Effects of Cr3+ concentration on the optical properties of Cs2NaAlF6 single crystals

► We studied the optical properties of the elpasolite Cs2NaAlF6 with 0.1, 1.0, 3.0, 10.0, 30.0 and 50.0% of Cr3+ ions. ► We realized photoluminescence, excitation and absorption measurements at room and low temperatures. ► Vibrational modes of the [CrF6]3− complex were identified and the crystal field parameters were calculated. ► We were able to demonstrate that in this system the Cr3+ occupies two distinct crystallographic sites. ► The results lead us to conclude that the material has potential applications as a lasing system.