| abstract |
An efficient method is proposed for decolorizing a rare earth oxysulfide, which is usually slightly colored in grey as prepared by the sulfiding reaction of a rare earth oxide with hydrogen sulfide, by removing sulfur impurity. The method comprises two steps of heat treatmentof which the first step is conducted in air at 450° to 550° C. for 2 to 5 hours and the second step is conducted in an inert gas, e.g., argon, at 800° to 950° C. for 2 to 5 hours. |