DE102015102842A1 - Fluorescent composite ceramics and process for their preparation - Google Patents

Abstract

The present invention initially relates to a phosphor composite ceramic which can be used, for example, to convert light within a white-emitting LED. Furthermore, the invention relates to a method for producing a phosphor composite ceramic. The phosphor composite ceramic according to the invention comprises a polycrystalline ceramic material in which a plurality of individual particles of a phosphor is introduced. The particles of the phosphor are each included in the structure of the ceramic material. According to the invention, the ceramic material is formed by a spinel.

Description

The present invention initially relates to a phosphor composite ceramic which can be used, for example, to convert light within a white-emitting LED. Furthermore, the invention relates to a method for producing a phosphor composite ceramic.

BACKGROUND INFORMATION White light-emitting LEDs which are known from the prior art essentially consist of a base body, a blue-emitting semiconductor chip and a layer covering a semiconductor chip and comprising a luminescent substance which is bound in a matrix of organic material. This structure, in particular the layer of the converting phosphor, has some disadvantages. On the one hand there is the limited photochemical stability of the mostly used organic binders, such as. As epoxy or silicone, against the more intense blue radiation of the semiconductor chip. However, the rising temperature in the vicinity of the semiconductor chip also leads to irreversible damage to the organic matrix material. In addition, the increased temperature at the location of the phosphor caused by both heat buildup in the semiconductor chip and by heat buildup in the phosphor itself due to Stokes losses and a quantum efficiency of less than one causes a reversible thermal quenching of the emission.

The organic matrix materials used according to the prior art have a low thermal conductivity of about 0.15 W / mK to 0.25 W / mK, so that the resulting heat can be dissipated only insufficient. A further disadvantage of the incorporation of the phosphor into the matrix from the organic material is that a significant backscattering of the excitation radiation takes place at the interfaces between the grains of the phosphor and the organic matrix material. The cause of these high backscatter losses is the considerable refractive index difference Δη> 0.3 between the inorganic phosphor and the organic material of the matrix. On the one hand, when the excitation radiation is coupled in from the organic matrix into the phosphor, considerable backscatter occurs due to total reflection at the interface. This reflected radiation is largely absorbed by the semiconductor chip. This must be expected with losses of up to 30%. But also the decoupling of the converted radiation from the phosphor into the organic matrix is associated with large losses due to total reflection. Some of the disadvantages mentioned can be circumvented by replacing the organic material of the matrix with the inorganic material corundum Al ₂ O ₃ . In the case of this inorganic matrix system, this difference in the refractive indices is much smaller, so that the backscatter losses are significantly lower. The main disadvantage of the Al ₂ O ₃ matrix of the ceramic, however, is that corundum has a birefringence due to its hexagonal crystal structure, which leads to scattering losses in the polycrystalline ceramic. Scattering losses occur in polycrystalline structure due to scattering of pores, defects on the surface, roughness and by splitting the light beam into two components in the transition from a crystallite of the microstructure in the next crystallite, which represents a birefringence. This effect of birefringence affects all non-cubic crystals. If several mechanisms lead to scattering losses, a thickness dependence of the transmission of the material is usually given; ie with increasing material thickness, the transmission decreases.

The WO 02/057198 A2 describes the composition, production and use of polycrystalline phosphor ceramics for solid state lasers. These highly transparent conversion elements have the disadvantage that the excitation radiation moves in a straight line through the material due to lack of scattering centers. The homogeneity of the emitted light over the solid angle is thus insufficient.

The US 2004/0145308 A1 shows a phosphor ceramic, which consists of yttrium aluminate (YAG), subsequently impregnated with an activator solution and finally thermally treated. A particular disadvantage of this solution is that the activation is not homogeneous and thus can take place in the phosphor ceramics no uniform radiation conversion.

The DE 103 49 038 A1 describes a phosphor ceramic consisting of cerium-activated yttrium aluminate (YAG: Ce) with a low content of Al ₂ O ₃ as a sintering aid. The necessary scattering centers should be provided by remaining pores and foreign phases. Although this solution provides a conversion layer with improved thermal conductivity of up to 15 W / mK, the manufacturing cost is high because of the almost 100% use of YAG: Ce. In particular, the fairly large phosphor grains of the starting material have only a small sintering activity, which makes the formation of a ceramic much more difficult.

The WO 2005/119797 A1 shows a consisting of YAG: Ce phosphor ceramic, their production and their special shape as a lens, dome, Fresnel lens o. Ä.

The EP 0 816 537 A2 describes a porous, polycrystalline and multiphase ceramic and their Production and shaping. The phases of the ceramic are made of rare earth aluminates with garnet and / or perovskite structure, wherein the YAP phase YAlO _{3 has} an orthorhombic crystal structure and thus shows a birefringence. A use as a conversion element also seems less promising due to the large number of pores and the associated significant backscatter.

The WO 2010/024981 A1 shows a porous ceramic, which also contains SnO: In as a matrix material in addition to pores and phosphor particles.

The WO 2010/141291 A1 describes a ceramic composed of a garnet phosphor and a second phase consisting of compounds of the Al-YO system. Also in this solution, the latter crystal phase is birefringent.

The WO 2009/072029 A2 teaches a phosphor ceramic of Sr _1-xy M _y Si ₂ O ₂ N ₂ : Eu _x whose reflection properties were changed by a special guidance of the hot isostatic pressing.

The WO 2006/097876 A1 describes a composite ceramic of YAG: Ce as a phosphor and Al ₂ O ₃ as a matrix former. The phosphor is with max. 20% by volume. Al ₂ O ₃ has a high thermal conductivity of about 35 W / mK and determines as the main component the thermal conductivity of the entire composite ceramic. A disadvantage of this solution is that by the use of Al ₂ O ₃ considerable scattering losses due to birefringence occur. These losses can be partially compensated if the composite ceramic is composed of grains whose dimension is smaller than the wavelength of light. The provision of such submicroscale phosphors is very expensive and, in addition, such phosphors are less efficient. Therefore, subsequent structurings of the ceramic surface are proposed for improving the emission homogeneity.

The EP 1 369 935 A1 teaches that the phosphor content in a phosphor-matrix conversion element should not exceed 20% by volume in order for the backscatter losses to remain below that of the standard LEDs from 20% to 30%.

The WO 2014/053951 A1 shows a conversion element, which comprises an Al ₂ O ₃ ceramic, inside which a phosphor-filled cavity is formed. Due to the good thermal conductivity of the Al ₂ O ₃ ceramic excellent heat dissipation from the phosphor is postulated. The structure of the element and its processing, however, seem very complex. Parts of the Al ₂ O ₃ ceramic can also be replaced by a spinel, YAG or AlON ceramic.

The WO 2007/063460 A1 describes a combined ceramic conversion element in which the phosphor ceramic is sintered onto a ceramic support having a suitable refractive index and heat conduction. Suitable support materials are in particular Al ₂ O ₃ , Si, Al-Si-ON compounds, MgAl ₂ O ₄ , YAG and various metals. The problem with this solution is the complex multi-stage manufacturing process and the risk of spalling of layer parts in the final separation of the wafer into individual conversion elements.

The WO 2013/142276 A1 describes a combined ceramic conversion element, in which by the ceramic process already the final shape is preformed.

The WO 2014/056903 A1 shows that it is also possible to apply a plurality of layers of different phosphor ceramics to a carrier material. In all cases, however, the heat conduction within a layer is still significantly lower than within the support layer.

The WO 2014/013406 A1 shows the ability to combine conversion ceramics and phosphor binder pastes.

In the WO 2008/017353 A1 the possibility is mentioned of finally refining a fabricated luminescent ceramic on the side facing a semiconductor chip in order to reduce the backscatter of the excitation radiation. The required layer thickness d should correspond to the relationship d = λ _LED / (4 · d _ceramic ), where λ _{LED represents} the wavelength of the excitation radiation and d _{ceramic represents} the refractive index of the ceramic. In addition, a surface structuring of the ceramic is presented on the side facing away from the semiconductor chip by using a correspondingly structured pressing tool or by subsequent application of nanoparticles, whereby the backscattering of the emitted light is to be reduced.

The object of the present invention, starting from the prior art, is to provide a phosphor composite ceramic and a method for the production thereof in which an efficient phosphor is incorporated and the light hardly experiences any scattering losses in the phosphor composite ceramic.

The object is achieved by a phosphor composite ceramic according to the appended claim 1. The object is further achieved by a method for producing a A phosphor composite ceramic according to the attached independent claim 7 and a phosphor composite ceramic according to the attached independent claim 10.

The phosphor composite ceramics according to the invention serves for the conversion of electromagnetic radiation; in particular the conversion of light, for example in a white LED. The phosphor composite ceramics according to the invention can therefore also be referred to as a ceramic converter material. It comprises a polycrystalline ceramic matrix material in which a plurality of individual particles of a phosphor is distributed; is particularly preferably distributed homogeneously. Accordingly, the phosphor composite ceramic according to the invention consists at least of the ceramic matrix material and the phosphor, wherein the ceramic matrix material forms a ceramic matrix which is at least partially transparent to the radiation exciting the phosphor and the radiation that can be emitted by the phosphor. The phosphor is doped with at least one activator to act as a technical phosphor.

The particles of the phosphor are in particular grains. The particles of the phosphor are each included in the microstructure of the polycrystalline ceramic matrix material. The phosphor composite ceramic according to the invention is characterized in that the polycrystalline ceramic matrix material, which is not a phosphor, and the said phosphor are jointly subjected to a ceramic process. Thus, the phosphor composite ceramics according to the invention is thus not a so-called luminescent ceramics which consists only of a luminescent material which has been subjected to a ceramic process. Also, it is not a composite ceramic consisting of several layers.

According to the invention, the ceramic matrix material is formed by a cubic spinel; ie the ceramic matrix material essentially comprises a spinel. The spinel is a chemical compound of the general type AB ₂ X ₄ , wherein A and B are metal cations whose oxidation number gives the sum 8, and X predominantly a divalent chalcogenide anion, such as. B. O ^2- or S ^2- is. The crystal lattice of the spinels is formed by a cubic closest packing of the anions, whose tetrahedral holes are occupied to one-eighth and their octahedral holes in half with the corresponding metal cations. The chalcogenide anions can be partially replaced by pnictide anions, resulting in highly complex spinel compounds such. For example, the cubic defect spinels of composition Al _{23-x / 3} O _{27 + x} N _5-x , in which the positive excess charge of the Al ³⁺ ions is compensated by trivalent N ³ anions and those as aluminum oxynitride (AlON) in technical ceramics are used as a transparent optical material. The spinel is particularly preferably MgAl ₂ O ₄ , ZnAl ₂ O ₄ or AlON, ie the spinel essentially comprises MgAl ₂ O ₄ , ZnAl ₂ O ₄ or AlON. Particularly preferably, the ceramic matrix material consists of MgAl ₂ O ₄ , ZnAl ₂ O ₄ or AlON or mixtures of said spinels _.

Cubic transparent materials such as spinels (eg MgAl ₂ O ₄ , ZnAl ₂ O ₄ , AlON) have lower scattering losses and thus higher transmission values compared to hexagonal materials such as Al ₂ O ₃ since they do not cause birefringence. Due to the cubic crystal structure here is a reduction of the grain size in the structure in the range of the wavelength of the visible light as in the case of Al ₂ O _{3 is} not mandatory. The novel phosphor composite ceramics are characterized by the spinel as an inorganic matrix former, in contrast to organic binders. The spinel leads to a high thermal conductivity of the phosphor composite ceramics of about 15 W / mK, which is significantly greater than that in plastic-based composites. In the case of a preferred embodiment in which the phosphor is formed by a YAG phosphor, the phosphor of the phosphor composite ceramics according to the invention likewise has a thermal conductivity of about 15 W / mK. Because of this very similar thermal conductivity, thermal stresses which would lead to loss processes are avoided in the phosphor composite ceramics according to the invention.

In the case of a preferred embodiment in which the phosphor is formed by a YAG phosphor, the phosphor of the phosphor composite ceramics according to the invention has a refractive index which differs from the refractive index of the spinel by only less than 0.2. On the other hand, in the case of the organically based phosphor composites known from the prior art, the refractive indices of phosphor and binder differ significantly by more than 0.3. Consequently, the backscatters caused by the refractive index difference are significantly reduced in the phosphor composite ceramics according to the invention.

In preferred embodiments, the phosphor composite ceramic according to the invention consists predominantly of the ceramic matrix material. Accordingly, the phosphor composite ceramics according to the invention consists predominantly of the spinel. The proportion of spinel in the phosphor composite ceramics is preferably between 60% by mass and 99.9% by mass.

In preferred embodiments of the phosphor composite ceramic according to the invention, the proportion of the phosphor on the Fluorescent composite ceramics between 0.1% by mass and 40% by mass. This proportion is particularly preferably between 3% by mass and 10% by mass.

The phosphor is preferably formed by a conversion luminescent material that can be excited by electromagnetic radiation in a first wavelength range, as a result of which electromagnetic radiation in a second wavelength range other than the first wavelength range can be emitted by the luminescent material. This property of the phosphor gives the phosphor also the entire phosphor composite ceramics. The electromagnetic radiation of the first wavelength range and the electromagnetic radiation of the second wavelength range are preferably formed in each case by light, UV radiation and / or IR radiation. Particularly preferably, the electromagnetic radiation of the first wavelength range is formed by blue light. Particularly preferably, the electromagnetic radiation of the second wavelength range is formed by green, yellow, orange and / or red light.

The phosphor is preferably formed by a garnet phosphor. The garnet phosphor is preferably formed by a YAG phosphor. The YAG phosphor preferably has a host lattice of the chemical formula Y ₃ Al ₅ O ₁₂ , which is doped with cerium as activator. The phosphor is alternatively preferably formed by a silicate phosphor. The silicate phosphor preferably has a host lattice of the chemical formula A ₂ SiO ₄ with A = Ba, Sr and / or Ca, which is doped with europium as the activator. In principle, the phosphor of the phosphor composite ceramics according to the invention can also be formed by another technical phosphor or by a plurality of different technical phosphors.

The average size of the particles of the phosphor is preferably between 2 .mu.m and 20 .mu.m. The particles of the phosphor are preferably distributed homogeneously in the phosphor composite ceramic. Basically, the particles of the phosphor are distributed within the spatial extent of the phosphor composite ceramic.

The phosphor composite ceramic according to the invention is preferably designed as a disk in order to be able to act in particular as a converter disk in a white-emitting LED. The disk preferably has plane-parallel surfaces. The disc has a thickness, d. H. a distance of the two plane-parallel surfaces preferably between 0.1 mm and 1 mm.

The phosphor composite ceramics according to the invention can be used wherever a second, distinguishable radiation is required in addition to a primary radiation, which is produced by conversion from the first radiation. Typical fields of application of the phosphor composite ceramics according to the invention are LEDs, laser diodes, projectors and the like. ä.

The phosphor composite ceramic according to the invention is preferably designed such that it forms a white light source together with a blue-emitting LED. The light of the white light source in the CIE diagram preferably meets the white light curve of a Planckian radiator when the thickness of the phosphor composite ceramic is in the range of 0.1 mm and 1.0 mm and when the phosphor composite ceramics occupy a proportion of the phosphor between 2 Ma. % and 40% by mass.

The method according to the invention serves to produce a phosphor composite ceramics. In one step of the process, a powdery spinel is provided which will act as an inorganic matrix material. Furthermore, a phosphor is provided in the form of particles to be bound by the inorganic matrix material. The phosphor provided is already doped with at least one activator in order to function as a technical phosphor. In a further step of the process according to the invention, the pulverulent spinel and the particles of the phosphor are mixed to form a mixture. The mixing is preferably carried out homogeneously. In a further step, the mixture is sintered to a phosphor composite ceramics. Consequently, the phosphor and the spinel undergo the ceramic process together.

The mixing of the pulverulent spinel and the particles of the phosphor is preferably carried out by dispersing the pulverulent spinel in an aqueous suspension with the particles of the phosphor. The dispersion preferably takes place in a mill, for example in a high-performance stirred ball mill. For dispersing, in addition to the spinel and the water, preference is furthermore given to using a plasticizer and / or a binder and lubricant. By dispersing a slurry, which is preferably sieved through a sieve.

In a preferred step to be carried out, the mixture or the slip is first granulated to a granulate. For this purpose, the slurry is preferably sprayed in a spray tower. The granules obtained are preferably screened through a sieve.

In a further preferred step to be carried out, the mixture or the granulate is pressed to form a green body. The pressing is preferably carried out as dry pressing. The pressing is preferably uniaxial with a hydraulic or servo-electric press. The green body preferably has the shape of a disc with a diameter preferably between 20 mm and 50 mm or an edge length preferably between 40 mm and 100 mm and a height preferably between 0.2 mm and 5 mm. The specific pressing pressure during pressing is preferably in the range between 200 MPa and 300 MPa.

The sintering of the mixture or of the granulate or of the green body preferably takes place in several substeps. The green body or the granules or the mixture is preferably thermally debinded; in particular by a thermal treatment, preferably between 800 ° C and 1200 ° C, preferably over a period of time between 10 hours and 100 hours. In a further preferred sub-step to be carried out pre-sintering takes place by heating in a H ₂ or Formiergasatmosphäre to a temperature of preferably between 1200 ° C and 1800 ° C; more preferably between 1,400 ° C and 1,600 ° C; so that a pre-burned body is created. The pre-sintering is preferably carried out until no more open porosity is present. In a further sub-step, a re-compression takes place in the form of a heating of the prefired body to a temperature between 1200 ° C and 1800 ° C; more preferably between 1,400 ° C and 1,600 ° C. The densification is preferably carried out hot isostatic. The densification is preferably carried out under a pressure of more than 10 MPa; more preferably more than 100 MPa; preferably over a period of less than three hours; more preferably between one and three hours.

The phosphor composite ceramic produced as a result of the sintering is preferably ground plane-parallel.

A particular advantage of the method according to the invention is that the powdered spinel and the powdered phosphor need not have any particular fineness for the ceramic process, whereby the deployment effort is significantly reduced compared to the prior art.

The minimum absorption required for high transparency of the phosphor composite ceramics to be produced requires the use of highest purity raw materials, which is preferably greater than 99.9%. Impurities and introduced dopants would produce defects or scattering centers, which would in any case reduce the transmission. The transmission of the non-scattered straight light beam, which is crucial for the transparency, is considerably reduced by diffuse scattering even with the lowest residual porosity. Therefore, the elimination of last hundredth percent of porosity is critical to high transmission. Since this extreme compaction must be done with minimal grain growth, high sintering temperatures or long holding times are not applicable. Therefore, the hot isostatic recompression to achieve near theoretical density plays a crucial role. To achieve such microstructures, dry pressing as a molding process is a cost effective manufacturing technology.

In preferred embodiments of the method according to the invention, the mixture or the green body is compacted during sintering to a sintering density of more than 99.5% of the theoretical density.

In preferred embodiments of the method according to the invention, the particles of the phosphor provided have an average size between 2 μm and 20 μm. The particles of the phosphor provided have preferably a size between 2 .mu.m and 20 .mu.m.

In preferred embodiments of the method according to the invention, the particles or grains of the powdery spinel provided have an average size of between 0.3 μm and 20 μm. The particles or grains of the provided powdery spinel preferably have a size between 0.3 μm and 20 μm.

The process according to the invention preferably serves for the production of the phosphor composite ceramics according to the invention. The process according to the invention particularly preferably serves to prepare preferred embodiments of the phosphor composite ceramics according to the invention. The features specified for the phosphor composite ceramics according to the invention and their preferred embodiments are preferably also to be realized by the method according to the invention. For example, the quantitative details of the composition of the phosphor composite ceramics according to the invention are preferably to be used as quantitative data for the amounts of the starting materials of the process according to the invention.

A further subject of the invention is a phosphor composite ceramic which can be produced by the method according to the invention.

Further advantages, details and developments of the invention will become apparent from the following description of several embodiments.

Embodiment 1

A very finely divided spinel powder (MgAl ₂ O ₄ ) having an average particle size d ₅₀ = 300 nm is dispersed with a high-performance stirred ball mill in an aqueous suspension with a phosphor based on YAG: Ce ³⁺ (d ₅₀ = 1 μm to 20 μm). There are 2,700 g of spinel powder with the addition of 3.0 liters of distilled water; 0.5 wt .-% to 3.0 wt .-% plasticizer and 1.5 wt .-% to 7 wt .-% binder and lubricant for a period of z. B. dispersed in the circulation for 30 min. The slip is then screened through a 100 μm sieve. For the production of a pressed granules, the slurry is sprayed in a spray tower at a tower temperature of 200 ° C to 300 ° C. The granules obtained are sieved again through a 315 micron sieve and determines the granule size distribution. The X ₅₀ value is usually in a range between 20 μm and 60 μm; preferably at 40 microns. The granules after this treatment usually has a humidity of max. 1 %.

The uniaxial pressing of the components takes place on a hydraulic or servo-electric press. Slices with a diameter of 20 mm to 50 mm and a height of 0.2 mm to 5 mm are produced. The specific pressing pressure is in the range between 200 MPa and 300 MPa; preferably 200 MPa.

The thermal debinding of the green body takes place in a chamber furnace with thermal afterburning. In stages, the temperature is increased to 1,000 ° C over a period of 20 to 80 hours. Thereafter, it is cooled down to room temperature over a period of 360 min.

The pre-sintering takes place in a high-temperature furnace in H ₂ or Formiergasatmosphäre. For this purpose, the debinded shaped bodies are heated at a heating rate of 2 K / min up to a temperature of 1400 ° C to 1600 ° C and sintered with a holding time until no more open porosity is present. The cooling took place at 10 K / min.

The presintered moldings are densified in a hot isostatic press under argon atmosphere at a pressure of ≥ 100 MPa for two hours at 1,400 ° C to 1,600 ° C.

The components are placed on a fine grinding machine; preferably with a grain: diamond D64C50; Ground plane parallel.

Embodiment 2:

Another example is a composite ceramic prepared as Embodiment 1 wherein the phosphor YAG: Ce ³⁺ is substituted by Lu ₃ (Al _1-x Ga _x ) ₅ O ₁₂ : Ce ³⁺ as the phosphor component, and dry molded by planar molding different geometry can be produced.

Embodiment 3

A very finely divided spinel powder (MgAl ₂ O ₄ ) having an average particle size d ₅₀ = 300 nm is dispersed with a high-performance stirred ball mill in an aqueous suspension with a phosphor based on YAG: Ce ³⁺ (d ₅₀ = 1 μm to 20 μm). There are 200 g of spinel powder with the addition of 0.1 l of distilled water and 0.5 wt .-% to 3.0 wt .-% liquefier for a period of z. B. dispersed in the circulation for 30 min. Thereafter, the slurry is screened through a 100 micron sieve and poured into a mold of any geometry. Subsequently, the green body is removed from the mold and dried for 24 hours at room temperature. The thermal debinding of the green body takes place in a chamber furnace. The debindered moldings are heated at a heating rate of 2 K / min in H ₂ or Formiergasatmosphäre up to a temperature of 1400 ° C to 1600 ° C and sintered with a hold time until no more open porosity is present. Cooling is for example at a speed of 10 K / min. The presintered moldings are densified in a hot isostatic press under argon atmosphere at a pressure of ≥ 100 MPa for two hours at 1,400 ° C to 1,600 ° C. The components are placed on a fine grinding machine; preferably with a grain: diamond D64C50; Ground plane parallel.

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 02/057198 A2 [0004]
• US 2004/0145308 A1 [0005]
• DE 10349038 A1 [0006]
• WO 2005/119797 A1 [0007]
• EP 0816537 A2 [0008]
• WO 2010/024981 A1 [0009]
• WO 2010/141291 A1 [0010]
• WO 2009/072029 A2 [0011]
• WO 2006/097876 A1 [0012]
• EP 1369935 A1 [0013]
• WO 2014/053951 A1 [0014]
• WO 2007/063460 A1 [0015]
• WO 2013/142276 A1 [0016]
• WO 2014/056903 A1 [0017]
• WO 2014/013406 A1 [0018]
• WO 2008/017353 A1 [0019]

Claims (10)

A phosphor composite ceramic, comprising a ceramic matrix material, in which a plurality of individual particles of a phosphor is introduced, wherein the particles are each included in the structure of the ceramic matrix material, characterized in that the ceramic matrix material is formed by a spinel. Phosphor composite ceramics according to claim 1, characterized in that the proportion of the phosphor on the phosphor composite ceramics is between 0.1 and 40% by mass. Phosphor composite ceramics according to claim 1 or 2, characterized in that the proportion of the spinel in the phosphor composite ceramics is between 60% by mass and 99.9% by mass. Phosphor composite ceramics according to one of claims 1 to 3, characterized in that the phosphor is formed by a garnet phosphor. Phosphor composite ceramics according to one of claims 1 to 4, characterized in that the average size of the particles of the phosphor is between 2 microns and 20 microns. Phosphor composite ceramics according to one of claims 1 to 5, characterized in that it is formed as a disc with plane-parallel surfaces and has a thickness between 0.1 mm and 1 mm.  Process for the preparation of a phosphor composite ceramics, comprising the following steps: - Providing a powdery spinel; - Providing a phosphor in the form of particles; - Mixing the powdery spinel and the particles of the phosphor to a mixture; and - sintering the mixture into a phosphor composite ceramic. A method according to claim 7, characterized in that the mixing of the powdery spinel and the particles of the phosphor is effected in that the powdery spinel is dispersed in an aqueous suspension with the particles of the phosphor. A method according to claim 7 or 8, characterized in that the sintering of the mixture is carried out by heating the mixture to a temperature between 1200 ° C and 1800 ° C.  Phosphor composite ceramics, producible by a method according to one of claims 7 to 9.