Determination of the Ce+3 bonding in the Ca0.5Sr0.5Ga2S4 : Ce phosphor viax-ray photoelectron spectroscopy

The addition of oxygen in Ca0.5Sr0.5Ga2S4:Ce phosphor was found to nearly d ouble the luminance and to blue shift the emission spectrum of the Ce+3 4f- 5d transition. X-ray photoelectron spectroscopy (XPS) analysis was used to investigate the local chemistry of the Ce+3 luminescent center in the undop ed and oxygen-doped Ca0.5Sr0.5Ga2S4 phosphor. The shake up structure in the Ce+3 3d(3/2) and 3d(5/2) XPS spectra is due to a ligand-to-metal charge tr ansfer process, and the relative intensity of the charge transfer peaks inc reased when oxygen was introduced. Because the charge transfer probability is controlled by the local ionicity of the Ce bonds, the increase in the ch arge transfer peak intensity is consistent with the formation of Ce-O bonds . Furthermore, the binding energy of the charge transfer peaks and the Ce M NN Auger peak shifted, again consistent with oxygen bonding to the Ce+3 lum inescent center. A self-consistent field configuration interaction model is used to calculate the positions of the 4f and 5d levels with Ce-S and Ce-O bonds. By replacing the three of eight sulfur ligands with oxygen the SCF/ CI model predicted a 1035 cm(-1) blue shift in the 4f-5d transition energy which was in excellent agreement with the observed 730 cm(-1) blue shift. ( C) 1999 American Institute of Physics. [S0021-8979(99)07817-2].