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Luminescence studies of II-VI Nanocrystals
Kamal K. Kushwah1, 2, Pranav Singh2, and M.Ramrakhiani2 1. Department of Applied Physics, Jabalpur Engineering College, Jabalpur, M.P., India. 2. Department of Post Graduate Studies and Research in Physics and Electronics Rani Durgavati Vishwavidhyalaya, Jabalpur (M.P.) E-mail:kamal_kushwah2005@yahoo.com
Abstract The nanocomposite films of CdSe and ZnSe nanocrystals in polyvinyl alcohol (PVA) matrix were synthesized by environmental friendly chemical method. These composites were characterized by X-ray diffraction which indicates the nanocrystalline structure of CdSe and ZnSe in polymer matrix with particle size up to a few nm. The Particle size is found to decrease by increasing PVA Concentration and metal selenide (ZnSe/CdSe) content. The photoluminescence properties of these composite films with varying concentration of PVA and metal selenide (ZnSe/CdSe) content have been investigated. The PL peak of CdSe and ZnSe were observed at 510 nm and 465 nm respectively. The higher intensity is observed by increasing PVA content in CdSe and ZnSe nanocomposite films without any change in position of PL peak. It is also revealed that, In ZnSe & CdSe/PVA nanocomposites with varying ZnSe/CdSe content, PL peak shifts towards shorter wavelength as particle size is reduced. This PL emission may be attributed due to various surface states available and the Blue shift could be attributed to size reduction of PVA matrix to CdSe nanoparticles with variations of CdSe content. Due to proper passivation of surface states non-radiative transition are reduced which enhance the PL intensity. The polymer matrix acts to stabilize the nanoparticles. Due to the PL peak in green and blue region these composite films are promising materials for optical display devices.
1. INTRODUCTION 1. Polymer- inorganic nanocomposites have attracted much attention recently due to their unique size dependent chemical and physical properties [1]. 2. ZnSe & CdSe nanocomposites exhibit size dependent tunable photoluminescence [2]. 3. Studies have been under taken to prepare ZnSe/CdSe nanoparticles in PVA matrix and investigate their Photo luminescence.
2. EXPERIMENTAL
1. ZnSe/PVA Nanocomposites were prepared by chemical method. 2. First PVA solution was prepared in distilled water and then 1 ml ZnCl2 solution was added. 3. After setting the pH by NH3 solution at 10, 1 ml of freshly prepared Na2SeSO3 solution was added and stirred for 90 minutes to obtain ZnSe/PVA. 4. Solution was spread on glass plates and on solvent evaporation nanocomposites films were obtained. 5. A number of samples were prepared with different PVA concentration and subjected to X-ray diffraction and Photoluminescence investigations.
6. For CdSe/PVA nanocomposite CdCl2 is taken at the place of ZnCl2. 3. RESULT AND DISCUSSION 1.XRD pattern reveals cubic structure for ZnSe/PVA and hexagonal for CdSe/PVA Nanocomposite films . 2. Three Peaks are obtained at 2θ=27.57˚, 45.59˚, 53.27˚ indicating reflection from (111), (220), (311) planes for ZnSe/PVA. 3.The peak corresponding to 2θ=20˚ represents PVA matrix.
4. The Particles size of samples computed from Debye Scherrer formula are obtained up to 20nm. 5. The Particle size is found to decrease by increasing PVA Concentration. 6. PVA is acting as capping agent and by increasing its concentration smaller ZnSe/CdSe particles are formed in its matrix.
Fig.1. XRD pattern of ZnSe/PVA
7. Photoluminescence (PL) spectra of ZnSe/PVA samples excited by 230 nm UV light are shown in fig.2. 8. A single peak is obtained at 465 nm for ZnSe/PVA and the higher intensity is observed by increasing PVA content in ZnSe nanocomposite films without any change in position of PL peak. 9. Higher intensity is obtained for smaller ZnSe particles in PVA matrix. 10. The PL peak shifts toward lower wavelength region by increasing the ZnSe content shows strong quantum confinement effect due to smaller particle size. 11. The oscillator strength is increased by reducing the size which enhances the PL intensity. 12. Due to proper passsivation of surface states non radiative transitions are not increased which enhance the PL intensity.
S5 S4 S3 S2 S1
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Fig.2 Photoluminescence Spectra of ZnSe/PVA Samples.
4. CONCLUSION
1. ZnSe/PVA Nanocomposites can be synthesized by very simple chemical route. 2. XRD analysis revealed that, increasing PVA concentration in ZnSe/PVA composites, particle size is reduced. 3. PL intensity is increased with reduction in particle size, due to enhanced oscillator strength. 4. Due to the PL peak in green and blue region these composite films are promising materials for optical display devices.
ACKNOWLEDGEMENT
The authors gratefully acknowledge the valuable assistant provided by Inter University
consortium
(IUC) Indore for characterizing samples by XRD and also very much thankful to Department of Nanotechnology, MAINAT, Bhopal for PL Studies.
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