WO2006081803A1 - Illuminant emitting yellow light and light source provided with such an illuminant - Google Patents

Abstract

The illuminant with the structure A3SiO5:D, where A=(Sr,Ba,Ca) and D=Eu, provides a yellow-orange emission and is characterised by high stability. The above may be used for light sources of various types.

Description

Yellow emitting phosphor and light source with such phosphor

Technical area

The invention is based on a yellow-emitting phosphor and also relates to a light source, in particular LED, with such a phosphor. The phosphor belongs to the class of orthosilicates.

State of the art

So far, there are only a small number of technically usable phosphors, which are excitable in the UV and especially in the blue spectral range and emit in orange yellow (dominance wavelength 580-590 nm). Although the so-called Ca-alpha sialons emit in the stated range, they absorb the light of a blue LED only weakly. Due to the low absorption, the LED efficiency of an orange-yellow conversion LED is too low compared to the chip LED. The same goes for most other eligible phosphors. Long-wave emitting garnets generally show a very broad emission with a correspondingly low visual efficiency. In addition, the known long-wave, mostly Gd-containing garnets have never been used in practice because of their strong temperature dependence.

This is why conversion LEDs, which generally have a higher color stability, are not technically used today in traffic lights and turn signals.

An oxyorthosilicate of the stoichiometry A3SiO5: D is hitherto known only from DE 102 59 946. There it is a Ba3SiO5: Eu, Mn, which emits in the yellow orange at about 590 nm. It is used together with other phosphors. Furthermore, WO 2004/085570 describes an oxyorthosilicate Sr3SiO5: Eu. Presentation of the invention

It is an object of the present invention to provide a phosphor which emits orange-yellow, which can be excited in particular in the emission range of typical UV and blue LEDs.

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

Another object is to provide a light source, in particular an LED, with such a phosphor.

This object is solved by the characterizing features of claim 10. Particularly advantageous embodiments can be found in the dependent claims.

The phosphors of this invention may also be used in conjunction with other UV or blue light sources such as molecular radiators (e.g., in-discharge lamp), blue OLEDs, or in combination with blue EL phosphors.

The phosphor according to the invention makes it possible to produce color-stable, efficient turn signal or traffic light yellow LEDs or LED modules based on a conversion LED. Other areas of application include LEDs with good color rendering, color-on-demand LEDs or white OLEDs.

The newly synthesized phosphor A ₃ SiO ₅ : Eu emits with high efficiency. In the case of A = Sr, it is very narrow-band (FWHM <80 nm at 460 nm excitation) in orange-yellow. The dominant wavelength is 581 nm in the case of excitation at 460 nm. The Eu doping is 3%. It can be delayed by increasing the Eu content for a longer time. Conversely, the emission shifts to shorter wavelengths with low Eu content.

The phosphor is well excitable in the range 250-500 nm as well as in the extreme UV below 220 nm. Here, A = Sr, Ba, Ca may be alone or in combination.

The phosphor according to the invention can be prepared, for example, in the case of A = Sr from nine parts of SrCO ₃ , whereby, according to the doping, this material is partially substituted by Eu ₂ O ₃ , as well as a part of Si ₃ N ₄ . Alternatively, the route goes with three parts SrC03 and one part SiO2. The starting substances are mixed and annealed at high temperatures in forming gas (first synthesis: for example, at 1500 to 1600 ⁰ C, forming gas). The resulting phase was clearly identified by XRD as the Sr3SiO5 phase. In this case, a high proportion of Eu as doping cause a slight shift of the reflections, as known per se for doping.

Essential for the outstanding properties is the basic structure of the phosphor, without it being important to an exact adherence to the stoichiometry. The phosphor is very stable to radiation, which allows use in high-brightness LEDs.

The Sr can in particular be partially or completely substituted with Ba or Ca, so that other wavelengths can be achieved. Preferably, the Sr3SiO5 structure is retained, introducing only partial amounts of Ca and Ba.

In particular, this phosphor can be excited efficiently by a blue-emitting LED, in particular of the InGaN type. It is also suitable for use with other light sources, and in particular for use with other phosphors to produce very high Ra white light.

With several, in particular three, phosphors whose typical quantum efficiency is well over 70%, and which absorb very well in the range of short-wave UV or blue radiation, especially at 450 to 455 nm, where the strongest chips are available, can be provide efficient, especially warm white, LEDs with a color rendering index Ra of up to 97. Depending on the desired optimization, a typical Ra value is 88 to 95. In addition to the new yellow-orange oxyorthosilicate, a green-yellow phosphor is added, for example YAG: Ce, (Lu, Y) 3 (Al, Ga) 5O12: Ce , SrSi2O2N2: Eu or (Sr ₁ Ba, Ca) 2SiO4: Eu. These emit in the yellow-green range with peak emission at 530 to 570 nm. As additional red-emitting component with peak emission at 600 to 650 nm, in particular 605 to 615 nm, for example, a nitrile silicate such as (Sr, Ca) 2Si5N8: Eu or a sulfide.

In detail, an LED is further proposed, which is designed as a yellow-orange emitting luminescence conversion LED, with a primary radiation source, which is a chip emitting in the blue or UV spectral region and a layer of phosphor preceding it, which partially or fully converts the radiation of the chip, the phosphor being of the class of the above-described orthosilicates doped with europium.

The oxyorthosilicate is in a particularly suitable embodiment, a mixed silicate, and in particular the general formula (Sr _1-xy Ca _x Ba _{y) 3} Si0 _5: Eu _z where x ≤ 0.3, y ≤ 0.8, y ≤ preferably 0, 5, and x + y ≤ 0.8, and z ≤ 0.45. The often applicable codoping with Mn in addition to Eu shows here rather as counterproductive and leads to a significant deterioration of the phosphor properties. For x, a preferred lower limit of 0, more preferably 0.05, for y, is a preferred lower limit of 0.1.

An alternative is also pure Ba-oxy-orthosilicate Ba (1-z) 3SiO5: Euz and Ca-oxyorthosilicate Ca (1-z) 33SiO5: Euz. Here z is preferably <0.35.

In this case, the proportion z of the Eu should advantageously amount to a maximum of z = 0.45, since at even higher values the efficiency decreases. Preferably, z <0.15. The minimum proportion should be z = 0.03.

As a light source is particularly suitable an LED. Preferably, the emission of the chip is such that it has a peak wavelength in the range 445 to 465 nm, in particular 450 to 455 nm. Thus, the highest efficiencies of the primary radiation can be achieved.

Another field of application is a color-emitting LED (color-on-demand) whose emission is located in the orange-red to yellow region of the spectrum.

For the use in the LED standard procedures can be used. In particular, the following implementation options arise.

First, dispersing the phosphor into the LED encapsulant, for example a silicone or epoxy resin, and then applying it, for example, by casting, printing, spraying or, secondly, introducing the phosphor into a so-called molding compound and subsequent transfer molding process. Third, methods of near-chip conversion, ie applying the phosphors or their mixture on the Wafer processing level, after dicing the chips and after mounting in the LED housing. Reference is made in particular to DE 101 53 615 and WO 01/50540.

The invention further relates to an illumination system with LEDs, wherein the illumination system also contains electronic components. These convey, for example, the dimmability. Another task of the electronics is the control of individual LEDs or groups of LEDs. These functions can be realized by previously known electronic elements.

So far there is no such narrow-band yellow-orange emitting phosphor high efficiency, which is also insensitive to external influences and also by primary light sources that emit blue or UV, is well excitable. Such light sources are, in particular, UV or blue-emitting LEDs of the InGaN or InGaAIP type, as well as discharge lamps which use phosphors, as known per se, in particular high-pressure discharge lamps which have a high color rendering index Ra or are based on indium lamps which are either high-pressure or low-pressure can be operated. Due to its extraordinary radiation stability, the new phosphor is also suitable for discharge lamps, in particular for indium discharge lamps and in particular as a stable phosphor for discharge lamps with a high Ra, for example over Ra = 90.

characters

In the following the invention will be explained in more detail with reference to several embodiments. Show it:

FIG. 1 shows the emission spectrum of a phosphor according to the invention;

FIG. 2 shows an XRD spectrum of a phosphor according to the invention; Figure 3 shows the structure of a conversion LED;

FIG. 4 shows the excitation spectrum of a phosphor;

FIG. 5 shows the decrease in brightness of an LED as a function of the operating time;

FIG. 6 shows a low-pressure lamp with indium filling using a

Orthosilicate. Description of the drawings

A concrete example of the phosphor according to the invention is shown in FIG. It shows the emission of the phosphor Sr3SiO5: Eu with an Eu content of 3 mol% of the Sr occupied lattice sites. The emission maximum of the pure phosphor (peak) is 581 nm. The excitation was carried out at 460 nm. The FWHM is 72 nm. The dominant wavelength is 581 nm. The quantum efficiency is a good 80%.

FIG. 2 shows an XRD spectrum of this phosphor. The structure fits perfectly with the orthosilicate lattice A3SiO5 with the PDF number 26-984, but not with the common orthosilicate A2SiO4.

The construction of a light source for yellow light is shown explicitly in FIG. The light source is a semiconductor component with a chip 1 of the type InGaN with a peak emission wavelength of 440 to 470 nm, for example 460 nm, which is embedded in an opaque base housing 8 in the region of a recess 9. The chip 1 is connected via a bonding wire 14 to a first terminal 3 and directly to a second electrical terminal 2. The recess 9 is filled with a potting compound 5, which contains as main constituents an epoxy casting resin (80 to 90 wt .-%) and phosphor pigments 6 of a phosphors (less than 20 wt .-%). The phosphor is the Sr-Oxyorthosilikat presented as a first embodiment with 3% Eu. The recess 9 has a wall 17, which serves as a reflector for the primary and secondary radiation from the chip 1 and the pigments 6. The dominant wavelength at 581 nm just meets the specification for the yellow in traffic lights.

In general, the efficiency and the color rendering index Ra are adjusted by the level of doping with Eu, preferably a value for Eu of 2 to 4 mol% of the A.

In the case of a white LED with three phosphors, in addition to a new oxyorthosilicate, with A = Sr alone or predominantly (more than 55% portion A, in particular 55-80%), in particular also as a green emitting phosphor SrSi2O2N2: Eu and as a red one emissive phosphor used here, the nitridosilicate M _a Si _y N _z : Eu, which has as a permanent component Ca and as an admixture Sr in a proportion of 0 to 15 mol%. In other words, the nitridosilicate is through the Formula (Sr _x Ca _1-x ) _a SiyN _{z is characterized} by x = 0 to 0.15, wherein preferably y = 5 and z = 8 is selected. The combination of blue primary and red, yellow-green and orange-yellow secondary radiation mixes to warm white with high Ra from 88 to 97.

The excitation spectrum of a typical phosphor is shown in FIG. It shows the good excitability in the range 250 to 500 nm and the further good excitability in the range below 220 nm, which justifies a good suitability for the conversion of VUV sources, for example excimer radiators. Particularly good is the excitability at 320 to 460 nm.

FIG. 5 shows the decrease in brightness of the phosphor according to the invention during intensive irradiation with a laser for more than 100 minutes to demonstrate the high radiation stability. A decrease is in no way recognizable. The stability is thus significantly better than previously known yellow-orange phosphors, such as BasSi5N8: Eu.

FIG. 6 shows a low-pressure discharge lamp 20 with a mercury-free gas filling 21 (schematized) which contains an indium compound and a buffer gas analogously to WO 02/10374, wherein a layer 22 made of orthosilicate Sr ₃ SiO ₅ : Eu is attached to the inside of the piston 23. The particular advantage of this arrangement is that this orthosilicate is ideally adapted to the indium radiation because it has significant proportions in both the UV and in the blue spectral range, both of which are equally well absorbed by this orthosilicate, which it against in this use against makes the previously known phosphors superior. These known phosphors absorb appreciably either only the UV radiation or the blue radiation of the indium, so that the indium lamp according to the invention shows a significantly higher efficiency. This statement also applies to a high-pressure indium lamp as known per se from US Pat. No. 4,810,938.

Claims

claims 1. Yellow-orange emitting phosphor from the class of orthosilicates, which has substantially the structure A3SiO5: D, characterized in that the phosphor as component A = Sr, Ba and / or Ca alone or in combination, wherein the activating doping D is made of Eu. 2. Phosphor according to claim 1, characterized in that in the representation as (Sr1-x-yBayCax) 3SiO5: Euz the proportion of Eu A is between z = 0.03 and 0.45. 3. Phosphor according to claim 1, characterized in that A Sr is alone. 4. The phosphor according to claim 1, characterized in that A Ba is alone. 5. Light source with a primary radiation source that emits radiation in the short-wave range of the optical spectral range in the wavelength range 140 to 480 nm, said radiation is completely or partially converted by means of a first phosphor according to one of the preceding claims into secondary longer-wave radiation in the visible spectral range. 6. Light source according to claim 5, characterized in that the primary radiation source is a light-emitting diode based on InGaN or InGaAIP or a discharge lamp on a low-pressure or high-pressure basis, in particular with an indium-containing filling, or an electroluminescent lamp is used, wherein A in particular alone or predominantly with more than 55% share Sr. 7. Light source according to claim 5, characterized in that a part of the primary radiation is further converted by means of further phosphors into longer-wave radiation, wherein the phosphors are particularly suitably chosen and mixed to produce white light. 8. A process for producing a high-efficiency phosphor, characterized by the following process steps: a) providing the starting materials SiO ₂ and / or Si ₃ N ₄ , SrCO ₃ , BaCO ₃ , CaCO ₃ and the Eu precursor, in particular Eu2O3, in a substantially stoichiometric ratio; b) mixing the starting materials and annealing in a W or Mo crucible using a flux; c) wherein the annealing of the mixture at about 1300 to 1700 ⁰ C, preferably 1500 to 1600 ⁰ C takes place. 9. Light source according to claim 7, characterized in that the light source has a color temperature of at least 2000 K, in particular 2700 to 3500 K has. 10. Light source according to claim 5, characterized in that the emission of the chip has a peak wavelength in the range 445 to 475 nm, in particular 450 to 455 nm. 11. Light source according to claim 5, characterized in that the emission of the ortho- silicate has a peak wavelength in the range 575 to 620 nm, in particular 580 to 590 nm. 12. Light source according to claim 5, characterized in that a Ra of at least 88 is achieved, in particular more than 90.