Light emitting diode device with luminescent material

Abstract

The invention provides a light emitting diode device comprising a light emitting diode arranged on a substrate and a wavelength converting element. The wavelength converting element contains as a luminescent material a Mn.sup.4+-activated fluoride compound having a garnet-type crystal structure. The Mn.sup.4+-activated fluoride compound preferably answers the general formula {A.sub.3}[B.sub.2-x-yMn.sub.xMg.sub.y](Li.sub.3)F.sub.12-dO.sub.d, in which formula A stands for at least one element selected from the series consisting of Na.sup.+ and K.sup.+ and B stands for at least one element selected from the series consisting of Al.sup.3+, B.sup.3+, Sc.sup.3+, Fe.sup.3+, Cr.sup.3+, Ti.sup.4+ and In.sup.3+, and in which formula x ranges between 0.02 and 0.2, y ranges between 0.0 (and incl. 0.0) and 0.4 and d ranges between 0 (and incl. 0) and 1. Said compound is most preferably {Na.sub.3}[Al.sub.2-x-yMn.sub.xMg.sub.y](Li.sub.3)F.sub.12-dO.sub.d.

Claims

1. A light emitting diode device comprising: an AlInGaN-type light emitting diode, a first ceramic platelet formed of a Mn.sup.4+-activated fluoride compound, wherein the Mn.sup.4+-activated fluoride compound has a garnet-type crystal structure, the first ceramic platelet adjacent to the AlInGaN-type light emitting diode, a second ceramic platelet formed of a yellow phosphor atop the first ceramic platelet, and a lens placed on the second ceramic platelet.

2. A light emitting diode device according to claim 1, wherein the Mn.sup.4+-activated fluoride compound has the formula {A.sub.3}[B.sub.2-x-yMn.sub.xMg.sub.y](Li.sub.3)F.sub.12-dO.sub.d, wherein A is at least one element selected from the series consisting of Na.sup.+ and K.sup.+, B is at least one element selected from the series consisting of Al.sup.3+, B.sup.3+, Sc.sup.3+, Fe.sup.3+, Cr.sup.3+, Ti.sup.4+ and In.sup.3+, 0.02<x<0.2, 0.0y<0.4, and 0d<1.

3. A light emitting diode device according to claim 2, wherein the composition of the Mn.sup.4+-activated fluoride compound material has the formula {Na.sub.3}[Al.sub.2-x-yMn.sub.xMg.sub.y](Li.sub.3)F.sub.12-dO.sub.d.

4. A light emitting diode device according to claim 1, wherein the light emitting diode emits light having a peak wavelength of about 420-470 nm.

5. A light emitting diode device according to claim 1, wherein the Mn.sup.4+-activated fluoride compound emits light in the range of 600 to 660 nm.

6. A light emitting diode device comprising: a GaInN-type light emitting diode, and a wavelength converting Mn.sup.4+-activated fluoride compound with a garnet-type crystal structure mixed with silicone, wherein the silicone is formed into a lens positioned adjacent the GaInN-type light emitting diode.

7. A light emitting diode device comprising: a light emitting diode, and a wavelength converting Mn.sup.4+-activated fluoride compound with a garnet-type crystal structure compounded with a transparent fluoroplastic.

8. A light emitting diode device according to claim 7, wherein the transparent fluoroplastic and the Mn.sup.4+-activated fluoride compound have matching indices of refraction.

9. A material comprising a composite of {A.sub.3}[B.sub.2-x-yMn.sub.xMg.sub.y](Li.sub.3)F.sub.12-dO.sub.d type garnet and an oxide garnet, wherein A is at least one element selected from the series consisting of Na.sup.+ and K.sup.+, B is at least one element selected from the series consisting of Al.sup.3+, B.sup.3+, Sc.sup.3+, Fe.sup.3+, Cr.sup.3+, Ti.sup.4+ and In.sup.3+, 0.02<x<0.2, 0.0y<0.4, and 0d<1.

10. The material of claim 9 wherein the oxide garnet comprises one of Y.sub.3Al.sub.5O.sub.12, Mg.sub.3Al.sub.2Si.sub.3O.sub.12, and Ca.sub.3Al.sub.2Si.sub.3O.sub.12.

11. The material of claim 9 wherein the {A.sub.3}[B.sub.2-x-yMn.sub.xMg.sub.y](Li.sub.3)F.sub.12-dO.sub.d type garnet is {Na.sub.3}[Al.sub.2-x-yMn.sub.xMg.sub.y](Li.sub.3)F.sub.12-dO.sub.d phosphor particles, wherein the {Na.sub.3}[Al.sub.2-x-yMn.sub.xMg.sub.y](Li.sub.3)F.sub.12-dO.sub.d particles are surrounded by a shell formed from the oxide garnet.

12. The material of claim 9 wherein the {A.sub.3}[B.sub.2-x-yMn.sub.xMg.sub.y](Li.sub.3)F.sub.12-dO.sub.d type garnet is {Na.sub.3}[Al.sub.2-x-yMn.sub.xMg.sub.y](Li.sub.3)F.sub.12-dO.sub.d phosphor particles, wherein the {Na.sub.3}[Al.sub.2-x-yMn.sub.xMg.sub.y](Li.sub.3)F.sub.12-dO.sub.d particles are coated with the oxide garnet.

13. A material comprising mixed crystal A.sub.aB.sub.1-a, where is A is {Na.sub.3}[Al.sub.2-x-yMn.sub.xMg.sub.y](Li.sub.3)F.sub.12-dO.sub.d and B is at least one oxide garnet, and 0<a<1, 0.02<x<0.2, 0.0y<0.4, and 0d<1.

14. The material of claim 13 wherein the at least one oxide garnet comprises one of Y.sub.3Al.sub.5O.sub.12, Mg.sub.3Al.sub.2Si.sub.3O.sub.12, and Ca.sub.3Al.sub.2Si.sub.3O.sub.12.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The invention will be explained and illustrated in terms of a number of embodiments, with the help of the drawing, in which

(2) FIG. 1 shows a first embodiment of the LED device according to the invention,

(3) FIG. 2 shows a second embodiment of the LED device according to the invention,

(4) FIG. 3 shows a graph of the emission spectrum of the first embodiment according to the invention,

(5) FIG. 4 shows a graph of the emission spectrum of the second embodiment according to the invention, and

(6) FIG. 5 shows a graph of the x-ray pattern of a sample of the invented compound {Na.sub.3}[Al.sub.1.94Mn.sub.0.03Mg.sub.0.03](Li.sub.3)F.sub.12 having a garnet-type crystal structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(7) A first embodiment of the present invention is schematically illustrated by FIG. 1. This Figure shows a cross-section of a LED device comprising a semiconductor light emitting diode (1), which is connected to a substrate (2), sometimes referred to as sub-mount. The diode (1) and substrate (2) are connected by means of appropriate connecting means, like solder or (metal-filled) adhesive.

(8) The diode (1) is of the GaInN type, emitting during operation light having a wavelength of 450 nm. In the present embodiment, said light exits LED (1) via emitting surface (4). A wavelength converting element (3) formed as a convex lens shaped body is positioned adjacent to LED (1). This lens is largely made of a high temperature resistant silicone resin, in which grains are incorporated of a Mn.sup.4+-activated fluoride compound having a garnet-type crystal structure. Latter compound acts as a luminescent material in the lens. In the present embodiment said silicone resin contains 16 vol % {Na.sub.3}[Al.sub.1.94Mn.sub.0.03Mg.sub.0.03](Li.sub.3)F.sub.12, having a grain size of appr. 10 micron. The type of silicone is chosen so that its refractive index is almost identical with the refractive index of the phosphor compound, namely 1.34. By using (almost) identical refractive indices, scattering losses of the LED light through the wavelength converting element (3) are as low as possible.

(9) In an alternative embodiment, the invented luminescent material is compounded with highly transparent fluoroplastics (e.g. 3M Dyneon THV2030G or THV220) with matched refractive index. The resulting composite may be transferred into a suitable shape by known techniques. These shapes may be used as functional optical parts of the LED or simply as components for color conversion only.

(10) The amount of luminescent compound and the dimensions of the wavelength converting element (3) are chosen so that all the blue light generated by the LED (1) is converted into red light having a wavelength of appr. 630 nm. A typical emission spectrum of the light exiting the here described LED device is shown in FIG. 3. In this Figure, the intensity of the emission I (arbitrary units) is measured as a function of the wavelength (nm). It is stressed that, for adapting the color of the exiting red LED light, additional phosphors of other (known) types can be used. Thus, the invention is not limited to LED devices comprising only a single phosphor of garnet-type crystal structure in the wavelength converting element (3), but mixtures of this phosphor with other (known) phosphors can be applied as well.

(11) FIG. 2 depicts a schematic cross-section of a second embodiment of the present invention designed as a white light generating LED device. This Figure shows a conventional blue or (near) UV generating light emitting diode (11), which is attached to a substrate (12) using solder bumps (not shown). Substrate (12) has metal contact pads on its surface to which LED (11) is electrically connected (not shown). By means of these solder pads, LED (11) can be connected to a power supply. In the present example, LED (11) is of the AlInGaN type and emits blue light having a peak wavelength of appr. 420-470 nm. It goes without saying that other semiconductor materials having other peak wavelengths can be used as well within the scope of the present invention.

(12) Two wavelength converting elements formed as ceramic platelets (13) and (14) are positioned adjacent to LED (11). The platelets (13, 14) and LED (11) can mutually be affixed by means of an adhesive (like a high temperature resistant silicone material or a low melting glass) or by means of mechanical clamping. In the present embodiment, an adhesive is used. To keep unwanted absorptions as low as possible, the adhesive layers between LED (11) and element (13) as well as between element (13) and element (14) have been made as thin as possible.

(13) In the present embodiment, element (13) is shaped as a red phosphor plate whereas element (14) is shaped as a yellow phosphor plate. The surface dimensions of both plates are almost the same as the surface dimension of the light emitting surface (15) of LED (11), although they may be somewhat larger without having significant effect on the (white) exiting light. In case LED (11) is small enough, side emission of the blue radiation from the LED (11) can be ignored. The thicknesses of both elements are typically in the range of 50-300 micron. The actual thickness of the platelets of course depends on the spectral power distribution of the LED light and the type of phosphor compound present in the platelets.

(14) In the described embodiment, the red phosphor platelet of element (13) was prepared of a pure Mn.sup.4+-activated fluoride phosphor compound with a garnet-type crystal structure. For this purpose the phosphor compound substantially answered the formula {Na.sub.3}[Al.sub.1.94Mn.sub.0.03Mg.sub.0.03](Li.sub.3)F.sub.12 having a garnet-type crystal structure. For the yellow phosphor platelet of element (14), the compound Y.sub.3Al.sub.5O.sub.12:Ce (Ce-doped YAG) was used.

(15) On the LED (11) and both wavelength conversion elements (13, 14) an optical element (16) in the form of lens structure is placed, allowing optimization of the emission pattern of the LED device. By means of a proper choice of this optical element, a Lambertian pattern can be obtained, but also a pattern that allows a good coupling with an optical waveguide structure. It is also possible to design the optical element (16) in such a way that a uniform illumination distribution of the generated white light is obtained. This makes the present LED device very suitable for backlighting in LCD type applications.

(16) FIG. 4 shows a typical emission spectrum of the described white light generating LED device according to FIG. 2. In this Figure, the intensity of the emission I (arbitrary units) is measured as a function of the wavelength (nm). The spectrum shows emission in the red spectral region from appr. 600-appr. 660 nm, with an emission maximum around 630 nm.

(17) The luminescent material used in the wavelength converting element (3, 13) of the LED devices as described above substantially answers the formula {Na.sub.3}[Al.sub.1.94Mn.sub.0.03Mg.sub.0.03](Li.sub.3)F.sub.12 and has a garnet-type crystal structure. Said material was obtained as co-precipitates at room temperature from aqueous HF solution containing Mn.sup.4+ as a dopant. For the preparation of said {Na.sub.3}[Al.sub.1.94Mn.sub.0.03Mg.sub.0.03](Li.sub.3)F.sub.12, stoichiometric amounts of the starting materials NaCl, LiCl, MgCl.sub.2*6H.sub.2O and AlCl.sub.3*6H.sub.2O as well as a small amount of NaHF.sub.2 were dissolved in water and subsequently added to a 48% HF aqueous solution containing K.sub.2MnF.sub.6. The concentration of Mn.sup.4+ in the HF solution was 1 mol. %. The precipitates were filtered, washed repeatedly with 2-propanol, and then dried at 110 C. in vacuum. The obtained product was ground in a mortar.

(18) FIG. 5 shows an X-ray powder pattern spectrum measured on a representative sample of one of the precipitates, using Cu-K radiation. In this Figure, the number of counts (N) is shown as a function of the diffracted angle 2Theta. With this measurement, these samples could be identified to be {Na.sub.3}[Al.sub.1.94Mn.sub.0.03Mg.sub.0.03](Li.sub.3)F.sub.12 having a garnet-type crystal structure. No extra phases were detected in this sample.

(19) It is stressed that it is possible to use a variety of other starting materials to produce the inventive garnet-type fluoride phosphors via co-precipitation from aqueous solution. Especially hydroxides, nitrates, alkoxides, and carbonates are other good starting materials for use in the co-precipitation method. Also other metal ion salts can be used as starting material, like with salts of K.sup.+, B.sup.3+, Sc.sup.3+, Fe.sup.3+, Cr.sup.3+, Ti.sup.4+ and/or In.sup.3+. When using these starting materials, Mn.sup.4+-activated fluoride phosphor compound with garnet-type crystal structure of other compositions can be prepared as well.

(20) An amount of the {Na.sub.3}[Al.sub.1.94Mn.sub.0.03Mg.sub.0.03](Li.sub.3)F.sub.12 powder prepared as described above underwent further intense mechanically grinding until the mean particle size was appr. 5 micron. Subsequently the powder was pressed to a plate and sintered at 200 C. in a furnace under an axial pressure of 2 kbar. After cooling to room temperature, the so-obtained ceramic plate was scored with a laser and broken into individual platelets. These platelets were used as wavelength conversion elements in LED devices according to the present invention.

(21) While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. For example, it is possible to operate the invention in an embodiment wherein other (optical) element(s) are present between the LED and the wavelength converting elements or wherein more than one LED is operated in combination with one converting element.

(22) Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.