Arhipov P. Obtaining of YAG-based crystals by the Czochralski method under CO-containing atmosphere.

The work is devoted to the development of scientific and technological basics of obtaining of YAG-based crystals by the Czochralski method under COcontaining atmosphere. It is proposed to use tungsten (W) and molybdenum (Mo) crucibles with by 3 order of magnitude lower cost as an alternative to Ir crucibles, which are usually used at obtaining of crystals of this type. It was shown that the most reliable crucible material for YAG-based crystal growth is tungsten, as W crucibles lifetime exceeds 40 crystallization cycles. The methods of obtaining of YAG-based crystals by the Czochralski technique under CO-containing atmosphere were elaborated. In particular, a method of raw materials synthesis with minimal content of free oxygen was developed. It is shown that due to interactions between YAG raw material, crystal, and melt with Ar+CO raw material the crystal surface is depleted with oxygen and Al, and crystals may contain up to 1% of carbon. The developed method of YAG:Ce,С crystal obtaining in CO-containing atmosphere, in particular, a method of activator introduction in the trivalent state, in the form of crystalline CeAlO3, which minimizes oxidation of crucible and other crystallizer parts. Methods of large CeAlO3 crystal growth with the length up to 130 mm by the Czochralski and EGF methods were developed, as well as a procedure of crystal heat treatment. Optimal regimes of post-growth heat treatment of YAG:C and YAG:Ce,C were determined providing the irreversible elimination of color centers in UV- and visible bands. Annealing of YAG:Ce,C in oxidizing conditions provided the light yield of 28200 phot/MeV, energy resolution 7.8 -8.5 % at the 662 keV energy. The contribution of the fast luminescence decay with τ ~100 ns reaches 79 %. Keywords: garnet, YAG, YAG:Се, CeAlO3, Czochralski method, EFG method, post-growth annealing, scintillator.