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.