Light-emitting device with light scatter tuning to control color shift
View Patent ↗A system and methods for light-emitting diode (LED) devices with a dimming feature that can tailor a color point shift in the light color temperature of a scattering/transparent layer to enlarge a dim to warm range are disclosed herein. A light-emitting device may include a wavelength converting structure configured to receive light from a light emitting semiconductor structure and an adjacent light scattering structure. The light scattering structure may comprise a plurality of scattering particles with a lower refractive index (RI) than the RI of the matrix material in which the scattering particles are disposed. The wavelength converting structure may include a red phosphor and a green phosphor such that to adjust overlap between green emission and absorption by the red phosphor to correspondingly adjust scattering and magnitude of color shift. In an embodiment, the light scattering structure may be integrated in the wavelength converting structure.
1. A light-emitting device configured to produce a white light comprising:
a light emitting semiconductor structure configured to emit blue light at a first peak wavelength;
a wavelength converting structure disposed in a path of the light emitted by the light emitting semiconductor structure and comprising a first phosphor material configured to absorb the blue light at the first peak wavelength and in response emit green light at a second peak wavelength, and a second phosphor material configured to strongly absorb the blue light at the first peak wavelength and the green light at the second peak wavelength with an absorption maximum between about 450 nanometers and about 500 nanometers and in response emit red light at a third peak wavelength; and
a light scattering structure comprising a plurality of scattering particles of a first material having a first index of refraction n 1 dispersed in a second material having a second index of refraction n 2 , (n 2 −n 1 ) having a larger magnitude at 25° C. than at 85° C.,
the light scattering structure arranged with respect to the wavelength converting structure to scatter back toward the first and second phosphor materials at least a portion of light emitted by the light emitting semiconductor structure, the first phosphor material and the second phosphor material,
a concentration of scattering particles in the second material and a change in the value of (n 2 −n 1 ) between 25° C. and 85° C. such that in operation with the light scattering structure at 25° C., the white light output of the light-emitting device has a correlated color temperature of less than 2500K and with the light scattering structure at 85° C., the white light output of the light-emitting device has a correlated color temperature of greater than 2700K.
2. The light-emitting device of claim 1 wherein the first phosphor material comprises (Lu,Y) 3 (Al,Ga) 5 O 12 :Ce 3+ or (Ba,Sr) 2 SiO 4 :Eu 2+ .
3. The light-emitting device of claim 1 , wherein the second phosphor material comprises SLA phosphor Sr(LiAl 3 N 4 ):Eu 2+ .
4. The light-emitting device of claim 1 , wherein the second phosphor material emits red light over a narrow spectral range and light emitting device further comprising a third phosphor material configured to absorb the blue light at the first peak wavelength and the green light at the second peak wavelength and in response emits red light at a fourth peak wavelength and over a broad spectral range, the fourth peak wavelength shorter than the third peak wavelength.
5. The light-emitting device of claim 4 , wherein the third phosphor material comprises (Ca,Sr)AlSiN 3 :Eu 2+ or (Ga,Sr,Ba) 2 Si 5 N 8 :Eu 2+ .
6. The light-emitting device of claim 1 , wherein the second material comprises silicone and the first material comprises MgF 2 .
7. The light-emitting device of claim 1 , the light emitting semiconductor structure being a flip chip structure.
8. The light emitting device of claim 1 , wherein the first phosphor material comprises (Lu,Y) 3 (Al,Ga) 5 O 12 :Ce 3+ or (Ba,Sr) 2 SiO 4 :Eu 2+ , and the second phosphor material comprises SLA phosphor Sr(LiAl 3 N 4 ):Eu 2+ .
9. The light emitting device of claim 1 , wherein the first phosphor material is a plurality of first phosphor particles and the second phosphor material is a plurality of second phosphor particles.
10. The light-emitting device of claim 9 , wherein the first phosphor particles and the second phosphor particles are intermixed and dispersed in a binder material.
11. The light-emitting device of claim 9 , wherein the wavelength converting structure and the light scattering structure are integrated, and the integrated structure comprises the first phosphor particles, the second phosphor particles, and the particles of the first material having the first index of refraction intermixed and dispersed in the second material having the second index of refraction.
12. The light-emitting device of claim 1 , wherein the wavelength converting structure and the light scattering structure are separate structures, and the wavelength converting structure is disposed between the semiconductor structure and the light scattering structure.
13. The light-emitting device of claim 1 , wherein the first phosphor is a first ceramic phosphor plate and the second phosphor is a second ceramic phosphor plate.
14. The light-emitting device of claim 1 , wherein the second material comprises silicone and the first material comprises porous silica.