Abstract
Blue emission due to self trapped exciton recombination in CaWO4 is believed to be very sensitive to the nature of the WO4 structural units. The present manuscript deals with the probing of structural differences existing in WO4 tetrahedra of CaWO4 particles having varying average crystallite sizes and different blue light emission characteristics. Based on XRD, W L1 edge XANES and W L3 edge EXAFS studies, it is inferred that factors like average W–O and Ca–O bond lengths, average number of oxygen atoms around W6+ ions and disorder in WO4 tetrahedra do not have any effect on the blue luminescence intensity from the samples. The lifetime value of excitons is lower for the nanocrystals/nanoparticles of CaWO4 compared to the bulk sample. The lower lifetime of self trapped excitons and the associated decrease in blue luminescence intensity for nanoparticles/nanocrystals (compared to bulk) has been explained based on competing non-radiative processes involving the interaction of holes with surface hydroxyl groups and an associated decrease in the extent of radiative exciton recombination.
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