Solarization resistant materials having reduced ultraviolet absorption for use in fabrication of optical elements

Abstract

No-bridging fluorine sites in calcium fluoride (CaF2) caused by lanthanide, transition metal or actinide impurities are eliminated by doping the CaF2 with sodium or another monovalent anionic dopant during or after growth of the crystal. This doping technique may be applied in the growth of other UV-transmissive fluoride materials in a family designated by a general formula Z:XFN where X is one or some combination of magnesium, calcium, zinc, strontium, cadmium, and barium, Z is one or some combination of lithium, sodium, potassium, rubidium, cesium, thallium, copper, silver and gold, and N is an integer in the range 1 through 6, and dependant on X. Elimination of the non-bridging fluorine sites can provide solarization resistant materials with low UV absorption even when the material contains sufficient lanthanide transition metal, or actinide impurities to cause the fluoride materials to be highly absorbing for UV radiation in the absence of the monovalent anion doping.

Dependencies are inferred from the claim text.