Light emitting device with blue light LED and phosphor components
A light emitting device includes a light emitting component having an active layer of a semiconductor and a phosphor capable of absorbing a part of light emitted from the light emitting component and emitting light of wavelength different from that of the absorbed light, wherein the light emitting component is a LED which has an active layer constituting a gallium nitride based semiconductor containing Indium and is capable of emitting a blue color light with a peak wavelength within the range from 420 to 490 nm. The phosphor is a garnet fluorescent material activated with cerium which is capable of absorbing a part of the blue color light and thereby emitting light having a broad emission spectrum with a peak wavelength existing around the range from 510 to 600 nm and a tail continuing into the region from 700 to 750 nm.
1. A light emitting device which comprises a light emitting component having an active layer of a semiconductor and a phosphor capable of absorbing a part of light emitted from the light emitting component and emitting light of wavelength different from that of the absorbed light, wherein:
a) said light emitting component is an LED which has an active layer comprising a gallium nitride based semiconductor containing Indium and is capable of emitting a blue color light which spectrum has a peak wavelength within the range from 420 to 490 nm,
b) said phosphor is a garnet fluorescent material activated with cerium which is capable of absorbing a part of the blue color light which spectrum has the peak wavelength within the range from 420 to 490 nm and thereby emitting light having a broad emission spectrum comprising a peak wavelength existing around the range from 510 to 600 nm and a tail continuing beyond 700 nm, and
c) said emission spectrum emitted from the garnet fluorescent material activated with cerium and a spectrum of an unabsorbed light passed through said the garnet fluorescent material from said LED are capable of overlapping each other to make a continuous combined spectrum.
2. A light emitting device according to claim 1 , wherein the light color of the combined spectrum is white.
3. A light emitting device according to claim 1 , wherein the phosphor comprises two or more kinds of the garnet fluorescent materials activated with cerium.
4. A light emitting device according to claim 3 , wherein the two or more kinds of the garnet fluorescent materials activated with cerium including different compositions of Y and Al.
5. A light emitting device according to claim 1 , wherein the phosphor includes a first fluorescent material represented by a formula Y 3 (Al 1-s Ga s ) 5 O 12 :Ce and a second fluorescent material represented by a formula Re 3 Al 5 O 12 :Ce, where O≦s≦1 and Re is at least one selected from Y, Gd and La.
6. A light emitting device according to claim 1 , wherein the light color of the combined spectrum corresponds to a point on a straight line connecting points of chromacity genrated by the LED and the fluorescent material.
7. A light emitting device according to claim 1 , wherein the emission spectrum of said phosphor comprises a peak wavelength existing around the range from 530 to 570 mm and a tail continuing beyond 700 nm.