Tomohiko Satonaga

Color centers in LiCaAlF6 single crystals and their suppression by doping

LiCaAlF6 (LiCAF) single crystals pure and doped with MgF2 and BaF2 were successfully grown by the Czochralski technique. Optical absorption measurements in the UV/Visible spectral regions following x-ray irradiation (radiation induced absorption) were performed in order to investigate the radiation damage of the crystals. The F-center absorption band at 262 nm is the dominating induced absorption feature. The amplitude of the F-absorption band is suppressed by more than a factor of 3 in Mg-doped LiCAF compared to undoped, while for Ba-doped LiCAF, almost no variation is obtained. In Mg-doped crystals the optimum doping concentration is of about 0.2 mol % of MgF2 in the melt.

X-ray induced color centres in pure and doped LiYF4 and LiLuF4 single crystals

YLiF 4 and LuLiF 4 pure and doped with Yb 3+ ion were grown by the Czochralski technique under CF 4 atmosphere. X-ray irradiation was used to carry out a comparative study of the induced optical absorption phenomena and color center creation in the ultraviolet and visible spectral regions. The F-center absorption band at 315 and 340 v nm in LLF and YLF, respectively, is the dominating induced absorption feature. The amplitude of the induced absorption is reduced by more than a factor of 10 in Yb-doped crystals compared to the undoped ones.

Binary Fluorides: (Gd,Y)F3 and K(Y,Lu)3F10

The growth of rare-earth fluoride solid-solution crystals by the micro-pulling-down method is reviewed, focusing on the trifluorides Gd1−x YxF3 and Gd1−x YbxF3 (x = 0.12–0.42) in particular. Details on the growth of Pr-doped KY3F10 single crystals 0.5–3.0 mm in diameter and 35–45 mm in length are also presented. When single-phase solidification was achieved, the crystals had no any visible inclusions or cracks. The KY3F10 crystals were transparent and slightly green in color. The luminescence spectra and decay kinetics measured at 80–300K of a number of YF3-GdF3 mixed crystal hosts co-doped with Ce3+ and Me2+ (Me = Mg, Ca, Sr, Ba) cations are also discussed.