NONRESONANT ENERGY-TRANSFER FROM THE 5D4 LEVEL OF TB3+ TO THE 5D0 LEVEL OF EU3+

The infrared absorption spectrum and the visible emission spectra of Cs2NaTbCl6 are used to provide assignments for the energy levels of this cubic elpasolite system, up to 21 000 cm-1. The spectra have been interpreted in detail, particularly with respect to the vibrational sidebands of the electronic transitions. Together with the measured oscillator strengths from the 5D0<--F-7(0) absorption spectrum of Cs2NaEuCl6, the data are used in a spectral overlap model to calculate the energy transfer rate from the 5D4 term manifold of Tb3+ to the 5D0 term of Eu at 77 K. The calculated rate is 1.4 x 10(6) times smaller than the previously reported [1] energy transfer rate, so that it appears unlikely that the 5D4 luminescence quenching in Cs2NaTbCl6:EuCl63- is due to the proposed cross-relaxation mechanism.