Study of optical properties of Cr3+ ions in Cs2NaAlF6 single crystals

Emission and excitation spectra for Cs2NaAlF6:Cr3+ are presented. The near-infrared fluorescence observed at 77 and 4.2 K are attributed to the zero-phonon spin-forbidden transition 2E(2G)→4A2(4F) while at room-temperature the emission is assigned to the 2T2(2F)→4A2(4F) transition. Two non-equivalent octahedral sites are identified through time-resolved measurements and lifetime fluorescence bands are measured. The Racah and crystal-field parameters are calculated for both sites.