Method for producing rare earth aluminate sintered body

A method for producing a rare earth aluminate sintered body containing a crystal phase having a composition of a rare earth aluminate containing an oxide growth crystal phase and a fluorescent material growth crystal phase, including:

• preparing a molded body by molding a fluorescent material having a composition of a rare earth aluminate and a raw material mixture consisting of an oxide containing at least one rare earth element selected from the group consisting of Y, La, Lu, Gd, and Tb, an oxide containing Ce, an oxide containing Al, and optionally an oxide containing at least one element M1 selected from the group consisting of Ga and Sc;
• and
• calcining the molded body to obtain a sintered body,
• wherein an average particle diameter of the fluorescent material, as measured according to a Fisher Sub-Sieve Sizer method, is in a range of 0.3 μm or more and 10 μm or less,
• wherein an average particle diameter of each of the oxide containing the at least one rare earth element, the oxide containing Ce, the oxide containing Al, and optionally the oxide containing the element M1 is in a range of 0.01 μm or more and 1.5 μm or less,
• wherein a temperature at which the molded body is calcined is in a range of 1,650° C. or more and less than 1,800° C., and
• wherein a relative density of the rare earth aluminate sintered body is in a range of 85% or more and 93.6% or less, and the rare earth aluminate sintered body has an average number of voids per unit area 645 μm2 in a cross section in a range of 5 or more and 30 or less, and
• wherein the rare earth aluminate sintered body has a first crystal phase having a circle equivalent particle diameter in a plane in a range of 0.1 μm or more and 1.0 μm or less and a second crystal phase having a circle-equivalent particle diameter in arrange of 1.1 μm or more and 15 μm or less.