An α-sialon phosphor particle containing Eu. At least one slit is formed on a surface of the α-sialon phosphor particle. The α-sialon phosphor particle is preferably produced by undergoing a raw material mixing step, a heating step, a pulverizing step, and an acid treatment step.

An α-sialon phosphor particle containing Eu. At least one slit is formed on a surface of the α-sialon phosphor particle. The α-sialon phosphor particle is preferably produced by undergoing a raw material mixing step, a heating step, a pulverizing step, and an acid treatment step.

A phosphor powder composed of α-sialon phosphor particles containing Eu. The phosphor powder has an ammonium ion concentration C.sub.A of the phosphor powder of equal to or more than 15 ppm and equal to or less than 100 ppm, which is determined from the following extracted ion analysis. (Extracted Ion Analysis A) 0.5 g of a phosphor powder is added to 25 ml of distilled water in a polytetrafluoroethylene (PTFE)-made container with a lid and held at 60° C. for 24 hours, and then a total mass M.sub.A of ammonium ions included in an aqueous solution obtained by removing a solid content from the solution by filtration is determined using ion chromatography. Then, C.sub.A is determined by dividing M.sub.A by the mass of the phosphor powder.

A phosphor powder composed of α-sialon phosphor particles containing Eu. The phosphor powder has an ammonium ion concentration C.sub.A of the phosphor powder of equal to or more than 15 ppm and equal to or less than 100 ppm, which is determined from the following extracted ion analysis. (Extracted Ion Analysis A) 0.5 g of a phosphor powder is added to 25 ml of distilled water in a polytetrafluoroethylene (PTFE)-made container with a lid and held at 60° C. for 24 hours, and then a total mass M.sub.A of ammonium ions included in an aqueous solution obtained by removing a solid content from the solution by filtration is determined using ion chromatography. Then, C.sub.A is determined by dividing M.sub.A by the mass of the phosphor powder.

A scintillator for positron emission tomography is provided. The scintillator includes a garnet compound of a formula of A.sub.3B.sub.2C.sub.3O.sub.12 and an activator ion consisting of cerium. A.sub.3 is A.sub.2X. X consists of at least one lanthanide element. A.sub.2 is selected from the group consisting of (i), (ii), (iii), and any combination thereof, wherein (i) consists of at least one lanthanide element, (ii) consists of at least one group I element selected from the group consisting of Na and K, and (iii) consists of at least one group II element selected from the group consisting of Ca, Sr, and Ba. B.sub.2 consists of Sn, Ti, Hf, Zr, and any combination thereof. C.sub.3 consists of Al, Ga, Li, and any combination thereof. The garnet compound is doped with the activator ion.

A scintillator for positron emission tomography is provided. The scintillator includes a garnet compound of a formula of A.sub.3B.sub.2C.sub.3O.sub.12 and an activator ion consisting of cerium. A.sub.3 is A.sub.2X. X consists of at least one lanthanide element. A.sub.2 is selected from the group consisting of (i), (ii), (iii), and any combination thereof, wherein (i) consists of at least one lanthanide element, (ii) consists of at least one group I element selected from the group consisting of Na and K, and (iii) consists of at least one group II element selected from the group consisting of Ca, Sr, and Ba. B.sub.2 consists of Sn, Ti, Hf, Zr, and any combination thereof. C.sub.3 consists of Al, Ga, Li, and any combination thereof. The garnet compound is doped with the activator ion.

A phosphor having a variable wavelength and a light irradiation device having said phosphor. This phosphor contains an activating agent, and has a concentration gradient of the activating agent along at least one direction.

A phosphor having a variable wavelength and a light irradiation device having said phosphor. This phosphor contains an activating agent, and has a concentration gradient of the activating agent along at least one direction.

A ceramic complex that has improved optical characteristics including luminous efficiency is provided. A method for producing a ceramic complex, including: preparing a molded body containing rare earth aluminum garnet fluorescent material, aluminum oxide, and lutetium oxide, and having a content of the rare earth aluminum garnet fluorescent material in a range of 15% by mass or more and 50% by mass or less, and a content of the lutetium oxide in a range of 0.2% by mass or more and 4.5% by mass or less, based on the total amount of the rare earth aluminum garnet fluorescent material, the aluminum oxide, and the lutetium oxide; and calcining the molded body in an air atmosphere to provide a ceramic complex having a relative density in a range of 90% or more and less than 100%.

A ceramic complex that has improved optical characteristics including luminous efficiency is provided. A method for producing a ceramic complex, including: preparing a molded body containing rare earth aluminum garnet fluorescent material, aluminum oxide, and lutetium oxide, and having a content of the rare earth aluminum garnet fluorescent material in a range of 15% by mass or more and 50% by mass or less, and a content of the lutetium oxide in a range of 0.2% by mass or more and 4.5% by mass or less, based on the total amount of the rare earth aluminum garnet fluorescent material, the aluminum oxide, and the lutetium oxide; and calcining the molded body in an air atmosphere to provide a ceramic complex having a relative density in a range of 90% or more and less than 100%.