Electronic structure and optical properties of Ti-doped phosphate crystals

Luminescence properties of NaAl1−xTixP2O7 (x = 0–1) double phosphates under VUV excitation are studied. Partial densities of electronic states are calculated for perfect NaAlP2O7, NaTiP2O7 and Ti-doped NaAlP2O7 crystals. Pure NaAlP2O7 crystals exhibit emission bands peaking near 300 and 770 nm. Doping of NaAlP2O7 crystals with Ti ions leads to appearance of emission bands in blue-green spectral region with main peak near 500 nm. NaTiP2O7 exhibit emission in blue-green region with similar shape as for NaAlP2O7:Ti. The luminescence mechanisms in Ti-doped phosphates are discussed using both experimental and theoretical results. Observed emission bands in blue-green region of spectrum are ascribed to emission centers like Ti4+ + F-centers.