth, the oscillator strength and the quantum efficiency. A stacked growth of strain coupled SCQDs forming on wet chemically etched nanoholes provide the smallest linewidth with an average value of 210 μeV. Using time resolved photoluminescence studies on samples with a varying thickness of the capping...

Photoluminescence and radiation response properties of Ce3+-doped CsCaCl3 crystalline scintillator

International Nuclear Information System (INIS)

Fujimoto, Yutaka; Saeki, Keiichiro; Tanaka, Hironori; Yahaba, Takuma; Koshimizu, Masanori; Asai, Keisuke; Yanagida, Takayuki

2016-01-01

In this paper, we report on the photoluminescence and scintillation properties of a newly developed CsCaCl 3 :Ce (0.5 mol%) crystalline scintillator grown by the vertical Bridgman method. The fluorescence quantum efficiency for the Ce 3+ characteristic emission bands centered at around 350–400 nm was 76% under excitation at 330 nm light. The photoluminescence decay time of the Ce 3+ was approximately 32 ns. When x-ray excited the crystal, intense emission bands were observed at 350–400 nm, and could be attributed to the Ce 3+ emission. The scintillation light yield of the developed crystal was ∼7600 ph MeV −1 compared to a NaI:Tl commercial scintillator, and the principal scintillation decay time was approximately 340 ns plus two fast components of around 1.6 ns and 45 ns. (paper)

Optical and structural properties of MOVPE-grown GaInSb/GaSb quantum wells

Energy Technology Data Exchange (ETDEWEB)

Wagener, Viera, E-mail: viera.wagener@nmmu.ac.z [Physics Department, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth 6031 (South Africa); Olivier, E.J.; Botha, J.R. [Physics Department, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth 6031 (South Africa)

2009-12-15

This paper reports on the optical and structural properties of strained type-I Ga{sub 1-x}In{sub x}Sb quantum wells embedded in GaSb from a metal-organic vapour phase epitaxial growth perspective. Photoluminescence measurements and transmission electron microscopy were used to evaluate the effect of the growth temperature on the quality of Ga{sub 1-x}In{sub x}Sb strained layers with varied alloy compositions and thicknesses. Although the various factors contributing to the overall quality of the strained layers are difficult to separate, the quantum well characteristics are significantly altered by the growth temperature. Despite the high growth rates (approx2 nm/s), quantum wells grown at 607 deg. C display photoluminescence emissions with full-width at half-maximum of 3.5-5.0 meV for an indium solid content (x) up to 0.15.

Optical and structural properties of MOVPE-grown GaInSb/GaSb quantum wells

International Nuclear Information System (INIS)

Wagener, Viera; Olivier, E.J.; Botha, J.R.

2009-01-01

This paper reports on the optical and structural properties of strained type-I Ga 1-x In x Sb quantum wells embedded in GaSb from a metal-organic vapour phase epitaxial growth perspective. Photoluminescence measurements and transmission electron microscopy were used to evaluate the effect of the growth temperature on the quality of Ga 1-x In x Sb strained layers with varied alloy compositions and thicknesses. Although the various factors contributing to the overall quality of the strained layers are difficult to separate, the quantum well characteristics are significantly altered by the growth temperature. Despite the high growth rates (∼2 nm/s), quantum wells grown at 607 deg. C display photoluminescence emissions with full-width at half-maximum of 3.5-5.0 meV for an indium solid content (x) up to 0.15.

Optically detected SdH oscillations in CdTe/(CdMg)Te and CdTe/(CdMnMg)Te modulation doped quantum wells

Energy Technology Data Exchange (ETDEWEB)

Shen, J.X.; Ossau, W.; Fischer, F.; Waag, A.; Landwehr, G. [Physikalisches Institut der Uniwersitaet Wuerzburg, Wuerzburg (Germany)

1995-12-31

Oscillations of photoluminescence properties in external magnetic fields are investigated in CdTe modulation doped quantum wells. The oscillatory behaviour of the luminescence intensity, the line width and the g factor is due to many-body effects in the 2-dimensional electron gas. The oscillation of photoluminescence intensity can be easily used as optically detected Shubnikov de Haas effect to determine the electron concentration in quantum wells without contacts. (author). 5 refs, 3 figs, 1 tab.

Theoretical and experimental study of disordered Ba0.45Sr0.55 TiO3 photoluminescence at room temperature

International Nuclear Information System (INIS)

Souza, I.A.; Gurgel, M.F.C.; Santos, L.P.S.; Goes, M.S.; Cava, S.; Cilense, M.; Rosa, I.L.V.; Paiva-Santos, C.O.; Longo, E.

2006-01-01

Disordered and crystalline Ba 0.45 Sr 0.55 TiO 3 (BST) powder processed at low temperature was synthesized by the polymeric precursor method. The single-phase perovskite structure of the ceramics was identified by the Raman and X-ray diffraction techniques. Photoluminescence at room temperature was observed only in a disordered BST sample. Increasing the calcination time intensified the photoluminescence (PL), which reached its maximum value in the sample heat treated at 300 deg. C for 30 h. This emission may be correlated with the structural disorder. Periodic ab initio quantum-mechanical calculations using the CRYSTAL98 program can yield important information regarding the electronic and structural properties of crystalline and disordered solids. The experimental and theoretical results indicate the presence of intermediary energy levels in the band gap. This is ascribed to the break in symmetry, which is responsible for visible photoluminescence in the material's disordered state at room temperature

Proposed Quenching of Phonon-Induced Processes in Photoexcited Quantum Dots due to Electron-Hole Asymmetries

DEFF Research Database (Denmark)

Nysteen, Anders; Nielsen, Per Kær; Mørk, Jesper

2013-01-01

by photoluminescence excitation spectroscopy of a single quantum dot. We also investigate the implications for cavity QED, i.e., a coupled quantum dot-cavity system, and demonstrate that the phonon scattering may be strongly quenched. The quenching is explained by a balancing between the deformation potential...

On quantum harmonic oscillator being subjected to absolute

Indian Academy of Sciences (India)

In a quantum harmonic oscillator (QHO), the energy of the oscillator increases with increased frequency. In this paper, assuming a boundary condition that the product of momentum and position, or the product of energy density and position remains constant in the QHO, it is established that a particle subjected to increasing ...

Plasmon-Enhanced Photoluminescence of an Amorphous Silicon Quantum Dot Light-Emitting Device by Localized Surface Plasmon Polaritons in Ag/SiOx:a-Si QDs/Ag Sandwich Nanostructures

Directory of Open Access Journals (Sweden)

Tsung-Han Tsai

2015-01-01

Full Text Available We investigated experimentally the plasmon-enhanced photoluminescence of the amorphous silicon quantum dots (a-Si QDs light-emitting devices (LEDs with the Ag/SiOx:a-Si QDs/Ag sandwich nanostructures, through the coupling between the a-Si QDs and localized surface plasmons polaritons (LSPPs mode, by tuning a one-dimensional (1D Ag grating on the top. The coupling of surface plasmons at the top and bottom Ag/SiOx:a-Si QDs interfaces resulted in the localized surface plasmon polaritons (LSPPs confined underneath the Ag lines, which exhibit the Fabry-Pérot resonance. From the Raman spectrum, it proves the existence of a-Si QDs embedded in Si-rich SiOx film (SiOx:a-Si QDs at a low annealing temperature (300°C to prevent the possible diffusion of Ag atoms from Ag film. The photoluminescence (PL spectra of a-Si QDs can be precisely tuned by a 1D Ag grating with different pitches and Ag line widths were investigated. An optimized Ag grating structure, with 500 nm pitch and 125 nm Ag line width, was found to achieve up to 4.8-fold PL enhancement at 526 nm and 2.46-fold PL integrated intensity compared to the a-Si QDs LEDs without Ag grating structure, due to the strong a-Si QDs-LSPPs coupling.

The role of structural order-disorder for visible intense photoluminescence in the BaZr0.5Ti0.5O3 thin films

International Nuclear Information System (INIS)

Anicete-Santos, M.; Cavalcante, L.S.; Orhan, E.; Paris, E.C.; Simoes, L.G.P.; Joya, M.R.; Rosa, I.L.V.; Lucena, P.R. de; Santos, M.R.M.C.; Santos-Junior, L.S.; Pizani, P.S.; Leite, E.R.; Varela, J.A.; Longo, E.

2005-01-01

The nature of the intense visible room temperature photoluminescence of BaZr 0.5 Ti 0.5 O 3 non-crystalline thin films is discussed in the light of experimental results and theoretical calculations. The photoluminescence measurements reveal that the emission intensity changes with the degree of disorder in the BaZr 0.5 Ti 0.5 O 3 lattice. First principles quantum mechanical techniques, based on density functional theory at B3LYP level, have been employed to study the electronic structure of a crystalline model and of structurally disordered models in order to detect the influence of disorder on the electronic structure. An analysis of the electronic charge distribution reveals local polarization in the disordered structures. The relevance of the present theoretical and experimental results on the photoluminescence behavior of BZT is discussed

Air-Stable Surface-Passivated Perovskite Quantum Dots for Ultra-Robust, Single- and Two-Photon-Induced Amplified Spontaneous Emission

KAUST Repository

Pan, Jun; Sarmah, Smritakshi P.; Banavoth, Murali; Dursun, Ibrahim; Peng, Wei; Parida, Manas R.; Liu, Jiakai; Sinatra, Lutfan; AlYami, Noktan; Zhao, Chao; Alarousu, Erkki; Ng, Tien Khee; Ooi, Boon S.; Bakr, Osman; Mohammed, Omar F.

2015-01-01

We demonstrate ultra-air- and photostable CsPbBr3 quantum dots (QDs) by using an inorganic–organic hybrid ion pair as the capping ligand. This passivation approach to perovskite QDs yields high photoluminescence quantum yield with unprecedented

Time-resolved photoluminescence of SiOx encapsulated Si

Science.gov (United States)

Kalem, Seref; Hannas, Amal; Österman, Tomas; Sundström, Villy

Silicon and its oxide SiOx offer a number of exciting electrical and optical properties originating from defects and size reduction enabling engineering new electronic devices including resistive switching memories. Here we present the results of photoluminescence dynamics relevant to defects and quantum confinement effects. Time-resolved luminescence at room temperature exhibits an ultrafast decay component of less than 10 ps at around 480 nm and a slower component of around 60 ps as measured by streak camera. Red shift at the initial stages of the blue luminescence decay confirms the presence of a charge transfer to long lived states. Time-correlated single photon counting measurements revealed a life-time of about 5 ns for these states. The same quantum structures emit in near infrared close to optical communication wavelengths. Nature of the emission is described and modeling is provided for the luminescence dynamics. The electrical characteristics of metal-oxide-semiconductor devices were correlated with the optical and vibrational measurement results in order to have better insight into the switching mechanisms in such resistive devices as possible next generation RAM memory elements. ``This work was supported by ENIAC Joint Undertaking and Laser-Lab Europe''.

Interaction of Water-Soluble CdTe Quantum Dots with Bovine Serum Albumin

Science.gov (United States)

2011-01-01

Semiconductor nanoparticles (quantum dots) are promising fluorescent markers, but it is very little known about interaction of quantum dots with biological molecules. In this study, interaction of CdTe quantum dots coated with thioglycolic acid (TGA) with bovine serum albumin was investigated. Steady state spectroscopy, atomic force microscopy, electron microscopy and dynamic light scattering methods were used. It was explored how bovine serum albumin affects stability and spectral properties of quantum dots in aqueous media. CdTe–TGA quantum dots in aqueous solution appeared to be not stable and precipitated. Interaction with bovine serum albumin significantly enhanced stability and photoluminescence quantum yield of quantum dots and prevented quantum dots from aggregating. PMID:27502633

Directly deposited quantum dot solids using a colloidally stable nanoparticle ink

KAUST Repository

Fischer, Armin H.; Rollny, Lisa R.; Pan, Jun; Carey, Graham H.; Thon, Susanna; Hoogland, Sjoerd H.; Voznyy, Oleksandr; Zhitomirsky, David; Kim, Jinyoung; Bakr, Osman; Sargent, E. H.

2013-01-01

We develop a photovoltaic colloidal quantum dot ink that allows for lossless, single-step coating of large areas in a manufacturing-compatible process. Our materials strategy involves a solution-phase ligand exchange to transport compatible linkers that yield 1-thioglycerol-capped PbS quantum dots in dimethyl sulfoxide with a photoluminescence quantum yield of 24%. A proof-of-principle solar cell made from the ink exhibits 2.1% power conversion efficiency. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Directly deposited quantum dot solids using a colloidally stable nanoparticle ink

KAUST Repository

Fischer, Armin H.

2013-08-12

We develop a photovoltaic colloidal quantum dot ink that allows for lossless, single-step coating of large areas in a manufacturing-compatible process. Our materials strategy involves a solution-phase ligand exchange to transport compatible linkers that yield 1-thioglycerol-capped PbS quantum dots in dimethyl sulfoxide with a photoluminescence quantum yield of 24%. A proof-of-principle solar cell made from the ink exhibits 2.1% power conversion efficiency. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Absolute Configuration Determination by Quantum Mechanical Calculation of Chiroptical Spectra: Basics and Applications to Fungal Metabolites.

Science.gov (United States)

Superchi, Stefano; Scafato, Patrizia; Gorecki, Marcin; Pescitelli, Gennaro

2018-01-01

Quantum mechanical simulations of chiroptical properties, such as electronic circular dichroism (ECD), optical rotation (OR), and vibrational circular dichroism (VCD), have rapidly become very popular to assign the absolute configuration of novel natural products. We review the application of the ECD/OR/VCD computational methodology to chiral metabolites of fungal origin. First, we summarize the fundamentals of the three spectroscopies; then, we focus on the specific experimental and computational issues allied to the application of their calculations. We surveyed the entire literature describing the use of ECD/OR/VCD computations for fungal metabolites, and catalogued all papers according to the method employed and to the structural family of compounds. Then, we chose several examples to illustrate the use of the techniques and highlight the practical application of the computational approach. Our literature survey demonstrates that the simulation of ECD/OR/VCD spectra is nowadays widespread and accessible also to non-experts, although a good computational practice is necessary to avoid wrong assignments. ECD is still the most common technique used in the context of fungal metabolites. OR and VCD may be profitably employed when the compound of interest lacks chromophoric groups. Our examples illustrate that the combination of two or more chiroptical methods is strongly advisable in some cases, especially in the presence of high conformational flexibility, where a single technique does not lead to a safe conclusion. The ECD/OR/VCD computational approach is a reliable and versatile method to assign the absolute configuration of fungal metabolites and related natural products. Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.

Polarized time-resolved photoluminescence measurements of m-plane AlGaN/GaN MQWs

Science.gov (United States)

Rosales, Daniel; Gil, B.; Bretagnon, T.; Zhang, F.; Okur, S.; Monavarian, M.; Izioumskaia, N.; Avrutin, V.; Özgür, Ü.; Morkoç, H.; Leach, J. H.

2014-03-01

The optical properties of GaN/Al0.15Ga0.85N multiple quantum wells grown on m-plane oriented substrate are studied in 8K-300K temperature range. The optical spectra reveal strong in-plane optical anisotropies as predicted by group theory. Polarized time resolved temperature-dependent photoluminescence experiments are performed providing access to the relative contributions of the non-radiative and radiative recombination processes. We deduce the variation of the radiative decay time with temperature in the two polarizations.

Spectroscopy of Charged Quantum Dot Molecules

Science.gov (United States)

Stinaff, E. A.; Scheibner, M.; Bracker, A. S.; Ponomarev, I. V.; Ware, M. E.; Doty, M. F.; Reinecke, T. L.; Gammon, D.; Korenev, V. L.

2006-03-01

Spins of single charges in quantum dots are attractive for many quantum information and spintronic proposals. Scalable quantum information applications require the ability to entangle and operate on multiple spins in coupled quantum dots (CQDs). To further the understanding of these systems, we present detailed spectroscopic studies of InAs CQDs with control of the discrete electron or hole charging of the system. The optical spectrum reveals a pattern of energy anticrossings and crossings in the photoluminescence as a function of applied electric field. These features can be understood as a superposition of charge and spin configurations of the two dots and represent clear signatures of quantum mechanical coupling. The molecular resonance leading to these anticrossings is achieved at different electric fields for the optically excited (trion) states and the ground (hole) states allowing for the possibility of using the excited states for optically induced coupling of the qubits.

Phosphorescence quantum yield determination with time-gated fluorimeter and Tb(III)-acetylacetonate as luminescence reference

Energy Technology Data Exchange (ETDEWEB)

Penzkofer, A., E-mail: alfons.penzkofer@physik.uni-regensburg.de [Fakultät für Physik, Universität Regensburg, Universitätsstrasse 31, D-93053 Regensburg (Germany)

2013-03-29

Highlights: ► Procedure for absolute phosphorescence quantum yield measurement is described. ► Experimental setup for absolute luminescence quantum yield standard calibration. ► Tb(acac){sub 3} proposed as phosphorescence quantum yield reference standard. ► Luminescence quantum yield of Tb(acac){sub 3} in cyclohexane measured. ► Luminescence lifetime of Tb(acac){sub 3} in cyclohexane measured. - Abstract: Phosphorescence quantum yield measurements of fluorescent and phosphorescent samples require the use of time-gated fluorimeters in order to discriminate against the fluorescence contribution. As reference standard a non-fluorescent luminescent compound is needed for absolute phosphorescence quantum yield determination. For this purpose the luminescence behavior of the rare earth chelate terbium(III)-acetylacetonate (Tb(acac){sub 3}) was studied (determination of luminescence quantum yield and luminescence lifetime). The luminescence quantum yield of Tb(acac){sub 3} was determined by using an external light source and operating the fluorimeter in chemo/bioluminescence mode with a fluorescent dye (rhodamine 6G in methanol) as reference standard. A procedure is developed for absolute luminescence (phosphorescence) quantum yield determination of samples under investigation with a time-gated fluorimeter using a non-fluorescent luminescent compound of known luminescence quantum yield and luminescence lifetime.

Nearly suppressed photoluminescence blinking of small-sized, blue-green-orange-red emitting single CdSe-based core/gradient alloy shell/shell quantum dots: correlation between truncation time and photoluminescence quantum yield.

Science.gov (United States)

Roy, Debjit; Mandal, Saptarshi; De, Chayan K; Kumar, Kaushalendra; Mandal, Prasun K

2018-04-18

CdSe-based core/gradient alloy shell/shell semiconductor quantum dots (CGASS QDs) have been shown to be optically quite superior compared to core-shell QDs. However, very little is known about CGASS QDs at the single particle level. Photoluminescence blinking dynamics of four differently emitting (blue (λem = 510), green (λem = 532), orange (λem = 591), and red (λem = 619)) single CGASS QDs having average sizes 600 nm). In this manuscript, we report nearly suppressed PL blinking behaviour of CGASS QDs with average sizes correlation between the event durations and found that residual memory exists in both the ON- and OFF-event durations. Positively correlated successive ON-ON and OFF-OFF event durations and negatively correlated (anti-correlated) ON-OFF event durations perhaps suggest the involvement of more than one type of trapping process within the blinking framework. The timescale corresponding to the additional exponential term has been assigned to hole trapping for ON-event duration statistics. Similarly, for OFF-event duration statistics, this component suggests hole detrapping. We found that the average duration of the exponential process for the ON-event durations is an order of magnitude higher than that of the OFF-event durations. This indicates that the holes are trapped for a significantly long time. When electron trapping is followed by such a hole trapping, long ON-event durations result. We have observed long ON-event durations, as high as 50 s. The competing charge tunnelling model has been used to account for the observed blinking behaviour in these CGASS QDs. Quite interestingly, the PLQY of all of these differently emitting QDs (an ensemble level property) could be correlated with the truncation time (a property at the single particle level). A respective concomitant increase-decrease of ON-OFF event truncation times with increasing PLQY is also indicative of a varying degree of suppression of the Auger recombination processes in these four

Four-wave mixing in InAlGaAs quantum dots

DEFF Research Database (Denmark)

Leosson, Kristjan; Birkedal, Dan; Hvam, Jørn Märcher

2001-01-01

broadening strongly reduce the interaction with the electromagnetic field. Until now, four-wave mixing (FWM) in III-V quantum dots has only been reported in optical amplifiers at room temperature, where the interaction length is increased by waveguiding in the quantum dot plane. We have carried out...... degenerate FWM experiments in a slab geometry on a sample containing 10 layers of MBE-grown In0.5Al0.04Ga0.46As quantum dots (QDs) with 50-nm Al0.08Ga0.92As barriers. Ground state photoluminescence emission was measured....

Type II GaSb quantum ring solar cells under concentrated sunlight.

Science.gov (United States)

Tsai, Che-Pin; Hsu, Shun-Chieh; Lin, Shih-Yen; Chang, Ching-Wen; Tu, Li-Wei; Chen, Kun-Cheng; Lay, Tsong-Sheng; Lin, Chien-Chung

2014-03-10

A type II GaSb quantum ring solar cell is fabricated and measured under the concentrated sunlight. The external quantum efficiency confirms the extended absorption from the quantum rings at long wavelength coinciding with the photoluminescence results. The short-circuit current of the quantum ring devices is 5.1% to 9.9% more than the GaAs reference's under various concentrations. While the quantum ring solar cell does not exceed its GaAs counterpart in efficiency under one-sun, the recovery of the open-circuit voltages at higher concentration helps to reverse the situation. A slightly higher efficiency (10.31% vs. 10.29%) is reported for the quantum ring device against the GaAs one.

Photoluminescence investigation of ZnO quantum dots surface modified with silane coupling agent as a capping agent

Energy Technology Data Exchange (ETDEWEB)

Moghaddam, E., E-mail: e.moghaddam@merc.ac.ir; Youzbashi, A.A; Kazemzadeh, A.; Eshraghi, M.J.

2015-12-15

This report presents the luminescence measurement results of surface modified zinc oxide quantum dots (ZnO QDs) performed with different concentrations of 3-aminopropyltriethoxysilane (APTES) as a capping agent. Surface modification was performed by an in situ procedure on the surface of ZnO QDs in a sol gel solution route. The modified samples were characterized by various analytical techniques such as XRD, TEM, FT-IR, and UV–vis spectroscopy. Surface modification efficiency was experimentally investigated by variation of the photoluminescence) PL (emission intensities observed by changing the capping agent concentration. In order to investigate the effectiveness of the capping agent on the stability of the QDs, The PL spectra of the surface modified ZnO QDs were compared with that of unmodified ZnO QDs. Molecular layer of this type and similar silane based molecules with a variety of surface terminations that have the same molecular attachment schemes should enable interface engineering in optimizing the chemical selectivity of ZnO biosensors or electrical and optical properties of ZnO-polymer hybrid films. - Highlights: • Surface modification of ZnO QDs resulted in the small- size QDs (around 2 nm). • Surface modification resulted in the enhancement of the UV emission upon quenching the visible emission. • Surface modification efficiency was decreased with reduction of the QD size • Intensified stability of the surface modified ZnO QDs was obtained from surface modification.

Excitonic behavior in self-assembled InAs/GaAs quantum rings in high magnetic fields

NARCIS (Netherlands)

Kleemans, N.A.J.M.; Blokland, J.H.; Taboada, A.G.; Genuchten, van H.C.M.; Bozkurt, M.; Fomin, V.M.; Gladilin, V.N.; Granados, D.; Garcia, J.M.; Christianen, P.C.M.; Maan, J.C.; Devreese, J.T.; Koenraad, P.M.

2009-01-01

We investigate the exciton energy level structure of a large ensemble of InAs/GaAs quantum rings by photoluminescence spectroscopy in magnetic fields up to 30 T for different excitation densities. The confinement of an electron and a hole in these type I quantum rings along with the Coulomb

InGaAs Quantum Well Grown on High-Index Surfaces for Superluminescent Diode Applications

Directory of Open Access Journals (Sweden)

Wu Jiang

2010-01-01

Full Text Available Abstract The morphological and optical properties of In0.2Ga0.8As/GaAs quantum wells grown on various substrates are investigated for possible application to superluminescent diodes. The In0.2Ga0.8As/GaAs quantum wells are grown by molecular beam epitaxy on GaAs (100, (210, (311, and (731 substrates. A broad photoluminescence emission peak (~950 nm with a full width at half maximum (FWHM of 48 nm is obtained from the sample grown on (210 substrate at room temperature, which is over four times wider than the quantum well simultaneously grown on (100 substrate. On the other hand, a very narrow photoluminescence spectrum is observed from the sample grown on (311 with FWHM = 7.8 nm. The results presented in this article demonstrate the potential of high-index GaAs substrates for superluminescent diode applications.

InGaAs/InP, quantum wells and quantum wires grown by vapor levitation epitaxy using chloride transport

International Nuclear Information System (INIS)

Cox, H.M.; Morais, P.C.; Hwang, D.M.; Bastos, P.; Gmitter, T.J.; Nazar, L.; Worlock, J.M.; Yablonovitch, E.; Hummel, S.G.

1988-09-01

A variety of InGaAs/InP quantum structures have been grown by vapor levitation epitaxy (VLE) and investigated by low temperature photoluminescence (PL). Excellent long-range uniformity of QW peak positions across a two-inch diameter wafer is achieved. Monolayer thickness variations in single QW's are used to establish an essentially unambiguous correlation of QW thickness with energy upshift for ultra-thin quantum wells. PL evidence is presented of the growth, for the first time by any technique, of an InGaAs/InP QW of single monolayer thickness (2.93 (angstrom)). Quantum wires were fabricated entirely by VLE as thin as one monolayer and estimated to be three unit cells wide. (author) [pt

High Photoluminescence Quantum Yield in Band Gap Tunable Bromide Containing Mixed Halide Perovskites

OpenAIRE

Carolin M. Sutter-Fella Yanbo Li Matin Amani Joel W. Ager III Francesca M. Toma; Eli Yablonovitch Ian D. Sharp and Ali Javey

2016-01-01

Hybrid organic–inorganic halide perovskite based semiconductor materials are attractive for use in a wide range of optoelectronic devices because they combine the advantages of suitable optoelectronic attributes and simultaneously low cost solution processability. Here we present a two step low pressure vapor assisted solution process to grow high quality homogeneous CH3NH3PbI3–xBrx perovskite films over the full band gap range of 1.6–2.3 eV. Photoluminescence light in versus light out charac...

Modulation of the photoluminescence in carbon dots through surface modification: from mechanism to white light-emitting diodes

Science.gov (United States)

Zhu, Jinyang; Shao, He; Bai, Xue; Zhai, Yue; Zhu, Yongsheng; Chen, Xu; Pan, Gencai; Dong, Biao; Xu, Lin; Zhang, Hanzhuang; Song, Hongwei

2018-06-01

Carbon dots (CDs) have emerged as a new type of fluorescent material because of their unique optical advantages, such as high photoluminescence quantum yields (QYs), excellent photo-stability, excitation-dependent emissions, and low toxicity. However, the photoluminescence mechanism for CDs remains unclear, which limits their further practical application. Here, CDs were synthesized via a solvothermal route from citric acid and urea. Through the oxidation and reduction treatment of pristine CDs, the origin of the photoluminescence and the involved mechanism were revealed. We found that the blue/green/red emissions originated from three diverse emitting states, i.e. the intrinsic state, and C=O- and C=N-related surface states, respectively. Based on the as-prepared CDs, a pH sensor depending on the radiometric luminescence detection was developed. Furthermore, we constructed CD/PVP (PVP, polyvinylpyrrolidone) composite films, which exhibited white light emission with photoluminescence QYs of 15.3%. The white light emission with different correlated color temperatures (CCTs), from 4807 K to 3319 K, was obtained by simply changing the amount of PVP solution. Benefiting from the white light-emitting solid-state films, single-component white light-emitting diodes were fabricated with an average color rendering index value (Ra) of 80.0, luminous efficiency of 10.2 lm W‑1, and good working stability, thus indicating a promising potential for practical lighting applications.

Absolute measurement of the viscosity of classical and quantum fluids by rotating-cylinder viscometers

International Nuclear Information System (INIS)

Donnelly, R.J.; LaMar, M.M.

1987-01-01

We discuss the use of rotating-cylinder viscometers to determine absolute shear viscosities of classical fluids and of helium II in the context of past and current knowledge of the stability and flow of these fluids between concentric cylinders. We identify a problem in measuring the absolute viscosity when the inner cylinder is rotating and the outer cylinder is at rest. We conclude by discussing the design of viscometers for absolute viscosity measurements in helium I and helium II

Spin interactions in InAs quantum dots and molecules

Energy Technology Data Exchange (ETDEWEB)

Doty, M.F.; Ware, M.E.; Stinaff, E.A.; Scheibner, M.; Bracker, A.S.; Ponomarev, I.V.; Badescu, S.C.; Reinecke, T.L.; Gammon, D. [Naval Research Lab, Washington, DC 20375 (United States); Korenev, V.L. [A.F. Ioffe Physical Technical Institute, St. Petersburg 194021 (Russian Federation)

2006-12-15

Spin interactions between particles in quantum dots or quantum dot molecules appear as fine structure in the photoluminescence spectra. Using the understanding of exchange interactions that has been developed from single dot spectra, we analyze the spin signatures of coupled quantum dots separated by a wide barrier such that inter-dot interactions are negligible. We find that electron-hole exchange splitting is directly evident. In dots charged with an excess hole, an effective hole-hole interaction can be turned on through tunnel coupling. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Polarisation of the spontaneous emission from nonpolar and semipolar InGaN quantum wells

Energy Technology Data Exchange (ETDEWEB)

Schade, Lukas; Schwarz, Ulrich [Department of Microsystems Engineering, University of Freiburg (IMTEK) (Germany); Fraunhofer Institute for Applied Solid State Physics (IAF) (Germany); Ploch, Simon; Wernicke, Tim [Institute of Solid State Physics, Technical University Berlin (Germany); Knauer, Arne; Hoffmann, Veit; Weyers, Markus [Ferdinand-Braun-Institute (FBH) (Germany); Kneissl, Michael [Institute of Solid State Physics, Technical University Berlin (Germany); Ferdinand-Braun-Institute (FBH) (Germany)

2011-07-01

Spontaneously emitted light stemming from semipolar and nonpolar InGaN quantum wells is polarized. This property is a consequence of the broken in-plane symmetry of non c-plane wurtzite quantum wells. We studied the polarized photoluminescence of semipolar and nonpolar InGaN/InGaN multi quantum wells grown on low defect density GaN substrates with a setup for confocal microscopy. For excitation of charge carriers we use a 375 nm diode laser. The photoluminescence is collected with an objective of small NA, to avoid polarisation scrambling, and analyzed with a broadband polarizer and a spectrometer. The experimental results are compared to k.p band structure calculations for semipolar and nonpolar InGaN quantum wells. These simulations provide the polarisation degree of the confined states of the valence band and their energetic splitting. Next, from the thermal occupation the polarized spectra are calculated. The comparison with experimental results allows the determination of the valence subband splitting. Our experiments show a splitting of the two topmost valence subbands in nonpolar direction which is larger than predicted.

Quantum phase transitions

International Nuclear Information System (INIS)

Sachdev, S.

1999-01-01

Phase transitions are normally associated with changes of temperature but a new type of transition - caused by quantum fluctuations near absolute zero - is possible, and can tell us more about the properties of a wide range of systems in condensed-matter physics. Nature abounds with phase transitions. The boiling and freezing of water are everyday examples of phase transitions, as are more exotic processes such as superconductivity and superfluidity. The universe itself is thought to have passed through several phase transitions as the high-temperature plasma formed by the big bang cooled to form the world as we know it today. Phase transitions are traditionally classified as first or second order. In first-order transitions the two phases co-exist at the transition temperature - e.g. ice and water at 0 deg., or water and steam at 100 deg. In second-order transitions the two phases do not co-exist. In the last decade, attention has focused on phase transitions that are qualitatively different from the examples noted above: these are quantum phase transitions and they occur only at the absolute zero of temperature. The transition takes place at the ''quantum critical'' value of some other parameter such as pressure, composition or magnetic field strength. A quantum phase transition takes place when co-operative ordering of the system disappears, but this loss of order is driven solely by the quantum fluctuations demanded by Heisenberg's uncertainty principle. The physical properties of these quantum fluctuations are quite distinct from those of the thermal fluctuations responsible for traditional, finite-temperature phase transitions. In particular, the quantum system is described by a complex-valued wavefunction, and the dynamics of its phase near the quantum critical point requires novel theories that have no analogue in the traditional framework of phase transitions. In this article the author describes the history of quantum phase transitions. (UK)

Photoluminescence behavior of riboflavin and lumiflavin in liquid solutions and solid films

Energy Technology Data Exchange (ETDEWEB)

Penzkofer, A., E-mail: alfons.penzkofer@physik.uni-regensburg.de [Fakultaet fuer Physik, Universitaet Regensburg, Universitaetsstrasse 31, D-93053 Regensburg (Germany)

2012-05-25

Highlights: Black-Right-Pointing-Pointer Delayed fluorescence and phosphorescence spectra of flavins in starch films measured. Black-Right-Pointing-Pointer Quantum yield of singlet-triplet intersystem determined with a new approach. Black-Right-Pointing-Pointer Theory developed for determination of luminescence quantum yields of films. Black-Right-Pointing-Pointer Delayed fluorescence and phosphorescence lifetimes of flavins in starch films measured. Black-Right-Pointing-Pointer Singlet and triplet relevant parameters of riboflavin and lumiflavin determined. - Abstract: The absorption and emission behavior of riboflavin and lumiflavin in water, tetrahydrofuran (THF), water-starch, THF-polystyrene, starch films, and polystyrene films was studied at room temperature. Absorption cross-section spectra, fluorescence quantum distributions, and fluorescence quantum yields were determined. For the starch films additionally phosphorescence and delayed fluorescence spectra as well as phosphorescence lifetimes and delayed fluorescence lifetimes were measured and their quantum yields of intersystem-crossing, intrinsic triplet-based phosphorescence quantum yields, T{sub 1}-S{sub 0} radiative lifetimes, and S{sub 0}-T{sub 1} absorption strengths were calculated. A method of absolute intrinsic luminescence quantum distribution and quantum yield determination for dye doped films on transparent plates with a fluorimeter is described.

Spectral Irradiance Calibration in the Infrared. XIV: the Absolute Calibration of 2MASS

OpenAIRE

Cohen, Martin; Wheaton, Wm. A.; Megeath, S. T.

2003-01-01

Element-by-element we have combined the optical components in the three 2MASS cameras, and incorporated detector quantum efficiency curves and site-specific atmospheric transmissions, to create three relative spectral response curves (RSRs). We provide absolute 2MASS attributes associated with "zero magnitude" in the JHKs bands so that these RSRs may be used for synthetic photometry. The RSRs tie 2MASS to the Cohen-Walker-Witteborn framework of absolute photometry and spectra for the purpose ...

Photoluminescence from Cd{sub x}Hg{sub 1-x}Te

Energy Technology Data Exchange (ETDEWEB)

Breivik, M; Selvig, E; Tonheim, C R; Brendhagen, E; Brudevoll, T; Rheenen, A D van; Steen, H; Nicolas, S; Lorentzen, T; Haakenaasen, R [Norwegian Defence Research Establishment, P O Box 25, N-2027 Kjeller (Norway)], E-mail: magnus.breivik@gmail.com

2008-03-15

We present important aspects of photoluminescence (PL) of Cd{sub x}Hg{sub 1-x}Te in the infrared part of the spectrum where background thermal radiation significantly affects the PL spectrum. We show how the background spectrum can be removed from the data. We also show how the wavelength of the excitation laser affects the relative intensity of the PL peaks from a multi-layer structure. Finally, we present temperature dependent PL of a Cd{sub 0.36}Hg{sub 0.64}Te/Cd{sub 0.61}Hg{sub 0.39}Te multiple quantum well structure grown on a 4 {mu}m thick Cd{sub 0.36}Hg{sub 0.64}Te buffer layer. We attribute the low temperature peak from the buffer layer to impurities. The impurity levels are depopulated as the temperature increases, resulting in a decreased PL peak intensity. Above {approx}200 K a band-to-band peak from the buffer layer is observed. The quantum well peak persists up to {approx}200 K.

Dark-red-emitting CdTe0.5Se0.5/Cd0.5Zn0.5S quantum dots: Effect of chemicals on properties

International Nuclear Information System (INIS)

Yang, Ping; Zhang, Aiyu; Li, Xiaoyu; Liu, Ning; Zhang, Yulan; Zhang, Ruili

2013-01-01

CdTe 0.5 Se 0.5 /Cd 0.5 Zn 0.5 S core/shell quantum dots (QDs) with a tunable photoluminescence (PL) range from yellow to dark red (up to a PL peak wavelength of 683 nm) were fabricated using various reaction systems. The core/shell QDs created in the reaction solution of trioctylamine (TOA) and oleic acid (OA) at 300 °C exhibited narrow PL spectra and a related low PL efficiency (38%). In contrast, the core/shell QDs prepared in the solution of 1-octadecene (ODE) and hexadecylamine (HDA) at 200 °C revealed a high PL efficiency (70%) and broad PL spectra. This phenomenon is ascribed that the precursor of Cd, reaction temperature, solvents, and ligands affected the formation process of the shell. The slow growth rate of the shell in the solution of ODE and HDA made QDs with a high PL efficiency. Metal acetate salts without reaction with HDA led to the core/shell QDs with a broad size distribution. - Graphical abstract: CdTe 0.5 Se 0.5 /Cd 0.5 Zn 0.5 S quantum dots (QDs) with tunable photoluminescence, high PL efficiency, and high stability through organic synthesis, in which chemicals affected the properties of the QDs. Display Omitted - Highlights: • CdTe 0.5 Se 0.5 /Cd 0.5 Zn 0.5 S quantum dots created via organic synthesis. • Chemicals affected the properties of the quantum dots. • The quantum dots revealed high photoluminescence efficiency and stability. • The quantum dots with tunable photoluminescence in a range from yellow to dark red. • The QDs are utilizable for various applications such as biological labeling

Academic Training: The World of Quantum Matter

CERN Multimedia

Françoise Benz

2006-01-01

2005-2006 ACADEMIC TRAINING PROGRAMME LECTURE SERIES 23, 24, 25, 26 January 2006 from 11:00 to 12:00 - Main Auditorium, bldg. 500 The World of Quantum Matter M. WEIDEMUELLER / Albert-Ludwigs-Universität Freiburg In my lecture series, I will present the recent spectacular advances in the field of quantum gases and macroscopic quantum physics. A variety of subjects will be covered including Bose condensates and degenerate Fermi gases, ultracold molecules and chemistry near absolute zero, Rydberg gases, single-atom manipulation, quantum information processing, as well as applications of cold atoms as precision targets. The topics of the lectures are: Physics near absolute zero Bose condensation and Fermi degeneracy Molecules, Rydberg gases and other exotic species Single-atom manipulation, quantum information processing and ultracold atoms as targets in storage rings. ENSEIGNEMENT ACADEMIQUE ACADEMIC TRAINING Françoise Benz 73127 academic.training@cern.ch If you wish to participate in one of the f...

Fabrication of GaAs quantum dots by droplet epitaxy on Si/Ge virtual substrate

International Nuclear Information System (INIS)

Bietti, S; Sanguinetti, S; Somaschini, C; Koguchi, N; Isella, G; Chrastina, D; Fedorov, A

2009-01-01

We present here the fabrication, via droplet epitaxy, of GaAs/AlGaAs quantum dots with high optical efficiency on Si. The growth substrate lattice parameter was adapted to that of (Al)GaAs via Ge virtual substrates (GeVS). The samples clearly show the presence of quantum dot self-assembly, with the designed shape and density. Photoluminescence measurements, performed at low temperature, show an intense emission band from the quantum dots.

Determination of anisotropic dipole moments in self-assembled quantum dots using Rabi oscillations

OpenAIRE

Muller, A.; Wang, Q. Q.; Bianucci, P.; Xue, Q. K.; Shih, C. K.

2004-01-01

By investigating the polarization-dependent Rabi oscillations using photoluminescence spectroscopy, we determined the respective transition dipole moments of the two excited excitonic states |Ex> and |Ey> of a single self-assembled quantum dot that are nondegenerate due to shape anisotropy. We find that the ratio of the two dipole moments is close to the physical elongation ratio of the quantum dot.

Reduced reabsorption and enhanced propagation induced by large Stokes shift in quantum dot-filled optical fiber

Energy Technology Data Exchange (ETDEWEB)

Wu, Hua; Zhang, Yu, E-mail: yuzhang@jlu.edu.cn; Lu, Min; Liu, Wenyan [Jilin University, State Key Laboratory on Integrated Optoelectronics and College of Electronic Science and Engineering (China); Xu, Jian [The Pennsylvania State University, Department of Engineering Science and Mechanics (United States); Yu, William W., E-mail: wyu6000@gmail.com [Jilin University, State Key Laboratory on Integrated Optoelectronics and College of Electronic Science and Engineering (China)

2016-07-15

With tunable emission wavelength, high photoluminescence quantum yield, and broad absorption, colloidal quantum dots are attractive for the application in optical fiber as dopants. However, most of the quantum dots have a large overlap between their absorption and photoluminescence spectra, resulting in reabsorption loss which hinders the realization of long-distance waveguides. Therefore, ZnCuInS/ZnSe/ZnS quantum dots with large Stokes shift were proposed to fabricate a liquid-core optical fiber in this work. In this work, ZnCuInS/ZnSe/ZnS QDs with an average size of 3.3 nm were synthesized and the optical properties of the QD-filled fiber were also investigated as a function of fiber length and doping concentration. Compared to the control sample filled with CdSe/CdS/ZnS quantum dots, the ZnCuInS/ZnSe/ZnS quantum dot-based waveguides showed reduced reabsorption and enhanced signal propagation, which demonstrates great potential of large Stokes-shift quantum dots in optical waveguide devices.Graphical AbstractA reduced reabsorption and enhanced propagation of ZnCuInS/ZnSe/ZnS QDs-doped liquid-core optical fiber was achieved due to the large Stokes shift.

Ligand removal and photo-activation of CsPbBr3 quantum dots for enhanced optoelectronic devices.

Science.gov (United States)

Moyen, Eric; Kanwat, Anil; Cho, Sinyoung; Jun, Haeyeon; Aad, Roy; Jang, Jin

2018-05-10

Perovskite quantum dots have recently emerged as a promising light source for optoelectronic applications. However, integrating them into devices while preserving their outstanding optical properties remains challenging. Due to their ionic nature, perovskite quantum dots are extremely sensitive and degrade on applying the simplest processes. To maintain their colloidal stability, they are surrounded by organic ligands; these prevent efficient charge carrier injection in devices and have to be removed. Here we report on a simple method, where a moderate thermal process followed by exposure to UV in air can efficiently remove ligands and increase the photo-luminescence of the room temperature synthesized perovskite quantum dot thin films. Annealing is accompanied by a red shift of the emission wavelength, usually attributed to the coalescence and irreversible degradation of the quantum dots. We show that it is actually related to the relaxation of the quantum dots upon the ligand removal, without the creation of non-radiative recombining defects. The quantum dot surface, as devoid of ligands, is subsequently photo-oxidized and smoothened upon exposure to UV in air, which drastically enhances their photo-luminescence. This adequate combination of treatments improves by more than an order of magnitude the performances of perovskite quantum dot light emitting diodes.

Electronic structure properties of the In(Ga)As/GaAs quantum dot–quantum well tunnel-injection system

International Nuclear Information System (INIS)

Sęk, Grzegorz; Andrzejewski, Janusz; Ryczko, Krzysztof; Poloczek, Przemysław; Misiewicz, Jan; Semenova, Elizaveta S; Lemaitre, Aristide; Patriarche, Gilles; Ramdane, Aberrahim

2009-01-01

We report on the electronic properties of GaAs-substrate-based structures designed as a tunnel-injection system composed of self-assembled InAs quantum dots and an In 0.3 Ga 0.7 As quantum well separated by a GaAs barrier. We have performed photoluminescence and photoreflectance measurements which have allowed the determination of the optical transitions in the QW–QD tunnel structure and its respective references with just quantum dots or a quantum well. The effective mass calculations of the band structure dependence on the tunnelling barrier thickness have shown that in spite of an expected significant tunnelling between both parts of the system, its strong asymmetry and the strain distribution cause that the quantum-mechanical-coupling-induced energy shift of the optical transitions is almost negligible for the lowest energy states and weakly sensitive to the width of the barrier, which finds confirmation in the existing experimental data

Anti-Stokes Luminescence in High Quality Quantum Wells

Science.gov (United States)

Vinattieri, A.; Bogani, F.; Miotto, A.; Ceccherini, S.

1997-11-01

We present a detailed investigation of the anti-Stokes (AS) luminescence which originates from exciton recombination when below gap excitation is used, in a set of high quality quantum well structures. We observe strong excitonic resonances in the AS signal as measured from photoluminescence and photoluminescence excitation spectra. We demonstrate that neither the electromagnetic coupling between the wells nor the morphological disorder can explain this up-conversion effect. Time-resolved luminescence data after ps excitation and fs correlation spectroscopy results provide clear evidence of the occurrence of a two-step absorption which is assisted by the exciton population resonantly excited by the first photon.

Optical anisotropy in vertically coupled quantum dots

DEFF Research Database (Denmark)

Yu, Ping; Langbein, Wolfgang Werner; Leosson, Kristjan

1999-01-01

We have studied the polarization of surface and edge-emitted photoluminescence (PL) from structures with vertically coupled In0.5Ga0.5As/GaAs quantum dots (QD's) grown by molecular beam epitaxy. The PL polarization is found to be strongly dependent on the number of stacked layers. While single...... number due to increasing dot size....

The effect of multi active junctions on broadband emission from InAs/InGaAlAs quantum-dash structure

KAUST Repository

Tan, Cheeloon; Djie, Hery Susanto; Tan, C. K.; Hongpinyo, V.; Ding, Yunhsiang; Ooi, Boon S.

2009-01-01

We demonstrate the importance of multi active layer stacking in realizing a semiconductor broadband quantum-dash-in-well laser. The photoluminescence measurements show the negligible factor of largely localized inhomogeneous quantum-dash ensembles in producing ultra-wide envelope of emission. © 2009 IEEE.

The effect of multi active junctions on broadband emission from InAs/InGaAlAs quantum-dash structure

KAUST Repository

Tan, Cheeloon

2009-10-01

We demonstrate the importance of multi active layer stacking in realizing a semiconductor broadband quantum-dash-in-well laser. The photoluminescence measurements show the negligible factor of largely localized inhomogeneous quantum-dash ensembles in producing ultra-wide envelope of emission. © 2009 IEEE.

Tuning Single Quantum Dot Emission with a Micromirror.

Science.gov (United States)

Yuan, Gangcheng; Gómez, Daniel; Kirkwood, Nicholas; Mulvaney, Paul

2018-02-14

The photoluminescence of single quantum dots fluctuates between bright (on) and dark (off) states, also termed fluorescence intermittency or blinking. This blinking limits the performance of quantum dot-based devices such as light-emitting diodes and solar cells. However, the origins of the blinking remain unresolved. Here, we use a movable gold micromirror to determine both the quantum yield of the bright state and the orientation of the excited state dipole of single quantum dots. We observe that the quantum yield of the bright state is close to unity for these single QDs. Furthermore, we also study the effect of a micromirror on blinking, and then evaluate excitation efficiency, biexciton quantum yield, and detection efficiency. The mirror does not modify the off-time statistics, but it does change the density of optical states available to the quantum dot and hence the on times. The duration of the on times can be lengthened due to an increase in the radiative recombination rate.

Fluorescent porous silicon biological probes with high quantum efficiency and stability.

Science.gov (United States)

Tu, Chang-Ching; Chou, Ying-Nien; Hung, Hsiang-Chieh; Wu, Jingda; Jiang, Shaoyi; Lin, Lih Y

2014-12-01

We demonstrate porous silicon biological probes as a stable and non-toxic alternative to organic dyes or cadmium-containing quantum dots for imaging and sensing applications. The fluorescent silicon quantum dots which are embedded on the porous silicon surface are passivated with carboxyl-terminated ligands through stable Si-C covalent bonds. The porous silicon bio-probes have shown photoluminescence quantum yield around 50% under near-UV excitation, with high photochemical and thermal stability. The bio-probes can be efficiently conjugated with antibodies, which is confirmed by a standard enzyme-linked immunosorbent assay (ELISA) method.

Absolute quantum yield measurements for the formation of oxygen ...

Indian Academy of Sciences (India)

Unknown

Abstract. The dynamics of formation of oxygen atoms after UV photoexcitation of .... The SO2 pressure in the cell was typically 30–55 mTorr (monitored by an MKS .... With this value the quantum yield for O(3P) formation could be calculated to.

Combined experimental and theoretical investigations of the photoluminescent behavior of Ba(Ti, Zr)O3 thin films

International Nuclear Information System (INIS)

Cavalcante, L.S.; Gurgel, M.F.C.; Paris, E.C.; Simoes, A.Z.; Joya, M.R.; Varela, J.A.; Pizani, P.S.; Longo, E.

2007-01-01

The correlation between experimental data and theoretical calculations have been investigated to explain the photoluminescence at room temperature of Ba(Ti 0.75 Zr 0.25 )O 3 (BTZ) thin films prepared by the polymeric precursor method. The degree of structural order-disorder was investigated by X-ray diffraction, Fourier transform infrared spectroscopy, ultraviolet-visible absorption spectroscopy and photoluminescence (PL) measurements. First-principles quantum mechanical calculations based on density functional theory (B3LYP level) were employed to study the electronic structure of ordered and deformed asymmetric models. The electronic properties are analyzed and the relevance of the present theoretical and experimental results on the PL behavior is discussed. The presence of localized electronic levels and a charge gradient in the band gap due to a break in symmetry, are responsible for the PL in disordered BTZ lattice

Controlled fabrication and tunable photoluminescence properties of Mn2+ doped graphene–ZnO composite

International Nuclear Information System (INIS)

Luan, Xinglong; Zhang, Yihe; Tong, Wangshu; Shang, Jiwu; An, Qi; Huang, Hongwei

2014-01-01

Highlights: • Graphene–ZnO composites were synthesized by a mixed solvothermal method. • ZnO quantum dots are distributed uniformly on the graphene sheets. • A possible hypothesis is raised for the influence of graphene oxide on the nucleation of ZnO. • Mn 2+ doped graphene–ZnO composites were fabricated and the emission spectra can be tuned by doping. - Abstract: Graphene–ZnO composites (G–ZnO) with controlled morphology and photoluminescence property were synthesized by a mixed solvothermal method. Mixed solvent were composed by dimethyl sulfoxide and ethylene glycol. Fourier transform infrared spectroscopy, transmission electron microscopy and photoluminescence spectra were used to characterize G–ZnO. Graphene as a substrate can help the distribution and the dispersity of ZnO, and a possible model of the interaction between graphene oxide and ZnO particles is proposed. At the same time, graphene also reduce the size of ZnO particles to about 5 nm. Furthermore, Mn 2+ ions dopes G–ZnO successfully by the mixed solvothermal synthesis and the doping of Mn 2+ makes G–ZnO shift red from 465 nm to 548 nm and 554 nm in the emission spectrum. The changes of the emission spectrum by the adding of Mn 2+ make G–ZnO have tunable photoluminescence spectrum which is desirable for practical applications

Photoluminescence of nanocrystals embedded in oxide matrices

International Nuclear Information System (INIS)

Estrada, C.; Gonzalez, J.A.; Kunold, A.; Reyes-Esqueda, J.A.; Pereyra, P.

2006-12-01

We used the theory of finite periodic systems to explain the photoluminescence spectra dependence on the average diameter of nanocrystals embedded in oxide matrices. Because of the broad matrix band gap, the photoluminescence response is basically determined by isolated nanocrystals and sequences of a few of them. With this model we were able to reproduce the shape and displacement of the experimentally observed photoluminescence spectra. (author)

The influence of bio-conjugation on photoluminescence of CdSe/ZnS quantum dots

Energy Technology Data Exchange (ETDEWEB)

Torchynska, Tetyana V. [ESFM Instituto Politécnico Nacional, Av. Instituto Politécnico Nacional, México, D.F. 07738 (Mexico); Vorobiev, Yuri V. [Centro de Investigación y de Estudios Avanzados del IPN (CINVESTAV) Querétaro, Libramiento Norponiente 2000, Fracc. Real de Juriquilla, 76230 Querétaro (Mexico); Makhniy, Victor P. [Yuri Fedkovych Chernivtsi National University, 2 Kotsyubynsky Str., 58012 Chernivtsi (Ukraine); Horley, Paul P., E-mail: paul.horley@cimav.edu.mx [Centro de Investigación en Materiales Avanzados, S.C. (CIMAV), Chihuahua/Monterrey, 120 Avenida Miguel de Cervantes, 31109 Chihuahua (Mexico)

2014-11-15

We report a considerable blue shift in the luminescence spectra of CdSe/ZnS quantum dots conjugated to anti-interleukin-10 antibodies. This phenomenon can be explained theoretically by accounting for bio-conjugation as a process causing electrostatic interaction between a quantum dot and an antibody, which reduces effective volume of the dot core. To solve the Schrödinger equation for an exciton confined in the quantum dot, we use mirror boundary conditions that were successfully tested for different geometries of quantum wells.

Red to green emitters from InGaP/InAlGaP laser structure by strain-induced quantum-well intermixing

KAUST Repository

Al-Jabr, Ahmad; Majid, Mohammed Abdul; Shen, Chao; Ng, Tien Khee; Ooi, Boon S.

2016-01-01

We increased the Al content in the single quantum well InGaP/InAlGaP laser by strain-induced quantum well intermixing, and obtained a considerable enhancement (close to ten-fold increase) in the photoluminescence (PL) intensity. Among the annealing

Blue and green electroluminescence from CdSe nanocrystal quantum-dot-quantum-wells

International Nuclear Information System (INIS)

Lu, Y. F.; Cao, X. A.

2014-01-01

CdS/CdSe/ZnS quantum dot quantum well (QDQW) nanocrystals were synthesized using the successive ion layer adsorption and reaction technique, and their optical properties were tuned by bandgap and strain engineering. 3-monolayer (ML) CdSe QWs emitted blue photoluminescence at 467 nm with a spectral full-width-at-half-maximum of ∼30 nm. With a 3 ML ZnS cladding layer, which also acts as a passivating and strain-compensating layer, the QDQWs acquired a ∼35% quantum yield of the QW emission. Blue and green electroluminescence (EL) was obtained from QDQW light-emitting devices with 3–4.5 ML CdSe QWs. It was found that as the peak blueshifted, the overall EL was increasingly dominated by defect state emission due to poor hole injection into the QDQWs. The weak EL was also attributed to strong field-induced charge separation resulting from the unique QDQW geometry, weakening the oscillator strength of optical transitions

Electronic band structure in porous silicon studied by photoluminescence and photoluminescence excitation spectroscopy

International Nuclear Information System (INIS)

Lee, Ki-Won; Kim, Young-You

2004-01-01

In this research, we used photoluminescence (PL) and photoluminescence excitation (PLE) to visualize the electronic band structure in porous silicon (PS). From the combined results of the PLE measurements at various PL emission energies and the PL measurements under excitation at various PLE absorption energies, we infer that three different electronic band structures, originating from different luminescent origins, give rise to the PL spectrum. Through either thermal activation or diffusive transfer, excited carriers are moved to each of the electronic band structures.

Photoluminescence and Photoconductivity to Assess Maximum Open-Circuit Voltage and Carrier Transport in Hybrid Perovskites and Other Photovoltaic Materials.

Science.gov (United States)

Braly, Ian L; Stoddard, Ryan J; Rajagopal, Adharsh; Jen, Alex K-Y; Hillhouse, Hugh W

2018-06-06

Photovoltaic (PV) device development is much more expensive and time consuming than the development of the absorber layer alone. This perspective focuses on two methods that can be used to rapidly assess and develop PV absorber materials independent of device development. The absorber material properties of quasi-Fermi level splitting and carrier diffusion length under steady effective one-Sun illumination are indicators of a material's ability to achieve high VOC and JSC. These two material properties can be rapidly and simultaneously assessed with steady-state absolute intensity photoluminescence and photoconductivity measurements. As a result, these methods are extremely useful for predicting the quality and stability of PV materials prior to PV device development. Here, we summarize the methods, discuss their strengths and weaknesses, and compare photoluminescence and photoconductivity results with device performance for four hybrid perovskite compositions of various bandgaps (1.35 to 1.82 eV), CISe, CIGSe, and CZTSe.

Inter-Layer Energy Transfer through Wetting-Layer States in Bi-layer InGaAs/GaAs Quantum-Dot Structures with Thick Barriers

DEFF Research Database (Denmark)

Xu, Zhang-Cheng; Zhang, Ya-Ting; Hvam, Jørn Märcher

2009-01-01

The inter-layer energy transfer in a bi-layer InGaAs/GaAs quantum dot structure with a thick GaAs barrier is studied using temperature-dependent photoluminescence. The abnormal enhancement of the photoluminescence of the QDs in the layer with a larger amount of coverage at 110K is observed, which...

Localized surface plasmon resonance enhanced photoluminescence of CdSe QDs in PMMA matrix on silver colloids with different shapes

International Nuclear Information System (INIS)

Lu Liu; Xu Xiaoliang; Shi Chaoshu; Ming Hai

2010-01-01

Localized surface plasmon resonance (LSPR) enhanced photoluminescences (PL) from CdSe quantum dots (QDs) on worm-like or quasi-spherical silver colloids have been investigated. The shape of silver colloid film is controlled by annealing temperature (200 o C∼350 o C). Strong PL enhancements of CdSe QDs on both as-grown and annealed silver colloid films are observed. The results show that the PL enhancement factor of CdSe QDs on worm-like silver colloid film reaches as high as 15-fold. Moreover, the enhancement factor is 5 times larger than that obtained from the quasi-spherical silver colloids. The superiority of worm-like silver nanostructure on LSPR enhanced photoluminescence is attributed to its larger size, hot spots and multiple dipole resonance modes coupling, which are induced by aggregation effect.

Transparently wrap-gated semiconductor nanowire arrays for studies of gate-controlled photoluminescence

Energy Technology Data Exchange (ETDEWEB)

Nylund, Gustav; Storm, Kristian; Torstensson, Henrik; Wallentin, Jesper; Borgström, Magnus T.; Hessman, Dan; Samuelson, Lars [Solid State Physics, Nanometer Structure Consortium, Lund University, Box 118, S-221 00 Lund (Sweden)

2013-12-04

We present a technique to measure gate-controlled photoluminescence (PL) on arrays of semiconductor nanowire (NW) capacitors using a transparent film of Indium-Tin-Oxide (ITO) wrapping around the nanowires as the gate electrode. By tuning the wrap-gate voltage, it is possible to increase the PL peak intensity of an array of undoped InP NWs by more than an order of magnitude. The fine structure of the PL spectrum reveals three subpeaks whose relative peak intensities change with gate voltage. We interpret this as gate-controlled state-filling of luminescing quantum dot segments formed by zincblende stacking faults in the mainly wurtzite NW crystal structure.

Control of dynamic properties of InAs/InAlGaAs/InP hybrid quantum well-quantum dot structures designed as active parts of 1.55 μm emitting lasers

Energy Technology Data Exchange (ETDEWEB)

Rudno-Rudzinski, Wojciech; Syperek, Marcin; Marynski, Aleksander; Andrzejewski, Janusz; Misiewicz, Jan; Sek, Grzegorz [Faculty of Fundamental Problems of Technology, Department of Experimental Physics, Wroclaw University of Science and Technology, Wroclaw (Poland); Bauer, Sven; Sichkovskyi, Vitalii I.; Reithmaier, Johann P. [Institute of Nanostructure Technology and Analytics, CINSaT, University of Kassel (Germany); Schowalter, Marco; Gerken, Beeke; Rosenauer, Andreas [Institute of Solid State Physics, Universitaet Bremen (Germany)

2018-02-15

The molecular beam epitaxy grown structures are investigated, comprising of InGaAs quantum wells (QW) separated by a thin InGaAlAs barrier from InAs quantum dots (QDs), emitting at 1.55 μm, grown on an InP substrate. To control the coupling between QW and QD parts the thickness of the barrier is changed, which commands the wave function overlap. The tuning of that parameter allows for the study of the influence of the QW potential on the energy structure of states and their wave functions in QDs, changing from an uncoupled system, where the optical response is just a sum of responses from two isolated elements, to a strongly quantum mechanically coupled system, exhibiting mixed 2D-0D characteristics. The changes of the energy structure that are deduced from the photoreflectance and photoluminescence spectroscopy results, supported by 8-band k . p modeling, explain the measured differences in the photoluminescence decay times between samples with different barrier thicknesses. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Growth patterns of self-assembled InAs quantum dots near the two-dimensional to three-dimensional transition

Science.gov (United States)

Colocci, M.; Bogani, F.; Carraresi, L.; Mattolini, R.; Bosacchi, A.; Franchi, S.; Frigeri, P.; Rosa-Clot, M.; Taddei, S.

1997-06-01

Self-assembled InAs quantum dots have been grown by molecular beam epitaxy in such a way as to obtain a continuous variation of InAs coverages across the wafer. Structured photoluminescence spectra are observed after excitation of a large number of dots; deconvolution into Gaussian components yields narrow emission bands (full width at half-maximum 20-30 meV) separated in energy by an average spacing of 30-40 meV. We ascribe the individual bands of the photoluminescence spectra after low excitation to families of dots with similar shapes and with heights differing by one monolayer, as strongly supported by numerical calculations of the fundamental electronic transitions in quantum dot structures.

Carrier dynamics in InAs quantum dots embedded in InGaAs/GaAs multi quantum well structures

International Nuclear Information System (INIS)

Espinola, J L Casas; Dybic, M; Ostapenko, S; Torchynska, T V; Polupan, G

2007-01-01

Ground and multi excited state photoluminescence, as well as its temperature dependence, in InAs quantum dots embedded in symmetric In x Ga 1-x As/GaAs (x = 0.15) quantum wells (DWELL) have been investigated. The solution of the set of rate equations for exciton dynamics (relaxation into QWs or QDs and thermal escape) solved by us earlier is used for analysis the variety of thermal activation energies of photoluminescence thermal quenching for ground and multi excited states of InAs QDs. The obtained solutions were used at the discussion of the variety of activation energies of PL thermal quenching in InAs QDs. It is revealed three different regimes of thermally activated quenching of the QD PL intensity. These three regimes were attributed to thermal escape of excitons: i) from the high energy excited states of InAs QDs into the WL with follows exciton re-localization; ii) from the In x Ga 1-x As QWs into the GaAs barrier and iii) from the WL into the GaAs barrier with their subsequent nonradiative recombination in GaAs barrier

Increasing the quantum efficiency of GaAs solar cells by embedding InAs quantum dots

Science.gov (United States)

Salii, R. A.; Mintairov, S. A.; Nadtochiy, A. M.; Payusov, A. S.; Brunkov, P. N.; Shvarts, M. Z.; Kalyuzhnyy, N. A.

2016-11-01

Development of Metalorganic Vapor Phase Epitaxy (MOVPE) technology of InAs quantum dots (QDs) in GaAs for photovoltaic applications is presented. The growth peculiarities in InAs-GaAs lattice-mismatched system were considered. The photoluminescence (PL) intensity dependences on different growth parameters were obtained. The multimodal distribution of QDs by sizes was found using AFM and PL methods. GaAs solar cell nanoheterostructures with imbedded QD arrays were designed and obtained. Ones have been demonstrated a significant increase of quantum efficiency and photogenerated current of QD solar cells due to photo effect in InAs QD array (0.59 mA/cm2 for AM1.5D and 82 mA/cm2 for AM0).

Quantum efficiency of InAs/InP nanowire heterostructures grown on silicon substrates

International Nuclear Information System (INIS)

Anufriev, Roman; Chauvin, Nicolas; Bru-Chevallier, Catherine; Khmissi, Hammadi; Naji, Khalid; Gendry, Michel; Patriarche, Gilles

2013-01-01

Photoluminescence (PL) quantum efficiency (QE) is experimentally investigated, using an integrating sphere, as a function of excitation power on both InAs/InP quantum rod nanowires (QRod-NWs) and radial quantum well nanowires (QWell-NWs) grown on silicon substrates. The measured values of the QE are compared with those of the planar analogues such as quantum dash and quantum well samples, and found to be comparable for the quantum well structures at relatively low power density. Further studies reveal that the values of QE of the QRod-NWs and QWell-NWs are limited by the low quality of the InP NW structure and the quality of radial quantum well, respectively. (copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Deterministic self-organization: Ordered positioning of InAs quantum dots by self-organized anisotropic strain engineering on patterned GaAs(311)B

International Nuclear Information System (INIS)

Selcuk, E.; Hamhuis, G.J.; Noetzel, R.

2009-01-01

Laterally ordered InGaAs quantum dot (QD) arrays, InAs QD molecules, and single InAs QDs in a spot-like periodic arrangement are created by self-organized anisotropic strain engineering of InGaAs/GaAs superlattice (SL) templates on planar GaAs (311)B substrates in molecular beam epitaxy. On shallow- and deep-patterned substrates the respectively generated steps and facets guide the self-organization process during SL template formation to create more complex ordering such as periodic stripes, depending on pattern design. Here we demonstrate for patterns such as shallow- and deepetched round holes and deep-etched zigzag mesas that the self-organized periodic arrangement of QD molecules and single QDs is spatially locked to the pattern sidewalls and corners. This extends the concept of guided self-organization to deterministic self-organization. Absolute position control of the QDs is achieved without one-to-one pattern definition. This guarantees the excellent arrangement control of the ordered QD molecules and single QDs with strong photoluminescence emission up to room temperature, which is required for future quantum functional devices. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Synthesis and Adsorption Study of BSA Surface Imprinted Polymer on CdS Quantum Dots

Science.gov (United States)

Tang, Ping-ping; Cai, Ji-bao; Su, Qing-de

2010-04-01

A new bovine serum albumin (BSA) surface imprinting method was developed by the incorporation of quantum dots (QDs) into molecularly imprinted polymers (MIP), which can offer shape selectivity. Preparation and adsorption conditions were optimized. Physical appearance of the QDs and QDs-MIP particles was illustrated by scanning electron microscope images. Photoluminescence emission of CdS was quenched when rebinding of the template. The quenching of photoluminescence emissions is presumably due to the fluorescence resonance energy transfer between quantum dots and BSA template molecules. The adsorption is compiled with Langmuir isotherm, and chemical adsorption is the rate-controlling step. The maximum adsorption capacity could reach 226.0 mg/g, which is 142.4 mg/g larger than that of undoped BSA MIP. This study demonstrates the validity of QDs coupled with MIP technology for analyzing BSA.

Stokes and anti-Stokes photoluminescence towards five different In-x(Al0.17Ga0.83)(1-x)As/Al0.17Ga0.83As quantum wells

DEFF Research Database (Denmark)

Machida, S.; Tadakuma, T.; Satake, A.

2005-01-01

Stokes and anti-Stokes photoluminescence (AS-PL) has been investigated in a step-graded Inx(Al0.17Ga0.83)1–xAs/Al0.17Ga0.83As quantum-well (QW) heterostructure consisting of five QWs with different x values. Stokes PL spectra of this sample show a significant difference in PL intensity between...... the wells under indirect excitation conditions due to the existence of competitive resonant and nonresonant capture processes, while they exhibit a rather uniform PL intensity distribution under direct excitation. When the excitation wavelength is tuned to 810 nm for AS-PL detection, it is transparent...... is basically determined by the competitive capture of photoexcited carriers through the thick barriers, generated far from the five wells due to the nonlinear excitation processes in GaAs. ©2005 American Institute of Physics...

Influence of the GaN spacer thickness on the structural and photoluminescence properties of multi-stack InN/GaN quantum dots

International Nuclear Information System (INIS)

Ke, Wen-Cheng; Lee, Shuo-Jen; Chen, Shiow-Long; Kao, Chia-Yu; Houng, Wei-Chung; Wei, Chih-An; Su, Yi-Ru

2012-01-01

Highlights: ► We present structural and photoluminescence characteristics of multi-stack InN/GaN QDs. ► A single crystalline 10-nm thick GaN capping layer is grown on the InN QDs. ► The PL intensity of the three-layer stacked sample is about 3 times that of the single-layer sample. - Abstract: This paper reports the structural and photoluminescence (PL) characteristics of single-layer and multi-stack InN/GaN quantum dots (QDs) with varying spacer thickness. A single crystalline 10-nm thick GaN capping layer is grown on the InN QDs by the flow-rate modulation epitaxy (FME) method. The PL peak is red shifted down to 18 meV and its full width at half maximum (FWHM) was narrowed from 104 meV to 77 meV as increasing GaN capping layer thickness to 20-nm. The red-shift and the linewidth narrowing of the PL spectra for the single-layer InN QDs as a result of the increase in capping thickness are believed to be due to the fact that the GaN capping layer decreases the surface defect density thereby decreasing the surface electron concentration of the InN QDs. However, the PL intensity decreases rapidly with the increase in GaN spacer thickness for the three-layer stacked InN/GaN QDs. Because of kinetic roughening, the 20-nm thick GaN capping layer shows a roughened surface. This roughened GaN capping layer degrades the InN QDs growth in the next layer of multi-stack InN QDs. In addition, the increased compressive strain on the InN QDs with the increase in GaN spacer thickness increases the defect density at the InN/GaN capped interface and will further decrease the PL intensity. After the GaN spacer thickness is modified, the PL intensity of the three-layer stacked sample with a 10-nm thick GaN spacer layer is about 3 times that of the single-layer sample.

Influence of image charge effect on exciton fine structure in an organic-inorganic quantum well material

Energy Technology Data Exchange (ETDEWEB)

Takagi, Hidetsugu; Kunugita, Hideyuki; Ema, Kazuhiro [Department of Physics, Sophia University, 7-1 Kioi-cho, Chiyoda-ku, Tokyo 102-8554 (Japan); Sato, Mikio; Takeoka, Yuko [Department of Materials and Life Sciences, Sophia University, 7-1 Kioi-cho, Chiyoda-ku, Tokyo 102-8554 (Japan)

2013-12-04

We have investigated experimentally excitonic properties in organic-inorganic hybrid multi quantum well crystals, (C{sub 4}H{sub 9}NH{sub 3}){sub 2}PbBr{sub 4} and (C{sub 6}H{sub 5}−C{sub 2}H{sub 4}NH{sub 3}){sub 2}PbBr{sub 4}, by measuring photoluminescence, reflectance, photoluminescence excitation spectra. In these materials, the excitonic binding energies are enhanced not only by quantum confinement effect (QCE) but also by image charge effect (ICE), since the dielectric constant of the barrier layers is much smaller than that of the well layers. By comparing the 1s-exciton and 2s-exciton energies, we have investigated the influence of ICE with regard to the difference of the Bohr radius.

Dynamic Dipole-Dipole Interactions between Excitons in Quantum Dots of Different Sizes

DEFF Research Database (Denmark)

Matsueda, Hideaki; Leosson, Kristjan; Xu, Zhangcheng

2005-01-01

Micro-photoluminescence spectra of GaAs/AlGaAs coupled quantum dots (QDs) are given, and proposed to be analyzed by our resonance dynamic dipole-dipole interaction (RDDDI) model, based on parity inheritance and exchange of virtual photons among QDs of different sizes....

Spin effects in InAs self-assembled quantum dots

Directory of Open Access Journals (Sweden)

Brasil Maria

2011-01-01

Full Text Available Abstract We have studied the polarized resolved photoluminescence in an n-type resonant tunneling diode (RTD of GaAs/AlGaAs which incorporates a layer of InAs self-assembled quantum dots (QDs in the center of a GaAs quantum well (QW. We have observed that the QD circular polarization degree depends on applied voltage and light intensity. Our results are explained in terms of the tunneling of minority carriers into the QW, carrier capture by InAs QDs and bias-controlled density of holes in the QW.

Origin of low quantum efficiency of photoluminescence of InP/ZnS nanocrystals

DEFF Research Database (Denmark)

Shirazi, Roza; Kovacs, Andras; Corell, Dennis Dan

2013-01-01

In this paper, we study the origin of a strong wavelength dependence of the quantum efficiency of InP/ZnS nanocrystals. We find that while the average size of the nanocrystals increased by 50%, resulting in longer emission wavelength, the quantum efficiency drops more than one order of magnitude...

Electronic properties of excited states in single InAs quantum dots; Elektronische Struktur angeregter Zustaende einzelner InAs-Quantenpunkte

Energy Technology Data Exchange (ETDEWEB)

Warming, Till

2009-02-20

The application of quantum-mechanical effects in semiconductor nanostructures enables the realization of novel opto-electronic devices. Examples are given by single-photon emitters and emitters of entangled photon pairs, both being essential for quantum cryptography, or for qubit systems as needed for quantum computing. InAs/GaAs quantum dots are one of the most promising candidates for such applications. A detailed knowledge of the electronic properties of quantum dots is a prerequisite for this development. The aim of this work is an experimental access to the detailed electronic structure of the excited states in single InAs/GaAs quantum dots including few-particle effects and in particular exchange interaction. The experimental approach is micro photoluminescence excitation spectroscopy ({mu}PLE). One of the main difficulties using {mu}PLE to probe single QDs is the unambiguous assignment of the observed resonances in the spectrum to specific transitions. By comparing micro photoluminescence ({mu}PL) and {mu}PLE spectra, the identification of the main resonances becomes possible. The key is given by the fine structure of the hot trion. Excitation spectroscopy on single charged QDs enables for the first time the complete observation of a non-trivial fine structure of an excitonic complex in a QD, the hot trion. Modelling based on eight-band k.p theory in combination with a configuration interaction scheme is in excellent agreement. Therewith the simulation also enables realistic predictions on the fine structure of the ground-state exciton which is of large importance for single quantum dot devices. Theory concludes from the observed transitions that the structural symmetry of the QDs is broken. Micro photoluminescence excitation spectroscopy combined with resonantly excited micro photoluminescence enables an optical access to the single particle states of the hole without the influence of few-particle coulomb interactions. Based on this knowledge the exciton

Tuning the Emission Energy of Chemically Doped Graphene Quantum Dots

Directory of Open Access Journals (Sweden)

Noor-Ul-Ain

2016-11-01

Full Text Available Tuning the emission energy of graphene quantum dots (GQDs and understanding the reason of tunability is essential for the GOD function in optoelectronic devices. Besides material-based challenges, the way to realize chemical doping and band gap tuning also pose a serious challenge. In this study, we tuned the emission energy of GQDs by substitutional doping using chlorine, nitrogen, boron, sodium, and potassium dopants in solution form. Photoluminescence data obtained from (Cl- and N-doped GQDs and (B-, Na-, and K-doped GQDs, respectively exhibited red- and blue-shift with respect to the photoluminescence of the undoped GQDs. X-ray photoemission spectroscopy (XPS revealed that oxygen functional groups were attached to GQDs. We qualitatively correlate red-shift of the photoluminescence with the oxygen functional groups using literature references which demonstrates that more oxygen containing groups leads to the formation of more defect states and is the reason of observed red-shift of luminescence in GQDs. Further on, time resolved photoluminescence measurements of Cl- and N-GQDs demonstrated that Cl substitution in GQDs has effective role in radiative transition whereas in N-GQDs leads to photoluminescence (PL quenching with non-radiative transition to ground state. Presumably oxidation or reduction processes cause a change of effective size and the bandgap.

Spotlighting quantum critical points via quantum correlations at finite temperatures

International Nuclear Information System (INIS)

Werlang, T.; Ribeiro, G. A. P.; Rigolin, Gustavo

2011-01-01

We extend the program initiated by T. Werlang et al. [Phys. Rev. Lett. 105, 095702 (2010)] in several directions. Firstly, we investigate how useful quantum correlations, such as entanglement and quantum discord, are in the detection of critical points of quantum phase transitions when the system is at finite temperatures. For that purpose we study several thermalized spin models in the thermodynamic limit, namely, the XXZ model, the XY model, and the Ising model, all of which with an external magnetic field. We compare the ability of quantum discord, entanglement, and some thermodynamic quantities to spotlight the quantum critical points for several different temperatures. Secondly, for some models we go beyond nearest neighbors and also study the behavior of entanglement and quantum discord for second nearest neighbors around the critical point at finite temperature. Finally, we furnish a more quantitative description of how good all these quantities are in spotlighting critical points of quantum phase transitions at finite T, bridging the gap between experimental data and those theoretical descriptions solely based on the unattainable absolute zero assumption.

The Over-Barrier Resonant States and Multi-Channel Scattering in Multiple Quantum Wells

Directory of Open Access Journals (Sweden)

A Polupanov

2016-09-01

Full Text Available We demonstrate an explicit numerical method for accurate calculation of the scattering matrix and its poles, and apply this method to describe the multi-channel scattering in the multiple quantum-wells structures. The S-matrix is continued analytically to the unphysical region of complex energy values. Results of calculations show that there exist one or more S-matrix poles, corresponding to the over-barrier resonant states critical for the effect of the absolute reflection of holes in the energy range where only the heavy ones may propagate over barriers in a structure. Light- and heavy-hole states are described by the Luttinger Hamiltonian matrix. In contrast to the single quantum-well case, at some parameters of a multiple quantum-wells structure the number of S-matrix poles may exceed that of the absolute reflection peaks, and at different values of parameters the absolute reflection peak corresponds to different resonant states. The imaginary parts of the S-matrix poles and hence the lifetimes of resonant states as well as the widths of resonant peaks of absolute reflection depend drastically on the quantum-well potential depth. In the case of shallow quantum wells there is in fact a long-living over-barrier resonant hole state.

Femtosecond upconverted photocurrent spectroscopy of InAs quantum nanostructures

Energy Technology Data Exchange (ETDEWEB)

Yamada, Yasuhiro [Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011 (Japan); Tex, David M.; Kanemitsu, Yoshihiko, E-mail: kanemitu@scl.kyoto-u.ac.jp [Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011 (Japan); Japan Science and Technology Agency, CREST, Kyoto University, Uji, Kyoto 611-0011 (Japan); Kamiya, Itaru [Toyota Technological Institute, Nagoya, Aichi 468-8511 (Japan)

2015-07-06

The carrier upconversion dynamics in InAs quantum nanostructures are studied for intermediate-band solar-cell applications via ultrafast photoluminescence and photocurrent (PC) spectroscopy based on femtosecond excitation correlation (FEC) techniques. Strong upconverted PC-FEC signals are observed under resonant excitation of quantum well islands (QWIs), which are a few monolayer-thick InAs quantum nanostructures. The PC-FEC signal typically decays within a few hundred picoseconds at room temperature, which corresponds to the carrier lifetime in QWIs. The photoexcited electron and hole lifetimes in InAs QWIs are evaluated as functions of temperature and laser fluence. Our results provide solid evidence for electron–hole–hole Auger process, dominating the carrier upconversion in InAs QWIs at room temperature.

Correlation of electrical conductivity and photoluminescence in nanoporous silicon

International Nuclear Information System (INIS)

Bouaicha, M.; Khardani, M.; Bessais, B.

2006-01-01

The effective electrical conductivity of p type porous silicon is determined both theoretically and experimentally for different porosities ranging from 30% to 80%. In this work, Effective Medium Approximation (EMA) model was used as a theoretical support. The porous silicon samples were prepared by the electrochemical etching method for different values of the anodic current. The porous material is assumed to be formed of three phases; vacuum, oxide and Si nanocrystallites. The analytical expression of the electrical conductivity of the Si nanocrystallites was established using the quantum confinement theory. This enables us to correlate the electrical conductivity of a PS layer, to the peak energy of its photoluminescence (PL) spectrum. A perfect agreement between the theoretical and the experimental electrical conductivity values was obtained for all prospected PS porosities. The results are discussed as regard to other works

Photo-Induced Spin Dynamics in Semiconductor Quantum Wells.

Science.gov (United States)

Miah, M Idrish

2009-01-17

We experimentally investigate the dynamics of spins in GaAs quantum wells under applied electric bias by photoluminescence (PL) measurements excited with circularly polarized light. The bias-dependent circular polarization of PL (P(PL)) with and without magnetic field is studied. The P(PL) without magnetic field is found to be decayed with an enhancement of increasing the strength of the negative bias. However, P(PL) in a transverse magnetic field shows oscillations under an electric bias, indicating that the precession of electron spin occurs in quantum wells. The results are discussed based on the electron-hole exchange interaction in the electric field.

Hydrostatic pressure effects on the state density and optical transitions in quantum dots

International Nuclear Information System (INIS)

Galindez-Ramirez, G; Perez-Merchancano, S T; Paredes Gutierrez, H; Gonzalez, J D

2010-01-01

Using the effective mass approximation and variational method we have computed the effects of hydrostatic pressure on the absorption and photoluminescence spectra in spherical quantum dot GaAs-(Ga, Al) As, considering a finite confinement potential of this particular work we show the optical transitions in quantum of various sizes in the presence of hydrogenic impurities and hydrostatic pressure effects. Our first result describes the spectrum of optical absorption of 500 A QD for different values of hydrostatic pressure P = 0, 20 and 40 Kbar. The absorption peaks are sensitive to the displacement of the impurity center to the edge of the quantum dot and even more when the hydrostatic pressure changes in both cases showing that to the extent that these two effects are stronger quantum dots respond more efficiently. Also this result can be seen in the study of the photoluminescence spectrum as in the case of acceptor impurities consider them more efficiently capture carriers or electrons that pass from the conduction band to the valence band. Density states with randomly distributed impurity show that the additional peaks in the curves of the density of impurity states appear due to the presence of the additional hydrostatic pressure effects.

A Comparison of the recombination efficiency in green-emitting InGaN quantum dots and quantum wells

International Nuclear Information System (INIS)

Park, Il-Kyu; Kwon, Min-Ki; Park, Seong-Ju

2012-01-01

A comparative investigation of the recombination efficiency of green-emitting InGaN quantum dots (QDs) and quantum wells (QWs) is reported in this paper. Optical investigations using temperature dependent photoluminescence (PL) results showed that the internal quantum efficiency of InGaN QDs at room temperature was 8.7 times larger than that found for InGaN QWs because they provided dislocation-free recombination sites for the electrical charge carriers. The excitation power-dependent PL and electroluminescence results showed that the effect of the polarization induced electric field on the recombination process of electrical charge carriers in the QDs was negligibly small whereas it was dominant in the QWs. These results indicate that InGaN QDs are more beneficial than QWs in improving the luminescence efficiency of LEDs in the green spectral range.

Photoluminescence enhancement of porous silicon particles by microwave-assisted activation

Energy Technology Data Exchange (ETDEWEB)

Xia, Bing [Key Laboratory of Forest Genetics and Biotechnology (Ministry of Education of China), Nanjing Forestry University, Nanjing 210037 (China); Advanced Analysis and Testing Center, Nanjing Forestry University, Nanjing 210037 (China); Zhang, Wenyi; Dong, Chen; Shi, Jisen [Key Laboratory of Forest Genetics and Biotechnology (Ministry of Education of China), Nanjing Forestry University, Nanjing 210037 (China); Bao, Weiyi [Advanced Analysis and Testing Center, Nanjing Forestry University, Nanjing 210037 (China); Zhang, Junfeng [State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing 210093 (China)

2012-11-15

Photoluminescence (PL) of porous silicon (PSi) particles can be significantly enhanced in some organic solvents (i.e., ethanol or dimethyl sulfoxide) under microwave irradiation. Fourier transform infrared spectra, dynamic-light-scattering measurements, and scanning electron microscopy had been adopted to explore the mechanism of PL enhancement of PSi particles under microwave irradiation, which is attributed to the formation of higher porosity and the growth of silicon oxide by microwave-assisted wet etching. Compared with that fabricated by ultrasonication, smaller luminescent PSi nanoparticles (average size {proportional_to}60 nm) with stronger orange-red fluorescence (PL quantum yield {proportional_to}14.8%) and higher dispersibility can be large-scale prepared for cellular imaging and drug delivery in biomedical applications. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Ligand-assisted fabrication, structure, and luminescence properties of Fe:ZnSe quantum dots

International Nuclear Information System (INIS)

Xie, Ruishi; Zhang, Xingquan; Liu, Haifeng

2014-01-01

Highlights: • A green route is developed for synthesis of water-soluble and fluorescent Fe:ZnSe quantum dots. • Tunable luminescence intensity can be realized with different ligand-to-Zn molar ratios. • The obtained quantum dots are in the so-called “quantum confinement regime”. -- Abstract: Here, we report a synthetic route for highly emissive Fe:ZnSe quantum dots in aqueous media using the mercaptoacetic acid ligand as stabilizing agent. The structural, morphological, componential, and optical properties of the resulting quantum dots were explored by the X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy, inductively coupled plasma mass spectrometry, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, photoluminescence and UV–visible absorption spectroscopies. The average crystallite size was calculated to be about ca., 4.0 nm using the Scherrer equation, which correlates well with the value obtained from the transmission electron microscopy analysis. The obtained water-soluble Fe:ZnSe quantum dots in the so-called “quantum confinement regime” are spherical shaped, possess the cubic sphalerite crystal structure, and exhibit tunable luminescence properties. The presence of mercaptoacetic acid on the surface of Fe:ZnSe quantum dots was confirmed by the Fourier transform infrared spectroscopy measurements. As the ligand/Zn molar ratio increases from 1.3 to 2.8, there is little shift in the absorption peak of the Fe:ZnSe sample, indicating that the particle size of the obtained quantum dots is not changed during the synthetic process. The photoluminescence quantum yield of the as-prepared water-soluble Fe:ZnSe quantum dots can be up to 39%. The molar ratio of ligand-to-Zn plays a crucial role in determining the final luminescence properties of the resulting quantum dots, and the maximum PL intensity appears as the ligand-to-Zn molar ratio is 2.2. In addition, the underlying mechanism for

Ligand-assisted fabrication, structure, and luminescence properties of Fe:ZnSe quantum dots

Energy Technology Data Exchange (ETDEWEB)

Xie, Ruishi, E-mail: rxie@foxmail.com; Zhang, Xingquan; Liu, Haifeng

2014-03-15

Highlights: • A green route is developed for synthesis of water-soluble and fluorescent Fe:ZnSe quantum dots. • Tunable luminescence intensity can be realized with different ligand-to-Zn molar ratios. • The obtained quantum dots are in the so-called “quantum confinement regime”. -- Abstract: Here, we report a synthetic route for highly emissive Fe:ZnSe quantum dots in aqueous media using the mercaptoacetic acid ligand as stabilizing agent. The structural, morphological, componential, and optical properties of the resulting quantum dots were explored by the X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy, inductively coupled plasma mass spectrometry, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, photoluminescence and UV–visible absorption spectroscopies. The average crystallite size was calculated to be about ca., 4.0 nm using the Scherrer equation, which correlates well with the value obtained from the transmission electron microscopy analysis. The obtained water-soluble Fe:ZnSe quantum dots in the so-called “quantum confinement regime” are spherical shaped, possess the cubic sphalerite crystal structure, and exhibit tunable luminescence properties. The presence of mercaptoacetic acid on the surface of Fe:ZnSe quantum dots was confirmed by the Fourier transform infrared spectroscopy measurements. As the ligand/Zn molar ratio increases from 1.3 to 2.8, there is little shift in the absorption peak of the Fe:ZnSe sample, indicating that the particle size of the obtained quantum dots is not changed during the synthetic process. The photoluminescence quantum yield of the as-prepared water-soluble Fe:ZnSe quantum dots can be up to 39%. The molar ratio of ligand-to-Zn plays a crucial role in determining the final luminescence properties of the resulting quantum dots, and the maximum PL intensity appears as the ligand-to-Zn molar ratio is 2.2. In addition, the underlying mechanism for

Fine structure and optical pumping of spins in individual semiconductor quantum dots

Science.gov (United States)

Bracker, Allan S.; Gammon, Daniel; Korenev, Vladimir L.

2008-11-01

We review spin properties of semiconductor quantum dots and their effect on optical spectra. Photoluminescence and other types of spectroscopy are used to probe neutral and charged excitons in individual quantum dots with high spectral and spatial resolution. Spectral fine structure and polarization reveal how quantum dot spins interact with each other and with their environment. By taking advantage of the selectivity of optical selection rules and spin relaxation, optical spin pumping of the ground state electron and nuclear spins is achieved. Through such mechanisms, light can be used to process spins for use as a carrier of information.

Fine structure and optical pumping of spins in individual semiconductor quantum dots

International Nuclear Information System (INIS)

Bracker, Allan S; Gammon, Daniel; Korenev, Vladimir L

2008-01-01

We review spin properties of semiconductor quantum dots and their effect on optical spectra. Photoluminescence and other types of spectroscopy are used to probe neutral and charged excitons in individual quantum dots with high spectral and spatial resolution. Spectral fine structure and polarization reveal how quantum dot spins interact with each other and with their environment. By taking advantage of the selectivity of optical selection rules and spin relaxation, optical spin pumping of the ground state electron and nuclear spins is achieved. Through such mechanisms, light can be used to process spins for use as a carrier of information

Complex logic functions implemented with quantum dot bionanophotonic circuits.

Science.gov (United States)

Claussen, Jonathan C; Hildebrandt, Niko; Susumu, Kimihiro; Ancona, Mario G; Medintz, Igor L

2014-03-26

We combine quantum dots (QDs) with long-lifetime terbium complexes (Tb), a near-IR Alexa Fluor dye (A647), and self-assembling peptides to demonstrate combinatorial and sequential bionanophotonic logic devices that function by time-gated Förster resonance energy transfer (FRET). Upon excitation, the Tb-QD-A647 FRET-complex produces time-dependent photoluminescent signatures from multi-FRET pathways enabled by the capacitor-like behavior of the Tb. The unique photoluminescent signatures are manipulated by ratiometrically varying dye/Tb inputs and collection time. Fluorescent output is converted into Boolean logic states to create complex arithmetic circuits including the half-adder/half-subtractor, 2:1 multiplexer/1:2 demultiplexer, and a 3-digit, 16-combination keypad lock.

On the radiative recombination and tunneling of charge carriers in SiGe/Si heterostructures with double quantum wells

Energy Technology Data Exchange (ETDEWEB)

Yablonsky, A. N., E-mail: yablonsk@ipmras.ru; Zhukavin, R. Kh.; Bekin, N. A.; Novikov, A. V.; Yurasov, D. V.; Shaleev, M. V. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation)

2016-12-15

For SiGe/Si(001) epitaxial structures with two nonequivalent SiGe quantum wells separated by a thin Si barrier, the spectral and time characteristics of interband photoluminescence corresponding to the radiative recombination of excitons in quantum wells are studied. For a series of structures with two SiGe quantum wells different in width, the characteristic time of tunneling of charge carriers (holes) from the narrow quantum well, distinguished by a higher exciton recombination energy, to the wide quantum well is determined as a function of the Si barrier thickness. It is shown that the time of tunneling of holes between the Si{sub 0.8}5Ge{sub 0.15} layers with thicknesses of 3 and 9 nm steadily decreases from ~500 to <5 ns, as the Si barrier thickness is reduced from 16 to 8 nm. At intermediate Si barrier thicknesses, an increase in the photoluminescence signal from the wide quantum well is observed, with a characteristic time of the same order of magnitude as the luminescence decay time of the narrow quantum well. This supports the observation of the effect of the tunneling of holes from the narrow to the wide quantum well. A strong dependence of the tunneling time of holes on the Ge content in the SiGe layers at the same thickness of the Si barrier between quantum wells is observed, which is attributed to an increase in the effective Si barrier height.

Does time exist in quantum gravity?

Directory of Open Access Journals (Sweden)

Claus Kiefer

2015-12-01

Full Text Available Time is absolute in standard quantum theory and dynamical in general relativity. The combination of both theories into a theory of quantum gravity leads therefore to a “problem of time”. In my essay, I investigate those consequences for the concept of time that may be drawn without a detailed knowledge of quantum gravity. The only assumptions are the experimentally supported universality of the linear structure of quantum theory and the recovery of general relativity in the classical limit. Among the consequences are the fundamental timelessness of quantum gravity, the approximate nature of a semiclassical time, and the correlation of entropy with the size of the Universe.

Dark-red-emitting CdTe{sub 0.5}Se{sub 0.5}/Cd{sub 0.5}Zn{sub 0.5}S quantum dots: Effect of chemicals on properties

Energy Technology Data Exchange (ETDEWEB)

Yang, Ping, E-mail: mse_yangp@ujn.edu.cn; Zhang, Aiyu; Li, Xiaoyu; Liu, Ning; Zhang, Yulan; Zhang, Ruili

2013-08-15

CdTe{sub 0.5}Se{sub 0.5}/Cd{sub 0.5}Zn{sub 0.5}S core/shell quantum dots (QDs) with a tunable photoluminescence (PL) range from yellow to dark red (up to a PL peak wavelength of 683 nm) were fabricated using various reaction systems. The core/shell QDs created in the reaction solution of trioctylamine (TOA) and oleic acid (OA) at 300 °C exhibited narrow PL spectra and a related low PL efficiency (38%). In contrast, the core/shell QDs prepared in the solution of 1-octadecene (ODE) and hexadecylamine (HDA) at 200 °C revealed a high PL efficiency (70%) and broad PL spectra. This phenomenon is ascribed that the precursor of Cd, reaction temperature, solvents, and ligands affected the formation process of the shell. The slow growth rate of the shell in the solution of ODE and HDA made QDs with a high PL efficiency. Metal acetate salts without reaction with HDA led to the core/shell QDs with a broad size distribution. - Graphical abstract: CdTe{sub 0.5}Se{sub 0.5}/Cd{sub 0.5}Zn{sub 0.5}S quantum dots (QDs) with tunable photoluminescence, high PL efficiency, and high stability through organic synthesis, in which chemicals affected the properties of the QDs. Display Omitted - Highlights: • CdTe{sub 0.5}Se{sub 0.5}/Cd{sub 0.5}Zn{sub 0.5}S quantum dots created via organic synthesis. • Chemicals affected the properties of the quantum dots. • The quantum dots revealed high photoluminescence efficiency and stability. • The quantum dots with tunable photoluminescence in a range from yellow to dark red. • The QDs are utilizable for various applications such as biological labeling.

High quantum yield graphene quantum dots decorated TiO_2 nanotubes for enhancing photocatalytic activity

International Nuclear Information System (INIS)

Qu, Ailan; Xie, Haolong; Xu, Xinmei; Zhang, Yangyu; Wen, Shengwu; Cui, Yifan

2016-01-01

Highlights: • High concentration yellow GQDs and TiO_2 nanotubes were achieved by a simple and green method. • High quantum yield GQDs enhanced the photodegradation capacity of TiO_2 nanotube. • The catalytic performance of GQDs/TiO_2 depends on the GQDs loading. • The improved photocatalytic activity of GQDs/TiO_2 was attributed to three aspects. - Abstract: Graphene quantum dots (GQDs) with high quantum yield (about 23.6% at an excitation wavelength of 320 nm) and GQDs/TiO_2 nanotubes (GQDs/TiO_2 NTs) composites were achieved by a simple hydrothermal method at low temperature. Photoluminescence characterization showed that the GQDs exhibited the down-conversion PL features at excitation from 300 to 420 nm and up-conversion photoluminescence in the range of 600–800 nm. The photocatalytic activity of prepared GQDs/TiO_2 NTs composites on the degradation of methyl orange (MO) was significantly enhanced compared with that of pure TiO_2 nanotubes (TiO_2 NTs). For the composites coupling with 1.5%, 2.5% and 3.5% GQDs, the degradation of MO after 20 min irradiation under UV–vis light irradiation (λ = 380–780 nm) were 80.52%, 94.64% and 51.91%, respectively, which are much higher than that of pure TiO_2 NTs (35.41%). It was inferred from the results of characterization that the improved photocatalytic activity of the GQDs/TiO_2 NTs composites was attributed to the synergetic effect of up-conversion properties of the GQDs, enhanced visible light absorption and efficient separation of photogenerated electron-holes of the GQDs/TiO_2 composite.

Generalized inequalities for quantum correlations with hidden variables

International Nuclear Information System (INIS)

Vinduska, M.

1991-01-01

Renowned inequalities for quantum correlations are generalized for the case when quantum system cannot be described with an absolute independent measure of the probability. Such a formulation appears to be suitable for the formulation of the hidden variables theory in terms of non-Euclidean geometry. 10 refs

Time-resolved ultraviolet near-field scanning optical microscope for characterizing photoluminescence lifetime of light-emitting devices.

Science.gov (United States)

Park, Kyoung-Duck; Jeong, Hyun; Kim, Yong Hwan; Yim, Sang-Youp; Lee, Hong Seok; Suh, Eun-Kyung; Jeong, Mun Seok

2013-03-01

We developed a instrument consisting of an ultraviolet (UV) near-field scanning optical microscope (NSOM) combined with time-correlated single photon counting, which allows efficient observation of temporal dynamics of near-field photoluminescence (PL) down to the sub-wavelength scale. The developed time-resolved UV NSOM system showed a spatial resolution of 110 nm and a temporal resolution of 130 ps in the optical signal. The proposed microscope system was successfully demonstrated by characterizing the near-field PL lifetime of InGaN/GaN multiple quantum wells.

Quantum coherence phenomena in semiconductor quantum dots: quantum interference, decoherence and Rabi oscillation

International Nuclear Information System (INIS)

Htoon, H.; Shih, C.K.; Takagahara, T.

2003-01-01

We performed extensive studies on quantum decoherence processes of excitons trapped in the various excited states of SAQDs. Energy level structure and dephasing times of excited states were first determined by conducting photoluminescence excitation spectroscopy and wave-packet interferometry on a large number of individual SAQDs. This large statistical basis allows us to extract the correlation between the energy level structure and dephasing times. The major decoherence mechanisms and their active regime were identified from this correlation. A significant suppression of decoherence was also observed in some of the energetically isolated excited states, providing an experimental evidence for the theoretical prediction, known as 'phonon bottleneck effect'. Furthermore, we observed the direct experimental evidence of Rabi oscillation in these excited states with long decoherence times. In addition, a new type of quantum interference (QI) phenomenon was discovered in the wave-packet interferometry experiments performed in the strong excitation regime where the non-linear effects of Rabi oscillation become important. Detailed theoretical investigations attribute this phenomenon to the coherent dynamics resulting from the interplay of Rabi oscillation and QI

Ultrafast spontaneous emission modulation of graphene quantum dots interacting with Ag nanoparticles in solution

Energy Technology Data Exchange (ETDEWEB)

Zhao, Jianwei [Department of Physics, Shanghai University, Shanghai 200444 (China); Research Center of Quantum Macro-Phenomenon and Application, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201210 (China); Lu, Jian, E-mail: luj@sari.ac.cn; Wang, Zhongyang, E-mail: wangzy@sari.ac.cn [Research Center of Quantum Macro-Phenomenon and Application, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201210 (China); Wang, Liang [School of Environmental and Chemical Engineering, Shanghai University, Shanghai 200444 (China); Institute of Nanochemistry and Nanobiology, Shanghai University, Shanghai 200444 (China); Tian, Linfan [Research Center of Quantum Macro-Phenomenon and Application, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201210 (China); School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210 (China); Deng, Xingxia [Research Center of Quantum Macro-Phenomenon and Application, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201210 (China); School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Tian, Lijun [Department of Physics, Shanghai University, Shanghai 200444 (China); Pan, Dengyu [School of Environmental and Chemical Engineering, Shanghai University, Shanghai 200444 (China)

2016-07-11

We investigated the strong interaction between graphene quantum dots and silver nanoparticles in solution using time-resolved photoluminescence techniques. In solution, the silver nanoparticles are surrounded by graphene quantum dots and interacted with graphene quantum dots through exciton-plasmon coupling. An ultrafast spontaneous emission process (lifetime 27 ps) was observed in such a mixed solution. This ultrafast lifetime corresponds to the emission rate exceeding 35 GHz, with the purcell enhancement by a factor of ∼12. These experiment results pave the way for the realization of future high speed light sources applications.

Optical Pumping of the Electronic and Nuclear Spin of Single Charge-Tunable Quantum Dots

Science.gov (United States)

Bracker, A. S.; Stinaff, E. A.; Gammon, D.; Ware, M. E.; Tischler, J. G.; Shabaev, A.; Efros, Al. L.; Park, D.; Gershoni, D.; Korenev, V. L.; Merkulov, I. A.

2005-02-01

We present a comprehensive examination of optical pumping of spins in individual GaAs quantum dots as we change the net charge from positive to neutral to negative with a charge-tunable heterostructure. Negative photoluminescence polarization memory is enhanced by optical pumping of ground state electron spins, which we prove with the first measurements of the Hanle effect on an individual quantum dot. We use the Overhauser effect in a high longitudinal magnetic field to demonstrate efficient optical pumping of nuclear spins for all three charge states of the quantum dot.

Photoluminescence characteristics of InAs quantum dots grown by STM/MBE site-control technique

Energy Technology Data Exchange (ETDEWEB)

Nishikawa, S.; Kohmoto, S.; Nakamura, H.; Ishikawa, T.; Asakawa, K.; Wada, O. [Femtosecond Technology Research Association, Tsukuba, Ibaraki (Japan). FESTA Lab.

2001-03-08

This paper describes micro-photoluminescence (PL) analysis of site-controlled QDs (SCQDs) grown using a novel in-situ MBE growth technique in which sites of self-assembled InAs QDs are controlled by forming nanometer deposits using a scanning tunneling microscope (STM) probe. We found from the temperature dependence of PL that the carrier collection at QDs at low temperature is limited by carrier diffusion in the wetting layer. The analysis of PL data considering this effect has indicated that individual QDs grown have high crystalline quality in spite of the addition of an artificial STM process during growth. (orig.)

A two-step obtainment of quantum confinement in ZnO nanorods

Energy Technology Data Exchange (ETDEWEB)

Mofor, A C; El-Shaer, A; Suleiman, M; Bakin, A; Waag, A [Institute of Semiconductor Technology, Technical University Braunschweig, Hans-Sommer-Strasse 66, D-38106 Braunschweig (Germany)

2006-10-14

ZnO nanorod-based single quantum well heterostructures were fabricated in a two-step process. Nanorods were first grown using vapour transport. Subsequently, high-quality ZnO/Zn{sub 0.85}Mg{sub 0.15}O heterostructures were grown on the nanorods using molecular beam epitaxy. The nanorods are well aligned along the c-axis of ZnO, as indicated by a very narrow rocking curve full width at half maximum. Quantum confinement was clearly observed within the ZnO well for different well widths. The quantum wells show photoluminescence peaks with a full width at half maximum as small as 15 meV.

Real-Time Observation of Exciton-Phonon Coupling Dynamics in Self-Assembled Hybrid Perovskite Quantum Wells.

Science.gov (United States)

Ni, Limeng; Huynh, Uyen; Cheminal, Alexandre; Thomas, Tudor H; Shivanna, Ravichandran; Hinrichsen, Ture F; Ahmad, Shahab; Sadhanala, Aditya; Rao, Akshay

2017-11-28

Self-assembled hybrid perovskite quantum wells have attracted attention due to their tunable emission properties, ease of fabrication, and device integration. However, the dynamics of excitons in these materials, especially how they couple to phonons, remains an open question. Here, we investigate two widely used materials, namely, butylammonium lead iodide (CH 3 (CH 2 ) 3 NH 3 ) 2 PbI 4 and hexylammonium lead iodide (CH 3 (CH 2 ) 5 NH 3 ) 2 PbI 4 , both of which exhibit broad photoluminescence tails at room temperature. We performed femtosecond vibrational spectroscopy to obtain a real-time picture of the exciton-phonon interaction and directly identified the vibrational modes that couple to excitons. We show that the choice of the organic cation controls which vibrational modes the exciton couples to. In butylammonium lead iodide, excitons dominantly couple to a 100 cm -1 phonon mode, whereas in hexylammonium lead iodide, excitons interact with phonons with frequencies of 88 and 137 cm -1 . Using the determined optical phonon energies, we analyzed photoluminescence broadening mechanisms. At low temperatures (photoluminescence line shape observed in hybrid perovskite quantum wells and provide insights into the mechanism of exciton-phonon coupling in these materials.

Structure and optical anisotropy of vertically correlated submonolayer InAs/GaAs quantum dots

DEFF Research Database (Denmark)

Xu, Zhangcheng; Birkedal, Dan; Hvam, Jørn Märcher

2003-01-01

A vertically correlated submonolayer (VCSML) InAs/GaAs quantum-dot (QD) heterostructure was studied using transmission electron microscopy, high-resolution x-ray diffraction (HRXRD) and polarization-dependent photoluminescence. The HRXRD (004) rocking curve was simulated using the Tagaki-Taupin...

Photoluminescence light-up detection of zinc ion and imaging in living cells based on the aggregation induced emission enhancement of glutathione-capped copper nanoclusters.

Science.gov (United States)

Lin, Liyun; Hu, Yuefang; Zhang, Liangliang; Huang, Yong; Zhao, Shulin

2017-08-15

In this work, we prepared glutathione (GSH)-capped copper nanoclusters (Cu NCs) with red emission by simply adjusting the pH of GSH/Cu 2+ mixture at room temperature. A photoluminescence light-up method for detecting Zn 2+ was then developed based on the aggregation induced emission enhancement of GSH-capped Cu NCs. Zn 2+ could trigger the aggregation of Cu NCs, inducing the enhancement of luminescence and the increase of absolute quantum yield from 1.3% to 6.2%. GSH-capped Cu NCs and the formed aggregates were characterized, and the possible mechanism was also discussed. The prepared GSH-capped Cu NCs exhibited a fast response towards Zn 2+ and a wider detection range from 4.68 to 2240μM. The detection limit (1.17μM) is much lower than that of the World Health Organization permitted in drinking water. Furthermore, taking advantages of the low cytotoxicity, large Stokes shift, red emission and light-up detection mode, we explored the use of the prepared GSH-capped Cu NCs in the imaging of Zn 2+ in living cells. The developed luminescence light-up nanoprobe may hold the potentials for Zn 2+ -related drinking water safety and biological applications. Copyright © 2017 Elsevier B.V. All rights reserved.

Photovoltaic devices based on quantum dot functionalized nanowire arrays embedded in an organic matrix

Science.gov (United States)

Kung, Patrick; Harris, Nicholas; Shen, Gang; Wilbert, David S.; Baughman, William; Balci, Soner; Dawahre, Nabil; Butler, Lee; Rivera, Elmer; Nikles, David; Kim, Seongsin M.

2012-01-01

Quantum dot (QD) functionalized nanowire arrays are attractive structures for low cost high efficiency solar cells. QDs have the potential for higher quantum efficiency, increased stability and lifetime compared to traditional dyes, as well as the potential for multiple electron generation per photon. Nanowire array scaffolds constitute efficient, low resistance electron transport pathways which minimize the hopping mechanism in the charge transport process of quantum dot solar cells. However, the use of liquid electrolytes as a hole transport medium within such scaffold device structures have led to significant degradation of the QDs. In this work, we first present the synthesis uniform single crystalline ZnO nanowire arrays and their functionalization with InP/ZnS core-shell quantum dots. The structures are characterized using electron microscopy, optical absorption, photoluminescence and Raman spectroscopy. Complementing photoluminescence, transmission electron microanalysis is used to reveal the successful QD attachment process and the atomistic interface between the ZnO and the QD. Energy dispersive spectroscopy reveals the co-localized presence of indium, phosphorus, and sulphur, suggestive of the core-shell nature of the QDs. The functionalized nanowire arrays are subsequently embedded in a poly-3(hexylthiophene) hole transport matrix with a high degree of polymer infiltration to complete the device structure prior to measurement.

Exploring the Nature of Exciton Localization in Quasi One-Dimensional GaAs/AlGaAs Quantum Well Tube Nanowires

Science.gov (United States)

Jackson, Howard; Badada, Bekele; Shi, Teng; Smith, Leigh; Zheng, Changlin; Etheridge, Joanne; Jiang, Nian; Tan, Hoe; Jagadish, Channupati

We explore the nature of exciton localization in single GaAs/AlGaAs nanowire quantum well tube (QWT) devices using photocurrent (PC) spectroscopy combined with simultaneous photoluminescence (PL) and photoluminescence excitation (PLE) measurements. Excitons confined to GaAs quantum well tubes of 8 and 4 nm widths embedded into an AlGaAs barrier are seen to ionize at high bias. Spectroscopic signatures of the ground and excited states confined to the QWT seen in PL, PLE and PC data are consistent with simple numerical calculations. The demonstration of good electrical contact with the QWTs enables the study of Stark effect shifts in the sharp emission lines of excitons localized to quantum dot-like states within the QWT. Atomic resolution cross-sectional TEM measurements, an analysis of the temperature dependence of PL and time-resolved PL as well as the quantum confined Stark effect of these dots provide insights into the nature of the exciton localization in these nanostructures. We acknowledge the financial support of NSF DMR 1507844, DMR 151373 and ECCS 1509706 and the Australian Research Council.

Significant internal quantum efficiency enhancement of GaN/AlGaN multiple quantum wells emitting at ~350 nm via step quantum well structure design

KAUST Repository

Wu, Feng; Sun, Haiding; Ajia, Idris A.; Roqan, Iman S.; Zhang, Daliang; Dai, Jiangnan; Chen, Changqing; Feng, Zhe Chuan; Li, Xiaohang

2017-01-01

Significant internal quantum efficiency (IQE) enhancement of GaN/AlGaN multiple quantum wells (MQWs) emitting at similar to 350 nm was achieved via a step quantum well (QW) structure design. The MQW structures were grown on AlGaN/AlN/sapphire templates by metal-organic chemical vapor deposition (MOCVD). High resolution x-ray diffraction (HR-XRD) and scanning transmission electron microscopy (STEM) were performed, showing sharp interface of the MQWs. Weak beam dark field imaging was conducted, indicating a similar dislocation density of the investigated MQWs samples. The IQE of GaN/AlGaN MQWs was estimated by temperature dependent photoluminescence (TDPL). An IQE enhancement of about two times was observed for the GaN/AlGaN step QW structure, compared with conventional QW structure. Based on the theoretical calculation, this IQE enhancement was attributed to the suppressed polarization-induced field, and thus the improved electron-hole wave-function overlap in the step QW.

Significant internal quantum efficiency enhancement of GaN/AlGaN multiple quantum wells emitting at ~350 nm via step quantum well structure design

KAUST Repository

Wu, Feng

2017-05-03

Significant internal quantum efficiency (IQE) enhancement of GaN/AlGaN multiple quantum wells (MQWs) emitting at similar to 350 nm was achieved via a step quantum well (QW) structure design. The MQW structures were grown on AlGaN/AlN/sapphire templates by metal-organic chemical vapor deposition (MOCVD). High resolution x-ray diffraction (HR-XRD) and scanning transmission electron microscopy (STEM) were performed, showing sharp interface of the MQWs. Weak beam dark field imaging was conducted, indicating a similar dislocation density of the investigated MQWs samples. The IQE of GaN/AlGaN MQWs was estimated by temperature dependent photoluminescence (TDPL). An IQE enhancement of about two times was observed for the GaN/AlGaN step QW structure, compared with conventional QW structure. Based on the theoretical calculation, this IQE enhancement was attributed to the suppressed polarization-induced field, and thus the improved electron-hole wave-function overlap in the step QW.

Piezo-Phototronic Effect in a Quantum Well Structure.

Science.gov (United States)

Huang, Xin; Du, Chunhua; Zhou, Yongli; Jiang, Chunyan; Pu, Xiong; Liu, Wei; Hu, Weiguo; Chen, Hong; Wang, Zhong Lin

2016-05-24

With enhancements in the performance of optoelectronic devices, the field of piezo-phototronics has attracted much attention, and several theoretical works have been reported based on semiclassical models. At present, the feature size of optoelectronic devices are rapidly shrinking toward several tens of nanometers, which results in the quantum confinement effect. Starting from the basic piezoelectricity equation, Schrödinger equation, Poisson equation, and Fermi's golden rule, a self-consistent theoretical model is proposed to study the piezo-phototronic effect in the framework of perturbation theory in quantum mechanics. The validity and universality of this model are well-proven with photoluminescence measurements in a single GaN/InGaN quantum well and multiple GaN/InGaN quantum wells. This study provides important insight into the working principle of nanoscale piezo-phototronic devices as well as guidance for the future device design.

Trap elimination and reduction of size dispersion due to aging in CdS x Se1- x quantum dots

Science.gov (United States)

Verma, Abhishek; Nagpal, Swati; Pandey, Praveen K.; Bhatnagar, P. K.; Mathur, P. C.

2007-12-01

Quantum Dots of CdS x Se1- x embedded in borosilicate glass matrix have been grown using Double-Step annealing method. Optical characterization of the quantum dots has been done through the combinative analysis of optical absorption and photoluminescence spectroscopy at room temperature. Decreasing trend of photoluminescence intensity with aging has been observed and is attributed to trap elimination. The changes in particle size, size distribution, number of quantum dots, volume fraction, trap related phenomenon and Gibbs free energy of quantum dots, has been explained on the basis of the diffusion-controlled growth process, which continues with passage of time. For a typical case, it was found that after 24 months of aging, the average radii increased from 3.05 to 3.12 nm with the increase in number of quantum dots by 190% and the size-dispersion decreased from 10.8% to 9.9%. For this sample, the initial size range of the quantum dots was 2.85 to 3.18 nm. After that no significant change was found in these parameters for the next 12 months. This shows that the system attains almost a stable nature after 24 months of aging. It was also observed that the size-dispersion in quantum dots reduces with the increase in annealing duration, but at the cost of quantum confinement effect. Therefore, a trade off optimization has to be done between the size-dispersion and the quantum confinement.

Enhanced Emission of Quantum System in Si-Ge Nanolayer Structure.

Science.gov (United States)

Huang, Zhong-Mei; Huang, Wei-Qi; Dong, Tai-Ge; Wang, Gang; Wu, Xue-Ke

2016-12-01

It is very interesting that the enhanced peaks near 1150 and 1550 nm are observed in the photoluminescence (PL) spectra in the quantum system of Si-Ge nanolayer structure, which have the emission characteristics of a three-level system with quantum dots (QDs) pumping and emission of quasi-direct-gap band, in our experiment. In the preparing process of Si-Ge nanolayer structure by using a pulsed laser deposition method, it is discovered that the nanocrystals of Si and Ge grow in the (100) and (111) directions after annealing or electron beam irradiation. The enhanced PL peaks with multi-longitudinal-mode are measured at room temperature in the super-lattice of Si-Ge nanolayer quantum system on SOI.

GaAsSb/InGaAs type-II quantum wells for long-wavelength lasers on GaAs substrates

International Nuclear Information System (INIS)

Klem, J. F.; Blum, O.; Kurtz, S. R.; Fritz, I. J.; Choquette, K. D.

2000-01-01

We have investigated the properties of GaAsSb/InGaAs type-II bilayer quantum-well structures grown by molecular-beam epitaxy for use in long-wavelength lasers on GaAs substrates. Structures with layer strains and thicknesses designed to be thermodynamically stable against dislocation formation exhibit room-temperature photoluminescence at wavelengths as long as 1.43 μm. The photoluminescence emission wavelength is significantly affected by growth temperature and the sequence of layer growth (InGaAs/GaAsSb versus GaAsSb/InGaAs), suggesting that Sb and/or In segregation results in nonideal interfaces under certain growth conditions. At low-injection currents, double-heterostructure lasers with GaAsSb/InGaAs bilayer quantum-well active regions display electroluminescence at wavelengths comparable to those obtained in photoluminescence, but at higher currents the electroluminescence shifts to shorter wavelengths. Lasers have been obtained with threshold current densities of 120 A/cm2 at 1.17 μm, and 2.1 kA/cm2 at 1.21 μm. (c) 2000 American Vacuum Society

Quantum mechanics versus relativity: an experimental test of the structure of spacetime

International Nuclear Information System (INIS)

Emelyanov, S A

2012-01-01

We have performed an experimental test under the conditions in which quantum mechanics predicts spatially discontinuous single-particle transport. The transport is beyond the relativistic paradigm of movement in Cartesian space and therefore may well be nonlocal. Our test has demonstrated that such transport does exist. This fact opens the door for a realistic interpretation of quantum mechanics in so far as the requirement of Lorentz invariance appears inapplicable to any version of quantum theory. Moreover, as quantum mechanics proposes a particle dynamics beyond relativity, it automatically requires an adequate ‘quantum’ concept of spacetime, for which the relativistic concept is only a limiting case. The quantum concept allows absolute simultaneity and hence revives the notion of absolute time. It also goes beyond the relativistic curvilinear Cartesian order of space to account for quantum phenomena such as discontinuity and nonlocality in the spirit of Bohm's concept of the implicate order.

Group-III vacancy induced InxGa1-xAs quantum dot interdiffusion

International Nuclear Information System (INIS)

Djie, H. S.; Wang, D.-N.; Ooi, B. S.; Hwang, J. C. M.; Gunawan, O.

2006-01-01

The impact of group-III vacancy diffusion, generated during dielectric cap induced intermixing, on the energy state transition and the inhomogeneity reduction in the InGaAs/GaAs quantum-dot structure is investigated. We use a three-dimensional quantum-dot diffusion model and photoluminescence data to determine the thermal and the interdiffusion properties of the quantum dot. The band gap energy variation related to the dot uniformity is found to be dominantly affected by the height fluctuation. A group-III vacancies migration energy H m for InGaAs quantum dots of 1.7 eV was deduced. This result is similar to the value obtained from the bulk and GaAs/AlGaAs quantum-well materials confirming the role of SiO 2 capping enhanced group-III vacancy induced interdiffusion in the InGaAs quantum dots

Determination of anisotropic dipole moments in self-assembled quantum dots using Rabi oscillations

Science.gov (United States)

Muller, Andreas; Wang, Qu-Quan; Bianucci, Pablo; Xue, Qi-Kun; Shih, Chih-Kang

2004-03-01

By investigating the polarization-dependent Rabi oscillations using photoluminescence spectroscopy, we determined the respective transition dipole moments of the two excited excitonic states |Ex> and |Ey> of a single self-assembled quantum dot that are nondegenerate due to shape anisotropy. We find that the ratio of the two dipole moments is close to the physical elongation ratio of the quantum dot. We also measured the ground state radiative lifetimes of several quantum dots. The dipole moments calculated from the latter are in reasonable agreement with the dipole moments determined from the periodicity of the Rabi oscillations.

Formation Mechanism of Carbogenic Nanoparticles with Dual Photoluminescence Emission

KAUST Repository

Krysmann, Marta J.

2012-01-18

We present a systematic investigation of the formation mechanism of carbogenic nanoparticles (CNPs), otherwise referred to as C-dots, by following the pyrolysis of citric acid (CA)-ethanolamine (EA) precursor at different temperatures. Pyrolysis at 180 °C leads to a CNP molecular precursor with a strongly intense photoluminescence (PL) spectrum and high quantum yield formed by dehydration of CA-EA. At higher temperatures (230 °C) a carbogenic core starts forming and the PL is due to the presence of both molecular fluorophores and the carbogenic core. CNPs that exhibit mostly or exclusively PL arising from carbogenic cores are obtained at even higher temperatures (300 and 400 °C, respectively). Since the molecular fluorophores predominate at low pyrolysis temperatures while the carbogenic core starts forming at higher temperatures, the PL behavior of CNPs strongly depends on the conditions used for their synthesis. © 2011 American Chemical Society.

Geometrical-confinement effects on excitons in quantum disks

International Nuclear Information System (INIS)

Song, J.; Ulloa, S.E.

1995-01-01

Excitons confined to flat semiconductor quantum dots with elliptical cross sections are considered as we study geometrical effects on exciton binding energy, electron-hole separation, and the resulting linear optical properties. We use numerical matrix diagonalization techniques with appropriately large and optimized basis sets in an effective-mass Hamiltonian approach. The linear optical susceptibilities of GaAs and InAs dots for several different size ratios are discussed and compared to experimental photoluminescence spectra obtained on GaAs/Al x Ga 1-x As and InAs/GaAs quantum dots. For quantum dots of several nm in size, there is a strong blueshift of the luminescence due to geometrical-confinement effects. Also, transition peaks are split and shifted towards higher energy, in comparison with dots with circular cross sections

Synthesis and photoluminescence property of silicon carbide ...

Indian Academy of Sciences (India)

Administrator

The β-SiC nanowires thin films exhibit the strong photoluminescence (PL) peak at a wavelength of. 400 nm, which is significantly ... in the nanowires. Keywords. SiC nanowires; nanocrystalline diamond; crystal growth; photoluminescence. 1. ... unique mechanical, electrical and thermal properties. Due to the wide band gap ...

Photo-Induced Spin Dynamics in Semiconductor Quantum Wells

Directory of Open Access Journals (Sweden)

Miah M

2009-01-01

Full Text Available Abstract We experimentally investigate the dynamics of spins in GaAs quantum wells under applied electric bias by photoluminescence (PL measurements excited with circularly polarized light. The bias-dependent circular polarization of PL (P PL with and without magnetic field is studied. TheP PLwithout magnetic field is found to be decayed with an enhancement of increasing the strength of the negative bias. However,P PLin a transverse magnetic field shows oscillations under an electric bias, indicating that the precession of electron spin occurs in quantum wells. The results are discussed based on the electron–hole exchange interaction in the electric field.

Quantum glassiness in clean strongly correlated systems: an example of topological overprotection

Science.gov (United States)

Chamon, Claudio

2005-03-01

Describing matter at near absolute zero temperature requires understanding a system's quantum ground state and the low energy excitations around it, the quasiparticles, which are thermally populated by the system's contact to a heat bath. However, this paradigm breaks down if thermal equilibration is obstructed. I present solvable examples of quantum many-body Hamiltonians of systems that are unable to reach their ground states as the environment temperature is lowered to absolute zero. These examples, three dimensional generalizations of quantum Hamiltonians proposed for topological quantum computing, 1) have no quenched disorder, 2) have solely local interactions, 3) have an exactly solvable spectrum, 4) have topologically ordered ground states, and 5) have slow dynamical relaxation rates akin to those of strong structural glasses.

Synthesis and characterization of (3-Aminopropyl)trimethoxy-silane (APTMS) functionalized Gd2O3:Eu(3+) red phosphor with enhanced quantum yield.

Science.gov (United States)

Jain, Akhil; Hirata, G A; Farías, M H; Castillón, F F

2016-02-12

We report the surface modification of nanocrystalline Gd2O3:Eu(3+) phosphor by (3-Aminopropyl)trimethoxysilane (APTMS). The nanoparticles were first coated with silica using the Stöber process, and then annealed at 650 °C for 2 h. Afterwards, APTMS was functionalized onto the silica layer to obtain Gd2O3:Eu(3+) nanoparticles bearing amine groups on the surface. The effect of silica coating, and the subsequent annealing process on the crystallization of the nanophosphor were analyzed by x-ray diffraction (XRD). High-resolution transmission electron microscopy (HR-TEM) confirmed the presence of a silica layer of ∼45 nm thickness. X-ray photoelectron (XPS) and Fourier transform infrared (FTIR) spectroscopy confirmed the presence of silica and the amine groups. Photoluminescence (PL) analysis demonstrated an increased emission after functionalization of nanoparticles. Absolute quantum yield (QY) measurements revealed an 18% enhancement in QY in functionalized nanoparticles compared with unmodified nanoparticles, which is of great importance for their biomedical applications.

Synthesis and characterization of (3-Aminopropyl)trimethoxy-silane (APTMS) functionalized Gd2O3:Eu3+ red phosphor with enhanced quantum yield

Science.gov (United States)

Jain, Akhil; Hirata, G. A.; Farías, M. H.; Castillón, F. F.

2016-02-01

We report the surface modification of nanocrystalline Gd2O3:Eu3+ phosphor by (3-Aminopropyl)trimethoxysilane (APTMS). The nanoparticles were first coated with silica using the Stöber process, and then annealed at 650 °C for 2 h. Afterwards, APTMS was functionalized onto the silica layer to obtain Gd2O3:Eu3+ nanoparticles bearing amine groups on the surface. The effect of silica coating, and the subsequent annealing process on the crystallization of the nanophosphor were analyzed by x-ray diffraction (XRD). High-resolution transmission electron microscopy (HR-TEM) confirmed the presence of a silica layer of ∼45 nm thickness. X-ray photoelectron (XPS) and Fourier transform infrared (FTIR) spectroscopy confirmed the presence of silica and the amine groups. Photoluminescence (PL) analysis demonstrated an increased emission after functionalization of nanoparticles. Absolute quantum yield (QY) measurements revealed an 18% enhancement in QY in functionalized nanoparticles compared with unmodified nanoparticles, which is of great importance for their biomedical applications.

Synthesis and characterization of (3-Aminopropyl)trimethoxy-silane (APTMS) functionalized Gd2O3:Eu3+ red phosphor with enhanced quantum yield

International Nuclear Information System (INIS)

Jain, Akhil; Hirata, G A; Farías, M H; Castillón, F F

2016-01-01

We report the surface modification of nanocrystalline Gd 2 O 3 :Eu 3+ phosphor by (3-Aminopropyl)trimethoxysilane (APTMS). The nanoparticles were first coated with silica using the Stöber process, and then annealed at 650 °C for 2 h. Afterwards, APTMS was functionalized onto the silica layer to obtain Gd 2 O 3 :Eu 3+ nanoparticles bearing amine groups on the surface. The effect of silica coating, and the subsequent annealing process on the crystallization of the nanophosphor were analyzed by x-ray diffraction (XRD). High-resolution transmission electron microscopy (HR-TEM) confirmed the presence of a silica layer of ∼45 nm thickness. X-ray photoelectron (XPS) and Fourier transform infrared (FTIR) spectroscopy confirmed the presence of silica and the amine groups. Photoluminescence (PL) analysis demonstrated an increased emission after functionalization of nanoparticles. Absolute quantum yield (QY) measurements revealed an 18% enhancement in QY in functionalized nanoparticles compared with unmodified nanoparticles, which is of great importance for their biomedical applications. (paper)

Control of Emission Color of High Quantum Yield CH3NH3PbBr3 Perovskite Quantum Dots by Precipitation Temperature.

Science.gov (United States)

Huang, He; Susha, Andrei S; Kershaw, Stephen V; Hung, Tak Fu; Rogach, Andrey L

2015-09-01

Emission color controlled, high quantum yield CH 3 NH 3 PbBr 3 perovskite quantum dots are obtained by changing the temperature of a bad solvent during synthesis. The products for temperatures between 0 and 60 °C have good spectral purity with narrow emission line widths of 28-36 nm, high absolute emission quantum yields of 74% to 93%, and short radiative lifetimes of 13-27 ns.

A novel synthesis of magnetic and photoluminescent graphene quantum dots/MFe2O4 (M = Ni, Co) nanocomposites for catalytic application

Science.gov (United States)

Naghshbandi, Zhwan; Arsalani, Nasser; Zakerhamidi, Mohammad Sadegh; Geckeler, Kurt E.

2018-06-01

In recent year, the research is focused on the nanostructured catalyst with increase physiochemical properties. Herein, Different magnetic nanocomposites of graphene quantum dots (GQD) and MFe2O4 (M = Ni, Co) with intrinsic photoluminescent and ferromagnetic properties were synthesized by a convenient co-precipitation method. The structure, morphology, and properties of these nanocomposites as well as the catalytic activity of the nanocomposites for the reduction of p-nitrophenol were investigated. The catalytic activity was found to be in the order of NiFe2O4/GQD > CoFe2O4/GQD > NiFe2O4 > CoFe2O4. The sample NiFe2O4/GQD exhibited the best catalytic activity with an apparent rate constant of 3.56 min-1 and a reduction completion time to p-aminophenol of 60 s. The catalysts can be reused by a magnetic field and display good stability, which can be recycled for six successive experiment with a conversion percentage of more than 95%. These results demonstrate that the nanocomposite NiFe2O4/GQD is an efficient catalyst for the reduction of p-nitrophenol compound. Also, the new nanocomposites have shown a significant reduction in the direct and indirect energy bandgaps when compared to pure GQD and the corresponding magnetic metal oxides.

Polarization spectroscopy of positive and negative trions in an InAs quantum dot

Science.gov (United States)

Ware, Morgan E.; Bracker, Allan S.; Stinaff, Eric; Gammon, Daniel; Gershoni, David; Korenev, Vladimir L.

2005-02-01

Using polarization-sensitive photoluminescence and photoluminescence excitation spectroscopy, we study single InAs/GaAs self-assembled quantum dots. The dots were embedded in an n-type, Schottky diode structure allowing for control of the charge state. We present here the exciton, singly charged exciton (positive and negative trions), and the twice negatively charged exciton. For non-resonant excitation below the wetting layer, we observed a large degree of polarization memory from the radiative recombination of both the positive and negative trions. In excitation spectra, through the p-shell, we have found several sharp resonances in the emission from the s-shell recombination of the dot in all charged states. Some of these excitation resonances exhibit strong coulomb shifts upon addition of charges into the quantum dot. One particular resonance of the negatively charged trion was found to exhibit a fine structure doublet under circular polarization. This observation is explained in terms of resonant absorption into the triplet states of the negative trion.

Effects of precursors on the crystal structure and photoluminescence of CdS nanocrystalline

International Nuclear Information System (INIS)

Fu Zuoling; Zhou Shihong; Shi Jinsheng; Zhang Siyuan

2005-01-01

A series of cadmium sulfide (CdS) nanocrystalline were synthesized by precipitation from a mixture of aqueous solutions of cadmium salts and sulfur salts without adding any surface-termination agent. Their crystal structures and particle sizes were determined by X-ray diffraction (XRD). The CdS nanocrystalline precipitated from different precursors exhibited three cases: cubic phase, hexagonal phase and a hybrid of cubic and hexagonal phases. The photoluminescence (PL) of cadmium salt precursors and CdS nanocrystalline is also analyzed. Similar spectral band structure of cadmium salt precursors and CdS nanocrystalline is found. The PL of 3.4, 2.4 and 2.0 nm sized CdS nanocrystalline with the same crystal structure indicated quantum confinement effect

Diamond photonic crystal slab: leaky modes and modified photoluminescence emission of surface-deposited quantum dots

Czech Academy of Sciences Publication Activity Database

Ondič, Lukáš; Babchenko, Oleg; Varga, Marián; Kromka, Alexander; Čtyroký, Jiří; Pelant, Ivan

2012-01-01

Roč. 2, Dec (2012), s. 1-6 ISSN 2045-2322 R&D Projects: GA ČR(CZ) GAP108/11/0794; GA AV ČR(CZ) IAA101120804; GA AV ČR KJB100100903; GA ČR(CZ) GAP205/10/0046 Grant - others:AVČR(CZ) M100100902 Institutional research plan: CEZ:AV0Z10100521; CEZ:AV0Z20670512 Keywords : photonic crystal * diamond * photoluminescence Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.927, year: 2012 http://www.nature.com/srep/2012/121203/srep00914/full/srep00914.html

Tellurium quantum dots: Preparation and optical properties

Science.gov (United States)

Lu, Chaoyu; Li, Xueming; Tang, Libin; Lai, Sin Ki; Rogée, Lukas; Teng, Kar Seng; Qian, Fuli; Zhou, Liangliang; Lau, Shu Ping

2017-08-01

Herein, we report an effective and simple method for producing Tellurium Quantum dots (TeQDs), zero-dimensional nanomaterials with great prospects for biomedical applications. Their preparation is based on the ultrasonic exfoliation of Te powder dispersed in 1-methyl-2-pyrrolidone. Sonication causes the van der Waals forces between the structural hexagons of Te to break so that the relatively coarse powder breaks down into nanoscale particles. The TeQDs have an average size of about 4 nm. UV-Vis absorption spectra of the TeQDs showed an absorption peak at 288 nm. Photoluminescence excitation (PLE) and photoluminescence (PL) are used to study the optical properties of TeQDs. Both the PLE and PL peaks revealed a linear relationship against the emission and excitation energies, respectively. TeQDs have important potential applications in biological imaging and catalysis as well as optoelectronics.

Effect of annealing on the structure and optical properties of InGaAs/GaAs quantum dots

DEFF Research Database (Denmark)

Xu, Zhangcheng; Leosson, Kristjan; Birkedal, Dan

2002-01-01

We report the effect of annealing on self-assembled InGaAs/GaAs quantum dots, as investigated by means of resonant photoluminescence (PL), resonant Raman scattering, polarization dependent PL, and high resolution X-ray diffraction....

On quantum efficiency of photoluminescence in ZnO layers and nanostructures

Energy Technology Data Exchange (ETDEWEB)

Reshchikov, M.A., E-mail: mreshchi@vcu.ed [Physics Department, Virginia Commonwealth University, 701 W. Grace St., Richmond, VA 23284 (United States); El-Shaer, A.; Behrends, A.; Bakin, A.; Waag, A. [Institute of Semiconductor Technology, Technical University of Braunschweig, Braunschweig D-38106 (Germany)

2009-12-15

In this work we studied PL in ZnO layers and nanostructures, including ZnO homoepitaxial layers on ZnO substrate and ZnO-Zn{sub 1-x}Mg{sub x}O single quantum well (SQW) structures grown on sapphire substrates by MBE, and ZnO nanowires grown on sapphire by MOCVD. The external quantum efficiency (QE) of PL in O-face ZnO layers exceeded that in Zn-face ZnO layers by two orders of magnitude at low temperatures. In a sample with SQW the combined external QE from the 4.6-nm-wide SQW and 50-nm-thick Zn{sub 1-x}Mg{sub x}O barriers achieved 28% at 15 K. The highest external QE was observed in one of the samples with ZnO nanowires-52% at 15 K and 2% at 300 K. Contribution of defect-related PL bands in ZnO nanowires samples was extremely low.

Influence of the quantum dot geometry on p -shell transitions in differently charged quantum dots

Science.gov (United States)

Holtkemper, M.; Reiter, D. E.; Kuhn, T.

2018-02-01

Absorption spectra of neutral, negatively, and positively charged semiconductor quantum dots are studied theoretically. We provide an overview of the main energetic structure around the p -shell transitions, including the influence of nearby nominally dark states. Based on the envelope function approximation, we treat the four-band Luttinger theory as well as the direct and short-range exchange Coulomb interactions within a configuration interaction approach. The quantum dot confinement is approximated by an anisotropic harmonic potential. We present a detailed investigation of state mixing and correlations mediated by the individual interactions. Differences and similarities between the differently charged quantum dots are highlighted. Especially large differences between negatively and positively charged quantum dots become evident. We present a visualization of energetic shifts and state mixtures due to changes in size, in-plane asymmetry, and aspect ratio. Thereby we provide a better understanding of the experimentally hard to access question of quantum dot geometry effects. Our findings show a method to determine the in-plane asymmetry from photoluminescence excitation spectra. Furthermore, we supply basic knowledge for tailoring the strength of certain state mixtures or the energetic order of particular excited states via changes of the shape of the quantum dot. Such knowledge builds the basis to find the optimal QD geometry for possible applications and experiments using excited states.

Synthesis and Properties of Water-Soluble Blue-Emitting Mn-Alloyed CdTe Quantum Dots

Science.gov (United States)

Tynkevych, Olena; Karavan, Volodymyr; Vorona, Igor; Filonenko, Svitlana; Khalavka, Yuriy

2018-05-01

In this work, we prepared CdTe quantum dots, and series of Cd1-xMnxTe-alloyed quantum dots with narrow size distribution by an ion-exchange reaction in water solution. We found that the photoluminescence peaks are shifted to higher energies with the increasing Mn2+ content. So far, this is the first report of blue-emitting CdTe-based quantum dots. By means of cyclic voltammetry, we detected features of electrochemical activity of manganese energy levels formed inside the Cd1-xMnxTe-alloyed quantum dot band gap. This allowed us to estimate their energy position. We also demonstrate paramagnetic behavior for Cd1-xMnxTe-alloyed quantum dots which confirmed the successful ion-exchange reaction.

Synthesis and Properties of Water-Soluble Blue-Emitting Mn-Alloyed CdTe Quantum Dots.

Science.gov (United States)

Tynkevych, Olena; Karavan, Volodymyr; Vorona, Igor; Filonenko, Svitlana; Khalavka, Yuriy

2018-05-02

In this work, we prepared CdTe quantum dots, and series of Cd 1-x Mn x Te-alloyed quantum dots with narrow size distribution by an ion-exchange reaction in water solution. We found that the photoluminescence peaks are shifted to higher energies with the increasing Mn 2+ content. So far, this is the first report of blue-emitting CdTe-based quantum dots. By means of cyclic voltammetry, we detected features of electrochemical activity of manganese energy levels formed inside the Cd 1-x Mn x Te-alloyed quantum dot band gap. This allowed us to estimate their energy position. We also demonstrate paramagnetic behavior for Cd 1-x Mn x Te-alloyed quantum dots which confirmed the successful ion-exchange reaction.

Atom-chip-based quantum gravimetry for the precise determination of absolute gravity

Science.gov (United States)

Abend, Sven; Schubert, Christian; Ertmer, Wolfgang; Rasel, Ernst

2017-04-01

We present a novel technique for the precise measurement of absolute local gravity with a quantum gravimeter based on an atom chip. Atom interferometry utilizes the interference of matter waves interrogated by laser light to read out inertial forces. Today's generation of these devices typically operate with test mass samples, that consists of ensembles of laser cooled atoms. Their performance is limited by the velocity spread and finite-size of the test masses that impose systematic uncertainties at the level of a few μGal [1]. Rather than laser cooled atoms we employ quantum degenerate ensembles, so called Bose-Einstein condensates [2], as ultra-sensitive probes for gravity. These sources offer unique properties that will allow to overcome the current limitations in the next generation of sensors. Furthermore, atom-chip technology offers the possibility to generate Bose-Einstein condensates in a fast and reliable way. We present a lab-based prototype that uses the atom chip itself to retro-reflect the interrogation laser and thus serves as inertial reference inside the vacuum [3]. With this setup, it is possible to demonstrate all necessary steps to measure gravity, including the preparation of the source, spanning an interferometer as well as the detection of the output signal. All steps are pursued on a baseline of 1 cm right below the atom chip and to analyze relevant systematic effects. In the framework of the center of excellence geoQ a next generation device is under construction at the Institut für Quantenoptik, that will target for in-field measurements. This device will feature a state-of-the-art atom-chip source with a high-flux of ultra-cold atoms at a repetition rate of 1-2 Hz [4]. The device will be characterized in cooperation with the Müller group at the Institut für Erdmessung the sensor and finally employed in a campaign to measure the Fennoscandian uplift at the level of 1 μGal. The presented work is supported by the CRC 1227 DQ-mat, the

Fast and Straightforward Synthesis of Luminescent Titanium(IV Dioxide Quantum Dots

Directory of Open Access Journals (Sweden)

Václav Štengl

2017-01-01

Full Text Available The nucleus of titania was prepared by reaction of solution titanium oxosulphate with hydrazine hydrate. These titania nuclei were used for titania quantum dots synthesis by a simple and fast method. The prepared titanium(IV dioxide quantum dots were characterized by measurement of X-ray powder diffraction (XRD, X-ray photoelectron spectroscopy (XPS, atomic force microscopy (AFM, high-resolution electron microscopy (HRTEM, and selected area electron diffraction (SAED. The optical properties were determined by photoluminescence (PL spectra. The prepared titanium(IV dioxide quantum dots have the narrow range of UV excitation (365–400 nm and also a close range of emission maxima (450–500 nm.

Optical Properties of GaAs Quantum Dots Fabricated by Filling of Self-Assembled Nanoholes