Phosphor and method of producing the same
A phosphor of an embodiment has a composition represented by a composition formula: Na x RM y S z O a , where R represents at least one element selected from the group consisting of Y, La, Gd, and Lu, M represents at least one element selected from the group consisting of Bi, Ce, Eu, and Pr, x is an atomic ratio satisfying 0.93<x<1.07, y is an atomic ratio satisfying 0.00002<y<0.01, z is an atomic ratio satisfying 1.9<z<2.1, and a is an atomic ratio satisfying 0.001<a<0.05.
1. A phosphor comprising a composition represented by a composition formula:
Na x RM y S z O a
where R represents at least one element selected from the group consisting of Y, La, Gd, and Lu, M represents at least one element selected from the group consisting of Bi, Ce, Eu, and Pr, x is an atomic ratio satisfying 0.93<x<1.07, y is an atomic ratio satisfying 0.00002<y<0.01, z is an atomic ratio satisfying 1.9<z<2.1, and a is an atomic ratio satisfying 0.001<a<0.05.
2. The phosphor according to claim 1 , wherein the element R in the composition formula contains Gd.
3. The phosphor according to claim 1 , wherein the element M in the composition formula contains Eu.
4. A method of producing the phosphor according to claim 1 , the method comprising:
preparing a raw material mixture by mixing at least one first compound selected from the group consisting of an oxide, an oxoacid, and a halide of sodium, at least one second compound selected from the group consisting of an oxide, an oxoacid, and a halide of the element R, and at least one third compound selected from the group consisting of an oxide, an oxoacid, and a halide of the element M, at such a desired ratio for the resultant phosphor to have the composition represented by the composition formula;
producing a first burned product by burning the raw material mixture, which is filled in a boron nitride vessel, in a hydrogen sulfide atmosphere at a temperature of 1000° C. or lower; and
producing a second burned product as the phosphor by burning the first burned product, which is filled in a quartz glass vessel, in a hydrogen sulfide atmosphere at a temperature that is equal to or higher than 900° C. and is higher than the burning temperature of the first burning.
5. The method according to claim 4 , wherein the raw material mixture contains at least one selected from the group consisting of the halide of the sodium, the halide of the element R, and the halide of the element M.
6. The method according to claim 4 , wherein at least one selected from the first compound, the second compound, and the third compound contains the oxide or oxoacid and the halide.
7. The method according to claim 4 , wherein the raw material mixture contains the oxoacid of the sodium, the halide of the sodium, the oxide of the element R, and the oxide or oxoacid of the element M.
8. The method according to claim 7 , wherein the oxoacid of the sodium is sodium carbonate, and the halide of the sodium is sodium fluoride.
9. The method according to claim 4 , wherein the raw material mixture is burned at a temperature of not lower than 800° C. nor higher than 1000° C.
10. The method according to claim 4 , wherein the first burned product is burned at a temperature of not lower than 900° C. nor higher than 1100° C.
11. The method according to claim 4 , wherein a burning time of the raw material mixture is one hour or more, and a burning time of the first burned product is one hour or more.