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 4f1 and the excited 5d1 configurations is described. High-resolution f−f absorption and f−2T2g d absorption and emission spectra have been recorded at low temperatures for Ce3+ diluted into various hexachloroelpasolite lattices. A fluorescence spectrum at ∼50 000 cm-1 is tentatively assigned to the emission from the highest 5d crystal field level, 2Eg, of a Ce3+ impurity in Cs2NaErCl6, enabling the values of all the energy levels of both the 4f1 and 5d1 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 4f1 and 5d1 configurations is ∼0.04 Å. Ab initio model potential calculations on the (CeCl6)3- cluster embedded in a reliable representation of the Cs2NaYCl6 host support these conclusions.