PRETREATED METAL FLUORIDES AND PROCESS FOR PRODUCTION OF FLUORIDE CRYSTALS

摘要

[Problem] To provide a method of producing a pretreated metal fluoride containing impurities such as oxygen in decreased amounts and a fluoride crystal containing impurities such as oxygen in decreased amounts and having excellent optical properties such as transparency. [Means for Solution] A metal fluoride is heated in a temperature range of not lower than 300° K but not higher than 1780° K in the co-presence of a carbonyl fluoride of an amount of not less than 1/100 mol per mol of the metal fluoride to thereby obtain a pretreated metal fluoride while removing oxygen and water from the starting metal fluoride and from the interior of the production furnace. Further, the pretreated metal fluoride as a starting material is heated and melted, and a fluoride crystal of a high quality is obtained from the obtained melt by a crystal growing method such as a melt pull-up method or a melt pull-down method.