• B P Chandra

      Articles written in Bulletin of Materials Science

    • Influence of surface treatments on CdSe thin films in photoelectro-chemical solar energy conversion

      Shikha Mishra Sanjay Tiwari B P Chandra

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      Photovoltaic performance of semiconductor-liquid junction solar cell using electro-codeposited thin filmn-CdSe is found to improve significantly by proper surface treatments. The solid state parameters of annealed films are calculated and compared with those of unannealed film-based cells. Chemical etching is found to improve short circuit current and fill factor whereas photoelectrochemical etching technique improves the stability of photoanode in polysulphide electrolyte. Annealing promotes incipient fusion of small crystallites, thus reducing the grain boundaries which are known to act as recombination centres for minority carriers and trapping centre for majority carriers. The conversion efficiency and stability are found to improve by chemical etching of the semiconductor layer because chemical etching pins Fermi level of CdSe photoanode and promotes exchange current density.

    • Photoplastic effect in polycarbonate using microhardness measurements

      R Bajpai Sandhya Sharma V K Vastal B P Chandra

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      Vickers microhardness indentation technique has been employed to detect the photoplastic effect in the transparent polycarbonate specimens in darkness and under mercury illumination. For low applied loads, the hardening of specimens under illumination confirms the positive photoplastic effect that causes illumination-induced increase of crosslinking (in polymer). For high applied loads the positive photoplastic effect decreases as the level of microhardness decreases.

    • Temperature dependence of pulse-induced mechanoluminescence excitation in coloured alkali halide crystals

      Namita Rajput S Tiwari B P Chandra

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      In practice, the relative efficiencies of different crystals are often determined under identical conditions of temperature and excitation. If the temperature of a crystal is increased or decreased with respect to room temperature, luminescence efficiency may get increased or decreased according to the composition of the crystal. When coloured crystals of NaCl, NaBr, KCl and KBr are excited by pulse-induced excitation at different temperatures, the mechanoluminescence (ML) intensity increases with temperature. The ML intensity of first peak, 𝐼ml, second peak, 𝐼_m2 and the total ML intensity, 𝐼T, initially increase with temperature and then tend to attain an optimum value for a particular temperature of crystals. The ratio, 𝐼m2/𝐼ml, is found to increase with increasing temperature of the crystals. The expression derived on the basis of rate equations, are able to explain the temperature dependence of ML intensity on several parameters.

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