The optical properties of Bi3+ and Sb3+ in YNbTiO6 analysed by means of DOS and semi-empirical calculations
This paper reports on the synthesis and optical properties of YNbTiO6 doped with Bi3+ or Sb3+ ions. This crystal system features unique properties ascribed to the presence of transition metal cations with d0 electron configuration, the Nb/Ti site being equally shared between these atoms. In this chemical environment, Bi3+ shows an intense yellow emission upon near-UV pumping while Sb3+ induces bright yellow body pigmentation. The absorption/excitation features are reproduced by means of DOS calculations in conjunction with semi-empirical methods allowing the intra-ionic s2 → s1p1 (A transition) and charge-transfer (CT) states of s2 cations to be located from the sole knowledge of the structural characteristics of the crystal lattice. The origin of the Bi3+ emission is analyzed in the frame of semi-empirical models that are revisited and refined based on a re-actualized review of the luminescent properties of 30 Bi3+-doped closed-shell transition (i.e. titanates, zirconates, vanadates, niobates, tantalates, molybdates, and tungstates) and post-transition (e.g. stannates) metal oxides. Although A and CT states have similar energies in YNbTiO6:Bi3+, the Bi3+ emission is demonstrated to have a CT character in this compound.