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Samavati A.,University of Technology Malaysia | Othaman Z.,University of Technology Malaysia | Dabagh S.,University of Technology Malaysia | Ghoshal S.K.,Advanced Optical Material Research Group
Journal of Nanoscience and Nanotechnology

Controlled growth and characterization of germanium (Ge) and silicon (Si) nanostructure are the key issues for optoelectronic device fabrication. The role of post-annealing on the structural and optical properties of radio frequency (rf) magnetron sputtering grown of Ge and Si quantum dots (QDs) deposited on Si(100) substrate is studied. Atomic force microscopy confirmed the formation of Si and Ge QDs with estimated sizes lower than ~17 nm and ~14 nm respectively. The X-ray diffraction analysis revealed the formation of Si and Ge QDs accompanied by SiO2 with estimated sizes of ~5 and ~7 nm for post-annealed Si and pre-annealed Ge QDs respectively. The room temperature photoluminescence spectra for Ge and Si demonstrated an emission peak at 3.20 and 2.72 eV respectively, which are attributed to the electron and hole recombination within QDs. A shift in the PL peak is observed through annealing which is ascribable to the changes in size of QDs and quantum confinement effect. The thermal annealing at 600 °C is found to play an important role in controlling the shape, number density, root mean square (rms) roughness and the energy shift of the luminescence band for both Si and Ge QDs. The influence of annealing on growth morphology for Ge QDs is appeared to be stronger than Si. Copyright © 2014 American Scientific Publishers All rights reserved. Source

Amjad R.J.,Advanced Optical Material Research Group | Amjad R.J.,University of Punjab | Sahar M.R.,Advanced Optical Material Research Group | Ghoshal S.K.,Advanced Optical Material Research Group | Riaz S.,University of Punjab
Advanced Materials Research

Phosphate glasses containing fixed concentration of rare-earth with and without metallic nanoparticles (NPs) having compositions (59.5-X) P 2O 5-MgO-xAgCl-0.5Er 2O 3, where 0 <: x <: 1.5 mol% was prepared using melt-quenching technique. Spectral characterizations were made using UV-VIS-IR spectroscopy and photoluminescence spectroscopy. Addition of silver NPs enhanced the corresponding absorption and was optimum at 1.5 mol% AgCl. Infrared to visible frequency upconversion (UC) emission were observed in the glass on pumping with 797 nm radiation. Furthermore, it was found that the emission at 540 nm, due to Er 3+transition ( 4S 3/2- 4I 15/2) was much more influenced by the silver NPs in comparison to the emission at 632 nm ( 4F 9/2 - 4I 15/2). These enhancements were attributed to the local fields present in the vicinity of silver NPs. Moreover, the rapid increase in the intensity of the green band as compared to the red band was due to the charge cloud effect of the plasmon band. Since green band lie more close to the plasmon frequency band of Ag and hence showed rapid increase compared to the far lying red bands. Our findings may contribute towards the development of solid state laser and sensors. © (2012) Trans Tech Publications. Source

Dousti M.R.,Advanced Optical Material Research Group | Ghoshal S.K.,Advanced Optical Material Research Group | Sahar M.R.,Advanced Optical Material Research Group | Sharma S.,Inter University Accelerator Center | Arifin R.,Advanced Optical Material Research Group
Asian Journal of Spectroscopy

A four-level model is developed and the rate equations are derived to examine the mechanism of up-conversion (UC) emission process and the radiative relaxational behavior of Er3+- doped zinc tellurite glass under the excitation of 797 nm. Semi-empirical methods are used in simulating the rate equations for the fluorescence emission characteristics of the green ( 4S3/2→4I15/2) and red ( 4F9/2→4I15/2) bands. The population dynamics of the ground and excited states are studied. NR (NR) multi-phonon relaxation rates for 2, 4 and 6-phonos processes and their quantum efficiencies are calculated. A much higher population for the 4S 3/2 level is achieved in contrast to the population of 4F9/2 level. In addition, the quantum efficiency for the up-converted green emission is found to be higher than the red emission. These observations are attributed to the energy transfer and cross relaxational mechanisms among various levels of Er3+ ions. The radiative and NR rate processes and the level populations for green and red transitions are analyzed in detail and understood. The present model is quite generic and can be extended to study the mechanism of luminescence to other glasses with different rare earth dopants of varying concentrations an temperature. The model parameters are tuned to determine the desired quantities in rare-earth doped tellurite glasses and are tallied with experimental data. Up-conversion, Luminescence, Nonradiative process, Radiative process, Multi-phonon relaxation, Rate equation, Quantum efficiency. Source

Sazali E.S.,Advanced Optical Material Research Group | Sahar M.R.,Advanced Optical Material Research Group | Jan N.A.M.,Advanced Optical Material Research Group | Hamzah K.,Advanced Optical Material Research Group | Arifin R.,Advanced Optical Material Research Group
Advanced Materials Research

The study of the crystallization kinetics of rare-earth doped glass stimulated much interest especially for crystallization process. In this work transparent Eu 2O 3 doped glasses with composition TeO 2 - Na 2O - MgO were prepared using conventional melt-quenching technique. The amorphous nature of glass was confirmed using X-ray diffraction method. The influence of Eu 3+ content on the crystallization kinetics of the glass such as activation energy (E a) was thoroughly evaluated under non-isothermal conditions using DTA. The crystallization kinetic at different heating rate from 5 °C min -1 to 25 °C min -1 at different crystallization temperature (T p) were examined and verified using Ozawa method. The result showed that the activation energy (E a) was decreased with the increasing of the dopant concentration from 319.8 eV to 93.5 eV. © (2012) Trans Tech Publications. Source

Hamzah K.,Advanced Optical Material Research Group | Yassin M.A.I.,Advanced Optical Material Research Group | Sahar M.R.,Advanced Optical Material Research Group | Ghoshal S.K.,Advanced Optical Material Research Group | And 2 more authors.
Advanced Materials Research

Series of glass based on (80-x)TeO 2-10PbO-10PbCl 2-xYb 2O 3 where 0.0 ≤: x ≤: 3.0 has been successfully prepared by melt quenching technique. The amorphous nature of glass has been determined by X-ray diffraction method. Their corrosion behavior was investigated using the FTIR spectroscopy technique on the sample that has been immersed in distilled water and in aqueous solution of pH 4 and pH 9 for 10 days. There were three major absorption peaks around 3600 cm -1, 889 cm -1 and 470 cm -1 has been observed. The intensity of each peak was found to vary with the Yb 3+ content. © (2012) Trans Tech Publications. Source

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