Light emitting diode with wavelength conversion

(54) LIGHT EMITTING DIODE WITH WAVELENGTH CONVERSION

(75) Inventors: Bert Braune, Wenzenbach (DE);

Marcus Ruhnau, Teublitz (DE)

(73) Assignee: Osram Opto Semiconductors GmbH

(DE)

( * ) Notice: Subject to any disclaimer, the term of this patent is extended or adjusted under 35 U.S.C. 154(b) by 9 days.

(21) Appl. No.: 10/429,916

(22) Filed: May 5, 2003

(65) Prior Publication Data

US 2004/0094757 Al May 20, 2004

Related U.S. Application Data

(60) Provisional application No. 60/387,338, filed on Jun. 10, 2002.

(30) Foreign Application Priority Data

May 6, 2002 (DE) 102 20 137

4,365,052 A 12/1982 Reeh et al 528/92

4,481,422 A * 11/1984 deMarco et al 250/459.1

5,811,924 A * 9/1998 Okumura et al 313/487

6,066,861 A 5/2000 Hohn et al 257/99

6,552,487 Bl 4/2003 Ellens et al.

6,614,170 Bl* 9/2003 Wang et al 313/498

6,642,652 Bl* 11/2003 Collins et al 313/512

6,650,044 Bl* 11/2003 Lowery 313/502

6,669,866 Bl 12/2003 Kummer et al.

6,717,355 Bl* 4/2004 Takahashi et al 313/503

2001/0048966 Al 12/2001 Tramble et al.

FOREIGN PATENT DOCUMENTS

DE 26 42 465 9/1976

DE 26 42 465 3/1978

EP 0 039 017 4/1981 59/42

EP 1 024 185 A2 8/2000 11/2

EP 1 024 185 A3 9/2001 11/2

WO WO 98/12757 3/1998

WO WO 01/08452 2/2001

WO WO 01/08453 2/2001

WO WO 01/51585 Al 7/2001 11/2

OTHER PUBLICATIONS

Copy of International Search Report, PCT/DE03/01452.

* cited by examiner

Primary Examiner—Joseph Williams

(74) Attorney, Agent, or Firm—Fish & Richardson PC.

(57) ABSTRACT

The invention relates to a wavelength-converting reaction resin compound into which a wavelength-converting luminescent material and a thixotroping agent are mixed, wherein the luminescent material contains inorganic luminescent particles. The thixotroping agent is present, at least in part, in the form of nanoparticles. Methods of producing the reaction resin compound and light-emitting diode elements having such reaction resin compounds are indicated.

21 Claims, 2 Drawing Sheets

1

LIGHT EMITTING DIODE WITH
WAVELENGTH CONVERSION

CROSS-REFERENCE TO RELATED

APPLICATIONS 5

This application claims the benefit of U.S. Provisional Application No. 60/387,338, filed Jun. 10, 2002.

FIELD OF THE INVENTION 10

The invention relates to a wavelength-converting reaction resin compound and a method of producing it and a lightemitting diode element having a reaction resin compound.

15

BACKGROUND OF THE INVENTION

A wavelength-converting reaction resin compound of the type initially referenced is known from WO 98/12757. A wavelength-converting reaction resin compound is 2o described therein in which an inorganic luminescent pigment powder having grain sizes = 20 urn and a mean grain diameter d50 = 5 urn is dispersed in a transparent casting resin.

In the field of light-emitting diodes (LEDs), the use of 2s conversion luminescent materials makes it possible to produce multicolored light by means of a single LED chip. In this process, at least part of the radiation emitted by an LED chip is absorbed by the conversion luminescent material, which then in turn emits radiation of a different wavelength 30 than the absorbed radiation. This radiation emitted by the luminescent material, and radiation emitted by the LED chip and not absorbed by the luminescent material, together then produce the multicolored radiation.

In known light-emitting diode elements made with reac- 35 tion resin compounds of the type initially referenced, luminescent materials having a density between 4 and 5 g/cm3 are used. The luminescent powders used have luminescent particles whose mean diameter is generally less than 5 urn.

When larger luminescent particles are used in conven- 40 tionally available reaction resin systems such as epoxy resin, they precipitate during the production process.

In particular during the phase of heating up a resin, shortly before the beginning of the hardening process, its viscosity drops far enough that luminescent particles are no longer 45 held in suspension and precipitate out.

As proposed in WO 98/12757, by adding aerosil to the casting resin for luminescent particles having a mean grain diameter d50 = 5 urn, this sedimentation may be reduced sufficiently so that very good distribution of the luminescent 50 particles in the casting resin may be achieved after the hardening process of the casting resin.

With this method of thixotroping by means of aerosil, it is also possible to use luminescent materials with larger particles if larger volumes of aerosil are added. But because 55 adding conventional aerosil reduces the transparency of the resin material, for the conventional types the volume of such aerosil to be added is limited to such a degree that in the case of YAG:Ce luminescent material, for example, the limit of the mean particle diameter is approximately 5 um. 60

SUMMARY OF THE INVENTION

The invention is based on the problem of developing a thixotroping of reaction resin compounds with which it is 65 possible to prevent to a very great degree the sedimentation of luminescent particles having a mean particle diameter

2

greater than 5 um, preferably greater than 5 um and less than or equal to 20 um, while at the same time retaining sufficient transparency of the reaction resin compound.

In the case of the wavelength converting reaction resin compound according to the invention, at least part of the thixotroping material is present in the form of nanoparticles. Such nanoparticles are preferably particles having a mean particle diameter between 1 nm and 100 nm.

This permits inorganic luminescent particles having a mean particle diameter greater than 5 um to be dispersed advantageously in the reaction resin, without the transparency of the reaction resin compound being degraded in an unacceptable manner by the thixotroping.

The inorganic luminescent particles can advantageously have a d50 value, measured in Q3, which is between 10 um inclusive and 20 um inclusive.

It is preferable if the thixotroping agent contains nanoparticles having a d50 value measured in Q3 between 1 nm inclusive and 25 nm inclusive. It is particularly preferable if the d50 value is between 5 nm inclusive and 15 nm inclusive, especially between 9 nm inclusive and 12 nm inclusive.

As used herein, the "d50 value measured in Q3" for a distribution of particles is the median particle diameter of a cumulative volume distribution. This means that 50% of the volume of particles have particles with a diameter greater than the d50 value and 50% of the volume of particles have particles with a diameter less than the d50 value.

It is preferable if the reaction resin compound has at least one material from the group consisting of epoxy resin, silicone resin and acrylic resin. These are advantageously the reaction resin compounds traditionally used in optoelectronics, for example for LED chips. Alternatively, other optically transparent reaction resin compounds may be used, for example heteropolymers such as cellulose derivatives, polycarbonates, polysulfones, polyimides, polyamides, etc., polyolefins (such as polyethylene), styrol polymerisates, polyurethanes, etc.

It is preferable if the thixotroping agent contains a colloidal Si02 solution. The following materials are also usable as thixotroping agents: titanium dioxide, zirconium oxide or Si02. Especially suitable here are pyrogenically produced oxides that also have a surface coating matched to the reaction resin. Examples in this regard are surface-treated aerosils (Si02), such as those from the Degussa company, which correspond in terms of their properties to colloidal Si02. Coated aerosil powders have the advantage that, while they have a thixotropic effect similar to that of the colloidal Si02 solution, they can be added to the reaction resin as powder, whereas in the case of a mixture of reaction resin and colloidal solution, it is preferable if the solvent is extracted before the hardening. Other nanoparticles, whether produced in a colloid chemistry process, made by a progenic process in a gas phase reaction or produced in a colloidalsolution-gel procedure are also conceivable. In principle, all methods of production that are able to produce particles of nanometer size are suitable for the nanoparticles.

It is especially preferable if the reaction resin compound is suitable for enclosing a radiation-emitting body, especially a semiconductor chip, whose radiation emission spectrum includes at least radiation from the ultraviolet, blue or green spectral regions. In this connection, it is advantageous for it to be pervious to at least part of the radiation emitted by the body, and for the luminescent material to contain, preferably, at least luminescent particles from the group of garnets doped with rare earths, thiogallates doped with rare earths, aluminates doped with rare earths or orthosilicates doped with rare earths.