Preparation and Single Crystal Growth of LiYF4 Laser Materials

The report describes techniques for preparation of high purity fluorides suitable for laser crystal hosts. Growth methods for LiYF4 were also developed using a constant flow of HF. The YF3 and rare earth fluorides are prepared from 5 or 6-9's polycrystalline oxides. A special platinum reactor was designed to convert oxides to fluorides via an HF reaction. Trifluorides were prepared at 800-900C and melted under HF at 1050-1200C. This prevented formation of oxide and oxyfluoride impurities in the melt. Growth of LiYF4 was accomplished in a resistively heated platinum apparatus and crucible using a modified Czochralski method. Growth occurred under a fixed pressure of HF. Preliminary results gave crystals of high optical quality, free of OH(-), scattering sites, and low impurity level. The procedures should be applicable to other YLF materials in volume production. (Author)