阅读说明：本技术 碱土金属硅酸盐-发光物质和提高碱土金属硅酸盐-发光物质长期稳定性的方法 (Alkaline earth silicate phosphor and method for increasing the long-term stability of alkaline earth silicate phosphors ) 是由 西尔克·罗斯勒 安妮·施密特 多米尼克·乌利希 于 2019-10-15 设计创作，主要内容包括：本发明涉及一种用于改善碱土金属硅酸盐-发光物质的长期稳定性的方法。发光物质以晶粒的形式形成,并具有化学通式为EA-xSi-yO-z的基本晶格,其中x,y,z>0。组分EA由一种或多种碱土金属组成。激活剂被掺杂到基本晶格中。在该方法的一个步骤中,将发光物质的晶粒在反应室(01)中加热。挥发性有机铝化合物被加热,并且使第一载气流过所述有机铝化合物,借此获得包含所述挥发性有机铝化合物的第一载气混合物。另外,水被加热,并且使第二载气流过所述水,借此获得包含所述水的第二载气混合物。第一载气混合物和第二载气混合物被引入反应室(01),在该反应室中,碱土金属硅酸盐-发光物质的晶粒被所述载气混合物包围。结果,挥发性有机铝化合物和水相互反应,至少主要生成偏氢氧化铝,其在碱土金属硅酸盐-发光物质的晶粒上形成涂层。本发明还涉及碱土金属硅酸盐-发光物质。(The invention relates to a method for improving the long-term stability of alkaline earth silicate phosphors. The luminescent material is formed in the form of crystal grains and has the chemical formula EA x Si y O z Of the basic lattice, wherein x, y, z>0. The component EA consists of one or more alkaline earth metals. The activator is doped into the basic lattice. In one step of the method, hair is deliveredThe grains of the photo-substance are heated in the reaction chamber (01). A volatile organoaluminum compound is heated and a first carrier gas is flowed over the organoaluminum compound, thereby obtaining a first carrier gas mixture comprising the volatile organoaluminum compound. In addition, water is heated and a second carrier gas is flowed through the water, thereby obtaining a second carrier gas mixture containing the water. The first carrier gas mixture and the second carrier gas mixture are introduced into a reaction chamber (01) in which the grains of the alkaline earth silicate phosphor are surrounded by the carrier gas mixture. As a result, the volatile organoaluminum compound and water react with each other to form at least mainly aluminum metahydroxide, which forms a coating on the crystal grains of the alkaline earth metal silicate-luminescent material. The invention also relates to alkaline earth metal silicate phosphors.)

1. A method for improving the long-term stability of alkaline earth silicate phosphors, which are formed in the form of crystallites and have the general chemical formula EA_xSi_yO_zWith EA consisting of one or more alkaline earth metals as the basic lattice, and with the proviso that x, y, z>0, wherein an activator is doped into the base lattice, and wherein the method comprises the steps of:

-heating the alkaline earth silicate-luminophore grains in a reactor chamber (01);

-heating a volatile organoaluminum compound and flowing a first carrier gas through said heated volatile organoaluminum compound, thereby obtaining a first carrier gas mixture comprising said volatile organoaluminum compound;

-heating water and flowing a second carrier gas through said heated water, thereby obtaining a second carrier gas mixture comprising said water;

-introducing said first carrier gas mixture comprising a volatile organo aluminium compound and said second carrier gas mixture comprising water into a reaction chamber (01) in which the grains of alkaline earth silicate-luminescent substance are surrounded by said carrier gas mixture, whereby said volatile organo aluminium compound and water react with each other to at least predominantly form aluminium metahydroxide which forms a coating on the grains of alkaline earth silicate-luminescent substance.

2. The process according to claim 1, characterized in that the volatile organo-aluminum compound is formed from trimethylaluminum.

3. The process according to claim 1 or 2, characterized in that the volatile organoaluminium compound is heated to a temperature between 15 ℃ and 70 ℃.

4. A method according to any one of claims 1 to 3, characterized in that the water is heated to a temperature between 50 ℃ and 90 ℃.

5. The method according to any of claims 1 to 4, characterized in that the crystal grains of alkaline earth silicate-luminescent substances in the reactor chamber (01) are heated to a temperature between 150 ℃ and 250 ℃.

6. The process according to any of claims 1 to 5, characterized in that the heating and the flow-through of the volatile organoaluminium compound and the heating and the flow-through of the water are separated and carried out in respective bubblers (03, 13).

7. The process according to any one of claims 1 to 6, characterized in that the first carrier gas mixture comprising the volatile organoaluminum compound is guided into the reaction chamber (01) through the floor of the reaction chamber (01) and the second carrier gas mixture comprising water is guided into the reaction chamber (01) through the feed device (11) which protrudes into the reaction chamber (01).

8. An alkaline earth silicate phosphor by means of which light radiation in a first wavelength range can be absorbed and light radiation in a second wavelength range, which is different from the first wavelength range, can be emitted, wherein the alkaline earth silicate phosphor is in the form of grains and has the general chemical formula EA_xSi_yO_zAs a basic lattice, which is doped with an activator and in which EA is formed from one or more alkaline earth metals, and the conditions x, y, z>0, characterized in that said grains have a coating of aluminum metahydroxide on their surface.

9. Alkaline earth silicate-luminescent substance according to claim 8, characterized in that the basic lattice is described by one of the following formulae:

-(Ba_aSr_bCa_c)₂SiO₄wherein at least one of the variables a, b and c is greater than zero and a + b + c is 1; and

-Sr₃MgSi₂O₈。

10. alkaline earth silicate-luminescent substance according to claim 8 or 9, characterized in that the activator is formed by Eu²⁺And/or Mn²⁺And (4) forming.

11. The alkaline earth silicate phosphor according to any of claims 8 to 10, wherein the crystal grains of the alkaline earth silicate phosphor each have a diameter of between 1 μm and 2 mm.

12. The alkaline earth silicate-luminescent substance according to any of claims 8 to 11, characterized in that the coating is produced on the surface of the grains by means of the method according to any of claims 1 to 7.

Technical Field

The invention relates firstly to a method for increasing the long-term stability of alkaline earth silicate phosphors by applying the alkaline earth silicate phosphors in the form of grains. Alkaline earth silicate phosphors are used, for example, as conversion phosphors in white LED-based light sources. The invention also relates to alkaline earth metal silicate phosphors.

Background

Alkaline earth silicate phosphors have a considerable instability with respect to moisture, which has so far severely limited their usefulness in many applications. The following chemical reactions are considered to be undesirable reactions of the alkaline earth orthosilicate-luminescent substance, mainly caused by moisture:

(Ba,Sr,Ca)₂SiO₄+2H₂O→2(Ba,Sr,Ca)(OH)₂+SiO₂

alkaline earth silicate phosphors tend to aggregate and agglomerate during long term storage, which severely limits the use of phosphors. Furthermore, many alkaline earth silicate phosphors show irreversible luminescence loss and signs of degradation after long-term storage or use, especially in LED-based light sources. In addition to the moisture problem, halogens can be problematic for application. Many LED manufacturers therefore set limit values for the halide fraction in the light-emitting substance.

Alkaline earth orthosilicate-luminescent substances are not the only powders that have to counter mass loss due to moisture, oxygen or other compounds in the air. To solve this problem, many tests were carried out to protect the powders by barrier layers. The following are summarized significant solutions.

US 7,202,598B 2, US 6,890,593B 2, US 2,905,572, US 2002/0150760 a1, US 4,199,617 and US 4,690,832 show different methods of applying the luminescent substance.

In Guo, c.; the science of Chu, B and Su, Q, in applied surface science, 225(2004), pages 198-203 describes alkaline earth sulfide-based phosphors Ca for increasing the stability of alkaline earth sulfide-based phosphors_0,8Sr_0,2S:Eu²⁺,Tm³⁺By passing ZnO^-And Al₂O₃The particles are coated. Here, a wet chemical process is used, followed by tempering and calcination. The semimetal oxide is preferably deposited in the form of islands, whereby the top layer of the coated luminescent substance is preferably porous.

US 5,958,591, US 2003/0168669 Al and US 5,220,243 show different methods of coating the luminescent substance with alumina.

US 5,080,928 shows a CVD process for depositing aluminum metahydroxide on zinc sulfide luminescent materials.

DE 69830180T 2 shows encapsulated electroluminescent phosphor particles based on zinc sulphide, each particle having in each case one or more substantially transparent and largely connected multiple oxide coatings based on aluminum oxide. Both the phosphor-multilayer metal oxide layer structure and the phosphor-pure aluminum oxide-multilayer oxide layer structure are described here. The multi-layer metal oxide coating includes an aluminum oxide and at least one other metal oxide. The aluminum oxide layer and the multi-layer oxide layer are coated by a chemical vapor deposition method in the presence of water. Luminescent substances have a low resistance to condensed moisture and liquid water compared to materials in which the luminescent substance is coated with only aluminum oxide.

DE 102007053285 Al shows coated phosphor particles which are produced according to a wet-chemical process by mixing at least two starting materials and at least one dopant and subsequently calcining to form a phosphor precursor. In the wet-chemical process, the metal, transition metal or semimetal oxide is preferably deposited in the form of islands, whereby the top layer of the coated luminescent substance is preferably porous. By calcination, subsequent grinding may be necessary, wherein partial damage to the protective layer cannot be ruled out. The metal oxide is formed of, for example, alumina.

EP 2396385 Bl shows a method for increasing the long-term stability of alkaline earth silicate phosphors. In the wet-chemical process, the grain surfaces of the alkaline earth silicate luminophores are modified by chemical reaction of the alkaline earth metal on the surface with anions, such as SO₄ ^2-、PO₄ ^3-、CO₃ ^2-、C₂O₄ ^2-、SiO₃ ^2-And SiF₆ ^2-。

Published in J.American ceramics. Soc.53(1970) at Wong, P. and Robinson, M.₂O₃The CVD process for depositing aluminum oxide is known from "american ceramic. soc.53(1970), page 617-621, and from US 4,999,219, US 4,950,948, US 5,223,341 and US 2012/0199793 a 1. In which precursors containing aluminium are reacted, e.g. AlCl₃Or TMA, with CO₂、O₂Or H₂The O reacts to form alumina, aluminum hydroxide or aluminum metahydroxide.

EP 0160856B 1 teaches a CVD process in which a halogenated calcium phosphate light-emitting substance is coated with a uniform layer of aluminum oxide. Trimethylaluminum and oxygen were used as starting materials. With the highest temperature reaching most predominantly 550 c.

EP 2209869B 1 and DE 102007056343A 1 show that the compounds based on (Ca, Sr, Ba)₂SiO₄The surface-modified phosphor particles of (a), onto which a metal oxide coating, a transition metal oxide coating or a semimetal oxide coating and an organic coating are applied. The coating with metal, transition metal or semimetal oxides is carried out by a wet-chemical process for adapting the surface properties of the luminescent substance to the chemical properties of the binder used in the LED-based light source. The metal oxide is formed, for example, from alumina. Sodium and chloride remain as impurities in the coating of the luminescent substance particles. Especially chlorides, can cause problems in use. Many LED manufacturers therefore have a limit to the halogen in the phosphor powder. When sufficient coatings are simultaneously applied, it is problematic whether halogen contents below this limit can be achieved by this method. In order to obtain sufficient moisture stability, a polymer layer is additionally applied.

US 2016/0264862 a1 shows europium-doped silicate phosphors coated with aluminum oxide. For example, named Ba_1,8Sr_0,15SiO₄:Eu_0,05Nomenclature wherein atomic layer deposition on Ba is performed using trimethylaluminum and water vapor_1,8Sr_{0, 15}SiO₄:Eu_0,05The above. During this deposition an alumina coating is generated.

WO 2004/104131 a2 shows a CVD process for coating luminescent substance grains. In this case, water vapor and trimethylaluminum are introduced into the reaction chamber by means of a carrier gas, respectively, to form a coating on the luminescent material grains in the reaction chamber. The preferred temperature of the reaction chamber is 430 ℃. The trimethylaluminum was heated to 34 ℃. The water will be heated to 70 deg.c.

WO 2016/173691 a1 shows the coating of disilicate luminescent substances with aluminum oxide. Trimethylaluminum and water vapor were used as raw materials for coating with nitrogen as a carrier gas. The basic lattice of the luminescent substance has, for example, Ba₂MgSi₂O₇The composition of (1).

The prior art shows that there are basically three methods for encapsulating luminescent substance particles. The first method is a mechanical mixture of luminescent substances and nanoparticulate foreign substances. The second method is to deposit a protective layer or precursor of the luminescent substance on the luminescent substance in a wet-chemical process. A third method is to deposit a protective layer by CVD in a fluidized bed.

One advantage of encapsulating the luminescent substance with a mechanical mixture is that the exact composition of the protective layer is known and very simple to implement. However, the thickness of the protective layer also depends to a large extent on the mass ratio of the luminescent substance to the protective layer and the diameter of the luminescent substance crystal grains to be coated. The smaller the diameter of the material to be coated, the larger the surface area to volume ratio and hence the larger the surface area to mass ratio. If not enough coating material is added, the luminescent substance surface will not be completely covered and the layer will leak. If too much coating material is added, they converge to form a polymer, and the layer thickness is not uniform, and/or the coated luminescent substance is contaminated by lumps of coating material that are difficult to separate. Even if this ratio is optimal, the coating material is only physically adsorbed on the light-emitting substance, which is porous and leaky. In order to obtain a closed protective layer, the mixture must also be additionally tempered. Such a tempering step must be carried out in the presence of an alkaline earth orthosilicate luminophore in a reducing gas atmosphere, which significantly reduces the strength. Therefore, mechanical mixing and subsequent tempering are not suitable for alkaline earth orthosilicate luminophores.

In the case of wet-chemical coating, the luminescent substance is suspended in a solvent, for example water or ethanol. Different methods are used to add the two starting materials to the suspension, which ideally react to form the coating material or its precursor compound on the surface of the luminescent substance. Process conditions, such as pH and temperature, must generally be observed very accurately. The coated luminescent substance is separated from the liquid phase and dried. In practical cases, the metal of the coating or its precursor compound is also formed in the free solution. The particles formed in this way are attached to the surface of the luminescent substance. This results in the creation of a porous layer that is not completely closed, so that moisture, oxygen and other substances in the air can still attack the light-emitting substances. Different methods of sealing the layer have been described. The first method is to temper the material after, for example, mechanical mixing. In addition to the problems described above, sintering of the coated phosphor particles cannot be completely prevented. Due to the porosity of the protective layer, the protective layer can also be partially damaged again, although it can be separated by grinding. The second method is to deposit a mixed metal oxide. For example, the protective effect of an aluminum-metal oxide layer can be significantly improved compared to a pure aluminum oxide layer. This method is not present for alkaline earth orthosilicate luminophores. A third method is to settle additional layers of polymer or mixed metal oxide. By this means contact between the alumina layer and moisture can be prevented. In addition to the significant increase in production costs, the amount of waste is also increased. The method is also used for alkaline earth orthosilicate luminophores.

Another problem with wet chemical coating is impurities. The starting material forming the protective layer always contains foreign elements, e.g. AlCl₃+NaOH→Al(OH)₃+(NaCl)→Al₂O₃(+H₂O) Na and Cl. Although the bonding of these foreign elements to the protective layer can be minimized by the low reaction speed and the washing process, it cannot be completely avoided. These elements can cause problems in use. Other problems with this process are the difficult separation of the by-products and the relatively large amount of waste, such as solvent.

The deposition of the protective layer by the low-waste CVD method has already been described for different phosphor systems. The great advantage of this process is that the particles are present in a separated state through the fluidized bed. Thus, the adhesion of the individual luminescent substance particles can be largely avoided and a uniform and closed layer formation can be ensured. Similar to wet chemical processes, it cannot be ruled out that the layer material is formed in a fluid and not only on the surface of the luminescent substance. However, these particles are still transported out of the reaction chamber during this process due to the main gas flow. Contamination of the luminescent substances coated, for example, with aluminum oxide can thereby be avoided.

The CVD method described does not appear to be suitable for the coating of alkaline earth orthosilicate luminophores. Provided that an aluminum precursor and CO are used₂Then it is very muchHigh temperatures are necessary for the formation of alumina. At these temperatures, it can be expected that the alkaline earth orthosilicate-luminescent substance will become grey and lose intensity. Provided that the aluminum precursor and O are used₂Then high temperatures are also necessary for the formation of alumina. In this case, it is expected that the alkaline earth orthosilicate luminophores will become grey, which is accompanied by a loss of intensity. Due to the presence of 0₂Also present are (Eu)²⁺) The risk of the activator being oxidized, thus causing a color change. Provided that the aluminum precursor and H are considered₂In the case of O, it must be taken into account that alkaline earth orthosilicate-luminescent substances are highly sensitive to water and moisture. In the case of reactions which take place in the presence of water, it is therefore expected that the alkaline earth orthosilicate luminophore intensity will be decomposed and thus lost.

Disclosure of Invention

The object of the present invention is to improve the long-term stability of alkaline earth silicate phosphors, without having to accept a significant reduction in emission intensity, based on the prior art.

Said task is solved by a method according to the appended claim 1. This object is also achieved by an alkaline earth metal silicate phosphor according to the appended claim 8.

The method according to the invention serves to improve the long-term stability of the phosphor. The phosphor is an alkaline earth metal silicate phosphor. The luminescent substance has a general formula EA_xSi_yO_zWherein EA is formed from one or more alkaline earth metals, and the conditions x, y, z>0 applies. The luminescent substances to be improved are in the form of grains. The grains appear as particles. The method according to the invention is used in particular for coating crystal grains of a phosphor.

Activators such as Eu²⁺Or Mn²⁺Doped into the basic lattice. Several activators and other co-activators or sensitizers may also be doped into the basic lattice.

The luminescent substance has the basic property of absorbing optical radiation in a first wavelength range and emitting optical radiation in a second wavelength range different from the first wavelength range. It is therefore a conversion phosphor. In a typical embodiment, the luminescent substance absorbs light radiation in the blue wavelength range and/or in the ultraviolet wavelength range and emits light radiation in the visible wavelength range, for example in the blue, green, yellow-green, yellow and/or orange wavelength range. However, the present invention is not limited to a specific wavelength range.

The method according to the invention relates to Chemical Vapor Deposition (CVD), wherein individual grains of the alkaline earth silicate-luminescent substance are preferably suspended in a fluidized bed.

In one step of the method according to the invention, the crystal grains consisting of the alkaline earth silicate luminophore are heated in the reaction chamber. For this purpose, the reaction chamber preferably comprises a furnace heater, by means of which the crystal grains of the alkaline earth silicate-luminescent substance are heated. The crystal grains consisting of the alkaline earth silicate phosphor are heated until the phosphor reaches a decomposition temperature which is preferably below the decomposition temperature of the not yet applied alkaline earth silicate phosphor. The luminescent material grains are preferably located in a fluidized bed in the reaction chamber so that the surfaces of the grains are exposed and constantly mixed.

In a further step a volatile organo aluminium compound, preferably trimethylaluminium TMA, is heated. It is also feasible to use other organoaluminum compounds besides trimethylaluminum and in accordance with the spirit of the invention. A first carrier gas flows through the heated volatile organoaluminum compound. Thereby obtaining a first carrier gas mixture comprising the volatile organoaluminum compound. In addition, the water H is treated₂And (4) heating the O. A second carrier gas flows through the heated water. Thereby obtaining a second carrier gas mixture comprising said water. The first carrier gas and the second carrier gas may be, but need not be, the same.

According to the invention, a first carrier gas mixture comprising a volatile organoaluminum compound and a second carrier gas mixture comprising water are introduced into a reaction chamber in which the crystallites of the alkaline earth metal silicate-luminescent substance are surrounded by the first carrier gas mixture comprising the volatile organoaluminum compound and the second carrier gas mixture comprising water. The volatile organoaluminum compound reacts with water in the reaction chamber and forms at least predominantly aluminum metahydroxide Al0 (OH). This reaction takes place in the region of the grains of the alkaline earth silicate phosphor, whereby a homogeneous, closed coating of the grains of the alkaline earth silicate phosphor is formed. The coating is formed in particular from aluminum metahydroxide.

A particular advantage of the process according to the invention is that the aluminum metahydroxide deposited by CVD on the alkaline earth orthosilicate-luminescent substance grains forms only a very thin coating on the luminescent substance grains, which does not or does not significantly impair the emission intensity of the alkaline earth orthosilicate-luminescent substance. However, this very thin coating significantly increases the resistance to water, air and moisture and improves the long-term stability of the preferred use of alkaline earth orthosilicate phosphors in LEDs.

The coating of the grain surface is transparent or at least largely transparent to optical radiation in the first wavelength range and to optical radiation in the second wavelength range. In particular, the coating does not have any absorption properties for light radiation having a wavelength of more than 380 nm. Preferably, the surfaces of the luminescent substance crystal grains are each coated with aluminum metahydroxide.

The coating forms a barrier layer made of aluminum metahydroxide which preferably wraps the grains over their entire surface. The thickness of the coating is preferably between 10nm and 1 μm. The barrier layer formed by the coating layer is characterized in that aluminum metahydroxide contained therein is preferably free of halogen and alkali elements.

The present invention surprisingly shows how aluminum metahydroxide as a protective coating can be applied to crystal grains of alkaline earth orthosilicate luminophores by means of a CVD method in the presence of water. The method according to the invention does not lead to a significant change in the color locus or in the initial intensity, even in the water-sensitive embodiment of the alkaline earth orthosilicate luminophore, compared to the alkaline earth orthosilicate luminophore which has not yet been coated. However, the coated alkaline earth orthosilicate luminophores according to the invention exhibit a significantly higher stability with respect to water and moisture and an improved long-term stability in the lamp.

To be coatedThe basic lattice of the coated alkaline earth silicate phosphor is preferably represented by the formula (Ba)_a,Sr_b,Ca_c)₂SiO₄To describe. At least one of the variables a, b and c is greater than 0, and a + b + c is 1. The phosphor is an alkaline earth orthosilicate, which is particularly suitable for use in LED-based light sources. The activator is preferably europium Eu²⁺. The phosphor can be represented by the simplified symbol (Ba, Sr, Ca)₂SiO₄Eu. Such luminescent substances preferably emit light radiation in the green, yellow-green, yellow and/or orange wavelength range when excited.

In a preferred embodiment, the EA comprises magnesium and another alkaline earth metal in the basic lattice. In these embodiments, the base lattice has one of the following formulas: EA'₃MgSi₂O₈，EA'₂MgSi₂O₇And EA'₂MgSiO₅Wherein EA' is formed from one or more alkaline earth metals other than magnesium. A particularly preferred formula of the base lattice is EA'₃MgSi₂0₈Wherein EA is preferably formed from Sr. Correspondingly, the basic lattice has the formula Sr₃MgSi₂0₈. The activator is preferably europium Eu²⁺. The phosphor can be described by the simplified symbol Sr₃MgSi₂0₈: and Eu. Such a luminescent substance preferably emits optical radiation in the blue wavelength range when excited.

In other preferred embodiments, the base lattice has an EA₃SiO₅Or EASiO₃The chemical formula (2).

The silicon in the alkaline earth metal silicate may be partly replaced by aluminum, boron, germanium, gallium and/or phosphorus. The possibility of modification of such alkaline earth metal silicate phosphors is known to the person skilled in the art. In any case, the person skilled in the art will also refer to the luminophores modified in this way as alkaline earth silicates and in most cases use the general formula EA_xSi_yO_zThey are named. For a particularly precise nomenclature, the skilled worker may, if desired, use the formula EA_X(Si，Al，B，Ge，Ga，P)_yO_zOr of the formula EA_X(Si_1-e-f-g-h-iAl_eB_fGe_gGa_hP_i)_yO_zWherein e, f, g, h and/or i>0. Another possible modification of the alkaline earth metal silicate luminophore is the addition of up to 10 Mol-% of halide ions.

The crystal grains of the alkaline earth metal silicate phosphor form particles, the preferred diameter of which is in each case between 1 μm and 2 mm. Furthermore, diameters of between 1 μm and 2mm are preferred, and between 10 μm and 50 μm are particularly preferred. The present invention is not limited to a particular grain size.

The volatile organoaluminium compound is preferably formed from an alkyl derivative of aluminium or an acrylic acid derivative, and preferably has the general formula R₃AI，R₂AIX，RA1X₂Wherein X represents-H, -halogen, -NR₂OR-OR, OR 2X represents ═ 0. It is particularly preferred that X represents-H OR-OR, OR 2X represents ═ 0, so that no halogen OR nitrogen impurities are doped into the coating.

The volatile organic aluminium compound is particularly preferably formed from trimethylaluminium TMA. In another alternative preferred embodiment, the volatile organo-aluminium compound is formed from triethylaluminium, TEA.

The heating and flowing of the volatile organoaluminum compound is preferably carried out in a first bubbler. The volatile organic aluminium compound, preferably formed from trimethylaluminium, is preferably heated to a temperature between 15 ℃ and 70 ℃, particularly preferably between 40 ℃ and 55 ℃. Another alternative volatile organoaluminium compound, preferably formed from triethylaluminium, is preferably heated to a temperature between 150 ℃ and 200 ℃. The primary carrier gas is preferably introduced into the feed tube of the bubbler. The first carrier gas mixture comprising the volatile organoaluminum compound preferably flows out of the discharge tube of the first bubbler.

The heating and flowing through of water is preferably carried out in a second bubbler. The water is preferably heated to a temperature between 50 ℃ and 90 ℃, particularly preferably to a temperature between 70 ℃ and 90 ℃. The secondary carrier gas is preferably introduced into the feed tube of the bubbler. The second carrier gas mixture comprising water preferably flows out of the discharge pipe of the second bubbler.

The heating and flowing through the volatile organoaluminum compound and the heating and flowing through the water are preferably carried out separately, and preferably in one bubbler, respectively. The bubblers are preferably each a vapor pressure saturator.

The first carrier gas mixture comprising the volatile organoaluminum compound is preferably introduced into the reaction chamber at a theoretical volumetric flow rate of between 2 and 30 liters per minute. The theoretical volume flow is particularly preferably 5 to 15 liters per minute.

The second carrier gas mixture comprising water is preferably introduced into the reaction chamber at a theoretical volumetric flow rate of between 2 and 10 liters per minute. The theoretical volume flow is particularly preferably 5 to 8 liters per minute.

The first carrier gas flowing through the volatile organoaluminum compound and the second carrier gas flowing through the water are preferably composed of nitrogen N and water, respectively₂And (4) forming.

The phosphor grains are preferably heated in the reaction chamber to a temperature of between 150 ℃ and 250 ℃, particularly preferably between 170 ℃ and 180 ℃. The luminescent substance grains are preferably heated in the reaction chamber before the first carrier gas mixture comprising the volatile organoaluminum compound and the second carrier gas mixture comprising water are introduced into the reaction chamber. The heating of the crystal grains of the light-emitting substance in the reaction chamber is preferably carried out in an inert atmosphere, and for this purpose, the same gas as the first carrier gas and the second carrier gas is preferably introduced into the reaction chamber. For this purpose, it is preferred to short-circuit the feed and discharge pipes of one of the bubblers or of both bubblers, so that the gas from the carrier gas source is introduced into the reaction chamber bypassing this bubbler. Once the luminescent material grains in the reaction chamber are heated to a given temperature, the short circuit between the feed and discharge pipes of the bubbler concerned is broken, and the carrier gas absorbs the volatile organoaluminum compound or water and is introduced into the reaction chamber together therewith. The first bubbler containing trimethylaluminum is preferably short-circuited so that gas from the carrier gas source is introduced into the reaction chamber bypassing the bubbler, thereby creating a fluidized bed.

The first carrier gas mixture comprising the volatile organoaluminum compound is preferably introduced into the reaction chamber through the floor of the reaction chamber so that it flows into the reaction chamber from below.

The second carrier gas mixture comprising water is preferably guided through a feed device projecting into the reaction chamber. The feed device is preferably formed by a lance which projects into the reaction chamber from above, so that the second carrier gas mixture comprising water flows into the reaction chamber from above. A first carrier gas mixture comprising a volatile organoaluminum compound flows into the reaction chamber from below and a second carrier gas mixture comprising water flows into the reaction chamber from above, thereby ensuring that the volatile organoaluminum compound and water meet and react in the region of the alkaline earth silicate-luminescent material crystallites located in the reaction chamber. Alternatively, the feeding means preferably consist of nozzles in the bottom plate. Alternatively, it is preferred to direct a first carrier gas mixture comprising a volatile organoaluminum compound through the lance into the reaction chamber, and a second carrier gas mixture comprising water through the floor of the reaction chamber into the reaction chamber.

The aluminum metahydroxide particles, which are formed in the gas phase but do not adhere to the surface of the alkaline earth silicate-luminophore grains, are transported out of the reaction chamber as a result of the main gas flow. This makes it possible to avoid contamination of the alkaline earth silicate luminophore with aluminum metahydroxide.

A first carrier gas mixture comprising a volatile organoaluminum compound, preferably formed from trimethylaluminum, and a second carrier gas mixture comprising water are introduced into the reaction chamber until an amount of volatile organoaluminum compound, preferably between 20 and 120 grams of luminescent species per kilogram of alkaline earth silicate-luminescent species located in the reaction chamber, has been introduced into the reaction chamber. This amount particularly preferably means that the alkaline earth silicate luminophore present in the reaction chamber amounts to between 40 and 75 g per kg luminophore.

After the introduction of the first carrier gas mixture comprising the volatile organoaluminum compound and the second carrier gas mixture comprising water into the reaction chamber is completed, it is preferable to further introduce an inert gas into the reaction chamber, particularly the same gas as the carrier gas. For this purpose, it is preferred to short-circuit the feed and discharge pipes of one of the bubblers or of both bubblers, so that the gas from the carrier gas source is introduced into the reaction chamber bypassing this bubbler. This is done for a period of time until the coated grains cool. During this time, the coated grains of the alkaline earth silicate luminophore are preferably no longer heated, so that the grains cool. The introduction of the inert gas into the reaction chamber is preferably terminated as soon as the temperature of the coated crystallites of the alkaline earth metal silicate luminophore is below 40 ℃. The coated grains of alkaline earth silicate-luminescent substance can then be removed from the reaction chamber. The alkaline earth silicate phosphor is preferably not subsequently tempered. The crystal grains of the alkaline earth silicate luminophore are preferably not further coated.

By means of the alkaline earth silicate luminophores according to the invention, it is possible to absorb optical radiation in a first wavelength range and to emit optical radiation in a second wavelength range which is different from the first wavelength range. Alkaline earth silicate luminophores having the general formula EA_xSi_yO_zWherein EA is formed from one or more alkaline earth metals, and the conditions x, y, z>0 applies. The alkaline earth metal silicate luminophores are present in the form of crystallites. Activators such as Eu²⁺Or Mn²⁺Is incorporated into the basic lattice.

According to the invention, the grains have on their surface a coating of aluminum metahydroxide, possibly also containing some aluminum oxide and/or hydroxide.

The alkaline earth silicate phosphors according to the invention are distinguished by a core-shell structure. The core consists of a doped basic crystal lattice which is surrounded by a homogeneous, dense, preferably halogen-free, aluminum metahydroxide coating as a shell. The diameter of the core formed by the alkaline earth silicate-luminophore grains is preferably between 1 μm and 2 mm.

The grain coating of the alkaline earth silicate phosphor has a thickness of preferably at least 10 nm. The thickness is preferably at most 1 μm.

In a preferred embodiment of the alkaline earth metal silicate luminophore according to the invention, the coating of the crystallites also comprises organic and/or organoaluminium aliphatics, alcohols, carbonyl groups and/or carboxyl groups. These compounds are formed from incompletely reacted volatile organoaluminum compounds which coat the crystallites of the alkaline earth metal silicate-luminescent substance. The coating of the grains preferably does not contain alkali metals and halogens, which are present as impurities in the coatings according to the prior art.

The alkaline earth silicate luminophores according to the invention preferably also have the features described in connection with the method according to the invention.

Drawings

Further advantages, details and improvements of the invention are given by the following description of preferred embodiments of the invention and with reference to the drawings. In the figure:

figure 1 shows an apparatus for carrying out a preferred embodiment of the method according to the invention;

FIG. 2 shows a diagram of the relative intensity as a function of the operating time in a first example of an alkaline earth silicate phosphor according to the invention;

FIG. 3 shows a diagram of the relative intensity as a function of the operating time in a second example of an alkaline earth silicate phosphor according to the invention; and

fig. 4 shows a diagram of the relative intensity as a function of the operating time in a third example of an alkaline earth silicate phosphor according to the invention.

Detailed Description

Fig. 1 shows a device for carrying out a preferred embodiment of the method according to the invention for improving the long-term stability of alkaline earth silicate phosphors. The apparatus comprises a reaction chamber 01 in which the alkaline earth silicate phosphor to be treated is located in the form of grains (not shown). The reaction chamber 01 is heated by a furnace heater 02.

The apparatus also comprises a first bubbler 03, said first bubbler 03 being adapted to heat the trimethylaluminum or other organoaluminium compound and to flow a first carrier gas through said trimethylaluminum, said first carrier gas being optimally constituted by nitrogen. The carrier gas is supplied from a first carrier gas source 04 and is introduced via a first front short-circuit valve 06 into a first feed line 07, which first feed line 07 leads into the interior of a first bubbler 03. A first discharge pipe 08 passes from the inner space of the first bubbler 03 through a first rear-side short-circuiting valve 09 and through a lance 11 into the reaction chamber 01. The carrier gas supplied by the first carrier gas source 04 carries the heated trimethylaluminum in the first bubbler 03 to be introduced into the reaction chamber 01 through the first discharge pipe 08 and through the spray pipe 11. If the first front-side short-circuit valve 06 and the first rear-side short-circuit valve 09 are actuated, pure carrier gas without trimethylaluminum is introduced into the reaction chamber 01 via the first short-circuit 12 and via the lance 11.

The device further comprises a second bubbler 13, said second bubbler 13 being intended for heating the water and for letting a second carrier gas, preferably also constituted by nitrogen, flow through said water. The second carrier gas is supplied from a second carrier gas source 14 and is introduced through a second front side short-circuit valve 16 into a second feed pipe 17, which second feed pipe 17 opens into the inner space of the second bubbler 13. A second discharge tube 18 enters the reaction chamber 01 from the inner space of the second bubbler 13 through a second back-side short-circuiting valve 19 and through an inlet connection 21. The carrier gas supplied from the second carrier gas source 14 carries the water heated in the second bubbler 13, and is thus introduced into the reaction chamber 01 through the second discharge pipe 18 and through the inlet connection 21. If the second front short-circuit valve 16 and the second rear short-circuit valve 19 are actuated, pure carrier gas free of water is introduced into the reaction chamber 01 via the second short-circuit 22 and via the inlet connection 21. The carrier gas introduced into the reaction chamber 01, which carries the heated water according to the positional arrangement of the second front-side short-circuiting valve 16 and the second rear-side short-circuiting valve 19, is distributed in the reaction chamber 01 by the distributor 23 so as to be uniformly guided through the crystal grains of the alkaline earth metal silicate-luminous substance.

Fig. 2 shows a graph of the relative intensity as a function of the operating time for a first exemplary embodiment of an alkaline earth silicate phosphor applied according to the invention in LED applications in comparison with a corresponding, yet uncoated alkaline earth silicate phosphor. In addition to the coating, this first example of an alkaline earth silicate phosphor has (Sr, Ba, Ca)_2-xEu_xSiO₄Wherein x is more than 0 and less than or equal to 0.5.

To produce this first example, 4.5kg of the uncoated alkaline earth silicate luminophore having the above-mentioned formula were introduced into the reaction chamber 01 (shown in FIG. 1) in order to coat it according to the invention. The alkaline earth silicate phosphor which has not yet been applied is heated in the reaction chamber 01 (shown in FIG. 1) to a temperature of between 170 ℃ and 190 ℃. Trimethylaluminum is heated to a temperature of 50 ℃ in a first bubbler 03 (shown in fig. 1). The water is heated to a temperature of 90 c in the second bubbler 13 (shown in fig. 1). Nitrogen was used as the carrier gas, respectively. The theoretical volumetric flow rate of the first carrier gas mixture containing trimethylaluminum was 15 liters per minute. The theoretical volumetric flow rate of the second carrier gas mixture comprising water is 5 liters per minute. 0.3kg of trimethylaluminum was consumed.

Table 1 shows the different properties of the first example thus obtained of the alkaline earth silicate phosphor coated according to the invention compared to the alkaline earth silicate phosphor which has not yet been coated.

The main color of the first example of the alkaline earth silicate phosphor is yellow-green and there is no color change after coating.

The coating formed by the method according to the invention is very dense. If the alkaline earth silicate phosphor is left in the aqueous suspension for 60 minutes, the conductivity in the first exemplary embodiment of the alkaline earth silicate phosphor according to the invention is two orders of magnitude less than the conductivity of the corresponding, yet uncoated, alkaline earth silicate phosphor, which indicates that the coating of aluminum metahydroxide is closed. The results show that the alkaline earth silicate phosphors applied according to the invention can be used at least for a short time in a phosphor aqueous medium, for example during stirring of a phosphor paste.

The emission intensity of the first exemplary embodiment of the coated alkaline earth silicate phosphor according to the invention is almost identical compared to the corresponding, yet uncoated, alkaline earth silicate phosphor in the unaged state. Table 1 shows the relative luminescence intensity with respect to a reference luminescent substance at 254nm EM₂₅₄Is used for emission and EM at 465nm₄₆₅Used in the unaged state as a starting material. If the alkaline earth silicate phosphor coated according to the invention is used in a first embodimentExample and corresponding uncoated alkaline earth silicate phosphor the relative emission intensity EM of the uncoated alkaline earth silicate phosphor is determined after one week in a climate chamber with a temperature of 60 ℃ and a humidity of 90%₂₅₄60/90 and EM₄₆₅60/90, and the emission intensity EM of the alkaline earth silicate phosphors applied according to the invention₂₅₄60/90 and EM₄₆₅60/90 remain unchanged.

The diagram shown in fig. 2 compares the long-term stability of the use of alkaline earth silicate phosphors in LED lamps when placed in a climate chamber at a temperature of 60 c and a humidity of 90% for several weeks. The run time in hours is plotted on the x-axis of the graph. The relative luminous flux of the first exemplary embodiment of the alkaline earth silicate phosphor coated according to the invention or of a corresponding, yet uncoated, alkaline earth silicate phosphor is plotted on the y-axis of the figure. The first graph 25 marked with circles shows the measured values of a first exemplary embodiment of the alkaline earth silicate phosphor applied according to the invention, while the second graph 26 marked with squares shows the measured values of the corresponding, yet uncoated alkaline earth silicate phosphor. In both cases, five of the LED lamps in each pair were averaged. In table 1, the values of the relative luminous flux after 1000 hours of operation are additionally compared with the respective initial values in the unaged state.

Watch 1

Fig. 3 shows a graph of the relative intensity as a function of the operating time in a second exemplary embodiment of a coated alkaline earth silicate phosphor according to the invention in comparison with a corresponding, yet uncoated alkaline earth silicate phosphor in an LED application. In addition to the coating, this second example of an alkaline earth silicate phosphor has (Ba, Sr, Ca)_{2- x}Eu_xSiO₄Of the formula (II) wherein 0<x≤0.5。

To produce this second example, 4.5kg of the uncoated alkaline earth silicate luminophore having the above-mentioned formula were introduced into the reaction chamber 01 (shown in FIG. 1) in order to coat it according to the invention. The alkaline earth silicate phosphor which has not yet been applied is heated in the reaction chamber 01 (shown in FIG. 1) to a temperature of between 170 ℃ and 190 ℃. Trimethylaluminum is heated to a temperature of 50 ℃ in a first bubbler 03 (shown in fig. 1). The water is heated to a temperature of 75 c in the second bubbler 13 (shown in fig. 1). Nitrogen was used as the carrier gas, respectively. The theoretical volumetric flow rate of the first carrier gas mixture containing trimethylaluminum was 15 liters per minute. The theoretical volumetric flow rate of the second carrier gas mixture comprising water is 5 liters per minute. 0.2kg of trimethylaluminum was consumed.

Table 2 shows the different properties of the second example thus obtained of the alkaline earth silicate phosphor coated according to the invention compared to the alkaline earth silicate phosphor which has not yet been coated.

The host color of the second example of the alkaline earth silicate luminophore is green and there is no color change after application.

The coating formed by the method according to the invention is very dense. If the alkaline earth silicate phosphor is left in the aqueous suspension for 60 minutes, the electrical conductivity in the second exemplary embodiment of the alkaline earth silicate phosphor according to the invention is approximately an order of magnitude less than the electrical conductivity of the corresponding, yet uncoated, alkaline earth silicate phosphor, which indicates that the coating of aluminum metahydroxide is closed. The results show that the alkaline earth silicate phosphors applied according to the invention can be used at least for a short time in a phosphor aqueous medium, for example during stirring of a phosphor paste.

The emission intensity of the second exemplary embodiment of the coated alkaline earth silicate phosphor according to the invention is almost identical compared to the corresponding, yet uncoated, alkaline earth silicate phosphor in the unaged state. Table 2 shows the relative luminescence intensity with respect to a reference luminescent substance at 254nm EM₂₅₄Is used for emission and EM at 465nm₄₆₅Used in the unaged state as a starting materialState. If the second example of the alkaline earth silicate phosphor coated according to the invention and the corresponding uncoated alkaline earth silicate phosphor are left to stand for one week in a climate chamber with a temperature of 60 ℃ and a humidity of 90%, the relative emission intensity EM of the alkaline earth silicate phosphor is the relative emission intensity EM₂₅₄60/90 and EM₄₆₅60/90 dropped almost equally significantly.

The diagram shown in fig. 3 compares the long-term stability of the use of alkaline earth silicate phosphors in LED lamps when placed in a climate chamber at a temperature of 60 c and a humidity of 90% for several weeks. The run time in hours is plotted on the x-axis of the graph. The relative luminous flux of a second example of an alkaline earth silicate phosphor coated according to the invention or of a corresponding, yet uncoated, alkaline earth silicate phosphor is plotted on the y-axis of the figure. The third graph 28 marked with circles shows the measured values of a second exemplary embodiment of the alkaline earth silicate phosphor applied according to the invention, while the fourth graph 29 marked with squares shows the measured values of the corresponding, yet uncoated alkaline earth silicate phosphor. In both cases, five of the LED lamps in each pair were averaged.

The second exemplary embodiment of the alkaline earth silicate phosphor applied according to the invention has a significantly higher stability when used in an LED lamp than the corresponding, yet uncoated, alkaline earth silicate phosphor. After a day of operation, the relative luminous flux has already differed by more than 3%, and after a 1000-hour operation, the second exemplary embodiment of the alkaline earth silicate phosphor applied according to the invention has a relative luminous flux which is reduced by more than 20% compared to the corresponding phosphor not yet applied. At the same time, the second exemplary embodiment of the alkaline earth silicate phosphor applied according to the invention has a significantly smaller shift in color coordinates after 1000 hours of operation. This slight shift only reaches Δ x-0.003; Δ y is-0.018, while the color coordinates of the corresponding uncoated alkaline earth silicate phosphor are shifted by Δ x is-0.011; Δ y ═ 0.056. These values show that the alkaline earth silicate phosphors applied according to the invention are significantly more stable even when used in LED lamps.

In table 2, the values of the relative luminous flux after 1000 hours of operation are additionally compared with the respective initial values in the unaged state.

Watch two

Fig. 4 shows a graph of the relative intensity as a function of the operating time in a third exemplary embodiment of a coated alkaline earth silicate phosphor according to the invention in comparison with a corresponding, yet uncoated alkaline earth silicate phosphor in an LED application. This third exemplary embodiment of the alkaline earth silicate phosphor has Sr in addition to the coating_3-xMgEu_xSi₂O₈Of the formula (II) wherein 0<x≤0.5。

To produce this third example, 4.0kg of the uncoated alkaline earth silicate phosphor of the above formula were introduced into the reaction chamber 01 (shown in FIG. 1) in order to coat it according to the invention. The alkaline earth silicate phosphor which has not yet been applied is heated in the reaction chamber 01 (shown in FIG. 1) to a temperature of between 170 ℃ and 195 ℃. Trimethylaluminum is heated to a temperature of 50 ℃ in a first bubbler 03 (shown in fig. 1). The water is heated to a temperature of 70 c in the second bubbler 13 (shown in fig. 1). Nitrogen was used as the carrier gas, respectively. The theoretical volumetric flow rate of the first carrier gas mixture containing trimethylaluminum was 7.5 liters per minute. The theoretical volumetric flow rate of the second carrier gas mixture comprising water is 5 liters per minute. 0.3kg of trimethylaluminum was consumed.

Table 3 shows the different properties of the third example thus obtained of the alkaline earth silicate phosphor coated according to the invention compared to the alkaline earth silicate phosphor which has not yet been coated.

The host color of the third example of the alkaline earth silicate phosphor is light blue-green and there is no color change after coating.

The coating formed by the method according to the invention is very dense. If the alkaline earth silicate phosphor is left in the aqueous suspension for 60 minutes, the conductivity in the third exemplary embodiment of the alkaline earth silicate phosphor according to the invention is an order of magnitude less than the conductivity of the corresponding, yet uncoated alkaline earth silicate phosphor, which indicates that the coating of aluminum metahydroxide is closed. The results show that the alkaline earth silicate phosphors applied according to the invention can be used at least for a short time in a phosphor aqueous medium, for example during stirring of a phosphor paste.

The emission intensity of the third exemplary embodiment of the coated alkaline earth silicate phosphor according to the invention is almost identical compared to the corresponding, yet uncoated, alkaline earth silicate phosphor in the unaged state. Table 3 shows the relative luminescence intensity with respect to a reference luminescent substance at 405nm EM₄₀₅For emission and for an unaged state as a starting point. If the third exemplary embodiment of the alkaline earth silicate phosphor coated according to the invention and the corresponding, yet uncoated, alkaline earth silicate phosphor are left to stand for one week in a climate chamber with a temperature of 60 ℃ and a humidity of 90%, the relative emission intensity EM of the alkaline earth silicate phosphor₄₀₅60/90 rise almost as significantly.

The diagram shown in fig. 4 compares the long-term stability of the use of alkaline earth silicate phosphors in LED lamps when placed in a climate chamber at a temperature of 60 c and a humidity of 90% for several weeks. The run time in hours is plotted on the x-axis of the graph. The relative luminous flux of a third exemplary embodiment of the alkaline earth silicate phosphor according to the invention or of a corresponding, yet uncoated alkaline earth silicate phosphor is plotted on the y-axis of the figure. The fifth graph 31 marked with circles shows the measured values of the third exemplary embodiment of the alkaline earth silicate phosphor applied according to the invention, while the sixth graph 32 marked with squares shows the measured values of the corresponding, yet uncoated alkaline earth silicate phosphor. In both cases, ten of the LED lamps in each pair were averaged.

The third exemplary embodiment of the coated alkaline earth silicate phosphor according to the invention has a higher stability when used in an LED lamp than the corresponding uncoated alkaline earth silicate phosphor.

In table 3, the values of the relative luminous flux after 1000 hours of operation are additionally compared with the respective initial values in the unaged state.

Watch III

List of reference numerals