Zero-dimensional metal oxide Li4TiO4

Abstract

Low-dimensional metal halides have recently emerged as promising luminescent materials; however, chemical and thermal instabilities of halides present challenges to their practical applications. In this paper, we show that low-dimensional metal oxides can exhibit efficient exciton emission based on hybrid functional calculations. We investigated a zero-dimensional ternary oxide, Li₄TiO₄, in which the anionic TiO₄ tetrahedra are spatially separated by highly electropositive Li cations that largely decouple the TiO₄ tetrahedra electronically. The resulting exciton self-trapping leads to the formation of Ti³⁺ and O₂³⁻ (V_k center) within a TiO₄ tetrahedron. The calculated strong exciton binding against dissociation to polarons/free carriers and giant Stokes shift indicate great potential of efficient luminescence at room temperature. We further suggest that Li₄TiO₄ should be a promising self-activated neutron scintillator due to the strong neutron absorption by Li and the efficient exciton emission. This work broadens the current research of low-dimensional metal-halide-based luminescent materials to include oxides with improved stability and new functionalities.