Electronic structure of the luminescent centers in rare earth oxysalts doped by bismuth

Abstract

A cluster model is assumed for the luminescent centers in Y2O3:Bi, BiOCl, and LnOCl:Bi (Ln=La,Y). A semiempirical self-consistent charge and configuration molecular orbital theory has been used to determine valence MO energies and populations. Including spin orbit and configuration interactions, we compute the pattern of the excited levels. Changing the number and the nature of the ligands in the cluster, one can see the variation of the localized charge with respect to the constitution and symmetry of the several environments. Dependence of the electronic levels on distance indicates a large substitution effect comparing with presently available experimental data. The results confirm the presence of allowed electronic excited states with strong oscillator strength in the near uv range, and trap levels. One of the latter always is the lowest electronic level and thus suggests an interpretation of the luminescent processes similar to that proposed for the La2O3:Bi phosphor.