Luminescent material

1. An yttrium silicon oxynitride luminescent material comprising:

a crystalline phase including Y, Si, O and N; and

an activator comprising Tb and Ce, a molar fraction x1 of the Tb based on a total number of moles of Y, Tb and Ce being confined to a range defined by expression 1, below, and a molar fraction y1 of the Ce based on the total number of moles of Y, Tb and Ce being confined to a range defined by expression 2 below;

0 <x 1≦0.6  expression 1;

0 <y 1≦0.2  expression 2,

wherein the luminescent material has a composition represented by formula A1, below:

(Y 1−x1−y1 ,Tb x1 ,Ce y1 ) a Si b O c Nd  A1

wherein “a,” “b,” “c” and “d” are confined to the following ranges:

1.9 ≦a≦ 2.1  expression 3;

2.8 ≦b≦ 3.1  expression 4;

2.7 ≦c≦ 3.1  expression 5;

3.8 ≦d≦ 4.2  expression 6.

2. The luminescent material according to claim 1 , wherein “a” is 2, “b” is 3, “c” is 3 and “d” is 4.

3. The luminescent material according to claim 1 , wherein the molar fraction x1 and the molar fraction y1 are confined to meet the following relationship:

x 1 /y 1≧1.

4. The luminescent material according to claim 1 , wherein the molar fraction x1 and the molar fraction y1 are confined to meet the following relationship:

1 ≦x 1 /y 1≦100.

5. The luminescent material according to claim 1 , wherein the molar fraction x1 and the molar fraction y1 are confined to meet the following relationship:

2 ≦x 1 /y 1≦80.

6. An yttrium silicon oxynitride luminescent material comprising

a crystalline phase including Y, Si, O, N and M, M being at least one selected from a group consisting of La, Gd, and Lu; and

an activator comprising Tb and Ce, a molar fraction w2 of the M based on a total number of moles of Y, M, Tb and Ce being confined to a range defined by expression 7, below, a molar fraction x2 of the Tb based on the total number of moles of Y, M, Tb and Ce as defined by expression 8 below, and a molar fraction y2 of the Ce based on the total number of moles of Y, M, Tb and Ce being confined to a range defined by expression 9 below;

0.01 <w 2≦0.3  expression 7;

0 <x 2≦0.6  expression 8;

0 <y 2≦0.2  expression 9,

wherein the luminescent material has a composition represented by formula A2, below:

(Y 1−w2−x2−y2 ,M w2 ,Tb x2 ,Ce y2 ) a Si b O c N d   (A2)

wherein “a”, “b”, “c” and “d” are confined to the following ranges:

1.9 ≦a≦ 2.1  expression 10;

2.8 ≦b≦ 3.1  expression 11;

2.7 ≦c≦ 3.1  expression 12;

3.8 ≦d≦ 4.2  expression 13.

7. The luminescent material according to claim 6 , wherein the molar fraction x2 and the molar fraction y2 are confined to meet the following relationship:

x 2 /y 2≧1.

8. The luminescent material according to claim 6 , wherein the molar fraction x2 and the molar fraction y2 are confined to meet the following relationship:

1 ≦x 2 /y 2≦100.

9. The luminescent material according to claim 6 , wherein the molar fraction x2 and the molar fraction y2 are confined to meet the following relationship:

2 ≦x 2 /y 2≦80.

10. The luminescent material according to claim 6 , wherein “a” is 2, “b” is 3, “c” is 3 and “d” is 4.

11. The luminescent material according to claim 6 , wherein the M is La.

12. A light-emitting device comprising:

a light-emitting element emitting light, the light having a main emission peak in a wavelength ranging from 360 to 460 nm; and

a luminescent layer comprising a first luminescent material and configured to be irradiated with the light, the first luminescent material being formed of the luminescent material claimed in claim 1 .

13. The light-emitting device according to claim 12 , wherein the luminescent layer further comprises a second luminescent material having a peak wavelength ranging from 580 to 680 nm.

14. The light-emitting device according to claim 13 , wherein the luminescent layer further comprises a third luminescent material having a peak wavelength ranging from 430 to 510 nm.

15. A light-emitting device comprising:

a light-emitting element emitting light, the light having a main emission peak in a wavelength ranging from 360 to 460 nm; and

a luminescent layer comprising a first luminescent material and configured to be irradiated with the light, the first luminescent material being the luminescent material claimed in claim 6 .

16. The light-emitting device according to claim 15 , wherein the luminescent layer further comprises a second luminescent material having a peak wavelength ranging from 580 to 680 nm.

17. The light-emitting device according to claim 16 , wherein the luminescent layer further comprises a third luminescent material having a peak wavelength ranging from 430 to 510 nm.