Light emitting device

1. A light emitting device comprising:

a board;

a light emitting element mounted on a principal surface of the board, the light emitting element emitting light having a wavelength of 250 nm to 500 nm;

a red fluorescent layer formed on the light emitting element, the red fluorescent layer including a red phosphor expressed by equation (1), an outer circumference of the red fluorescent layer having a semicircular shape with a radius r in a section perpendicular to the principal surface;

(M 1−x1 Eu x1 ) a Si b AlO c N d   (1)

in the equation (1), M is Sr (strontium) or Sr with an element less than or eqaul to 10 mol %, the element being selected from IA group elements, IIA group elements, IIIA group elements, IIIB group elements except Al (aluminum), rare-earth elements, and IVB group elements, and x1, a, b, c, and d satisfy the following relationship:

0 <x 1<1,

0.55 <a< 0.95,

2.0< b< 3.9,

0 <c< 0.6,

4 <d< 5.7,

an intermediate layer formed on the red fluorescent layer, the intermediate layer being made of transparent resin, an outer circumference of the intermediate layer having a semicircular shape with a radius D in a section perpendicular to the principal surface; and

a green fluorescent layer formed on the intermediate layer, the green fluorescent layer including a green phosphor, an outer circumference of the green fluorescent layer having a semicircular shape in a section perpendicular to the principal surface,

wherein a relationship between the radius r and the radius D satisfies equation (2):

2.0 r (μm)≦ D ≦( r +1000)(μm)  (2) and

wherein a luminous flux loss γ is 5% or less, expressed by equation (5),

γ=βδ(1−(1−(1−( r/D ) 2 ) −1/2 ))  (5)

in which β is a product of absorptance of green light by the red phosphor, δ is a luminous factor difference between green light emitted by the green phosphor and red light emitted by the red phosphor.

2. The device according to claim 1 , wherein the green phosphor has a compsition expressed by equation (3):

(M′ 1−x2 Eu x2 ) 3−y Si 13−z Al 3+z O 2+u N 21−w   (3)

in the equation (3), M′ is Sr (strontium) or Sr with an element less than or eqaul to 10 mol %, the element being selected from IA group elements, IIA group elements, IIIA group elements, IIIB group elements except Al (aluminum), rare-earth elements, and IVB group elements, and x2, y, z, u, and w satisfy the following relationship:

0 <x 2<1,

−0.1 <y< 0.3,

−3 <z≦ 1,

−3 <u−w≦ 1.5.

3. The device according to claim 1 , wherein the green phosphor is an Eu activated alkaline earth orthosilicate phosphor.

4. The device according to claim 1 , wherein the light emitting element is a blue LED.

5. The device according to claim 1 , wherein the transparent resin is a silicone resin.

6. The device according to claim 1 , wherein the element M is strontium (Sr).

7. The device according to claim 2 , wherein the element M′ is strontium (Sr).

8. The device according to claim 1 , further comprising an outer surface layer made of a transparent resin, the outer surface layer being formed on the green fluorescent layer.

9. The device according to claim 1 , further comprising a yellow fluorescent layer including a yellow phosphor, the yellow fluorescent layer being formed between the red fluorescent layer and the intermediate layer.