PHONON STRUCTURE OF CR3+ PHOTOLUMINESCENCE IN CHROMIUM-DOPED MAF(3) (M=CD, CA A=RB, CS) CRYSTALS

The structure of the luminescence band of Cr3+ ions in CsCaF3, CsCdF3, RbCaF3 and RbCdF3 has been measured and analyzed using decay time measurements and time-resolved spectroscopy. The observed emission corresponds, in cubic Cr3+ centers, to the transition from the lowest spin-orbit (SO) component of the T-4(2g)(F-4) level to the (4)A(2g)(F-4) ground state. The structure has been associated with the zero phonon lines (ZPL) and vibrational replicas of several types of Cr3+ centers, mainly cubic and trigonal ones. Four different phonon modes have been found in each of the crystals. Their frequencies change with the host crystal but not with Cr3+ symmetry. A tentative assignment of these phonon frequencies to normal modes of the [CrF6](3-) complex has been proposed and discussed. The Cs compounds show a satellite at 14 cm(-1) in the high energy side of each of the lines. It has been associated with the emission from the next SO component of the T-4(2g) level. The strong reduction of the SO coupling constant with respect to the free ion value is likely due to a dynamic Jahn-Teller effect.