DE102013205329A1 - Method for producing a phosphor ceramic - Google Patents

Abstract

The invention relates to a method for producing a fluorescent ceramic (11) comprising: providing an inorganic matrix material (2) which has a silicon-nitride compound; Providing a doping element (12) for forming luminescence centers in the matrix material (2); Providing a sintering aid (3) for compacting the matrix material (2); Forming a green body (7, 15) by at least partially mixing the matrix material (2), the doping element (12) and the sintering aid (3) with one another; and sintering the green body (7, 15). The invention also relates to a fluorescent ceramic (11) produced by the method and a light-emitting device (17, 30) comprising the fluorescent ceramic (11).

Description

The present invention relates to a method for producing a phosphor ceramic. The invention also relates to a phosphor ceramic and a light-emitting device with the phosphor ceramic.

Phosphors are used in conversion elements, for example for light-emitting diodes (LED) or scintillators, in order to convert electromagnetic radiation of one wavelength range into electromagnetic radiation of another longer wavelength range of wavelengths. The conversion effect is based on photoluminescence, such as fluorescence or phosphorescence.

To fabricate such conversion elements, a phosphor is embedded in a matrix material, such as a transparent resin. In LEDs, the conversion element is placed over a light-emitting semiconductor chip to convert a portion of the blue primary light into longer-wavelength light and produce light of different colors. Additive color mixing of the primary light and the converted light produces the emission spectrum of the LED, such as white light. In scintillators, the conversion element is equipped with a photosensitive element in order, for example, to detect high-energy radiation in nuclear medicine or X-ray diagnostics. The phosphor here has the task to convert the high-energy radiation into visible light, which is then detected by the photosensitive element.

In addition to embedding the phosphor in a resin, inorganic phosphors in phosphor ceramics are also used in conversion elements. Inorganic phosphors are luminescent materials which consist of an inorganic host lattice in which luminescence centers (activator ions) are incorporated. Frequently used as host lattices are oxides, nitrides or silicon-aluminum oxynitrides (SiAlONs) whose luminescence properties are activated by doping with rare earth ions (for example cerium, europium). Compared with resin-based conversion elements, conversion elements based on phosphor ceramics have the advantage that they have better thermal conductivity and therefore enable improved conversion efficiency.

For producing such ceramics, different methods are known. For example, pressure-based sintering methods, such as gas pressure sintering (GPS), hot pressure sintering (HPS) or plasma sintering (SPS, spark plasma sintering) are used. The aim of these techniques is to provide ceramics with high densities. The production with pressure-based methods, however, is expensive. For mass production in particular, it is therefore desirable to use pressureless sintering processes. In particular, purely temperature-based sintering processes are suitable for this purpose. To achieve the desired high densities, the materials for making the ceramic are exposed to high temperatures between 1600-2200 ° C. In phosphors, in particular nitridic systems, however, such high temperatures can lead to degradation (decomposition) of the phosphor.

It is therefore an object of the invention to provide an improved, non-pressurized method for producing a phosphor ceramic, with which even at low temperatures, for example, <1700 ° C high densities are achieved in the phosphor ceramic.

A method for producing a phosphor ceramic is proposed, which comprises the following steps:
Providing an inorganic matrix material comprising a silicon nitride-based compound;
Providing a doping element for forming luminescent centers in the inorganic matrix material;
Providing a sintering aid for compacting the inorganic matrix material;
Forming a green body by at least partially mixing the inorganic matrix material, the doping element and the sintering aid; and
Sintering or heating the green body.

The use of the sintering aid in the manufacture of a phosphor ceramic makes it possible to achieve high densities in the phosphor ceramics using pressureless processes even at moderate temperatures, for example <1700 ° C, in particular between 800 and 1600 ° C. The sintering aid here causes oxynitridic and / or silicate-containing liquid phases of the nitridic matrix material and the sintering aid to form at moderate sintering temperatures during the heating, that is to say during sintering. By these liquid phases, the filling of pore spaces during sintering can be accelerated, and the density of the produced phosphor ceramics increases.

Pressure-free processes or pressureless sintering processes denote processes which are carried out at atmospheric pressure (1 atm) and are based exclusively on the increase in the temperature, ie the heating. Further measures to pressure the green body during the heating, that is to say the inorganic matrix material with the doping element and the sintering aid, exercise can thus be avoided. For example, it is neither necessary to apply a vacuum or to work under gas pressure nor to press the green body during sintering, thereby reducing the production outlay.

With the aid of the sintering aid, geometric densities> 70% and in particular> 80% can be realized in a pressureless process even at low temperatures <1700 ° C. and in particular <1600 ° C. The degradation or decomposition of the doping element is reduced by the moderate temperatures. In the present context, the geometric density designates the percentage of the material density, ie the density of the phosphor ceramics produced, in comparison to the pure solid density, ie the density of the starting materials for producing the phosphor ceramics. The geometric density thus results, for example, from the ratio between the density of the phosphor ceramics produced (calculated from mass and volume) and the powder density of the starting material for the ceramic. Starting materials here are the inorganic material, the doping element and the sintering aid. The geometric density is thus a measure of the volume of solids in the phosphor ceramics or a measure of the proportion of solids volume in the phosphor ceramics. Furthermore, the high density improves the optical transparency of the phosphor ceramics, since phase boundaries between pores and solid material are reduced, which leads to scattering and thus reduced light transmission.

A phosphor ceramic in the present context refers to a ceramic material with a doping element or phosphor which converts electromagnetic radiation of a first wavelength range or frequency range into electromagnetic radiation of a second wavelength range or frequency range. The first wavelength range or frequency range is given by the excitation wavelengths or excitation frequencies and the second wavelength range or frequency range by the emission wavelengths or emission frequencies of the phosphor ceramic and in particular the doping element embedded in the inorganic matrix material or host lattice. Furthermore, the excitation wavelengths or frequencies differ from the emission wavelengths or frequencies. In this case, the excitation wavelength is smaller than the emission wavelength or the excitation frequency is greater than the emission frequency.

For this purpose, the phosphor ceramic has an inorganic matrix material into which at least one doping element is embedded as a luminescence center. The inorganic matrix material can act as a host lattice for the doping element, wherein the dopant element forms the luminescence centers in the inorganic matrix material and provides the luminescent properties of the luminescent ceramic. The conversion occurring in the phosphor ceramics can be based on photoluminescence, in particular fluorescence or phosphorescence. That Electromagnetic radiation having the excitation wavelength is absorbed by the phosphor ceramic, in particular the doping element embedded in the inorganic matrix material, and then emitted spontaneously or with a time delay with an emission wavelength that is different, preferably smaller, than the excitation wavelength.

In one embodiment, the inorganic matrix material for producing the phosphor ceramics comprises a metal-silicon nitride or a metal-silicon oxynitride. In particular, the silicon nitride-based matrix material contains at least one inorganic compound selected from the group consisting of compounds of the structural formula MAILi ₃ , M ₂ Si ₅ N ₈ MYSi ₄ N ₇ or oxynitrides with general structural formula MSi ₂ O ₂ N ₂ , MSi ₃ O ₃ N ₄ , M _x Si _12-mn Al _{m + n} O _n N _16-n (0 <n, m <12 and n + m ≤ 12), Si _6-z Al _z O _z N _8-z (0 <z ≤ 4.2), wherein a part of the Si-N bonds is substituted by Al-O or Al-N bonds.

Furthermore, M denotes a metallic element which contains in particular at least one element selected from the group consisting of alkali metal, alkaline earth metal and transition metal. For example, the alkali metal may contain at least one element selected from the group consisting of lithium (Li), sodium (Na) and potassium (K). The alkaline earth metal may contain at least one element selected from the group consisting of magnesium (Mg), calcium (Ca), strontium (Sr) and barium (Ba). The transition metal may contain at least one member selected from the group consisting of titanium (Ti), manganese (Mn) and yttrium (Y).

The metallic element is preferably an alkali metal, in particular Li, an alkaline earth metal, in particular Ca, Sr or Ba, or a transition metal, in particular Y. Very particularly preferred as the metallic element is an alkaline earth metal, in particular Ca, Sr or the transition metal Y. In the systems MAlSiN ₃ and M ₂ Si ₅ N ₈ are preferably used alkaline earth metal ions, such as Ca ²⁺ , Sr ²⁺ or Ba ²⁺ . In M _x Si _12-mn Al _{m + n} O _n N _16-n , M is preferably Ca ²⁺ , Y ³⁺ . To compensate for charge effects when replacing divalent by trivalent ions Li ⁺ can be used.

In a further embodiment, the doping element or the phosphor contains at least one rare earth metal. That's how it works Doping element at least one element selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), Holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu). Preferred dopants are Ce, Eu, Nd and Gd. Particularly preferred are Ce and Eu. The doping element or the phosphor can contain a single rare earth metal ion or mixtures of two or more rare earth metal ions. The combination of inorganic matrix material and doping element can also be referred to as a phosphor system.

The doping element and the inorganic matrix material or host lattice can furthermore be selected as a function of the desired excitation and emission wavelength of the luminescent ceramic. Thus, the electronic states of the doping element embedded in the inorganic matrix material determine the possible transitions and thus the excitation and emission wavelengths of the phosphor ceramic. By selecting the doping element and the inorganic matrix material, the excitation and emission wavelength can be varied so that the phosphor ceramic can be adapted to different applications by selecting a suitable doping element or phosphor or phosphor system.

In a further embodiment, the doping element may be provided embedded in the inorganic matrix material. Ie. the doping element is already incorporated in the host lattice. In this case, a plurality of doping elements can also be embedded or integrated in the inorganic matrix material. Additionally or alternatively, the doping element may be provided embedded in the sintering aid. For example, ceria may be included in the sintering aid. Additionally or alternatively, the doping element can also be provided separately or independently of the inorganic matrix material or the host lattice. The doping element can thus be provided as a separate starting material for producing the phosphor ceramics. Subsequently, the doping element can be at least partially mixed with the inorganic matrix material. For example, the doping element can be applied to the inorganic matrix material. By heating, the doping element can then be introduced into the inorganic matrix material by diffusing into the inorganic matrix material. For this purpose, it is also possible to provide a plurality of doping elements which diffuse into the inorganic matrix element during heating. Since both the doping of the inorganic matrix material and the sintering of the green body by means of heat, both processes can be carried out simultaneously in a single process step.

In a further embodiment, the sintering aid contains at least one compound selected from the group consisting of metal oxide, metal fluoride, metal alkoxide, metal aluminate and metal silicate. Oxides, fluorides, alkoxides, aluminates or silicates of at least one metallic element can thus be used as sintering aids. Preferred sintering aids are metal oxides, metal fluorides, metal alkoxides or mixtures thereof, which have two or more of the sintering aids mentioned. Particularly preferred sintering aids are metal oxides and / or metal alkoxides. Other metal nitrides, in particular AlN, can also be used as sintering aid.

Suitable metal oxides are, for example, transition metal oxides, such as Al ₂ O ₃ , Y ₂ O ₃ or yttrium aluminum garnet (Y ₃ Al ₅ O ₁₂ , YAG for short), rare earth (SE) doped (eg Ce, Nd, Gd) yttrium Aluminum garnet (YAG: SE), lanthanide oxides, in particular Ce ₂ O ₃ , Eu ₂ O ₃ , EuO or Gd ₂ O ₃ , alkali oxides, in particular LiO ₂ , NaO ₂ , KO ₂ or RbO ₂ , alkaline earth oxides, in particular MgO, CaO, SrO or BaO, or semi-metal oxides, such as SiO ₂ , which may also be present in a mixture of two or more of said metal oxides. Preferred metal oxides are YAG, YAG: SE, Al ₂ O ₃ , SiO ₂ , Y ₂ O ₃ , MgO and mixtures thereof. Particularly preferred metal oxides are Al ₂ O ₃ , Y ₂ O ₃ , MgO and mixtures thereof. In particular, the last-mentioned metal oxides lead to rapid melting of the inorganic matrix material during heating and are therefore particularly suitable for compacting the light-emitting ceramic at low temperatures.

Suitable metal fluorides are, for example, LiF, CaF ₂ and MgF ₂ . Particularly preferred is LiF as the metal fluoride. The metal alkoxide may contain at least one alkoxide of aluminum (Al), magnesium (Mg), silicon (Si), yttrium (Y) and mixtures of two or more of these. Particularly suitable are metal alkoxides of the formula M (OR) _n , where M denotes a metallic element, such as Al or Y, and n denotes an integer with a value of 0 to 4. OR denotes an alkoxy radical in which each R radical can independently be an alkyl radical. Each R group may further independently be a linear or branched alkyl group having 1 to 20, preferably 3 to 6, carbon atoms.

Here, the inorganic matrix material and the sintering aid can be chosen so that the formation of liquid phases during the sintering process is favored. A suitable combination is, for example, a silicon nitride-based matrix material with a metal oxide, such as Al ₂ O ₃ , Y ₂ O ₃ or a mixture thereof, and / or a metal alkoxide, such as Al alkoxide, Y alkoxide or a mixture thereof, as a sintering aid. Another suitable combination is, for example, a silicon nitride-based matrix material a metal oxide, such as YAG or YAG: SE, as a sintering aid.

In a further embodiment, the sintering aid provided is selected such that its metallic element belongs to a same element group or class as the metallic element of the inorganic matrix material. Possible element groups are in particular alkali metals, alkaline earth metals or transition metals. The agreement in the metallic element avoids the incorporation of foreign ions into the inorganic matrix material and associated changes in the system. If, for example, the metallic element of the inorganic matrix material is an alkaline earth metal, alkaline earth fluorides, oxides, aluminates or silicates are particularly suitable as sintering aids. Further, the metallic element of the inorganic matrix material and the metallic element of the sintering aid may have the same metallic element, for example, Ca, Y, Mg or Al. Advantageous combinations with respect to the inorganic matrix material and the sintering aid are, for example: Al as a metallic element of the inorganic matrix material with Al ₂ O ₃ and / or Al alkoxide as a sintering aid, Y as a metallic element of the inorganic matrix material with Y ₂ O ₃ and / or Y-alkoxide as a sintering aid, Ca as a metallic element of the inorganic matrix material with CaO as a sintering aid or Y or Li as a metallic element of the inorganic matrix material with LiF as a sintering aid.

The starting materials of the process, that is to say the inorganic matrix material and the sintering aid and optionally the doping element, are preferably provided as powder. Here, the doping element may already be embedded in the inorganic matrix material and / or provided as a separate powder. In the following, references to the inorganic matrix material in addition to the matrix material without doping element, ie the undoped inorganic matrix material, should also include the possibility that the inorganic matrix material is doped.

The powder of the respective starting material may have particles with a composition for the respective starting material. Alternatively, the powder of the respective starting material may have a particle mixture with particles of different compositions and / or sizes for the respective starting material. For example, first particles having a first composition and / or size of the respective starting material and second particles having a second composition of the respective starting material may form the particle mixture, wherein the first and the second composition of the respective starting material differ. The particles of the powder for the respective starting material may have a particle size distribution of from 0.1 nm to 50 μm, preferably from 1 nm to 5 μm and particularly preferably 0.1-3 μm. In this case, the particles may be present in regular form approximately in spherical form. But also chopsticks or irregular shapes are conceivable.

In a further embodiment, the sintering aid and the inorganic matrix material are provided as a powder, wherein the average size of particles in the powder of the sintering aid is less than or equal to the average size of particles in the powder of the inorganic matrix material. The size distribution of the particles can have a monomodal, bimodal or multimodal distribution. The powder of the sintering aid and the powder of the inorganic matrix material preferably have a monomodal distribution. The mean size is determined from the mean of the size distribution. Thus, particles of the inorganic matrix material may have a size distribution in the range of 0.1-10 μm, preferably of 0.1-3 μm. Particles of the sintering aid may have a size distribution in the range of 10 nm-2 microns, preferably from 10 to 1000 nm. A monomodal size distribution and / or a fine-grained powder of the sintering aid thereby act in an increased sintering activity.

In a further embodiment, up to 50% by weight, in particular up to 20% by weight, of the sintering aid is at least partially mixed with the inorganic matrix material. In this case, data in% by weight relate to the inorganic matrix material. Furthermore, 0.1 to 10 wt .-%, preferably 0.1 to 3 wt .-% of the sintering aid may be at least partially mixed with the inorganic matrix material. In this case, the weight fraction of the sintering aid is chosen to be as small as possible in order to keep the proportion of foreign phases (liquid phase) as low as possible and thus to avoid undesired side reactions and the degradation of the doping element or phosphor. At the same time, however, the proportion by weight of the sintering aid is chosen to be so large that sufficient liquid phase forms on heating to achieve high densities.

In a further embodiment, a nitridic component is additionally provided and mixed with the sintering aid. By mixing the nitridic component with the sintering aid, a possible Si-N / Al-N depletion in the stoichiometry of the inorganic Matrix material to be counteracted. Si ₃ N ₄ , AlN, Ca ₃ N ₂ or mixtures thereof are particularly suitable as the nitridic component. Based on the inorganic matrix material, up to 50% by weight, in particular up to 20% by weight, of the nitridic component may be mixed with the sintering aid. In this case, details in% by weight are based on the inorganic matrix material. Furthermore, for example, 0.1 to 10 wt .-%, preferably 0.1 to 3 wt .-% of the nitridic component can be mixed with the sintering aid. Preferably, the nitridic component is mixed in a 1: 1 mixture with the sintering aid.

In a further embodiment, the inorganic matrix material, the sintering aid, optionally containing a doping element, and optionally the separately provided doping element are processed into a homogeneous mixture to form the green body. The mixing can be done by mixing the powders of the individual starting materials without additives. Solvent may also be added during mixing, the solvent being removed after mixing, for example by drying. During mixing, it is also possible to add a dispersing agent which is removed again by slow heating (1-5 K / min) to low temperatures (≦ 600 ° C.) before the actual sintering step. Furthermore, during mixing, a metal alkoxide such as Y or Al alkoxides may be added. In particular, the mixed powder may be coated with a metal alkoxide. Through the use of additives such as binders or metal alkoxides, a homogeneous distribution of the powder can be ensured.

The mixed powder may then be pressed into various shapes, for example a tablet form, to form a green body. Alternatively, it can be further processed with additives such as binders, plasticizers and / or dispersants, mixed powders as a paste or slip. For example, the slurry or paste may be used to form a flat green body in the form of a tape. Also methods such as slip casting, screen printing or dip coating can be used to mold green bodies of any shape. Thus, the use of an additive, such as a binder, in addition to the homogeneous distribution also allows different shape, which can be adapted to the desired application.

In a further embodiment, the inorganic matrix material, the sintering aid, optionally containing a doping element, and optionally the separately provided doping element are processed into an inhomogeneous mixture to form the green body. In this case, the inorganic matrix material, the sintering aid and optionally the doping element can be mixed inhomogeneously or locally so that a density structure and / or a doping structure is produced in the phosphor ceramic. Thus, the sintering aid can be applied locally or in a layer on the green body in order to realize density structures in the light-emitting ceramic, which allow modified properties such as chemical resistance or scattering properties. For this purpose, a green body of any shape can be provided, which can be coated locally with the sintering aid. In particular, the sintering aid can be applied to boundary surfaces of the green body.

Thus, a green body in the form of a band or in tablet form can be coated on at least one side with the sintering aid. As a result, a stronger compression of the phosphor ceramic starting from the at least one-sided coating can be achieved. Furthermore, a plurality of such strips or tablets can be arranged one after the other in a layer structure after heating in order to realize a three-dimensional density structuring of the phosphor ceramic. For example, a plurality of such strips or tablets can be glued together after heating or fixed to one another before being heated by pressing, so that a structured, all-ceramic body is formed during sintering.

Additionally or alternatively, a doping structure in the phosphor ceramic can be realized by at least one doping element is present as a separate starting material, for example as a powder. Thus, the doping element can be applied locally or in a layer to the green body in order to minimize unwanted edge effects in the phosphor ceramic or to realize logos within the phosphor ceramic. For this purpose, a green body with any shape can be provided, which can be coated locally with the doping element. In this case, the doping element can be applied in particular to boundary surfaces of the green body.

In a further embodiment, the green body comprising the inorganic matrix material with the doping element, the sintering aid and optionally the nitridic components is heated to a temperature between 800 and 2200 ° C, preferably between 1000 and 1500 ° C and more preferably between 1000 and 1300 ° C. The heating can be carried out, for example, in a graphite furnace, tube furnace, for example with aluminum oxide tube or by induction furnace. In this case, the heating ramp or the cooling ramp to achieve a Final temperature 1 to 50 K / min, preferably 5 to 30 K / min. The treatment at the final temperature between 800 and 2200 ° C may continue over a period of 1 minute to 12 hours, preferably over a period of 5 minutes to 1 hour.

It is also proposed a phosphor ceramic, which is prepared by the method described above. In this case, the luminescent ceramic has an inorganic matrix material with an embedded doping element, wherein oxynitrides and silicates are additionally contained in the luminescent ceramics. The oxynitrides and silicates form during the sintering process of the oxidic component of the sintering aid and the silicon nitride-based component of the inorganic matrix material. These have a low melting point and therefore form a liquid phase during the sintering process. Depending on the proportion of sintering aid, formation of liquid phases takes place, which remain detectable as foreign phases in the ceramic. Such foreign phases can be detected in the phosphor ceramics produced, for example with the aid of XRD (X-ray diffraction), SEM (scanning electron microscopy) or EDX (energy-dispersive X-ray diffraction). Furthermore, the phosphor ceramics may have a sintering aid. The content of the sintering aid that can be detected in the luminescent ceramics depends on what proportion of the sintering aid has been used to form the liquid phase.

Furthermore, the features of the phosphor ceramics explained in relation to the method also apply to the phosphor ceramics produced by the process. Thus, the phosphor ceramics may have a geometric density of> 70%, preferably of> 80%. It is also possible for starting materials of the process, such as the sintering aid used or the nitridic component or mixed phases resulting from the liquid phase, to be detectable in the phosphor ceramics produced. In particular, the phosphor ceramic produced by the method described above may have a doping structure if, for example, the sintering aid itself contains a doping element or activator ion, for example Ce, Eu, and / or has a density structure.

In addition, a light-emitting device, such as an LED or a scintillator, is proposed, which comprises the above-described phosphor ceramics. The light-emitting device may be an LED in which the phosphor ceramic is placed as a conversion element over a light-emitting semiconductor chip. In LEDs, for example, the excitation wavelengths are between 350 and 500 nm. The emission wavelengths may be, for example, between 500 and 800 nm.

Alternatively, the light emitting device may be a scintillator comprising the phosphor ceramic as the conversion element. The phosphor ceramic converts high-energy radiation, such as X-rays in a computer tomograph, into visible light. For detecting the visible light, the phosphor ceramic is equipped with a photosensitive element. In scintillators, which are used in particular in the field of nuclear medicine and medical technology, the excitation wavelengths are for example between 1 nm and 1 pm. The emission wavelengths may be, for example, between 350 and 800 nm.

In the following, embodiments of the invention will be explained in more detail with reference to the accompanying schematic drawings.

Showing:

1 an exemplary embodiment of a pressureless process for producing a phosphor ceramic;

2 a further exemplary embodiment of a pressureless process for producing a dense structured phosphor ceramic;

3 a computer tomograph in a schematic representation with an X-ray detector comprising scintillators based on the phosphor ceramics; and

4 a light emitting diode with the phosphor ceramic.

Identical or functionally identical elements are provided in the figures with the same reference numerals unless otherwise indicated.

1 shows an exemplary embodiment of a non-pressurized method for producing a phosphor ceramic 11 ,

This will be done in a first step 1 a doped inorganic matrix material 2 and a sintering aid 3 provided in the form of powder. The sintering aid 3 may additionally be mixed with a nitridic component. To form the green body, the powder 2 . 3 in a second step 4 to a homogeneous mixture 5 processed. This can be done with or without additives. For example, the powders 2 . 3 homogenized in a dispersion and then dried. The mixture 5 is then in a third step 6 to a green body 7 pressed about in tablet form or processed into films (tapes).

The green body thus produced 7 will be in step 8th by temperature treatment 9 sintered, for example, in a graphite furnace. This is the green body 7 for example, heated to a final temperature between 1000 and 1600 ° C and sintered at the final temperature for 5 to 60 minutes. Subsequently, the green body 7 in step 10 cooled. The resulting phosphor ceramic 11 has a homogeneous high density. The geometric density can be up to 99%. Due to the high density of the phosphor ceramic 11 is the optical transparency to phosphor ceramics, which are made without sintering aids, improved. In applications, the phosphor ceramics 11 Therefore, it can be better used as a conversion element and provides an increased conversion efficiency.

2 shows another exemplary embodiment of a pressureless process for producing a dense structured phosphor ceramic 11 ,

This will be done in a first step 1 an inorganic matrix material 2 which can be doped, a sintering aid 3 which itself is the doping element 12 , eg, ceria, provided in the form of powder. The sintering aid 3 may additionally be mixed with a nitridic component. To form the green body 15 First, the powder of the matrix material 2 to a shaped body 13 processed. For example, the powder 2 be pressed in tablet form. The use of an additive, such as a binder is possible. The resulting paste or the slip formed thereby can then by means of methods such as film drawing, slip casting, screen printing or dip coating to form the molding 13 be further processed. In a third step 14 becomes this shaped body 13 with the sintering aid 3 coated.

The green body thus produced 15 will be in step 8th in a temperature treatment 9 for example, heated to final temperatures between 1000 and 1600 ° C and sintered at the final temperature for 5 to 60 minutes. The heating causes the doping element to diffuse 12 into the inorganic matrix material 2 , In addition, they form through the sintering aid 3 Liquid phases in the green body 15 from which reduce the pore spaces during the sintering process, starting from the coated side. Subsequently, the sintered body 15 in step 10 cooled. The resulting phosphor ceramic 11 has an inhomogeneous density and doping distribution when the sintering aid 3 the doping element 12 contains.

3 shows a schematic representation of a computer tomograph 17 with an x-ray detector 21 , the scintillators 25 based on the phosphor ceramic 11 includes.

The computer tomograph 17 includes an X-ray source 18 , from which an x-ray beam 19 emanates. The x-ray beam 19 penetrates an object to be examined 20 and hits a flat X-ray detector 21 , The X-ray source 18 and the X-ray detector 21 are preferably in a manner not shown adjacent to each other on a rotating frame of the computer tomograph 17 arranged, wherein the rotating frame in a φ-direction about the system axis Z of the computer tomograph 17 is rotatably mounted. The x-ray detector 18 captures the through the object 20 passing radiation and generates signals from which an image calculator 22 calculated in known manner one or more two- or three-dimensional images displayed on a display 23 are representable.

The x-ray detector 21 In this embodiment, a pixelized scintillator detector is a scintillator 24 from a variety of pixels 25 includes, wherein the pixels 25 in the φ-direction and in the Z-direction are arranged side by side on a cylinder part surface and thus form a two-dimensional array.

In the enlarged view is schematically a section of the X-ray detector 21 shown in the Z direction, in which two pixels arranged side by side 25 can be seen. Every pixel 25 comprises a scintillator layer 26 with the phosphor ceramic 11 in which the X-radiation is converted into visible light. The pixel 25 In addition, a photosensitive element is assigned, for example a photodiode 27 that captures the generated light.

The pixels 25 a row of the scintillator arrangement 24 are on a common circuit board 28 attached. Between the scintillator layers 26 the single pixel 25 are reflectors 29 provided, which in particular the Szintillatorschichten 26 from four sides and thus the boundaries of the pixels 25 in the φ-Z plane. Through the reflectors 29 will prevent photons from being in the scintillator layer 26 of a particular pixel 25 be generated in the adjacent pixel 25 penetration.

4 schematically shows a light emitting diode 30 with the phosphor ceramic 11 ,

The LED 30 includes a substrate 32 in which a semiconductor chip 33 and the phosphor ceramics 11 are arranged. In this case, the semiconductor chip 33 on the bottom of the substrate 32 fixed and the phosphor ceramic 11 above the semiconductor chip 33 placed. The semiconductor chip 33 is still designed, short-wave primary light 34 for example, in the blue or ultraviolet frequency range. The primary light 34 is made of the phosphor ceramic 11 absorbed and in long-wave secondary light 35 transformed. The phosphor ceramics 11 thus acts as a conversion layer, which is the primary light 34 of the semiconductor chip 33 converted into radiation of another wavelength range. By the choice of the inorganic matrix material (host lattice) - and doping material, as well as the degree of doping in the phosphor ceramic 11 can different colors of the long-wave secondary light 35 will be realized. For example, Ce ³⁺ can be used as doping element to secondary light 35 to get in the yellow-green frequency range.

Examples

To characterize the effect of the sintering aid, phosphor ceramics were prepared based on an Eu-doped matrix material of the structural formula EAAlSiN ₃ , where EA stands for an alkaline earth metal ion. In particular, Y ₂ O ₃ , YAG and AlN were used as sintering aids.

To form the green body, a powder of the doped matrix material and powder of the sintering aid was weighed and dry-mixed (homogenized). The powder mixture was processed in a uniaxial press (pressing pressure 2 bar, 1 min) to tablets (diameter ~ 8 mm, height ~ 4 mm). The pressureless high temperature sintering was carried out in a graphite furnace under reducing atmosphere (1 atm) at temperatures between 1000-1700 ° C. For characterization, the powder density, which corresponds to the theoretical density, determined by pycnometer measurements and compared with the density of the produced phosphor ceramics. The geometric density (% of theoretical density) of the phosphor ceramics, which were produced with the addition of a sintering aid, is> 70% and is thus up to ~ 10% higher than for ceramics without sintering aid additive.

If one uses high amounts of sintering aid (<50%), this can lead to an influence on the silicon nitride-based phosphor system, in particular for oxidic sintering aids. As a result, a decrease in efficiency can occur, which can be up to 90% with respect to a reference sample without sintering aid. Nevertheless, the results with high levels of sintering aids indicate that their addition can provide high density luminescent ceramics.

In addition, the phosphor-oxide mixture Si ₃ N _{4 could} be buried as a compensator. In addition, holding times during sintering can be extended to achieve high densities at lower temperatures.

Although the invention has been described herein with reference to various embodiments, it is not limited thereto, but variously modifiable.

Claims (15)

Method for producing a phosphor ceramic ( 11 ) comprising: providing an inorganic matrix material ( 2 ) having a silicon nitride-based compound; Provision of a doping element ( 12 ) for forming luminescent centers in the inorganic matrix material ( 2 ); Providing a sintering aid ( 3 ) for compacting the inorganic matrix material ( 2 ); Forming a green body ( 7 . 15 ) by the inorganic matrix material ( 2 ), the doping element ( 12 ) and the sintering aid ( 3 ) are at least partially mixed together; and sintering the green body ( 7 . 15 ). Method for producing a phosphor ceramic ( 11 ) according to claim 1, wherein the inorganic matrix material ( 2 ) contains a metal-silicon nitride or a metal-silicon oxynitride. Method for producing a phosphor ceramic ( 11 ) according to claim 1 or 2, wherein the doping element ( 12 ) contains at least one metal of the rare earths. Method for producing a phosphor ceramic ( 11 ) according to any one of claims 1-3, wherein the doping element ( 12 ) embedded in the inorganic matrix material ( 2 ) embedded in the sintering aid ( 3 ) and / or separately from the inorganic matrix material ( 2 ) and the sintering aid ( 3 ) provided. Method for producing a phosphor ceramic ( 11 ) according to any one of claims 1-4, wherein the sintering aid ( 3 ) contains at least one compound selected from the group consisting of metal oxide, metal fluoride, metal alkoxide, metal aluminate and metal silicate. Method for producing a phosphor ceramic ( 11 ) according to any one of claims 1-5, wherein the provided sintering aid ( 3 ) is selected so that its metallic element belongs to a same element group as the metallic element of the inorganic matrix material ( 2 ). Method for producing a phosphor ceramic ( 11 ) according to any one of claims 1-6, wherein the sintering aid and the inorganic matrix material are provided as a powder, wherein the average size of particles in the powder of the sintering aid ( 3 ) less than or equal to the mean size of Particles in the powder of the inorganic matrix material ( 2 ). Method for producing a phosphor ceramic ( 11 ) according to any one of claims 1-7, wherein up to 50% by weight of the sintering aid ( 3 ) at least partially with the inorganic matrix material ( 2 ) are mixed. Method for producing a phosphor ceramic ( 11 ) according to any one of claims 1-8, further comprising: providing a nitridic component and mixing the nitridic component with the sintering aid ( 3 ). Method for producing a phosphor ceramic ( 11 ) according to any one of claims 1-9, wherein the inorganic matrix material ( 2 ), the sintering aid ( 3 ) and / or the doping element ( 12 ) for forming the green body ( 7 . 15 ) are processed into a homogeneous or inhomogeneous mixture. Method for producing a phosphor ceramic ( 1 ) according to claim 10, that the inorganic matrix material ( 2 ), the sintering aid ( 3 ), which optionally has a doping element ( 12 ), and optionally the separately provided doping element ( 12 ) are mixed so inhomogeneously that a density structure and / or a doping structure in the phosphor ceramic ( 11 ) is produced. Method for producing a phosphor ceramic ( 1 ) according to any one of claims 1-11, wherein the green body ( 7 . 15 ) is heated to a temperature between 800 and 2200 degrees Celsius. Phosphor ceramic ( 11 ), which is prepared by a method according to any one of claims 1-12. Phosphor ceramic ( 11 ) containing an inorganic matrix material ( 2 ) with embedded doping element ( 12 ), wherein in the phosphor ceramic ( 11 ) may additionally contain oxynitrides and silicates resulting from the liquid phase. Light emitting device ( 17 . 30 ) comprising a phosphor ceramic ( 11 ) according to claim 13 or 14.

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