| 摘要 |
PROBLEM TO BE SOLVED: To produce a crystal excellent in optical characteristics with stable quality by quantitatively analyzing a transition metal without the transition metal mainly included in a fluorinating agent, at least in one shape of a raw material, a pretreated product and an ingot, and carrying out the process control by using the result. SOLUTION: This method for producing a calcium fluoride crystal comprises a step for adding a fluorinating agent to a raw material and heating the resultant mixture to provide a pretreated product, and a step for melting and crystallizing the pretreated product to provide an ingot. The amount of the impurity of a transition metal is determined by an inductive coupling plasma emission analysis method, and the content of iron included in the raw material, the iron included in the pretreated product and the iron included in the ingot are preferably controlled so as to be <=1.0 ppm, <=0.5 ppm and <=0.5 ppm respectively. The calcium fluoride sample is preferably decomposed by dissolving the sample in perchloric acid to form perchlorate, and analyzed. The determination of the transition metal impurity becomes possible, and the process control based on the whole amount of the impurity can be carried out.
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