Size-induced symmetric enhancement and its relevance to photoluminescence of scheelite CaWO4 nanocrystals

This work explores size-induced lattice modification and its relevance to photoluminescence properties of scheelite nanostructures. CaWO4 nanocrystals, a prototype scheelite compound, exhibited a lattice expansion and an increased symmetry of structural units with physical dimension reduction, which is in contradiction to the trend previously reported in bulk CaWO4 at high pressures or high temperatures. Lattice variations in CaWO4 nanocrystals are probably due to the negative pressures that originated from strong defect dipole interactions on surfaces. The increased structural symmetry along with surface citric modifications produced a significant enhancement in photoluminescence of CaWO4 nanocrystals, indicating a quantitatively structural control over the electronic properties.