| abstract |
A mixing step of mixing at least one of aluminum oxide or silicon oxide with silicon nitride, aluminum nitride and a europium compound, and a sintering step of sintering the mixture after the mixing step at a temperature of 1950 占 폚 to 2200 占 폚 for 10 hours or longer And a heat treatment step of performing heat treatment in an atmosphere of an inert gas other than nitrogen having a partial pressure of 10 kPa or lower at 1300 DEG C or higher and 1600 DEG C or lower after the firing process. |