Patent ID: 7306673

Claim:
A method for growing metal fluoride single crystals in a crystal growth furnace, the method comprising the steps of: of placing a vessel containing a metal fluoride feedstock into a crystal growth furnace; heating the feedstock to a temperature above the melting point of the feedstock; and cooling the melted feedstock to form a metal fluoride single crystal, wherein, (a) prior to placing a metal fluoride feedstock into the furnace to grow the crystals, the furnace is purified at a temperature that is in the range of from above the melting point of the metal fluoride crystal that is to be grown in the furnace to 2000° C., said purification for a time of at least 12 hours; and (b) the furnace purification temperature is in the range of at least 50° C. to 600° C. above the melting point of the metal fluoride crystal to be grown, and (c) the purification procedure for said furnace comprises the steps of: evacuating to at least 10 −5 Torr a furnace suitable growing metal fluoride single crystals, heating the furnace to a temperature in the range of 1400-2000° C. and for said time with continuous application of vacuum; cooling the furnace to a temperature of 1400-1500° C.; admitting a selected gas into the furnace and holding the temperature of 1400-1500° C. for a time of at least 4 hours; evacuating the furnace to at least 10 −6 Torr; cooling the furnace to 18-30° C.; and admitting a dry, inert gas into the furnace prior to placing a metal fluoride feedstock into the furnace to grow the crystals.