LUMINESCENCE OF THE NEW ELPASOLITE RB2KGAF6 DOPED WITH CR-3+

Photoluminescence, lifetime, optical absorption and EPR measurements on Rb2KGaF6:Cr3+ have been carried out in the 10-300 K temperature range. The emission spectrum at 10 K shows a very rich vibrational structure which can be mainly explained through the vibrational modes of the CrF6(3-) complex. Comparison of the experimental vibrational frequencies and zero-phonon line with those for K2NaAlF6:Cr3+ indicates that the Cr3+-F- distance is about 1.5 pm larger for Rb2KGaF6:Cr3+. The present data clearly demonstrate the existence of a first order phase transition at 129 K (upon cooling) with an involved hysteresis DELTA-T = 6 K although the local geometry around Cr3+ in the noncubic phase remains essentially octahedral.