Thin compact wavelength converting structure for pcLED
This specification discloses pcLEDs in which the wavelength converting structure comprises one or more layers of phosphor particles disposed on a transparent substrate at high packing density. The particles are coated with an inorganic non-absorbing layer which mechanically stabilizes the phosphor particle layers and provides a thermally conductive connection between the phosphor particles. The wavelength converting structure is attached to a semiconductor LED die with the transparent substrate of the wavelength converting structure facing away from the die by a thin glue layer that bonds a light emitting surface of the die to the phosphor particle layers. Methods for fabricating such pcLEDs are also disclosed.
1. A pcLED comprising:
a wavelength converting structure comprising:
a transparent substrate;
one or more layers of phosphor particles disposed on the transparent substrate at a packing density of greater than 50% and less than 90%; and
a coating of non-absorbing inorganic material on the phosphor particle layers that mechanically and thermally connects the phosphor particles to each other and to the transparent substrate;
an LED die comprising a light emitting surface, the LED die arranged with the light emitting surface adjacent the one or more layers of phosphor particles in the wavelength converting structure and with the light emitting surface on an opposite side of the one or more layers of phosphor particles from the transparent substrate; and
a transparent glue layer disposed on and wetting the light emitting surface of the LED die and mechanically and optically bonding the light emitting surface to the one or more layers of phosphor particles.
2. The pcLED of claim 1 , wherein the transparent substrate is or comprises a transparent glass substrate.
3. The pcLED of claim 1 , wherein the transparent substrate has a thickness of about 5 microns to about 2 millimeters.
4. The pcLED of claim 1 , wherein the transparent substrate comprises one or more optical coatings.
5. The pcLED of claim 1 , wherein the phosphor particles are disposed on the transparent substrate at a packing density of greater than 55%.
6. The pcLED of claim 1 , wherein the phosphor particles are disposed on the transparent substrate at a packing density of greater than 60% and equal to or less than 74%.
7. The pcLED of claim 1 , wherein the phosphor particles have a median diameter d50 of 1 μm≤d50≤30 μm.
8. The pcLED of claim 1 , comprising a stack of two or more layers of phosphor particles, wherein:
each layer comprises phosphor particles of a different composition and a different peak or centroid emission wavelength from the other layers; and
the layers are stacked in order of peak or centroid emission wavelength, with the layer having the shortest peak or centroid emission wavelength closest to the transparent substrate and the layer having the longest peak or centroid emission wavelength farthest from the transparent substrate.
9. The pcLED of claim 1 , wherein the non-absorbing inorganic material is or comprises Al 2 O 3 .
10. The pcLED of claim 1 , wherein the transparent glue layer is or comprises a silicone.
11. The pcLED of claim 1 , wherein the transparent glue layer penetrates pores in the one or more inorganic-coated layers of phosphor particles.
12. The pcLED of claim 11 , wherein a pore volume of pores in the coated layers of phosphor particles not penetrated by the transparent glue layer is ≤1% of the volume of the one or more layers of coated phosphor particles.
13. The pcLED of claim 1 , wherein:
the transparent substrate is or comprises a transparent glass substrate;
the phosphor particles have a median diameter d50 of 1 μm≤d50≤30 μm;
the non-absorbing inorganic material is or comprises Al 2 O 3 ; and
the transparent glue layer is or comprises a silicone and penetrates pores in the one or coated layers of phosphor particles.
14. The pcLED of claim 13 , wherein a pore volume of pores in the coated layers of phosphor particles not penetrated by the transparent glue layer is ≤1% of the volume of the one or more layers of coated phosphor particles.