Investigation of Ce$^{3+}$ impurity centers in UV active media Ce:LiCaAlF$_{6}$ and Ce:LiSr$_{0.8}$Ca$_{0.2}$AlF$_{6}$

Fluoride crystals with the colquiriite structure LiCaAlF$_{6}$ doped with Ce$^{3+}$ ions are used as active media for lasers of ultraviolet spectral range with advantages of laser wavelength tuning range and no photoinduced degradation of laser properties. In this work we show that the multicenter character of Ce$^{3+}$ segregation in this matrix agrees with the previously known peculiarities. On the basis of spectral-kinetic properties investigation, we show the increase of segregation coefficient for Ce$^{3+}$ in LiSr$_{0.8}$Ca$_{0.2}$AlF$_{6}$ mixed crystal. In laser experiments with Ce:LiCaAlF$_{6}$ crystal, the differential efficiency of 47% and the wavelength tuning from 281 to 312 nm have been reached.