The invention provides a method for producing powder of magnesia roasts which releases efficiently ultraviolet light with peak wavelength near the wavelength of 250 nm when being excited by ultraviolet light generated by Xe gas. By sintering to generate magnesia, the powder of magnesium compound, in addition to magnesia and magnesium fluoride, is sintered at the temperature of 850 to 1500 degrees centigrade in the presence of fluoride source.