Reproduction of absorption spectra and analysis of multiplet energies for [formula omitted] phosphors using first-principles calculations

Abstract

In recent years, M2VO4ClM=Ca,Sr and M3VO42M=Mg,Zn have been synthesized as rare-earth-free, self-activated phosphors. It is generally accepted that charge transfer transitions between V5+ and O2− are responsible for their absorption and emission of light. In this study, we attempted to reproduce the experimental absorption spectra and analyze the multiplet energy structure of the symmetric TdVO43− cluster using a first-principles calculation method, DV-Xα. This is a type of density functional theory based on the linear combination of atomic orbitals approximation and discrete variational multi-electron method that can account for multiplet effects by including configuration interaction (CI) in the calculation. Herein, we show that although the experimental absorption spectra could not be reproduced by considering only the VO43− clusters, they were successfully reproduced by considering M8VO413+(M=Ca,Sr) clusters and M9VO415+(M=Mg,Zn) clusters. However, we discovered that Zn9VO415+ differs from the other three crystals because its molecular orbitals in the valence band are formed from Zn 3d orbitals and O 2p orbitals. This makes it extremely difficult to calculate the appropriate multi-electron wavefunctions using molecular orbitals using single-electron calculations. Accordingly, we obtained an approximately suitable multi-electron wavefunction using a CI calculation. We grouped the molecular orbitals according to the O 2p orbital population. It was found that the absorption spectra calculated using molecular orbitals with a high O 2p population reproduced the experimental absorption spectra. In addition, calculated multiplet energies and spectra of the Td symmetry VO43− cluster suggest that in this case the excitation model may differ from the conventional one.