Luminescence conversion of LED including two phosphors

#This is a U.S. national stage of application No. PCT/DE2006/000636, filed on 11 Apr. 2006.

#This patent application claims the priority of German patent application no. 10 2005 019 376.5 filed 26 Apr. 2005, the disclosure content of which is hereby incorporated by reference.

#The invention is related to a luminescence conversion LED having a radiation-emitting chip, the primary radiation of the chip being UV to blue and being at least partially converted into longer-wave radiation by a conversion element. It deals in particular with an LED with a high conversion efficiency.

#FIG. 1 shows a semiconductor component which serves as light source (LED) for white light;

#FIG. 2 shows a further exemplary embodiment of a semiconductor component;

#FIG. 3 diagrammatically depicts the absorption and emission properties of the first and second phosphors;

#By way of example, a structure which is fundamentally similar to that described in U.S. Pat. No. 5,998,925 (the content of which is hereby incorporated by reference) is used for a white LED together with an InGaN chip. The structure of a light source of this type for white light is specifically shown in FIG. 1. The light source is a semiconductor component 1 having a chip 2 of the InGaN type with a peak emission wavelength of 460 nm, i.e. in the blue, with first and second electrical terminals 3, 4, embedded in an opaque basic housing 8 in the region of a recess 9. One of the terminals 3 is connected to the chip 2 via a bonding wire 14. The recess has a wall 17 which serves as reflector for the blue primary radiation of the chip 2. The red phosphor is applied direct to the chip in the form of a thin film 11. This red phosphor is preferably a nitridosilicate of the MxSiyNz:Eu type, where M=Ca, Sr, Ba, Zn. In this context, it is preferable that z=2/3x+4/3y. This phosphor is known per se, for example from EP 1 153 101 (Eu-red LED).

#The layer thickness should preferably be less than 40 μm, in particular approximately 10 to 30 μm. This is advantageous to ensure that the blue radiation can partially penetrate through the layer 11. The recess 9 is filled with a potting compound 5, which as its main constituents contains silicone and green-emitting or yellow-emitting phosphor pigments 6. In a first embodiment, these phosphor pigments are yellow-emitting, preferably of the garnet type, for example YAG:Ce. One alternative is TbAG:Ce. Alternatively, the phosphor pigments may also be green-emitting, for example of the oxynitridosilicate type. One specific example is an alkaline-earth metal Sion, such as in particular SrSi2O2N2:Eu2+, with which overall a very good color rendering of Ra=85 or more can be achieved. The thickness of the potting compound is advantageously greater than 200 μm, and in particular it is approx. 300 to 500 μm, with the green-yellow-emitting second phosphor being distributed as homogenously as possible therein. To ensure layer thicknesses which are as uniform as possible with a high efficiency, it is recommended to use a mean grain size d50 which should be less than 15 μm and is in particular selected in the range from 5 to 12 μm. This phosphor is known per se, for example from EP-A 1449264.

#FIG. 2 shows an alternative embodiment of a semiconductor component 8 which does not use a housing. In this case, the potting compound 5 containing the second phosphor 6 rests directly on the chip 2 and the first thin film 11 of the red phosphor, without a housing being used. A reflector 9 is integrated in the chip 2, in a manner which is known per se, but with a particularly advantageous action in connection with the concept of using the two phosphors in accordance with the invention.