Fluorescent zinc blende structured pure and Mn 2+ ion doped ZnS (Mn-ZnS) quantum dots were prepared via a rapid microwave assisted technique without any surfactants and their photocatalytic activity was tested for the photodegradation of methyl orange dye under UV light irradiation. They were characterized by X-ray diffraction, FE-SEM, UV-Vis and photoluminescence spectroscopies, XRF and BET surface area analysis. The Mn-ZnS quantum dots possessed a cubic blende crystal structure without any impurity phases. The absorption maximum by UV-Vis spectroscopy showed a blue shift with increasing Mn 2+ content.Photoluminescence of Mn-ZnS was obtained as a result of combined broad blue emission from sulfur vacancies existing in the ZnS host and orange emission from the 4T 1 -6A 1 transition of Mn 2+ . The relative intensity of blue to orange emissions was found to be quenched with increasing Mn 2+ ion concentration.Methyl orange dye was photodegraded by Mn-ZnS quantum dots effectively up to a doping level of 4.28% Mn 2+ and further increase in Mn 2+ decreased the photocatalytic activity. Detailed mechanisms of photoluminescence and photocatalytic activity were proposed and discussed. The results suggested that the Mn-ZnS material is a potential candidate for photocatalytic applications.

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Abstract-Lead free piezoelectric single crystals of (K 0.5 Na 0.5 )NbO 3 and 0.5 wt%, 1.0 wt% and 1.5 wt% MnO 2 doped (K 0.5 Na 0.5 )NbO 3 (KNN) were grown by high-temperature solution method using K 2 CO 3 -Na 2 CO 3 eutectic composition as flux with addition of small amounts of boron oxide for lowering the melting temperature. The effect of the manganese dopant on the dielectric properties, surface morphology and the domain structure were investigated. The MnO 2 -doped KNN crystals were found to exhibit higher dielectric permittivity when compared with pure KNN single crystal. Mn doping increases the dielectric constant and decreases the dielectric loss. A slight decrease in the orthorhombic to tetragonal phase transition temperature T (O-T) and Curie temperature T C has been observed in manganese-doped KNN single crystals. From SEM and AFM analysis, the domain size of KNN-Mn crystal was found to be of the order of 5-13 µm at room temperature which is smaller than that of the pure KNN crystal (20-30 µm).

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