Experimental and theoretical study of the spectroscopic properties of Ce3+ doped LaCl3 single crystals

The spectroscopic properties of Ce3+ in LaCl3 single crystals were studied at a temperature of 8 K by means of (vacuum) ultra violet excitation between 4 and 20 eV. LaCl3:Ce shows an exceptionally small crystal field splitting of the Ce 5d levels and the Stokes shift between absorption and emission is large. Theoretical calculations were performed using a combination of the Hartree-Fock ionic cluster model and the density functional band structure model. Very good agreement with experiment was obtained. In the excited 5d configuration the Ce ion appears to move off-centre by lattice relaxation and the crystal field splitting almost doubles, resulting in the large Stokes shift. A comparison with the properties of the concentrated system CeCl3 is made. It seems that in this crystal a slight off-centre position already occurs in the ground state 4f configuration. (C) 2000 Elsevier Science B.V. All rights reserved.