Photodynamic Processes in LiCaAlF6 Crystals with Double Activation by Ce3+ and Yb3+ Ions

We presented the results of a spectroscopic study of LiCaAlF6 (LiCAF) samples doped with Ce3+ and Yb3+ ions. Change in the valence of the Yb3+ → Yb2+ ions were detected upon excitation resonant to Ce3+ absorption. Luminescence of Ce3+ and Yb2+ ions was observed at the wavelengths of 280–320 nm and 380 nm, respectively. We associate the appearance of divalent ytterbium with photoionization of Ce3+ ions and subsequent capture of a free charge carriers by Yb3+ ions. Based on the temperature dependence of the lifetimes of excited Yb2+, we conclude that energy transfer to the Yb3+ ion occurs due to the charge exchange processes of Yb2+ ions. However, we also see additional quenching of Yb2+ luminescence when the temperature is raised to room temperature.