DE102011079721A1 - LED-light source, has covering layer comprising particles e.g. glass spheres, embedded in silicone, where difference of respective indexes of material and particles of covering layer amounts to specific value - Google Patents

Abstract

The source (10) has a luminescence conversion layer (6) following a radiation-emitting active layer (3) of an LED chip (1) in a beam direction (11). A covering layer (7) has particles (9) e.g. glass balls and silicon dioxide, embedded in a base material (8) i.e. silicone. The material exhibits refraction indexes at room and operating temperatures. The particles exhibit refraction indexes at the temperatures, where difference of indexes of the material and the particles is greater than/equal to 0.02 und difference of other indexes of the material and the particles is less than/equal to 0.01. The temperatures lie between 80 degree Celsius and 100 degree Celsius. The room temperature is environment temperature. The active layer is designed as a PN junction, a double heterostructure, a single quantum well structure and multiple quantum well structure. The LED chip is designed as a substrateless thin film chip and an organic LED-chip.

Description

The invention relates to an LED light source having a luminescence conversion layer.

One known possibility for producing white or mixed-color light by means of LEDs is to arrange a luminescence conversion layer in the beam path of a luminescence diode chip, which converts at least part of the radiation emitted by the luminescence diode chip to a greater wavelength. A typical configuration comprises, for example, a luminescence diode chip emitting blue or ultraviolet radiation, and a luminescence conversion layer arranged above the luminescence diode chip, which converts part of the emitted radiation into yellow light. In this way, in particular white light can be generated.

The luminescence conversion layer arranged above the luminescence diode chip has the often undesirable effect that the LED light source in the off state appears colored, for example yellow or yellow-orange, due to the absorption spectrum of the luminescent substance used. This is the case in particular in the case of an LED light source with a comparatively large emission area or LED modules in which a multiplicity of LED chips are arranged on a common carrier.

In order to reduce the yellow color impression of an LED light source in the off state, is in the document WO 2010/038097 A1 proposed to arrange over the luminescence conversion layer a silicone layer in which particles of TiO ₂ having a size in the sub-micron range are embedded in a concentration between about 2.5 and 5 wt .-%. The color impression in the off state is in this case a function of the concentration of scattering particles. However, with a high concentration of the scattering particles, the efficiency of the LED may decrease and the heating increase due to absorption of the radiation scattered back into the LED chip.

Based on this, it is an object to provide an LED light source with a luminescence conversion layer in which the color impression is reduced in the off state, wherein the efficiency of the LED is not significantly affected in the on state and additional heating due to stray radiation is reduced.

This object is achieved by an LED light source according to independent claim 1. Advantageous embodiments and modifications of the invention are the subject of the dependent claims.

The LED light source according to at least one embodiment comprises at least one LED chip, which has a radiation-emitting active layer. The active layer preferably contains an electroluminescent material which emits in the blue or ultraviolet spectral range. The active layer contains, for example, a nitride compound semiconductor material, in particular In _x Al _y Ga _1-xy N with 0 ≤ x ≤ 1, 0 ≤ y ≤ 1 and x + y ≤ 1. Alternatively, the active layer may contain an organic light-emitting material that preferably emitted in the blue or ultraviolet spectral range. Organic light-emitting materials are particularly suitable for the production of large-area LED light sources. The LED light source may include a plurality of LED chips, for example, arranged side by side on a common carrier.

The LED light source further comprises a luminescence conversion layer following the active layer in a beam direction. The luminescence conversion layer contains at least one phosphor, by which part of the radiation emitted by the active layer is converted to a longer wavelength. The LED light source thus emits a mixed light from the light emitted by the at least one LED chip and the light having a longer wavelength produced by means of the luminescence conversion layer.

For example, white light can be generated by means of an LED chip whose active layer emits blue light and a luminescence conversion layer whose phosphor converts part of the blue light into yellow light. Alternatively, it would also be possible for the luminescence conversion layer to contain a phosphor which emits in the green or red spectral range. By a suitable choice of the wavelength of the LED chip and the phosphor, a defined color location can be achieved in the CIE color diagram. The luminescence conversion layer can also have a plurality of phosphors in order to set the color location of the LED light source in a targeted manner. Examples of suitable phosphors, such as a YAG: Ce powder, are e.g. B. in the document WO98 / 12757 whose contents are hereby incorporated by reference.

In accordance with at least one embodiment, the luminescence conversion layer follows a cover layer in the beam direction, the cover layer comprising a base material and particles embedded in the base material. The base material preferably comprises a polymer. The embedded particles have, for example, an inorganic material.

The base material has a refractive index n1 at room temperature and at a Operating temperature of the LED light source on a refractive index n2.

The particles have a refractive index n3 at room temperature and a refractive index n4 at the operating temperature of the LED light source.

Room temperature is understood here and below as the ambient temperature at which the LED light source is operated. The room temperature can be, for example, T _R = 20 ° C. The operating temperature is here and below to be understood as meaning the temperature which occurs during longer operation of the LED light source as the equilibrium temperature. The operating temperature of the LED light source, which is caused in particular by the heat loss generated during operation of the LED chip, is for example between 80 ° C. and 100 ° C. inclusive.

At room temperature, for example at T _R = 20 ° C, the amount of the difference in refractive indices is | n1 - n3 | advantageously 0.02 or more. At the operating temperature of the LED light source, the refractive indices of the base material and of the particles are advantageously matched to one another such that | n2-n4 | ≤ 0.01.

Because the refractive index n1 of the base material at room temperature and the refractive index n3 of the particles at room temperature differ by 0.02 or more, light scattering is caused by the particles in the base material. Preferably at room temperature | n1 - n3 | ≥ 0.03.

In particular, a portion of the incident on the LED light source ambient light is scattered by the particles in the base material and thus reduces any disturbing color impression of the luminescence conversion layer. In this way, for example, the yellow color impression of a luminescence conversion layer can be reduced, which is applied to produce white light on a blue emitting LED chip. Seen from the outside, the LED light source therefore advantageously has a neutral white color impression at room temperature.

At the operating temperature of the LED light source, the difference between the refractive indices of the base material and the particles is advantageously so small that the radiation emitted by the LED light source is not significantly affected by light scattering. This is achieved by | n2 - n4 | ≤ 0.01, preferably | n2 - n4 | ≤ 0.005, and more preferably | n2 - n4 | ≤ 0.002. Ideally, the refractive indices of the base material and the particles are the same at the operating temperature, so n2 = n4.

The efficiency of the LED light source at the operating temperature is increased in this way and reduces additional heating by backscattered light.

The base material and the particles advantageously have different temperature gradients in order to achieve that the difference between the refractive indices of the base material and the particles is high enough on the one hand at room temperature to achieve a desired light scattering to reduce the color impression, but on the other hand only at the operating temperature little or even no scattering occurs so as not to affect the efficiency of the LED chip. In a particularly advantageous embodiment, the refractive index of the base material and the refractive index of the particles have temperature gradients with opposite signs. For example, the base material may be a polymer whose refractive index decreases with increasing temperature, while the particles are formed from an inorganic material, in particular a glass, whose refractive index increases with increasing temperature.

In a preferred embodiment, the base material is a silicone. Silicone has a refractive index n = 1.49 at room temperature, with the temperature gradient of the refractive index, for example, dn / dT = -4 × 10 ^-4 1 / K.

The embedded in the base material particles are preferably formed from a glass. In particular, the particles may be glass beads. The glass may in particular be a quartz glass. The particles therefore preferably have SiO ₂ . The temperature gradient dn / dT of the refractive index of the glass is advantageously between 1 × 10 ^-6 1 / K and 1 × 10 ^-5 1 / K.

The particles advantageously have a concentration of at least 10% by weight, preferably at least 20% by weight, particularly preferably at least 30% by weight, in the base material. Due to the comparatively high concentration of the particles in the base material, a significant scattering of the ambient light is achieved at room temperature in order to minimize the color impression of the luminescence conversion layer arranged below the cover layer. Since the refractive index of the particles at the operating temperature is not or only slightly different from the refractive index of the base material, a comparatively high concentration of the particles in the base material is possible.

The particles preferably have a diameter between 0.2 μm and 10 μm. In particular, due to the adaptation of the refractive indices of the base material and the particles at the operating temperature, comparatively large particles can be embedded in the base material without significantly influencing the emitted radiation at the operating temperature. The particles may in particular have a diameter of 5 μm or more.

In an advantageous embodiment, the luminescence conversion layer is applied directly to the LED chip. In this way, a particularly efficient conversion of a part of the radiation emitted by the LED chip to a longer wavelength can be achieved.

In another embodiment, the luminescence conversion layer is spaced from the LED chip.

The luminescence conversion layer may, for example, be applied to a transparent cover or a lens of the LED light source. In particular, the LED light source may have the design of a conventional incandescent lamp with a glass bulb and a thread for a bulb socket. In this case, the luminescence conversion layer may, for example, be applied to the inside of the glass bulb.

In one embodiment, the cover layer is applied directly to the luminescence conversion layer. For example, it is possible that the luminescence conversion layer covers the radiation exit surface of the LED chip, wherein the cover layer is applied directly to the luminescence conversion layer. In this case, it is possible that the cover layer, the luminescence conversion layer and the LED chip have the same dimensions in the lateral direction.

Alternatively, it is also possible that the luminescence conversion layer is a potting that covers the entire LED chip including the side edges of the LED chip. The potting may have a lateral extent of 5 mm or more.

The invention will be described below with reference to an embodiment in connection with the 1 and 2 explained in more detail.

Show it:

1 a schematic representation of a cross section through an LED light source according to an embodiment, and

2 a schematic plan view of the LED light source of 1 ,

Identical or equivalent components are each provided with the same reference numerals in the figures. The components shown and the size ratios of the components with each other are not to be considered as true to scale.

In the 1 schematically illustrated in cross section along the line AB LED light source 10 has an LED chip 1 on that on a support 5 is arranged. At the carrier 5 it may be, for example, a circuit board. Instead of a single LED chip 1 Can the LED light source 10 also have multiple LED chips.

The LED chip 1 has an active layer 3 on, for the emission of electromagnetic radiation in a radiation direction 11 is provided. The active layer 3 For example, it may be formed as a pn junction, a double heterostructure, a single quantum well structure, or a multiple quantum well structure.

The active layer 3 is for example between two oppositely doped semiconductor regions 2 . 4 arranged. For example, the carrier facing the first semiconductor region 2 n-doped and the carrier 5 remote second semiconductor region 4 be p-doped. Alternatively, it is also possible that the carrier 5 facing first semiconductor region 2 p-doped and that of the carrier 5 remote second semiconductor region 4 n-doped. This is especially the case when it comes to the LED chip 1 is a substratlosen, so-called thin-film chip.

The LED chip 1 may be based in particular on a nitride compound semiconductor material. "Based on a nitride compound semiconductor" in the present context means that the semiconductor layer sequence or at least one layer thereof comprises a III-nitride compound semiconductor material, preferably In _x Al _y Ga _1-xy N, where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1 and x + y ≤ 1 holds. This material does not necessarily have to have a mathematically exact composition according to the above formula. Rather, it may comprise one or more dopants as well as additional constituents which do not substantially alter the characteristic physical properties of the In _x Al _y Ga _1-xy N material. For the sake of simplicity, however, the above formula contains only the essential constituents of the crystal lattice (In, Al, Ga, N), even if these may be partially replaced by small amounts of other substances. Such a nitride compound semiconductor material is particularly suitable for the emission of radiation in the blue and / or ultraviolet spectral range.

Alternatively, it is also possible that the LED chip 1 an OLED chip is its active layer 3 an organic electroluminescent material.

The active layer 3 of the LED chip 1 follows in the beam direction 11 a luminescence conversion layer 6 to.

The luminescence conversion layer 6 has a phosphor through which at least a portion of the of the active layer 3 emitted radiation is converted to a longer wavelength. For example, the active layer 3 of the LED chip 1 emit blue light, with part of the blue light from the luminescence conversion layer 6 converted to yellow light. During operation of the LED chip therefore a mixed-colored light is emitted, which is due to the superposition of the active layer 3 emitted light and that of the luminescence conversion layer 6 emitted light results. The mixed light can be, in particular, white light, for example a blue light-emitting active layer 3 coated with a luminescence conversion layer suitable for generating yellow light 6 is provided.

At the in 1 illustrated embodiment, the luminescence conversion layer 6 directly on the LED chip 1 applied. Alternatively, it would also be possible to use the luminescence conversion layer 6 on a transparent cover or lens of the LED light source.

The luminescence conversion layer 6 follows in the direction of radiation 11 of the LED chip 1 a cover layer 7 to. The cover layer 7 has a base material 8th on, in the particle 9 are introduced. In particular, the base material may be a silicone and the particles 9 to act on glass particles. The glass particles may, for example, be spherical and in particular have quartz glass (SiO ₂ ).

The basic material 8th the topcoat 7 has at room temperature, in particular at T _R = 20 ° C, a refractive index n1. At the operating temperature of the LED chip 1 , which is preferably between 80 ° C inclusive and 100 ° C inclusive, comprises the base material 8th a refractive index n2.

The in the base material 8th the topcoat 7 embedded particles 9 have a refractive index n3 at room temperature and at the operating temperature of the LED chip 1 a refractive index n4.

The basic material 8th and the particles 9 the topcoat 7 are selected such that at room temperature | n1 - n3 | ≥ 0.02. Particularly preferably, | n1-n3 | ≥ 0.03.

Due to the difference between the refractive indices of the base material 8th and the particle 9 cause the particles 9 At room temperature, a scattering of the ambient light on the cover layer 7 , In this way, an undesirable color impression of the luminescence conversion layer 6 For example, a yellow color, effectively reduced.

At the operating temperature of the LED light source 10 is the difference | n2 - n4 | the refractive indices n2 of the base material 8th and n4 of the particles 9 advantageously not more than 0.01, preferably not more than 0.005 and particularly preferably not more than 0.002. Ideally, the refractive index is n2 of the base material 8th and the refractive index n4 of the particles 9 at the operating temperature of the LED light source 10 even the same. The operating temperature of the LED light source 10 is, for example, between 80 ° C inclusive and 100 ° C inclusive. Under operating temperature is in doubt the temperature to be understood, resulting from prolonged operation of the LED light source 10 as the equilibrium temperature.

In this way it is achieved that during operation of the LED light source 10 no significant scattering of the active layer 3 emitted radiation in the cover layer 7 occurs. At the operating temperature, therefore, the efficiency of the LED light source 10 not by scattering in the topcoat 7 also reduces additional heating of the LED chip 1 is advantageously reduced by backscattered radiation.

In order to achieve that the refractive indices n1 and n3 at room temperature have a sufficiently large difference to cause a scattering effect, but on the other hand at the operating temperature, the refractive indices n2 and n4 are adapted to each other to avoid scattering effects in the operation of the LED light source the basic material 8th and the particles 9 preferably different temperature gradients of the refractive indices. Particularly preferred are the temperature gradients of the refractive index of the base material 8th and the particle 9 opposite signs on. For example, the base material 8th a silicone with a temperature gradient of about dn / dT = -4 × 10 ^-4 1 / K, wherein the particles 9 have a glass with a temperature gradient dn / dT = 1 × 10 ^-6 1 / K to 1 × 10 ^-5 1 / K.

The particles 9 exhibit in the base material 8th advantageously a concentration of at least 10 wt .-%, preferably of at least 20 wt .-% and particularly preferably of at least 30 wt .-% to. Due to the comparatively high concentration of the scattering particles, a significant scattering of the emitted radiation occurs at room temperature achieved. Due to the approximately the same refractive indices of the base material at the operating temperature 8th and the particle 9 On the other hand, however, the efficiency at the operating temperature is not significantly affected. The diameter of the particles 9 is for example between 0.2 .mu.m and 10 .mu.m, preferably 5 .mu.m or more.

The in the supervision of the 2 illustrated radiation exit surface of the LED light source 10 in which the exemplary embodiment is the surface of the cover layer 7 acts, at room temperature advantageously no or only a very small color impression. In particular, the often undesirable yellowish color impression of the under the cover layer 7 arranged luminescence conversion layer 6 by the scattering of the ambient light on the particles 9 in the topcoat 7 suppressed. This is particularly advantageous in large-area light sources, in which the cover layer has, for example, an extension of 5 mm or more.

The invention is not limited by the description with reference to the embodiments. Rather, the invention encompasses any novel feature as well as any combination of features, including in particular any combination of features in the claims, even if this feature or combination itself is not explicitly stated in the patent claims or exemplary embodiments.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2010/038097 A1 [0004]
• WO 98/12757 [0009]

Claims (15)

LED light source ( 10 ), comprising - at least one LED chip ( 1 ) comprising a radiation-emitting active layer ( 3 ), - a luminescence conversion layer ( 6 ), the active layer ( 3 ) in a beam direction ( 11 ), and - one of the luminescence conversion layer ( 6 ) in the beam direction ( 11 ) subsequent cover layer ( 7 ), wherein the top layer ( 7 ) a basic material ( 8th ) and into the basic material ( 8th ) embedded particles ( 9 ), wherein - the base material ( 8th ) at room temperature a refractive index n1 and at an operating temperature of the LED light source ( 10 ) has a refractive index n 2, - the particles ( 9 ) have a refractive index n3 at room temperature and a refractive index n4 at the operating temperature, and where | n1 - n3 | ≥ 0.02 and | n2 - n4 | ≤ 0.01. LED light source according to claim 1, wherein | n1 - n3 | ≥ 0.03 applies. LED light source according to one of the preceding claims, wherein | n2 - n4 | ≤ 0.005. LED light source according to one of the preceding claims, wherein | n2 - n4 | ≤ 0.002. LED light source according to one of the preceding claims, wherein the refractive index of the base material ( 8th ) and the refractive index of the particles ( 9 ) Have temperature gradient of opposite sign. LED light source according to one of the preceding claims, wherein the base material ( 8th ) is a silicone. LED light source according to one of the preceding claims, wherein the particles ( 9 ) have a glass. LED light source according to one of the preceding claims, wherein the particles ( 9 ) Are glass beads. LED light source according to one of the preceding claims, wherein the particles ( 9 ) SiO ₂ . LED light source according to one of the preceding claims, wherein the particles ( 9 ) in the base material ( 8th ) have a concentration of at least 10% by weight. LED light source according to one of the preceding claims, wherein the particles ( 9 ) have a diameter between 0.2 microns and 10 microns. LED light source according to one of the preceding claims, wherein the luminescence conversion layer ( 6 ) is applied to the LED chip. LED light source according to one of the preceding claims, wherein the cover layer ( 7 ) directly onto the luminescence conversion layer ( 6 ) is applied. LED light source according to one of the preceding claims, wherein the luminescence conversion layer ( 6 ) on a transparent cover or lens of the LED light source ( 10 ) is applied. LED light source according to one of the preceding claims, wherein the operating temperature is between 80 ° C and 100 ° C.

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