Bridgman growth of LiYF 4 single crystal in nonvacuum atmosphere

Using LiF and YF3 as starting materials, we prepare feed material from fluorides according to the molar ratio of LiF:YF3 = 51.5:48.5. The anhydrous LiYF4 polycrystalline material is synthesized via the fluoridation process with a dried HF flow at elevated temperature. By charging the feed material and adding a small amount of active carbon powder in a sealed platinum crucible, the crystal can be grown via the vertical Bridgman method in a nonvacuum atmosphere. This is possible because the oxidization and volatilization of the melt is avoided. Using optimum conditions, that is, a growth rate of 0.5-0.6 mm/h and a temperature gradient of 25-30 oC/cm across the solid-liquid interface under a furnace temperature of 920-930 oC, the colorless crystal LiYF4 with the size of φ25 x 50 (mm) is successfully grown. The optical transmittance of the crystal is as high as 85% above the absorption edge at 190 nm. The induced absorption bands are observed below 700 nm in the transmission spectrum after the crystal is subjected to a high dose of γ-ray irradiation.