Absorption and emission spectra of Ce3+ in elpasolite lattices

The experimental determination of the electronic energy levels for Ce3+ in some chloroelpasolite hosts for both the ground 4f(1) and the excited 5d(1) configurations is described. High-resolution f-f absorption and f-T-2(2g) d absorption and emission spectra have been recorded at low temperatures for Ce3+ diluted into various hexachloroelpasolite lattices. A fluorescence spectrum at similar to50 000 cm(-1) is tentatively assigned to the emission from the highest 5d crystal field level, E-2(g), of a Ce3+ impurity in Cs2NaErCl6, enabling the values of all the energy levels of both the 4f(1) and 5d(1) configurations to be given for Ce3+ in elpasolite hosts. Vibronic structure superimposed on the electronic transitions is analyzed in terms of a simple configurational coordinate model involving the ground and excited configurations. It is found that the difference in the Ce-Cl bond length between the 4f(1) and 5d(1) configurations is similar to0.04 Angstrom. Ab initio model potential calculations on the (CeCl6)(3-) cluster embedded in a reliable representation of the Cs2NaYCl6 host support these conclusions.