THE VIBRONIC SPECTROSCOPY AND LUMINESCENCE CONCENTRATION QUENCHING OFTHE PR-3(+) ION IN LA2O3 LAOF AND LIYF4

The luminescence spectra of the Pr3+ ion in (La1-xPrx)2O3 (x less-than -or-equal-to 0.2), La1-xPrxOF and LiY1-xPrxF4 (x less-than-or-equal-to 0.1) powder samples and in LiY1-xPrxF4 (x less-than-or-equal-to 0.02) single crystals have been investigated. The concentration quenching o f the Pr3+ emission is observed to be stronger in (La1-xPrx)2O3. This is ascribed to a more efficient cross-relaxation via superexchange int eraction between Pr3+ ions. This interaction is shown to be effective over longer distances in La2O3:Pr than in LiYF4:Pr (viz. 10 and 5 angs trom, respectively). The shift of the 4f5d configuration to lower ener gies with increasing Pr3+ concentration, which is only observed for (L a1-xPrx)2O3, gives support for this conclusion. Moreover, the vibronic spectra and the vibronic transition probabilities of Pr3+ in LaOF and La2O3 are reported and compared.