A method for the preparation of pure single crystals from alkaline earth fluorides or fluorides of rare earth metals

摘要

A colour-free crystal of alkaline earth or rare earth fluorides is obtained by melting and solidifying the fluorides in the presence of the vapour of CoF3 and/or MnF3. Fluorides of Mg, Ca, Sr, Ba, and all the rare earths La-Lu are specified, and mixtures, e.g. BaF2 with 10-30% CaF2. They may be synthetic (obtained by reacting acetate, carbonate, or nitrate with HF) or natural, e.g. fluorspar, and may be solid bodies grown previously from a melt but having an optical defect, or may be comminuted. The CoF3 or MnF3 in amounts of 0.25-2% b.w. of the charge is placed in a vented cup above the fluoride charge in a crucible, and vaporizes as the charge melts. The crucible is then lowered into a cooler zone across a sharp temperature gradient to effect crystal growth. The melt may also include 1-4% b.w. lead fluoride with or without PbO or Pb3O4 and Pb metal, or 0.05-0.2% V metal; alternatively the additive metal may be placed in a vented cup.ALSO:A colour-free crystal of alkaline earth or rare earth fluorides is obtained by melting and solidifying the fluorides in the presence of the vapour of CoF3 and/or MnF3. Fluorides of Mg, Ca, Sr, Ba, and all the rare earth La-Lu are specified, and mixtures, e.g. BaF2 with 10-30% CaF2. They may be synthetic (obtained by reacting acetate, carbonate, or nitrate with HF) or natural, e.g. fluorspar, and may be solid bodies grown previously from a melt but having an optical defect, or may be comminuted. The CoF3 or MnF2 in amounts of 0.25-2% b.w. of the charge is placed in a vented cup above the fluoride charge in a crucible, and vaporises as the charge melts. The crucible is then lowered into a cooler zone across a sharp temperature gradient to effect crystal growth. The melt may also include 1-4% b.w. lead fluoride with or without PbO or Pb3O4 and Pb metal, or 0.05-0.2% V metal; alternatively the additive metal may be placed in a vented cup.