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.