| 摘要 |
The invention is directed to a process of purifying metal fluoride materials used to make metal fluoride single crystals suitable for making optical elements used in the transmission of wavelengths below 200 nm, and in particular to a process of purifying such materials by the use of a halogen containing plasma to convert metal oxygenates contaminating the feedstocks used in the preparation of the crystals to metal fluorides. The invention also is directed to a process of growing a metal fluoride single crystal using a crystal growth furnace to carry out the foregoing purification procedure followed by the steps of melting the purified material and cooling it using s selected time and temperature cycle to from a metal fluoride single crystal. The plasmas used in practicing the invention can be derived from a variety of halogenated materials including, for example, fluorocarbons, chlorocarbons, boron trihalides, chlorine, fluorine, xenon difluoride and other gaseous or easily volatilized halogenated substances known in the art.
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