Patent Application
20130140981
The invention is based on a phosphor according to the preamble of claim 1 and a light source equipped with such a phosphor according to claim 8, in particular a conversion LED. Such conversion LEDs are suitable for general lighting, in particular.
U.S. Pat. No. 7,489,073 discloses a conversion LED which uses a modified regular orthosilicate as phosphor.
Stable green phosphors, in particular having an emission maximum around 520-540 nm, are scarcely available. That makes it more difficult to use conversion LEDs in display backlighting and limits the optimization of high-CRI LEDs or warm-white LEDs. Hitherto, in products, orthosilicates have principally been used as green phosphors for this range. Although they have high quantum efficiencies, they exhibit an inadequate aging behavior in LEDS.
U.S. Pat. No. 7,489,073 discloses a nitride-orthosilicate having the composition AE2-x-aRExEuaSiO4-xNx (AE=Sr, Ba, Ca, Mg; RE=rare earths, in particular Y and/or La). EA or else AE here stands for alkaline earth metal elements. The incorporation of YN and/or LaN results in a
red shift in the spectral position and usually an improvement in the quantum efficiency of the phosphor. With the production method described therein, the LED aging method of said phosphor is already significantly better than in the case of the conventional orthosilicates or other green Sion phosphors such as e.g. Ba3Si6O12N2:Eu.
For many applications, such as e.g. for LCD backlighting, the stability in humid surroundings and at relatively high temperatures is still not optimal, however.
The object of the present invention is to provide a phosphor according to the preamble of claim 1 which allows the properties of nitridic phosphors to be adapted to specific tests in a targeted manner.
This object is achieved by means of the characterizing features of claim 1.
Particularly advantageous configurations are found in the dependent claims.
According to the invention, a novel nitridic phosphor is now provided. This includes blue- or blue-green- to yellow-emitting phosphors which can be excited in particular in the emission range of typical UV and blue LEDs and at the same time have a very high stability in the LED. The phosphors can find applications in particular in LEDs with good color rendering, in LEDs for LCD backlighting, color-on-demand LEDs or white OLEDs.
White LEDs are increasingly gaining in importance in general lighting. In particular, there is a rising demand for warm-white LEDs having low color temperatures and good color rendering and at the same time high efficiency. Against the background of imminent prohibition of the general service incandescent lamp, which has low energy efficiency, alternative light sources having the best possible color rendering (CRI) are increasingly gaining in importance. Many consumers value luminous means having a light spectrum similar to an incandescent lamp.
The phosphors have to meet a series of requirements: a very high stability in relation to chemical influences, for example oxygen, moisture, interactions with potting materials, and in relation to radiation. In order to ensure a stable color locus as the system temperature rises, phosphors having a low temperature quenching behavior are additionally required.
Such phosphors are used in white LEDs and color-on-demand LEDs.
The excitation of such phosphors preferably takes place using short-wave radiation in the UV and short-wave blue, in particular in the range of 360 to 480 nm.
The invention is based on the provision of phosphors from the substance classes of the nitrido-orthosilicates.
It has been found that a deficiency of SiO2 leads to higher quantum efficiencies. This results in a composition of the batch mixture for the stabilized nitrido-orthosilicate of AE2-x-aRExEuaSi1-yO4-x-2yNx (AE=Sr, Ba, Ca, Mg; RE=rare earths, in particular Y and/or La), wherein x is preferably between 0.003 and 0.02, and a is preferably between 0.01 and 0.2. The factor Y crucial for the SiO2 deficiency is in the range of between 0<y≦0.1, preferably in the range of 0.002≦y≦0.02. In the method described here for producing a stabilized nitrido-orthosilicate, in one embodiment the starting material side is additionally preferably extended by Si3N4 and La2O3 or Y2O3.
For the preparation of AE2-x-aRExEuaSi1-yO4-x-2yNx either AECO3, SiO2 (La, Y)N and Eu2O3 or AECO3, SiO2, Si3N4, (La, Y)2O3 and Eu2O3 are required as starting substances. Furthermore, in particular fluorides and chlorides such AECl2, AEF2, and also NH4Cl/NH4F, H3BO3, LiF and cryolites, and combinations thereof, can be used as flux.
Essential features of the invention in the form of a numbered enumeration are:
The invention will be explained in greater detail below on the basis of a number of exemplary embodiments. In the figures:
(approximately 15 to 40% by weight) as main constituents. A first phosphor is a green-emitting nitrido-orthosilicate phosphor AE2-x-aRExEuaSi1-yO4-x-2yNx where AE is Ba and where RE is Y. Other exemplary embodiments use at least one of the following elements: for AE=Ba, Sr, Ca, Mg and for RE=La, Y. In addition, a red-emitting phosphor, for example an alumonitridosilicate or calsin, is used as second phosphor. The cutout has a wall 17 serving as a reflector for the primary and secondary radiation from the chip 1 and the phosphors 6, respectively. Concrete exemplary embodiments of further phosphors, for generating white, are (Lu,Y,Gd)3(Al,Ga)5O12:Ce or else a Cu-modified CaAlSiN3:Eu.
In principle, it is possible to use the phosphor mixture as a dispersion, as a thin film, etc., directly on the LED or else, as known per se, on a separate carrier disposed in front of the LED.
Other suitable light sources are fluorescent lamps or high-pressure discharge lamps in which the novel phosphor can be used for converting the primary radiation, alone or in combination with other phosphors.
The novel sub-stoichiometric phosphor is produced in the following way:
The starting materials analogous to the batch mixtures 1 to 4, preferably together with a suitable flux, are weighed in and homogenized. Afterward, the starting material mixture is annealed for a number of hours under a reducing atmosphere (in particular under N2 or Ar or a mixture of N2/H2 or Ar/H2) at temperatures of between 1000° C. and 1500° C. This can be followed by a second annealing, likewise under a reducing atmosphere (in particular under N2 or Ar or a mixture of N2/H2 or Ar/H2) at temperatures of between 800° C. and 1400° C. The synthesis is carried out in a suitable furnace, such as e.g. tubular furnace or chamber furnace.
73.4 g SrCO3, 98.0 g BaCO3, 30.8 g SiO2, 0.1 g Si3N4, 0.4 g La2O3 and 7.2 g Eu2O3;
Even as a result of the incorporation of lanthanum and nitrogen as in comparative example 2, a significant improvement in the LED stability can already be discerned at relatively high temperatures and in a humid environment. This stability is still not optimal, however, for many applications, such as e.g. for LCD backlighting.
The new batch stoichiometry described here in accordance with exemplary embodiment 3 or 4, respectively, with a corresponding deficiency of SiO2 demonstrably leads to an improved LED stability, primarily in a humid environment and at relatively high temperatures.
ordinate, and the abscissa is the time in minutes. It is evident that exemplary embodiments 3 and 4 are approximately equivalent to one another and both are appreciably superior to comparative examples 1 and 2.
The relative quantum efficiencies QE460 of the novel phosphors in accordance with exemplary embodiments 3 and 4 upon excitation with 460 nm is 3% higher than in the case of comparative example 2.
The presented nitrido-orthosilicates of the form AE2-x-aRExEUaSi1-yO4-x-2Nx are typically prepared from ARCO3, SiO2, REN and Eu2O3 or AECO3, SiO2, Si3N4, (RE)2O3 and Eu2O3 as starting substances. In the latter, the rare earths are used as (RE)2O3 if trivalent oxides are preferably formed. In the case of rare earth oxides which are preferably present as mixed oxides as, for example, Tb is usually present as a III/IV mixed oxide Tb4O7, the mixed oxides are preferably used. Furthermore, instead of REN or RE oxide in conjunction with Si3N4, it is also possible to use In, Y or Sc as nitride or as a combination of oxide and Si3N4.
Furthermore, in particular fluorides and chlorides such as AECl2 or RECl2, AEF2 or RECl2 but also NH4Cl/NH4F, H3BO3, LiF and cryolites, and combinations thereof, can be used as flux.
The starting materials analogous to the batch mixtures 1 to 15, preferably together with a suitable flux, are weighed in and homogenized. Afterward, the starting material mixture is annealed for a number of hours under a reducing atmosphere (in particular under N2 or Ar or a mixture of N2/H2 or Ar/H2)
at temperatures of between 1000° C. and 1500° C. This can be followed by a second annealing, likewise under a reducing atmosphere (for example under N2 or Ar or a mixture of N2/H2 or Ar/H2) at temperatures of between 800° C. and 1400° C. The synthesis is carried out in a suitable furnace, such as e.g. tubular furnace or chamber furnace.
Batch mixture 6:
Table 1 below reproduces a comparison of the spectral properties on the basis of the example of an La/N doping with and without SiO2 deficiency.
The spectral data of further exemplary embodiments are presented in Table 2 below.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2010 030 473.5 | Jun 2010 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2011/059412 | 6/7/2011 | WO | 00 | 12/20/2012 |
