Semiempirical SCF/CI modeling of Ce+3 4f and 5d energy levels in oxygen-doped SrS : Ce

Addition of oxygen in the Ca0.5Sr0.5Ga2S4:Ce phosphor has been found to nea rly double the efficiency and shift the Ce+3 4f-5d emission spectrum to a d eeper blue. To understand the effects that oxygen has on the Ce+3 4f-5d emi ssion spectrum, we used a self-consistent-field configuration interaction ( SCF/CI) model to calculate the electronic spectrum of oxygen-doped SrS:Ce. By replacing the appropriate number of sulfur ligands with oxygen ligands, the SCF/CI model predicted a blue shift for two different cerium-oxygen bon d distances that is in very good agreement with the 730 cm(-1) blue shift o bserved for Ca0.5Sr0.5Ga2S4:Ce. An analysis of atomic orbital electron popu lations indicates that changes in covalency of the Ce 5d orbitals upon inco rporation of smaller O-2 ions causes the observed blue shift. Calculated os cillator strengths indicate that the observed increase in electroluminescen t efficiency caused by addition of oxygen is not a result of changes in tra nsition intensities. (C) 2000 The Electrochemical Society. S0013-4651(99)04 -114-2. All rights reserved.