Nitride phosphor and method for producing the same

1. A nitride phosphor of formula (1):

Ln x Si y N n :Z  (1),

wherein:

Ln is a rare-earth element comprising La and optionally at least one selected from the group consisting of Sc, Y, Pm, Gd, and Lu and excluding Eu, Ce, Pr, Nd, Sm, Tb, Dy, Ho, Er, Tm, and Yb;

Z is an activator comprising at least one selected from the group consisting of Eu, Ce, Cr, Mn, Fe, Pr, Nd, Sm, Tb, Dy, Ho, Er, Tm, and Yb;

x satisfies 2.7≦x≦3.3;

y satisfies 5.4≦y≦6.6; and

n satisfies 10≦n≦12, and

wherein the nitride phosphor has an x value of less than 0.43 in luminescent color coordinates (x, y) upon being excited with excitation light of 455 nm, and a reflectance Ra of 89% or more at 770 nm.

2. The nitride phosphor of claim 1 , wherein Ln comprises 80 mol % or more of La, based on a total amount of Ln.

3. The nitride phosphor of claim 1 , wherein Ln comprises 95 mol % or more of La, based on a total amount of Ln.

4. A phosphor-containing composition comprising the nitride phosphor of claim 1 , and a liquid medium.

5. A light-emitting unit comprising a first illuminant, and a second illuminant that emits visible light upon exposure to light from the first illuminant,

wherein the second illuminant contains one or more of the nitride phosphor of claim 1 as a first phosphor.

6. An image display device comprising the light-emitting unit of claim 5 as a light source.

7. A lighting device comprising the light-emitting unit of claim 5 as a light source.

8. A nitride phosphor of formula (1):

Ln x Si y N n :Z  (1),

wherein:

Ln is a rare-earth element comprising La and excluding Eu, Ce, Pr, Nd, Sm, Tb, Dy, Ho, Er, Tm, and Yb;

Z is an activator comprising at least one selected from the group consisting of Eu, Ce, Cr, Mn, Fe, Pr, Nd, Sm, Tb, Dy, Ho, Er, Tm, and Yb;

x satisfies 2.7≦x≦3.3;

y satisfies 5.4≦y≦6.6; and

n satisfies 10≦n≦12, and

wherein the nitride phosphor has an x value of 0.43 or more in luminescent color coordinates (x, y) upon being excited with excitation light of 455 nm, and a reflectance Ra of 87% or more at 770 nm.

9. The nitride phosphor of claim 8 , wherein Ln comprises 80 mol % or more of La, based on a total amount of Ln.

10. The nitride phosphor of claim 8 , wherein Ln comprises La and at least one selected from the group consisting of Sc, Y, Pm, Gd, and Lu.

11. The nitride phosphor of claim 8 , wherein Ln comprises 80 mol % or more of La, based on a total amount of Ln, and selected from the group consisting of Sc, Y, Pm, Gd, and Lu.

12. The nitride phosphor of claim 8 , wherein Ln comprises La and at least one selected from the group consisting of Y and Gd.

13. A phosphor-containing composition comprising the nitride phosphor of claim 8 , and a liquid medium.

14. A light-emitting unit comprising a first illuminant, and a second illuminant that emits visible light upon exposure to light from the first illuminant,

wherein the second illuminant contains one or more of the nitride phosphor of claim 8 as a first phosphor.

15. An image display device comprising the light-emitting unit of claim 14 as a light source.

16. A lighting device comprising the light-emitting unit of claim 14 as a light source.

17. A method for producing a nitride phosphor of formula (1):

Ln x Si y N n :Z  (1),

wherein:

Ln is a rare-earth element excluding Eu, Ce, Pr, Nd, Sm, Tb, Dy, Ho, Er, Tm, and Yb;

Z is an activator comprising at least one selected from the group consisting of Eu, Ce, Cr, Mn, Fe, Pr, Nd, Sm, Tb, Dy, Ho, Er, Tm, and Yb;

x satisfies 2.7≦x≦3.3;

y satisfies 5.4≦y≦6.6; and

n satisfies 10≦n≦12,

the method comprising:

a plurality of sintering steps that includes a first sintering step in which a sintering temperature is from 1100° C. to 1400° C., and a second sintering step in which source materials after the first sintering are redispersed, and subjected to a secondary sintering at a temperature between the first sintering temperature and 1900° C.