Light-emitting device, white light-emitting device, illuminator, and image display

1. A light-emitting device comprising:

a light source configured to emit light by a driving current; and

at least one wavelength-converting material which absorbs at least a part of the light from the light source and emits light having a different wavelength,

wherein the light-emitting device has an emission efficiency of 32 lm/W or more and a general color rendering index Ra of 80 or more; and

a color coordinate x 1 (17.5) and a color coordinate y 1 (17.5) of light emitted at a driving current density of 17.5 A/cm 2 , a color coordinate x 1 (70) and a color coordinate y 1 (70) of light emitted at a driving current density of 70 A/cm 2 , and shift amounts [x 1 (17.5)−x 1 (70)] and [y 1 (17.5)−y 1 (70)] in the color coordinates x and y satisfy Expressions (F) and (G):

−0.01 ≦x 1 (17.5)− x 1 (70)≦0.01  (F), and

−0.01 ≦y 1 (17.5)− y 1 (70)≦0.01  (G).

2. The light-emitting device according to claim 1 , wherein a special color rendering index R 9 is 64 or more.

3. The light-emitting device according to claim 1 , wherein

the at least one wavelength-converting material is a phosphor mixture of two or more phosphors; and

a brightness BR(25), a color coordinate x 2 (25), and a color coordinate y 2 (25) of fluorescence obtained by exciting the phosphor mixture with blue light having a peak wavelength of 455 nm at 25° C., and a brightness BR(125), a color coordinate x 2 (125), and a color coordinate y 2 (125) of fluorescence obtained by exciting the phosphor mixture with the blue light at 125° C. satisfy Expressions (A), (B), and (C):

0.85≦ BR (125)/ BR (25)≦1.15  (A),

−0.03≦ x 2 (25)− x 2 (125)≦0.03  (B), and

−0.03 ≦y 2 (25)− y 2 (125)≦0.03  (C).

4. The light-emitting device according to claim 1 , wherein the at least one wavelength-converting material comprises at least one green phosphor having a fluorescence intensity peak value in the wavelength range of 500 nm to 550 nm.

5. The light-emitting device according to claim 1 , wherein the at least one wavelength-converting material comprises at least one red phosphor having a fluorescence intensity peak value in the wavelength range of 610 nm to 680 nm.

6. A lighting system comprising the light-emitting device according to claim 1 .

7. A display comprising the light-emitting device according to claim 1 .

8. The light emitting device according to claim 1 , wherein a special color rendering index R15 of the light emitting device is 84.

9. The light emitting device according to claim 1 , wherein a special color rendering index R15 of the light emitting device is 90.

10. The light emitting device according to claim 1 , wherein a correlated color temperature of the light emitting device is in a range of from 5000K to 6500K.

11. The light emitting device according to claim 1 , wherein light emitted from the light emitting device includes white light emitted from the at least one wavelength-converting material;

the at least one wavelength-converting material comprises at least one of a green phosphor and a red phosphor;

the green phosphor is selected from the group consisting of MSi 2 N 2 O 2 :Eu, M-Si—Al—O—N:Ce, and M-Si—Al—O—N:Eu, where M denotes one or more alkaline-earth metals, and phosphors comprising at least Ce in a form of luminescent center ions in a host crystal and represented by Formula (1) or (2);

the red phosphor is selected from the group consisting of MSi 7 N 10 :Eu, M 2 Si 5 N 8 :Eu, and phosphors represented by Formula (3); and

a maximum intensity of an emission spectrum of the white light in a wavelength range of 500 nm to 650 nm is not higher than 150% of a minimum intensity of the emission spectrum in the wavelength range,

M 1 a M 2 b M 3 c O d   (1)

where M 1 denotes a bivalent metal element, M 2 denotes a trivalent metal element, and M 3 denotes a tetravalent metal element, and a, b, c, and d are numbers satisfying:

2.7 ≦a≦ 3.3,

1.8 ≦b≦ 2.2,

2.7 ≦c≦ 3.3, and

11.0 ≦d≦ 13.0;

M 4 e M 5 f O g   (2)

where M 4 denotes a bivalent metal element and M 5 denotes a trivalent metal element, and e, f, and g are numbers satisfying:

0.9 ≦e≦ 1.1,

1.8 ≦f≦ 2.2, and

3.6 ≦g≦ 4.4;

M a A b D c E d X e   (3)

where M denotes one or more elements selected from the group consisting of Mn, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, and Yb; A denotes one or more elements selected from the group consisting of bivalent metal elements other than the elements represented by M; D denotes one or more elements selected from the group consisting of tetravalent metal elements; E denotes one or more elements selected from the group consisting of trivalent metal elements; X denotes one or more elements selected from the group consisting of O, N, and F; and a, b, c, d, and e are numbers satisfying:

0.00001 ≦a≦ 0.1,

a+b= 1,

0.5 ≦c≦ 4,

0.5 ≦d≦ 8,

0.8×(2/3+4/3 ×c+d )≦ e , and

e≦ 1.2×(2/3+4/3× c+d ).

12. The light emitting device according to claim 11 , wherein the at least one wavelength-converting material comprises a green phosphor represented by the Formula (2).

13. The light emitting device according to claim 11 , wherein the at least one wavelength-converting material comprises a red phosphor represented by the Formula (3) where A denotes Ca and Sr.

14. The light-emitting device according to claim 11 , wherein the red phosphor comprises CaAlSiN 3 :Eu.

15. The light-emitting device according to claim 11 , wherein the green phosphor comprises an Si garnet phosphor comprising Sc.

16. The light-emitting device according to claim 11 , wherein at least one of the red phosphor and the green phosphor has an average particle size of 30 μm or less.

17. The light-emitting device according to claim 11 , wherein the at least one wavelength-converting material has a brightness at 100° C. not less than 80% of a brightness at 25° C.

18. The light-emitting device according to claim 11 , wherein the at least one wavelength-converting material has an absorption efficiency for a light with a peak wavelength emitted by the light source of 50% or more, and has an internal quantum efficiency of 40% or more.

19. The light-emitting device according to claim 1 , wherein the light source has an emission peak wavelength in a range of 370 nm or more and 500 nm or less.

20. The light-emitting device according to claim 11 , wherein:

the at least one wavelength-converting material comprises the green phosphor and the red phosphor; and

a percentage by weight of the green phosphor to a total weight of the green phosphor and the red phosphor is 65% or more and 99% or less.

21. The light-emitting device according to claim 1 , further comprising:

an ultraviolet light emitting diode device configured to emit light having a wavelength of 330 nm to 420 nm;

a blue phosphor which is excited by light having a wavelength of 330 nm to 420 nm and has an emission peak length of 420 to 480 nm;

a green phosphor which is excited by light having a wavelength of 330 nm to 420 nm and has an emission peak wavelength in a range of 500 nm to 550 nm; and

a red phosphor which is excited by light having a wavelength of 330 nm to 420 nm and has an emission peak wavelength in a range of 550 nm to 700 nm.

22. The light-emitting device according to claim 11 , wherein:

the at least one wavelength-converting material comprises a first wavelength-converting material and a second wavelength-converting material; and

a volume ratio of the second wavelength-converting material to the first wavelength-converting material is 0.05 or more and 1 or less.