In the present work, zinc tungstate (ZnWO 4 ) nanoparticles were synthesized by a simple co-precipitation technique without the addition of any templates and complexing agent. The X-ray diffraction study confirmed the formation of monoclinic structure ZnWO 4 . The annealing temperatures play a significant role on the crystallization of the samples and the crystallite size of ZnWO 4 nanoparticles are varied between 30 and 65 nm. The well dispersed spherical solid shells along with nanoplatelet like morphology was obtained from the surface morphological study. The concomitant decrease in optical energy band gap value of ZnWO 4 is due to the effect of crystallite size enhancement. It was observed that the crystallinity is one of the primary factors that affect the luminescence property of ZnWO 4 nanoparticles. The purity and stoichiometric nature of synthesized product was confirmed by compositional analysis. The highest degradation efficiency of 87% was observed for 300°C annealed ZnWO 4 nanoparticles in the photocatalytic study by the degradation of methylene blue dye under ultraviolet light irradiation. The photocatalytic study confirmed the decomposition of methylene blue after 1 h irradiation.

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Manganese sulphide (MnS) thin films were prepared by chemical bath deposition method. X-ray diffraction analysis was used to study the structure and the crystallite size of MnS thin films. The grain size and the surface morphology were studied using scanning electron microscopy. The optical properties were studied using the UVvisible absorption spectrum. The dielectric properties of MnS thin films were studied for different frequencies and different temperatures. Further, electronic properties, such as valence electron plasma energy, average energy gap or the Penn gap, the Fermi energy and electronic polarizability of the MnS thin films were calculated. The ac electrical conductivity study revealed that the conduction depended both on the frequency and the temperature. The temperature dependent conductivity study confirmed the semiconducting nature of the films.

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Figure 7. FESEM images of vanadium oxide thin films with different annealing temperatures: a) 250 C, b) 350 C, and c) 450 C.