Semiempirical Self-Consistent Field Modeling of the Ce⁺³ 4f AND 5d Energy Levels in Solid State Luminescent Materials

Abstract

Rare earth doped semiconductors are known to be efficient luminescent materials. In particular, SrS and Sr_xS and Sr_xGa₂S₄ doped with Ce⁺³ have recently been explored as efficient blue cathodoluminsecent and electroluminescent materials for flat panel display applications. The blue emission in these materials is due to Ce⁺³ 5d-4f transitions, and the transition energies are sensitive to the local chemistry of the Ce⁺³ ion. To understand the effect that the local chemistry has on the Ce⁺³ 4f-5d emission spectrum, we used a self-consistent-field configuration interaction (SCF/CI) model to calculate the electronic spectrum of the Ce⁻³ ion embedded in a cluster representation of the semiconductor lattice. The effects of changing nearest neighbor anions and cations have been modeled and are in excellent agreement with the experimental spectroscopy. While vibronic transitions are not calculated in this model, the calculated line transitions were fit to Gaussian peaks to generate absorption and emission spectra. Calculated and experimental Ce³⁺ 4f-5d emission spectra are compared for different materials, and the observed spectral changes are correlated to an analysis of the magnitude of the ligand field splitting and the nephelauxetic effect in various host lattices. Computed atomic orbital electron populations support these arguments.