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Optical and electrical properties and phonon drag effect in low temperature TEP measurements of Agsbse_2 thin films

Journal of semiconductors 2014年第5期35卷 1-6页

作者： T Namitha Asokan K s Urmila Rajani Jacob Rachel Reena Philip g s okram V ganesan B Pradeep solid state Physics Laboratory Department of Physics Cochin University of Science and Technology Thin Film Research Lab Department of Physics Union Christian College UgC-DAE Consortium for scientific Research

Polycrystalline thin films of silver antimony selenide have been deposited using a reactive evaporation technique onto an ultrasonically cleaned glass substrate at a vacuum of 10-5 torr. The preparative parameters, like substrate temperature and incident fluxes, have been properly controlled in order to get stoichiometric, good quality and reproducible thin film samples. The samples are characterized by XRD, sEM, AFM and a UV-vis-NIR spectrophotometer. The prepared sample is found to be polycrystalline in nature. From the XRD pattern, the average particle size and lattice constant are calculated. The dislocation density, strain and number of crystallites per unit area are evaluated using the average particle size. The dependence of the electrical conductivity on the temperature has also been studied and the prepared Agsbse2 samples are semiconducting in nature. The Agsbse2 thin films exhibited an indirect allowed optical transition with a band gap of 0.64 eV. The compound exhibits promising thermoelectric properties, a large seebeck coefficient of 30 mV/K at 48 K due to strong phonon electron interaction. It shows a strong temperature dependence on thermoelectric properties, including the inversion of a dominant carrier type from p to n over a low temperature range 9-300 K, which is explained on the basis of a phonon drag effect.

关键词： silver antimony selenide reactive evaporation thermoelectric power phonon drag effect

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solvent induced shape change in CePO_4:Dy^(3+) nanophosphors and effect of metal ions: A photoluminescence study

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Journal of Rare Earths 2012年第12期30卷 1217-1224页

作者： Reena okram N.Rajmuhon singh Department of Chemistry Manipur University

The influence of different solvents and metal ions （Li^＋, Ba^2＋, Bi^3＋） on the crystallization behaviour, morphology and enhancement in photoluminescence intensity of Dy^3＋ doped CePO4 were investigated. Highly crystalline luminescent nanophosphors of CePO4：DY^3＋ re-dispersible in polar solvents were successfully prepared via a simple polyol route at 140 ℃. As-prepared Dy^3＋ doped CePO4 nanophosphors prepared in Eg and DMF appeared to have crystalline monoclinic phase but exhibited hexagonal phase when prepared in water and water mixed solvents, The hexagonal phase transformed to monoclinic phase after heating at 900 ℃. TEM study revealed different shapes of the synthesized nanophosphors with change of solvents. The luminescence intensity of 4F9/2→6H15/2 at 478 nm （blue） was found to be more prominent than 4F9/2→6H13/2 at 572 nm （yellow）. The introduction of metal ions （Li＋, Ba2＋ and Bi3＋） in CePO4：Dy3＋ led to considerable luminescent enhancement. The nanophosphors were subsequently incorporated in polymer films of PVA which showed the characteristic emissions of Dy3＋. It also served as an effective method to improve the performance of polymer materials and brought about novel properties in them.

关键词： enhanced luminescence rare earth point defects nanophosphor re-dispersible

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A catalyst-free new polyol method synthesized hot-pressed Cu-doped Bi2s3 nanorods and their thermoelectric properties

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Nano Research 2016年第11期9卷 3291-3304页

作者： Tarachand Vikash sharma Ranu Bhatt Vedachalaiyer ganesan gunadhor singh okram UgC-DAE Consortium for scientific Research Indore 452001 India Technical Physics Division Bhabha Atomic Research Centre Mumbai 400085 India

This is the first report on the thermoelectric properties of a catalyst-free polyol method used to prepare stoichiometric Bi2-xCuxs3 samples, x = 0.1, 0.2, 0.3, 0.4, via hot pressing. Various systematic approaches to arrive at in their stoichiometric compositions are explored precisely with introduction of excess precursor of s. X-ray diffraction data analysis using Rietveld refinement confirms a polyhedral orthorhombic crystal structure with a space group Pnma, in contrast to Pbnm reported earlier. Raman data further substantiates this. X-ray photoelectron spectroscopy confirms the valence states of the constituent elements （Bi^3＋, Cu^2＋, and s^2-） and energy dispersive X-ray analysis corroborates their compositions. The particle sizes of the pure Bi2s3 nanoparticles were 20, 35, and 82 nm as determined from the scherrer formula, atomic force microscopy, and dynamic light scattering, respectively. Their transmission electron microscopy image shows rod-like nanostructures elongated in the 〈010〉 direction with an average diameter of 23 nm and a length of several hundreds of nanometers. A 34% improvement in the thermoelectric figure of merit is observed for Bi.6Cu0.4s3 as compared to pure Bi2s3 at 300 K.

关键词： Bi2s3 polyol nanorods thermoelectrics

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