Luminescence of VO43- centers in LiMgPO4 and LiMgVO4: Effect of [PO4]3-/[VO4]3- substitution on the structure and optical properties

The effect of V doping on the structure and optical properties of LiMgPO4 was studied. We found that LiMg(PO4)(1-x)(VO4)(x) with x<17% V retains the crystal structure of LiMgPO4 and demonstrates self-activated luminescence. All emission spectra under 320 nm excitation had the form of a broad band with a maximum at 490 nm and the emission intensity increased with the vanadium concentration. The luminescence with a peak at 560 nm was also observed for LiMgVO4. The UV-Vis diffuse reflectance spectra were recorded for LiMgPO4, and LiMgPO4 with 17% V and LiMgVO4, and the optical band gaps were estimated to be 4.05, 3.90 and 3.43 eV, respectively. The ab initio calculations predict an absorption edge shift to lower energies with growing vanadium concentration and reproduce very well the experimental band gaps for vanadium containing oxides (LiMgP0.75V0.25O4 and LiMgVO4), but provide a much larger value for LiMgPO4. (C) 2017 Elsevier B.V. All rights reserved.