EP2087064A1

EP2087064A1 - Light source

Info

Publication number: EP2087064A1
Application number: EP07819503A
Authority: EP
Inventors: Martin Jansen
Original assignee: Max Planck Gesellschaft zur Foerderung der Wissenschaften eV
Current assignee: Max Planck Gesellschaft zur Foerderung der Wissenschaften eV
Priority date: 2006-11-02
Filing date: 2007-10-31
Publication date: 2009-08-12
Also published as: WO2008052772A1; CN101528891B; US20100067215A1; DE102006051756A1; KR20090087899A; JP2010508665A; CN101528891A; US8339032B2; JP5328657B2

Abstract

The invention relates to a light source comprising a primary radiation source and a luminescent substance, and to a method for producing this light source. The invention relates, in particular, to a method for producing an electric light source using one or more luminescent substances emitting in the visible spectrum range, and at least one primary source emitting preferably in the UV range, and which is preferably, but not exclusively, an LED.

Description

light source

description

The invention relates to a light source comprising a primary radiation source and a phosphor and a method for producing such a light source. In particular, the invention relates to a method for producing an electric light source using one or more phosphors emitting in the visible spectral range and at least one preferably UV-emitting primary source which is preferably, but not exclusively, an LED.

Light sources based on at least one LED are realized by combining a UV-emitting primary source and one or more phosphors, which are excited by the UV light of the primary source and emit in the visible spectral range. In an exemplary implementation, a Ga (In) N LED emitting at about 460 nm and a yellow emitting phosphor YAG: Ce ³⁺ (WO 98/12757) are used. If a purely white light source is desired, several different phosphors, usually one each red, green and blue emitting material, must be used. This must be set according to the prior art to an optimal particle size and usually provided with a transparent protective layer. Finally, they are applied as a mixture or individually embedded in a polymer matrix onto the primary source, for example a Ga (In) N LED ₁ (WO 2006/061778 A1 and US 2003/0052595 A1). This method comprises several independent substeps and is obviously very expensive. Moreover, in the interests of a long service life of the luminous elements, high demands must be placed on the UV and temperature resistance and the optical transparency of the protective layers and polymer matrix. Above all, the manufacturing process should be in light of the fact that the new LED based light sources are mass-produced will have high potential for automated and therefore cost-effective production.

An object of the present invention was therefore to overcome the above-described disadvantages of the prior art and, in particular, to provide a light source which can be manufactured in a simple manner and which enables the emission of white light. This object is achieved according to the invention by a light source comprising (i) a primary radiation source and (ii) a phosphor layer or a phosphor based on an amorphous or partially crystalline network, wherein the network comprises nitrogen (N) and at least two elements selected from P Si ₁ B and Al, and wherein at least one activator is incorporated into the network.

The light source according to the invention comprises as component (i) a primary radiation source. This primary radiation source can basically emit light in any wavelength range. It preferably delivers UV-o radiation, in particular in a wavelength range from 250 to 450 nm, more preferably from 300 to 430 nm. Particularly preferred is a peak maximum of the emission of the primary radiation source in the specified ranges. Particularly preferably, the primary radiation source is an LED (light-emitting diode), in particular a GaN or Ga (In) N LED. The light emitted by the primary radiation source is also referred to herein as primary radiation.

Furthermore, the light source according to the invention comprises a phosphor layer or a phosphor based on an amorphous or partially crystalline network, wherein the network comprises N and at least two elements selected from P, Si, B and Al, and wherein at least one Activator is incorporated. The phosphors used according to the invention are distinguished, in particular, by the fact that they are not substances based on a crystalline network, but rather substances based on an amorphous or partially crystalline network. The base materials used to form the phosphor have networks which are particularly X-ray amorphous, that is, they do not have crystallites with a diameter of ≥300 nm, especially no crystallites with a diameter> 200 nm, and more preferably no crystallites with a diameter ≥ 100 nm. The base material of the phosphors thus has in particular no long-range lattice symmetry. In the network of the base material at least one activator is further incorporated in the phosphors. In contrast to conventional crystalline phosphors, there is no exchange of ions previously contained in the base material for activators, but the activators are additionally incorporated. This has the significant advantage that any activators can be incorporated into the same matrix, and thus phosphors can be provided which contain different activators.

The base material of the phosphors according to the invention, which has an amorphous or partially crystalline network, comprises at least two elements selected from P, Si, B, Al and, independently of this, always N. In particular, the network consists of the elements P, Si, B, Al and N or the respective subsystems P, Si, B and N, P, Si, Al and N, Si, B ₁ Al and N, P, B, Al and N, P, Si and N, P, B and N, P , Al and N, Si, B and N, Si, Al and N or B ₁ Al and N. In this network suitable activators are incorporated and incorporated. In particular, any metal ions can be introduced into the inorganic amorphous or partially crystalline network as activators. Preferred activator elements are Ba, Zn, Mn, Eu, Ce, Pr, Nd, Sm, Tb, Dy, Ho, Er, Tm, Yb, Sn, Sb, Pb or Bi. Preferably, the activators are Mn ²⁺ , Zn ²⁺ , Ba ²⁺ , Ce ³⁺ , Nd ³⁺ , Eu ²⁺ , Eu ³⁺ , Gd ³⁺ , Tb ³⁺ , Sn ²⁺ , Sb ³⁺ , Pb ²⁺ or Bi ³⁺ . The amount of activators in the phosphor is preferably ≥ 0.1% by weight, in particular ≥ 0.5% by weight and preferably up to 14% by weight, in particular up to 5% by weight. The activators may also have a sensitizer function.

The phosphor preferably emits at wavelengths between 480 and 740 nm. Preferably, the phosphor absorbs the primary radiation as completely as possible. Furthermore, it is preferable that the emitted light of the phosphor has different wavelengths from the absorbed light. Since according to the invention there is no exchange, but rather an introduction of the activator elements, it is also possible for any desired combinations of activator elements to be introduced into the luminescent material, thereby in particular coordinating the emission colors as desired. Most preferably, the activators are combined to emit white light.

According to the invention, the incorporation of suitable activators into an amorphous three-dimensional network of the composition Si / B / N is particularly preferred. This host material has no periodic lattice symmetry.

Due to advantageous effects on the crystal field strengths for the activators and to achieve high mechanical and thermal stability, the base material structure is preferably nitridic in nature, which may optionally be doped oxide.

According to the invention, the phosphor or the phosphor layer may further contain fillers. Preference is given to solid particles as fillers, which at the same time act as light scattering agents. Such solid particles are, for example, SiO ₂ , TiO ₂ , SnO ₂ , ZrO ₂ , HfO ₂ and / or Ta ₂ O ₅ . Preferably, the solid particles have a narrow particle size distribution, wherein the average particle size distribution is preferably chosen depending on the refractive indices of the respective material such that white light is optimally scattered. The layer thickness of the phosphor or of the phosphor layer is preferably between 200 and 3000 nm, in particular between 300 and 2000 nm.

According to the invention, the phosphor layer may be in direct contact with the primary radiation source, i. be applied directly to the primary radiation source. However, it is also possible to arrange the phosphor layer in indirect contact with the primary radiation source, that is to say that further materials or layers are arranged between the primary radiation source and the phosphor layer. Preferably, the intermediate layers or intermediate materials for the primary radiation are completely permeable.

The invention further relates to a method for producing a light source as described herein, which is characterized in that a phosphor precursor in liquid form or as a suspension is applied directly or indirectly to a primary radiation source and then cured.

In particular, the invention provides a method of liquid-phase coating a primary source having a phosphor emitting in the visible spectral range. The inventive method is based on a new family of phosphors consisting of an amorphous matrix, in which all conceivable activators can be introduced in widely variable concentrations. This very advantageous feature is brought about by incorporating the activators non-substitutively, that is to say replacing a matrix atom, but rather additively.

This new class of phosphors is obtained from molecular precursors via an oligomeric or polymeric intermediate and the final step of pyrolysis. As far as the molecular precursors with the activators dissolved therein or the partially crosslinked preceramic oligomers are liquid, they can be applied for example by dip coating (dipcoating), spin coating or spray coating, then fully crosslink by heating in an ammonia atmosphere and transfer by pyrolysis in 5 a firmly adhering ceramic layer.

In a first preferred embodiment, a mixture of at least one molecular precursor, at least one activator and optionally fillers is formed and applied to the primary source. Subsequently, a curing takes place, in particular by ammonolysis and subsequent pyrolysis. The viscosity of the mixture to be applied to the primary source can be adjusted by the nature and content of the fillers. In a further preferred embodiment, a mixture of at least one molecular precursor, at least one activator and optionally fillers is also applied to the primary source, but this mixture was first subjected to partial curing, for example, partial ammonolysis to adjust the viscosity to the desired value , Subsequently, the application to the primary source and subsequently the complete curing, for example by ammonolysis and pyrolysis.

In a further preferred embodiment, a preceramic polymer is first formed from the 5 molecular precursors, the activators and optionally fillers. This preceramic polymer is obtained, for example, by complete ammonolysis. This preceramic polymer is then applied to the primary source. Liquid preceramic polymers can be applied directly. If the preceramic polymer is resinous or solid, a finely divided suspension of the preceramic polymer is advantageously formed in a solvent and this suspension is applied to the primary source. The solvent is then evaporated and then the phosphor layer cured, for example by pyrolysis.

Furthermore, it is possible according to the invention to mix in the starting materials for the phosphor layer conventional solid powdered phosphors. By such admixture, fine tuning of the emission can be obtained.

The base material of the phosphors used according to the invention is accessible, in particular, via molecular precursors, which are processed to form a preceramic material, which is then converted by pyrolysis into the final ceramic state. The phosphor can be applied to the radiation source in the form of a molecular precursor or can be formed from a molecular precursor.

First, one or more molecular precursors are provided. The molecular precursors contain the elements of the base material, ie in particular at least two elements, preferably at least three elements selected from P, Si ₁ B and Al. The concentrations of P ₁ Si, B, Al are preferably each set between 0 and 100 atom%, more preferably between 10 and 80 atom%. Most preferably, the molecular precursors are halides, preferably chlorides.

It is possible to use as starting material several molecular precursors, in particular a mixture of molecular precursors, which are then subjected to co-ammonolysis. Mixtures of molecular precursors can be obtained, for example, by mixing a silazane and a boron and / or phosphorus halide.

In a further embodiment, a molecular precursor is used, which is a one-component precursor. Such a one-component precursor already contains all elements of the product. Particularly preferred as the starting point of the production Molecular compound CI ₃ Si (NH) BCI ₂ (TADB) is used, which already contains the desired end-product linkage Si-NB.

More preferred molecular component precursors are CI ₄ P (N) (BCI ₂₎ SiCl _3, Cl ₃ PNSiCI _3, (CI ₃ Si) ₂ NBCI _2, CI ₃ SiN (BCI ₂₎ _2, (H ₃ Si) ₂ NBCI _2, CI ₃ Si (NH) (BCI) (NH) SiCl ₃ , CI ₃ Si (NH) (AICI) (NH) SiCl ₃ , [(CI ₃ Si) (NH) (BNH) I ₃ , (CI ₃ Si ( NH) AICIz) ₂ or [CI ₃ PN (PCI ₂ ) ZN] ⁺ [AICI ₄ ] -.

The precursor material is then cured to a phosphor having an amorphous or partially crystalline network. The

Curing preferably takes place via the intermediate stage of a preceramic material. The phosphor precursors can by

Ammonolysis, polycondensation and pyrolysis in amorphous networks from the corresponding elements, which are linked together by nitrogen, are transferred. Nitrogen can be partially replaced by oxygen, whereby an oxide doping is obtained.

In the phosphor layer activators are incorporated, which are preferably introduced via the following routes.

Those metals which dissolve like europium or barium in liquid ammonia are presented as dissolved in liquid ammonia and the molecular precursor, e.g. TADB, is added dropwise. Conversely, the solution of the metals in ammonia can also be converted into precursors, e.g. TADB, to be dripped. The resulting polymeric imidamide contains, besides the base material elements, e.g. in addition to silicon and boron, the or the activator elements homogeneously distributed. By pyrolysis of the ceramic luminous body is obtained.

Activators that do not dissolve elementally in liquid ammonia can be incorporated as complex molecular compounds. The ligands used should preferably contain only system-inherent elements such as halide (chloride), hydrogen, silicon or boron. AIIe other elements would not be removed or only with additional effort from the final product. Particularly suitable and system compatible are metal complexes with, for example, [CI ₃ Si (N) SiCl ₃ ] ^' and chloride as ligands. Since all metals that can be used as activators form binary chlorides from which the desired complexes can be prepared by reaction with Li [CI ₃ Si (N) SiCl ₃ ], this approach is universal. The complex compounds of the activators are dissolved in the molecular precursor, for example in TADB, or, if appropriate, are dissolved together with the molecular precursor, for example with TADB _1, in a suitable solvent. This mixture or solution is added dropwise for the purpose of ammonolysis in liquid ammonia, and this can also be done in the opposite way.

The thickness of the polymer / oligomer layer can be adjusted via the viscosity of the solution and the parameters of the coating process. The viscosity, in turn, can be determined by the degree of polycondensation, i. be adjusted specifically by the average molecular weight of the oligomer, by the addition of solvents, by the addition of fillers and / or by the temperature. As fillers preferably materials are used, which act at the same time light scattering. For example, SiO.sub.2, TiO.sub.2, ZrO.sub.2, SnO.sub.2 or Ta.sub.2O.sub.5 having a narrow particle size distribution can be values which, depending on the calculation index of the respective material, optimally diffuse white light. The layer thicknesses are adjusted so that a crack-free ceramic layer is formed during pyrolysis. The layer thicknesses are preferably between 200 and 3000 nm, more preferably between 300 and 2000 nm. The layer thickness which can be achieved in a coating process depends essentially on the viscosity of the mixture to be applied and on the application method. If necessary for optimum optical performance of the LED-based light source, the entire coating process may be repeated several times to obtain the desired layer thickness.

The final curing to the phosphor or to the phosphor layer is preferably carried out by pyrolysis, wherein an amorphous or partially crystalline Network is formed. In pyrolysis, the preceramic amide obtained as an intermediate in the ammonolysis at temperatures between 600 ⁰ C and 1500 ⁰ C, preferably between 1000 ⁰ C and 1300 ⁰ C, transferred to the final product. The pyrolysis preferably takes place in an atmosphere comprising nitrogen, argon, ammonia or mixtures thereof.

In a preferred embodiment, the applied layer is cured in an ammonia atmosphere at room temperature to 200 ⁰ C. Thereafter, the temperature is gradually increased, for example to 620 ° C, and held at this temperature. Subsequently, a pyrolysis, for example, is carried out at 1050 ⁰ C. The heating elements can be electrical resistance furnaces or preferably infrared heaters, Spiegelöfen or lasers are used. The entire coating process can be carried out in parallel and continuously (flow-band-like). For example, the LEDs to be coated can be processed in parallel in a 100 × 80 matrix arrangement. Different durations of the individual process steps are compensated for at the same running speed by longer or parallel running distances.

Claims

claims

A light source comprising (i) a primary radiation source and

(ii) a phosphor layer based on an amorphous or semi-crystalline network, the network comprising N and at least two elements selected from P, Si and Al, and wherein at least one activator is incorporated in the network.

2. Light source according to claim 1, characterized in that the activator is selected from Ba, Zn, Mn, Eu, Ce, Pr, Nd, Sm, Tb, Dy, Ho, Er, Tm, Yb, Sn, Sb, Pb or / and Bi.

3. Light source according to claim 1 or 2, characterized in that the phosphor layer is based on a network of the composition Si ₃ B ₃ N ₇ .

4. Light source according to one of the preceding claims, characterized in that the primary radiation source emits light in the wavelength range of 250 to 450 nm.

5. Light source according to one of the preceding claims, characterized in that the primary radiation source is an LED.

6. Light source according to claim 5, characterized in that the primary radiation source is a GaN ^" or a Ga (In) N-LED.

7. Light source according to one of the preceding claims, characterized in that the phosphor layer is in direct or indirect contact with 5 of the primary radiation source.

8. Light source according to one of the preceding claims, characterized in that the phosphor layer comprises a phosphor which emits light at a wavelength between 480 and 740 nm.

9. Light source according to one of the preceding claims, characterized in that the phosphor layer further contains solid particles. 5

10. Light source according to claim 9, characterized in that the solid particles are selected from SiO ₂ , TiO ₂ , SnO ₂ , ZrO ₂ , HfO ₂ or / and Ta ₂ O ₅ . 0

11. Light source according to one of the preceding claims, characterized in that the phosphor layer has a layer thickness between 200 and 3000 nm. 5

12. A method for producing a light source according to any one of claims 1 to 11, characterized in that a phosphor precursor is applied directly or indirectly in liquid form or as a suspension aufo a primary radiation source and then cured.

13. The method according to claim 12, characterized in that the phosphor is applied as a preceramic material, in particular as a preceramic oligomer.

14. The method according to claim 12 or 13, characterized in that the phosphor is formed from a molecular precursor.

15. The method according to claim 14, characterized in that the molecular precursor is a one-component precursor, in particular selected from CI ₃ Si (NH) BCl ₂ (TABD), CI ₃ PNSiCl ₃ , CI ₄ P (N) (BCI ₂ ) SiCl ₃ , (CI ₃ Si) ₂ NBCI ₂ , CI ₃ SiN (BCI ₂ ) ₂ , (H ₃ Si) ₂ NBCI ₂ ,

CI ₃ Si (NH) (BCI) (NH) SiCl ₃ , [(CI ₃ Si) (NH) (BNH)] ₃ ,

CI ₃ Si (NH) (AICI) (NH) SiCI ₃ , (CI ₃ Si (NH) AICI ₂ ) ₂ or [CI ₃ PN (PCI ₂ ) ₂ N] ⁺ [AICI ₄ ] -.

16. The method according to any one of claims 12 to 15, characterized in that the phosphor precursor is applied by dip coating, by spin coating or by spray coating.

17. The method according to any one of claims 12 to 16, characterized in that the viscosity of the phosphor precursor is adjusted to 0.01 to 10 Pa ^· s.

18. The method according to any one of claims 12 to 17, characterized in that the phosphor is applied in several layers.

19. The method according to any one of claims 12 to 18, characterized in that the phosphor precursor is cured by pyrolysis.

20. A wavelength converting material comprising a phosphor layer as defined in claim 1.