Excitonic effects are observed in the optical absorption and photoluminescence of strongly confined CdS quantum dots embedded in the polymer Nafion. The three bands identified in the optical absorption spectra could be attributed to 1s e-1s h, 1p e-1p h, and 2s e-2s h transitions of the noninteracting particle model. Photoluminescence spectra show a strong emission band corresponding to electron-hole recombination and a weak band due to emission from defect states. The strength of electron-phonon coupling is small in the regime of strong confinement and decreases with decreasing particle size. © 2002 American Institute of Physics.

C. Vijayan

Department Of Physics

P. Nandakumar

Absorption and photoluminescence

CDS QUANTUM DOTS

Defect state

ELECTRON PHONON COUPLINGS

ELECTRON-HOLE RECOMBINATION

Emission bands

EXCITONIC EFFECT

NON-INTERACTING PARTICLES

Photoluminescence spectrum

Strong confinement

Cadmium compounds

Cadmium sulfide

Light absorption

Semiconductor quantum dots

photoluminescence

Fulltext

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Optical absorption and photoluminescence studies on CdS quantum dots in Nafion

Journal of Applied Physics

We report on the visible-light-driven photocatalytic activity of highly stable β-indium sulfide (In2S3) quantum dots embedded in Nafion matrix. β-indium sulfide (In2S3) quantum dots (6-10 nm) embedded in Nafion matrix with strong quantum confinement were synthesized by a simple chemical route. The UV-Vis absorption spectrum shows a large blue shift (∼1 eV) which can be controlled by the reaction temperature and time. Strong broadband photoluminescence is observed in the blue, green and red regions of the emission spectrum with variation in particle size and stoichiometry of the quantum dots. Photocatalytic activity measurements show that these hybrid membranes synthesized with equimolar precursors of In and S show paramount photocatalytic activity under visible-light irradiation, with the degradation of Rhodamine-6G dyes up to 95% within 90 min. The photocatalytic membranes are tested for reusable and stable operation. © 2014 IOP Publishing Ltd.

Journal of Physics D: Applied Physics

Visible-light driven photocatalytic activity of β-indium sulfide (In2S3) quantum dots embedded in Nafion matrix

In this paper, we demonstrate a simple and efficient method for synthesis of β-indium sulphide (In 2 S 3 ) nanoparticles embedded in an ionomer matrix (nafion membrane). The influence of reaction temperature on structural, compositional and optical properties of these films were analysed using X-Ray Diffraction, EDAX, UV-Vis absorption spectroscopy and photoluminescence studies. Average particle diameter was estimated using modified effective mass approximation method. Absorption spectra of In 2 S 3 nanoparticles show blue shift compared to bulk In 2 S 3 , indicating strong quantum size confinement effects. PL emission in the wavelength range 530-600 nm was recorded using a 488 nm line from an Ar + laser as the excitation source. © 2014 AIP Publishing LLC.

AIP Conference Proceedings

Synthesis of indium sulphide quantum dots in perfluoronated ionomer membrane

This study is aimed at identifying a suitable organic thiol for CdS by studying its structural, thermal and photophysical characteristics. Quantum dots of the II-VI semiconductor CdS, in the size regime of 2.0-3.3 nm, were prepared in the cubic phase by a wet chemical method. Five organic thiols were used for capping: (i) 1,4-dithiothreitol (DTT), (ii) 2-mercaptoethanol (ME), (iii) cysteine (Cys), (iv) methionine (Meth), and (v) glutathione (GSH). Structural studies were carried out by x-ray diffraction (XRD) and transmission electron microscopy (TEM), which revealed the cubic phase of CdS. Optical properties were studied by FT-IR, UV-visible and fluorescence spectroscopic techniques, and a comparison was made between uncapped and capped CdS. FT-IR studies suggested two different bonding mechanisms of the capping agents with the CdS. GSH and DTT capped CdS showed significant decrease in absorption wavelengths. An increase in band gap was observed in two cases: when (i) capped and (ii) decreased in size. The band gap was increased from 2.50 eV for the uncapped to 2.77 eV for the DTT capped CdS. DTT was found to be the best capping agent for CdS among these five organic thiols in two aspects: (i) yielding lower grain size in cubic phase, and (ii) good fluorescence properties with efficient quenching of the surface traps. © IOP Publishing Ltd.

Nanotechnology

Surface modification of CdS quantum dots using thiols - Structural and photophysical studies

Stable films containing CdS quantum dots of mean size 3.4 nm embedded in a solid host matrix are prepared using a room temperature chemical route of synthesis. CdS/synthetic glue nanocomposites are characterized using high resolution transmission electron microscopy, infrared spectroscopy, differential scanning calorimetry and thermogravimetric analysis. Significant blue shift from the bulk absorption edge is observed in optical absorption as well as photoacoustic spectra indicating strong quantum confinement. The exciton transitions are better resolved in photoacoustic spectroscopy compared to optical absorption spectroscopy. We assign the first four bands observed in photoacoustic spectroscopy to 1s e -1s h , 1p e -1p h , 1d e -1d h and 2p e -2p h transitions using a non interacting particle model. Nonlinear absorption studies are done using z-scan technique with nanosecond pulses in the off resonant regime. The origin of optical limiting is predominantly two photon absorption mechanism.

Nanoscale Research Letters

Excitonic transitions and off-resonant optical limiting in CdS quantum dots stabilized in a synthetic glue matrix

Nanoclusters of PbS embedded in polymer matrices have recently been shown to have interesting optical properties with the capability of tuning the effective band gap over a wide spectral range. The results of a systematic investigation of the preparation and characterization of size-tuned PbS nanocrystals stabilized in the polymer nanotemplate of Nafion and their size-dependent physical properties are presented in this paper. These nanocrystals exhibit large characteristic blueshift in optical absorption from the bulk absorption onset value of 3020 nm. XRD and HRTEM measurements indicate the presence of PbS nanocrystals in the size range of 2-6 nm, in the regime of strong quantum confinement. Thermal and electrical properties of the polymer are found to be influenced to a great extent by the embedded PbS nanocrystals. © 2006 Elsevier Ltd. All rights reserved.

Materials Research Bulletin

Properties of size-tuned PbS nanocrystals stabilized in a polymer template

Optical nonlinearities of CdS quantum dots in the strongly confined regime are probed through degenerate four-wave-mixing experiments in an attempt to study the size dependence of the third order optical susceptibility χ(3). The results indicate that χ(3) is strongly dependent on the diameter of the dots and that there is a large increase in χ(3) values as the diameter decreases below 2 nm. Polarization discrimination studies point to nonthermal contributions to the mechanism of optical nonlinearity.

Optics Communications

Quantum size effects on the third order optical nonlinearity of CdS quantum dots in Nafion

Quantum confinement effects on the excitonic transitions in CdS quantum dots embedded in the polymer matrix Nafion are studied using the technique of photoacoustic spectroscopy. The characteristic blueshift in the absorption onset with decreasing quantum dot size is in agreement with that observed in the optical absorption spectra. Excitonic transitions are better resolved in the photoacoustic spectra when compared to the corresponding optical absorption spectra. The results are discussed in relation to existing theoretical models. © 1998 Published by Elsevier Science Ltd.

Solid State Communications

Photoacoustic response of CdS quantum dots in Nafion

Perfluoroethylene sulfonic acid polymer (NAFION) films are subjected to ion exchange in the medium of aqueous solutions of cadmium acetate, followed by ammonia passivation. The films are then treated with hydrogen sulfide gas for prescribed times. X-ray powder diffraction data of these samples have been analyzed for estimating the sizes of the nanocrystallites. The optical absorption spectra of the samples show an absorption edge beginning at 525 nm for the largest size clusters. A broad absorption band appears with a maximum around 410 nm-440 nm in the smaller size clusters.

Bulletin of Materials Science

Preparation and characterization of CdS nanocrystallites in nafion

Essentials of Nonlinear Optics

Optical phonon confinement in zinc oxide nanoparticles

Journal	Journal of Applied Physics
Publisher	AIP
ISSN	00218979
Open Access	No