Size dependent structural, vibrational, and luminescence properties of nanocrystalline LiIn(WO4)2:Cr3+.

X-ray, electron transmission spectroscopy, vibrational and luminescence studies of LiIn(WO4)2:Cr+ nanoparticles prepared by Pechini method are reported. On annealing the sample several structural changes were observed resulting in a creation of three new, previously unknown polymorphs. It was shown that this tungstate undergoes two size-induced phase transitions from the structure similar to LiFe(WO4)2 into the structure similar to LiYb(WO4)2 and then into the structure of LiGa(WO4)2 type. These transitions occur for the critical particle size of about 100 and 30 nm, and they could be attributed mainly to some changes in the distribution of the sites occupied by Li+ and In3+ ions. Luminescence studies revealed decrease of the covalent character of chromium environment and electron-phonon coupling strength with decreasing size of the nanoparticles.