Crystal growth and radiation-induced defects of rare earth doped lithium yttrium fluoride laser host materials.

摘要

Scope of study. Single crystals of undoped and rare-earth doped lithium yttrium fluoride (YLF) crystals were grown using the Czochralski and vertical Bridgman techniques. This material has an incongruent melting point and as a consequence the growth material must contain excess LiF.; Single crystals of undoped YLF were irradiated with 1.75 MeV electrons. This irradiation was found to create defects which exhibited polarized absorption bands in the UV-visible region of the spectrum. In order to associate the absorption bands to F and F-aggregate centers, optical relations were used to correlate four of these bands to the previously identified 3.7 eV F-center absorption band.; Findings and conclusions. The Czochralski growth of YLF produced large, oriented crystals. However growth of these crystals by this method was difficult and time consuming. The Bridgman method was shown to rapidly produce rare earth doped research samples at a growth rate of 1.5 millimeters per hour and a temperature gradient of 50{dollar}spcirc{dollar}C per centimeter at the melting point. The system in which these crystals were grown produced crystals with near 100% yield.; Two radiation-induced absorption bands, located at 2.85 and 4.43 eV, were found to grow linearly with the 3.7 eV F-center band. These bands were identified as due to the F-center. A band centered at 1.97 eV was found to grow quadratically with the 3.7 eV F-center band. This band was identified as due to the M-center. A band centered at 2.3 eV grew as the cube of 3.7 eV F-center band. This band was identified as due to the R-center.