Comparison of experimental and computational Bi^4+/3+ charge transition level energies relative to the vacuum level

Abstract

Bismuth, in the form of Bi²⁺, Bi³⁺, and Bi⁴⁺, is utilized in luminescence phosphors, scintillators, afterglow phosphors, and storage phosphors. The preferred valence of bismuth, wavelength of emission, quantum efficiency, thermal quenching, and whether bismuth can trap an electron or a hole depend on the location of the Bi^3+/2+ and Bi^4+/3+ charge transition levels in the band gap of the inorganic compound. The Bi^4+/3+ charge transition level energy relative to the vacuum level is equivalent to the vacuum referred binding energy (VRBE) in the ground state of Bi³⁺. Methods for obtaining Bi³⁺ VRBEs in inorganic compounds have become available past ten years. One method uses experimental data on Bi spectroscopy combined with the semi-empirical chemical shift method that was originally developed for the lanthanides. Another method is fully computational. The Bi^4+/3+ CTL location above the valence band (VB) top is first computed. A separate computation with the slab and vacuum method provides the energy at the VB-top relative to the vacuum level. Here we will compare the results of both methods to explore to what extend they are consistent with each other.