EP1390989A1

EP1390989A1 - Highly efficient luminescent substance

Info

Publication number: EP1390989A1
Application number: EP01947188A
Authority: EP
Inventors: Manfred Kobusch; Martin Judenhofer
Original assignee: Osram Opto Semiconductors GmbH
Current assignee: Ams Osram International GmbH
Priority date: 2001-05-29
Filing date: 2001-06-07
Publication date: 2004-02-25
Also published as: CA2448529A1; DE20108873U1; JP2004527638A; CN1444776A; WO2002097901A1; KR20030020413A; US20040135123A1

Abstract

The invention relates to a luminescent substance of the thiometallate class, preferably thiogallates. The thiometallate is prepared according to the formula (AS)<.>w(B2S3), whereby A is at least a bivalent cation selected from the Ba group, either individually or in combination with Mg and/or Ca, B is at least a trivalent cation from the Al, Ga, Y group and the factor w can lie both in the range 0.8 </= w </= 0.98 and in the range 1.02 </= w </= 1.2.

Description

Highly efficient fluorescent

Technical field

The invention is based on a phosphor from the class of thiometalates according to the preamble of claim 1, the thiometalate being derived from the general formula AB ₂ S ₄ : D ²⁺ , where A at least one divalent cation from the group Ba individually or in Is a combination with Mg and / or Ca, and where B is at least one trivalent cation from the group Al, Ga, Y and where the dopant / activator D is europium and / or cerium. The proportion of divalent cation A is reduced by the proportion t of activator D added. These are in particular thiogallates which have light emission in the green spectral range. The composition of the phosphor is set up in such a way that the molar proportion of divalent ions A to trivalent ions B in the general empirical formula AB ₂ S ₄ does not exactly correspond to the ratio A: B = 1: 2.

State of the art

US Pat. No. 3,639,254 and US Pat. No. 5,834,053 already disclose thiogallates whose emission spectra are in the blue or green spectral range. These phosphors follow the formula AGa ₂ S ₄ , where A represents at least one element from the group of alkaline earth metals, in particular Ca, Ba, Sr, or also Zn. Activators are europium, lead or cerium. However, the luminescent materials mentioned have emission efficiencies which are too low for applications with high luminous efficiency requirements (for example lighting technology). This emission efficiency is expressed by the so-called quantum efficiency QE (ratio of the number of emitting quanta to the number of absorbed quanta). Typical quantum efficiency values for the phosphors mentioned are between 60% and 70%. From WO 98/18721 an electroluminescent phosphor from the group of thiometalates is known, with Sr or another alkaline earth metal as the divalent cation, Ga, Al or In taking on the role of the trivalent cation. In particular, a manufacturing process is described there while maintaining a certain proportion of residual oxygen.

Presentation of the invention

It is an object of the present invention to provide a phosphor which has the highest possible quantum efficiency at a given emission wavelength.

This object is achieved by the characterizing features of claim 1. Particularly advantageous configurations can be found in the dependent claims.

According to the invention, the composition of the phosphor is selected such that the proportion of divalent ions A to trivalent ions B, based on the general empirical formula AB ₂ S ₄ , deviates from the ratio A: B = 1: 2. The concept according to the invention can also be represented in a different notation if the thiometalates of the original empirical formula AB ₂ S _{4 are written} as a product of the components AS and B ₂ S ₃ in the form AS ^» B ₂ S ₃ . The ratio of component AS to component B ₂ S ₃ is described below with the factor w = B ₂ S ₃ / AS. Overall, the thiometalate is shown as (AS) ^« w (B ₂ S ₃ ). It can be seen that phosphors with the composition (AS) ^» w (B ₂ S ₃ ) have higher quantum efficiencies both in the range 0.8 ≤ w <0.98 and in the range 1.02 <w ≤ 1.2 deliver as phosphors with the composition w = 1.

By combining different cations of type A and B, different emission wavelengths and color locations can be achieved and adapted to the respective application. For an efficient ("bright") phosphor, it must also apply that there is little reflection in the excitation area and high quantum efficiency.

Ba can be used as cation A individually or in combination with Mg, Ca, in particular in combination of all three cations. As an activator, as a partial replacement for A, europium and / or cerium can be used. Ga, but also Al or Y, is preferably used as the cation B. The gallium can in particular be partially (up to 10 mol%) replaced by aluminum. The dopant D (D = Eu and / or Ce) is completely assigned to the subcomponent AS, that is to say in a more detailed representation Aι. _t D _t S.

Phosphors with the composition (AS) ^» w (B ₂ S ₃ ) show particularly high quantum efficiency, where A = Mg _a Ca _b Ba _c Eu _t with a + b + c + t = 1 with the following ranges: 0.4 <a ≤0,8; 0.05 ≤ b <0.35; 0.05 ≤c ≤ 0.4; 0.01 <t <0.1; such as

B = (Ga _x Al _y Y _z ) ₂ with x + y + z = 1 and 0.9 ≤ x <1 and 0 <y <0.1 and 0 <z <0.1; and 0.8 ≤ w ≤ 0.98 or 1.02 ≤w <1.2.

Another preferred embodiment is phosphors with the composition (AS) ^» w (B ₂ S ₃ )

A = Mg _a Ba _b Eu _t with a + b + t = 1:

0.4 <a <0.8; 0.1 <b <0.59; 0.01 ≤ t ≤ 0.1; as well as B = (Ga _x Al _y Y ₂ ) ₂ with x + y + z = 1 and0.9≤x≤ 1 and O≤y ≤ 0.1 and0≤z <0.1; and 0.8 ≤w≤ 0.98 or 1.02≤w <1.2.

A manufacturing process uses the following steps:

a) preparing a suspension of nitrates according to the desired composition;

b) drying this suspension to a residual moisture of <1% by weight at T <300 ° C. to produce a finely dispersed nitrate mixture;

c) Grinding the nitrate mixture in a mortar mill at room temperature for 10 minutes to 60 minutes, preferably 15 to 25 minutes.

d) pyrolysis of the ground nitrate at 500-700 ° C, preferably at 600 ° C, in an Ar or N ₂ atmosphere to produce a finely dispersed metal oxide mixture with the desired composition. e) First reaction of the metal oxide mixture at 800-1000 ° C, preferably 900-950 ° C, in a flowing H ₂ S or CS ₂ atmosphere or combinations thereof for 1-6 hours, preferably 4 hours.

f) grinding the reaction mixture as in step c;

g) Second reaction at 800-1000 ° C, preferably 900-950 ° C, in a flowing H ₂ S or CS ₂ atmosphere or combinations thereof for 1-6 hours, preferably for 2 hours.

In steps e) and g) the flow rate is preferably 50-500 ml / min, preferably 120 ml / min, and the gas atmosphere preferably consists of H ₂ S or CS ₂ and Ar or N ₂ as carrier gas with 10-50% H ₂ S or CS ₂ or mixtures thereof, preferably 30% H ₂ S or CS ₂ or mixtures thereof.

In steps e) and g), the mixture is gradually heated up to the reaction temperature, preferably at the rate 0.5-20 K / min, preferably 10 K / min.

In addition, in steps e) and g), a gradual cooling is carried out after the reaction, preferably at the rate 0.5-20 K / min, preferably 10 K / min.

The phosphors according to the invention are particularly suitable for use in UV or blue-emitting LEDs for color conversion. For this purpose, they can be used individually or in combination with other phosphors, in particular in combination with other phosphors according to the invention. Another possible application is plasma displays. For this purpose too, the phosphors can be used individually or in combination with other phosphors, in particular in combination with other phosphors according to the invention, in order to convert the short-wave plasma discharge radiation into visible light.

characters

In the following, the invention will be explained in more detail using an exemplary embodiment. Show it: Figure 1 shows the emission spectrum of the phosphor

(Bao, ₂ Cao, i ₅ Mgo, ₆ Euo, o ₅ ) S ^» 1, 1Ga ₂ S3, produced according to the method described in the exemplary embodiment;

FIG. 2 shows the reflection spectrum of the phosphor from FIG. 1.

embodiments

To produce a phosphor with the composition (Bao _{, 2} Cao, i ₅ Mgo _{, 6} Euo, o ₅ ) S »1, 1Ga ₂ S ₃ , high-purity oxides and / or carbonates are weighed in in the amounts corresponding to the formula and a homogeneous one , finely ground mixture of oxides. This raw material mixture is mixed with approx. 30% nitric acid in equimolar amounts, heated to weak boiling and converted to nitrates. The following reaction equation applies:

0.20 mol BaCO ₃ + 0.15 mol CaCO ₃ + 0.6 mol MgO + 0.025 mol Eu ₂ O ₃ + 1, 100 mol Ga ₂ O ₃ + 8.6 mol HNO ₃ -> 0.20 mol Ba ²⁺ + 0 , 15 mol Ca ²⁺ + 0.60 mol Mg ²⁺ + 0.05 mol Eu ³⁺ + 2.20 mol Ga ³⁺ + 8.6 mol NO ₃ ^" + 4.3 mol H ₂ O + 0.35 mol CO ₂ T

This creates a white suspension of precipitated nitrates. This suspension is evaporated until it has a highly viscous state. The nitrate suspension obtained is transferred to a quartz boat and dried at 300 ° C. in a stream of nitrogen.

The dried nitrate mixture is ground in a mortar mill for 20 minutes and then pyrolyzed at 600 ° C. for 4 hours under nitrogen using the following reaction equation:

0.20 mol Ba (NO ₃ ) ₂ + 0.15 mol Ca (NO ₃ ) ₂ + 0.60 mol Mg (NO ₃ ) ₂ + 0.05 mol Eu (NO ₃ ) ₃ + 2.20 mol Ga (NO ₃ ) ₃ -> 1 mol [0.20BaO ^» 0.15CaO ^» 0.60MgO ^» 0.025Eu ₂ O ₃ ^» 1, 10Ga ₂ O ₃ ] + 8.6mol NO ₂ + 2.15mol O ₂

The oxide mixture generated is filled into a quartz boat and heated to 900 ° C in a tube furnace under protective gas (argon). After reaching the reaction temperature, hydrogen sulfide is introduced with 120 ml of 30% H ₂ S / min in a stream of nitrogen and the oxide mixture is converted into the thiogallate within four hours using the following reaction equation: 1 mol [0.20BaO »0.15CaO» 0 ₎ 60MgO ^» 0.025Eu ₂ θ ₃ ^» 1, 10Ga ₂ θ3] + 4.325mol H ₂ S -> (Ba _0.2 oCa _0, i ₅ go _{, 60} Euo _, o ₅ ) S »1, Ga ₂ S ₃ + 4.325mol H ₂ O + 0.025mol S

A temperature of 870 to 930 ° C has proven to be the optimal conversion temperature for a highly efficient phosphor.

The reaction product is ground in a mortar mill for 10 minutes and reacted again in a 20% hydrogen sulfide stream at 900 ° C. for three hours.

With this method, highly efficient phosphors of the compositions mentioned can be produced reproducibly.

Compared to a phosphor of the formula (Bao _ι2 oCao, i ₅ Mgo, ₆ oEuo, o ₅ ) S »1, OGa ₂ S ₃ (w = 1), this phosphor shows a quantum yield improved by 16% with an unchanged emission spectrum with an intensity maximum at 535 nm + 3 nm, or shows the phosphor (Ba ₀ , ₃₈ Mgo _{, 57} Euo, o ₅ ) S ^» 0.9 Ga ₂ S ₃ (w = 0.9) compared to the phosphor (Ba _0.2 oCa _0ι ι ₅ Mgo, ₆ oEuo, o ₅ ) S »1, θGa ₂ S ₃ (w = 1) a quantum efficiency increased by 16%, the intensity maximum of the emission spectrum of these phosphor compositions is in the range of 508 - 513 nm.

Further exemplary embodiments led to the phosphor compositions described in Table 1. This table shows the results of the quantum efficiency determination for phosphors which were produced analogously to the exemplary embodiment mentioned, with the A cation mixture Ba ₀ , ₂ oCao, ₁₅ Mgo, 6oEUo, o ₅ or the A cation mixture Ba ₀ , ₃ 8Mg ₀ , 57Euo, o5 but each with a different ratio w = B ₂ S ₃ / AS. The quantum efficiency increases significantly if w is chosen to be both lower and higher than 1, the emission wavelength remaining unchanged at a maximum emission intensity of 532 nm - 538 nm or 508 nm - 513 nm. For w = 1, 2, a decrease in quantum efficiency, an increase in reflectivity and another maximum of the emission wavelength of 548 nm was found, which indicates that the range of existence of the relevant phosphor formation has been exceeded. In particular, the emission wavelength of 548 nm indicates the formation of a calcium-rich thiogallate grating. This limit value varies somewhat depending on the exact composition of the cation mixture A. Due to the complex reaction mechanisms for the formation of the phosphor compositions mentioned in the exemplary embodiments and the modification of the atomic crystal structure resulting from the composition changes, several effects probably contribute to the observed dependence of the quantum efficiency on the cation ratio A: B. On the one hand, the change in the A: B ratio can contribute to a better implementation of the reaction product. This avoids disadvantageous secondary products and remaining precursors and intermediates. On the other hand, the installation of the activator Eu ^{2+ can be} favored in terms of more complete and trouble-free installation in the crystal lattice of the thiometalates. It can also be important to achieve a more favorable sulfur stoichiometry in line with the balance sheet, which can be better adapted to the local atomic cation composition according to the model of coreshell formation. Overall, the changed phosphor composition leads to an increased perfection of the phosphor product and / or to a reduction in QE-reducing non-radiative recombination centers.

Figure 1 shows the emission spectrum of the phosphor

(Bao, 2oCao, i5Mgo, 6oEuo, o5) S ^» 1, 1 Ga ₂ S ₃ , which is described in the exemplary embodiment. The emission band lies in the green spectral range between about 460 nm and 620 nm. The emission maximum is 538 nm, the mean wavelength is 544 nm. The color locus components are x = 0.306; y = 0.641. The quantum efficiency reaches 78% with narrow-band excitation at 400 nm. In comparison, the quantum efficiency of the phosphor with w = 1.0 is 62%.

This phosphor can be excited well by short-wave radiation between 300 and 450 nm. It is particularly advantageous for use with LEDs for color conversion, as a so-called LED converter. The emission radiation of a UV-emitting LED is converted into visible light (here green or blue-green) or white light (mixture of red, green and blue emitting phosphors) using one or more phosphors. A second variant, when using a blue LED, is the use of one phosphor or two phosphors (for example yellow- or green- and red-emitting phosphors), so that white light also results here. Technical details on this can be found, for example, in US Pat. No. 5,998,925. These phosphors can be applied as LED converters, for example, in full encapsulation using epoxy resins. For this purpose, the phosphor powder is dispersed in an epoxy resin, placed as a drop on the chip and cured. It is important here that the thiometalates have a similarly non-polar surface as the likewise non-polar resin, which leads to good wetting. Further advantages lie in the fact that mixtures with other phosphors such as YAG: Ce or YAG: Ce -based phosphors work well because the specific weight of the two phosphor classes is similar, so that no segregation occurs due to sedimentation effects with a comparable particle size. The specific weight of typical thiometalates is approximately 4.4 to 4.5 g / cm ³ , while that of YAG: Ce-based phosphors is typically 4.6 to 4.7 g / cm ³ . Sedimentation in the resin can be minimized by average particle sizes <5μm, especially around 2 + 1 μm. The particle size is adjusted by grinding, for example in ball mills.

Table 1 :

Results of the quantum efficiency determination for phosphors with the A cation _mixture Ba _0ι 2oCa ₀ , i5Mgo, 6oEuo, o5 or Ba ₀ , 38Mgo, 57Eu ₀ , o5 but each with a different B ₂ S ₃ / AS ratio w

Claims

Expectations

1. Highly efficient phosphor from the class of thiometalates, starting from the general formula AB ₂ S: D ²⁺ , where A is selected at least one divalent cation from the group Ba individually or in combination with Mg and / or Ca, and where B is at least is a trivalent cation from the group AI, Ga, Y and is selected as activator D europium and / or cerium, characterized in that the

The composition of the phosphor is set so that it corresponds to the general formula (AS) »w (B ₂ S ₃ ), the factor w being both in the range 0.8 w w 0,9 0.98 and in the range 1, 02, w <1, 2 can be.

2. thiometalate phosphor according to claim 1, characterized in that gallium is chosen as the cation B, which can be partially replaced by aluminum.

3. thiometalate phosphor according to claim 1, characterized in that a combination of the metals Mg, Ca, Ba alone is chosen as the cation A.

4. thiometalate phosphor according to claim 1, characterized in that Europium is chosen as the activator (which A is substituted).

5. thiometalate phosphor according to claim 1, characterized in that (AS) ^» w (Ga ₂ S ₃ ), where A = Mg _a Ca _b Ba _c Eu _t with a + b + c + t = 1 with the areas: 0.4 ≤ a <0.8; 0.05 ≤ b ≤ 0.35; 0.05 ≤ c ≤ 0.4; 0.01 <t <0.1; 0.8 ≤ w ≤ 0.98 or 1, 02 ≤ w <1, 2.

6. thiometalate phosphor according to claim 1, characterized in that (AS) ^» w (Ga ₂ S ₃ ), where A = Mg _a Ba _b Eu _t with a + b + t = 1 with the areas:

0.4 ≤ a <0.8; 0.1 <b ≤ 0.59; 0.01 ≤ t ≤ 0.1; 0.8 ≤ w ≤ 0.98 or 1, 02 <w <1, 2.

7. A process for producing a highly efficient phosphor from the class of thiometalates according to one of the preceding claims, characterized by the following process steps:

a) Preparation of a suspension of nitrates according to the desired

The composition of claims 1 to 6; b) drying this suspension to a residual moisture content of <1% by weight at T ≤ 300 ° C. to produce a finely dispersed nitrate mixture;

c) grinding the nitrate mixture in a mortar mill at room temperature for 10 min to 60 min, preferably 20 min.

d) pyrolysis of the ground nitrate at 500-700 ° C, preferably at

600 ° C, in Ar or N ₂ atmosphere to produce a finely dispersed metal oxide mixture with the desired composition.

e) First reaction of the metal oxide mixture at 800-1000 ° C, preferably 900-950 ° C, in a flowing H ₂ S or CS ₂ atmosphere or combinations thereof for 1-6 hours, preferably 4 hours.

f) grinding the reaction mixture as in step c;

g) Second reaction at 800-1000 ° C, preferably 900-950 ° C, in a flowing H ₂ S or CS ₂ atmosphere or combinations thereof for 1 -6 hours, preferably 2 hours.

8. The method according to claim 7, characterized in that in step e) and g) the flow rate is 50-500 ml / min, preferably 120 ml / min, and the gas atmosphere of H ₂ S or CS ₂ and Ar or N ₂ the carrier gas consists of 10-50% H ₂ S or CS ₂ or mixtures thereof, preferably 30% H ₂ S or CS ₂ or mixtures thereof.

9. The method according to claim 7, characterized in that in steps e) and g) the heating up to the reaction temperature is 0.5-20 K / min, preferably 10 K / min.

10. The method according to claim 7, characterized in that in steps e) and g) the cooling is 0.5-20 K / min, preferably 10 K / min.

11. Use of the phosphors according to claims 1-6, characterized in that they are used individually, for example in UV or blue-emitting LEDs for color conversion, in combination with other phosphors of claims 1-6 and in combinations with other known phosphors.

2. Use of the phosphors according to claims 1-6, characterized in that they e.g. Plasma displays can be used individually, in combination with other phosphors of claims 1-6 and in combinations with other known phosphors, in order to convert the short-wave plasma discharge radiation into visible light.