Furnace purification and metal fluoride crystals grown in a purified furnace

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,
• prior to placing a metal fluoride feedstock into the furnace to grow the crystals, the furnace is purified at a temperature in the range that is above the melting point of the metal fluoride crystal that is to be grown in the furnace, said purification for a time of at least 12 hours.

A method for growing a metal fluoride single crystal in a furnace, said method comprising 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. with continuous application of vacuum and holding the furnace temperature in that range for a time of at least 12 hours;
• 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 ambient temperature;
• admitting a dry, inert gas into the furnace;
• placing at least one vessel containing a metal fluoride feedstock into the furnace;
• and
• heating, melting and cooling the melted feedstock to thereby grow a metal fluoride single crystal.

A high-purity metal fluoride crystal, said crystal being made by a method comprising 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. with continuous application of vacuum and holding the furnace temperature in that range for a time of at least 12 hours;
• 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 ambient temperature;
• admitting a dry, inert gas into the furnace;
• placing at least one vessel containing a metal fluoride feedstock into the furnace;
• and
• heating, melting and cooling the melted feedstock to thereby grow a metal fluoride single crystal;
• wherein said metal of said metal fluoride crystal is selected from the group consisting of calcium, barium, magnesium and strontium, or a mixture of any of the foregoing.