Influence of Various Impurities on the Optical Properties of YbF$\text{}_{3}$-Doped CaF$\text{}_{2}$ Crystals

Calcium fluoride crystals doped with YbF$\text{}_{3}$ and co-doped with LiF and NaF were grown using the vertical Bridgman method. Several of rare-earth ions (such as Eu, Sm, Ho, Tm, and Yb) can be stabilized in the divalent state in the CaF$\text{}_{2}$. The change of valence was attained by various methods. The optical absorption spectra reveal the characteristic absorption bands of the Yb$\text{}^{3+}$ and Yb$\text{}^{2+}$ ions. This means that the developed crystal growth process achieves a good Yb$\text{}^{3+}$ to Yb$\text{}^{2+}$ conversion in the as-grown crystals. The influence of other impurities, such as Na$\text{}^{+}$ or Li$\text{}^{+}$, on the absorption and emission spectrum of YbF$\text{}_{3}$-doped CaF$\text{}_{2}$ was studied. The Li$\text{}^{+}$ and Na$\text{}^{+}$ ions drastically decrease the absorption coefficient of the Yb$\text{}^{2+}$ ions in the UV band and the emission intensity by excitation in 230 nm.