Role of the 4f55dband in the radiationless5D1rarr;5D0coupling in BaCl2:Sm2+and BaBr2:Sm2+thinsp;

摘要

In this paper, the adiabatic relaxation theory is applied to investigate the origin of rarehyphen;earth fluorescence quenching involving multiphonon transitions. The energy level schemes for BaCl2:Sm2+and BaBr2:Sm2+have been obtained from the observed fluorescence spectra. The phonon cutoff frequencies, 210 and 140 cmminus;1for BaCl2and BaBr2, respectively, have been determined from vibronic sidebands. From the observed temperature dependence of the fluorescence intensities and lifetimes, it is shown that the5D1and5D0levels are thermally quenched through radiationless excitation to the 4f55dband and that the population of the5D0level from5D1involves the 4f55dband as an intermediary. This indirectf(rarr;d) rarr;frelaxation mechanism appears to have resulted from the proximity and relatively large displacement between the adiabatical surfaces of the lowhyphen;lying 4f55dand the5D1states of Sm2+in BaCl2and BaBr2.