WO2006011096A2

WO2006011096A2 - Photonic band gap material comprising activator ions

Info

Publication number: WO2006011096A2
Application number: PCT/IB2005/052345
Authority: WO
Inventors: Cornelis Reinder Ronda
Original assignee: Philips Intellectual Property & Standards Gmbh; Koninklijke Philips Electronics N. V.
Priority date: 2004-07-22
Filing date: 2005-07-14
Publication date: 2006-02-02
Also published as: TW200621945A

Abstract

L'invention concerne l'utilisation d'ions activateurs dans des matériaux à bande interdite photonique et des céramiques luminescentes. Ces matériaux à bande interdite et céramiques luminescentes jouent un rôle important au niveau des DEL comme sources lumineuses dans des applications où une radiance élevée est recherchée ou des DEL sont utilisées dans des systèmes optiques. Les propriétés optiques des DEL courantes sont telles que la radiance est relativement faible et ne peut être augmentée par les moyens standard. L'invention concerne par conséquent l'amélioration de la radiance des dispositifs électroluminescents par le biais de l'utilisation d'ions activateurs dans des matériaux à bande interdite photonique et des céramiques luminescentes. Une caractéristique essentielle selon l'invention consiste par conséquent à fournir des ions activateurs dans des matériaux à bande interdite photonique et des céramiques luminescentes qui permettent d'accroître le transfert d'énergie, ce que l'on peut réaliser en premier lieu en faisant appel à des ions de terre rare et, en second lieu, par le biais d'une distance moyenne plus grande entre les ions activateurs que de telles structures permettent.The invention relates to the use of activator ions in photonic bandgap materials and luminescent ceramics. These bandgap and luminescent ceramics play an important role in LEDs as light sources in applications where high radiance is desired or LEDs are used in optical systems. The optical properties of the current LEDs are such that the radiance is relatively low and can not be increased by standard means. The invention therefore relates to improving the radiance of electroluminescent devices through the use of activator ions in photonic bandgap materials and luminescent ceramics. An essential feature of the invention therefore is to provide activating ions in photonic bandgap materials and luminescent ceramics which increase energy transfer, which can be achieved primarily by to rare earth ions and, secondly, through a greater average distance between activating ions than such structures allow.

Description

Photonic Band Gap Material Comprising Activator Ions

The present invention relates to the use of activator ions in photonic band gap materials and luminescent ceramics.

Photonic band gap materials and luminescent ceramics play an important role for LEDs (light emitting diodes) as light sources in applications where either a high radiance is desirable or LEDs are used in optical systems. The optical properties of current LEDs are such that the radiance is rather low and cannot be increased by standard means. Although LEDs offer high switching speeds their low radiance, i.e. the low amount of lumens generated per m² and per sr makes them less suitable for optical systems. LEDs are made using so-called luminescent materials that emit photons once they have been excited electrically or optically. In many regular luminescent materials used to generate emission, relatively high concentrations of rare earth ions are needed, either to get sufficiently high an absorption or sufficiently efficient an energy transfer up to several mole percents.

In US 2002/0179886 Al are disclosed preferred phosphors, which include a host crystal or matrix and a small amount of activator. According to the description heavy metal ions or rare earth ions are used as activators generally.

The use of rare earth ions results, just to mention two examples, in many cases in green Tb³⁺ emission and orange or red Eu³⁺ emission, whereas excited states of these ions would allow more colors. Moreover, some ions do not show emission at higher concentrations at all, due to concentration quenching or distribution of the excitation energy over two ions mediated by a process called cross relaxation and subsequent quenching on each of the ions like for example on Sm³⁺ and Dy³⁺.

Transition metal ions for which optical absorption and emission originates from d-d optical transitions cannot be used either without using energy transfer as the optical absorption is too weak. The so caused low radiance of LEDs hampers or prevents LEDs from applications where high radiances are needed like in endoscopy or where LEDs are applied in optical systems to generate a specific light distribution like in car lamps. These deficiencies are illustrated by the following table.

Light source Radiance [10⁶cd /m7sr]

Fluorescent lamp 0.05

LED 1 - 10

Halogen lamps 20 - 30

MPXL (micro rjower xenon light) 100

UHP (ultra high pressure) 1000

Tab. 1

It is an object of the invention to improve the radiance of light emitting devices by making use of activator ions in photonic band gap materials and luminescent ceramics.

According to the invention a luminescent material comprises luminescent ions or luminescent small particles which are incorporated in a photonic band gap material or a luminescent ceramic material. In a preferred embodiment the luminescent material comprises phosphor particles doped with activator ions showing emission wherein the activator ions are arranged with a mean distance larger than 1 nm for energy transfer mediated by electric dipole-electric quadrupole interaction or for energy transfer mediated by exchange interaction.

A further embodiment provides a luminescent material comprising phosphor particles doped with activator ions showing emission wherein the activator ions are arranged with a mean distance larger than 3.5 nm for energy transfer mediated by electric dipole-electric dipole interaction. The distances of 1 nm and 3.5 nm, respectively are bigger than distances in conventional luminescent materials. In another embodiment the luminescent material comprises very small phosphor particles with a mean distance larger than 3.5 nm.

According to another preferred embodiment the activator ions are excited by optical transitions involving electronic states with the same parity or a different spin usually referred to as forbidden transitions.

The activator ions are preferably transition metal ions or rare earth ions. In case of rare earth ions there are preferably used Eu³⁺ ions showing efficient emission from the ⁵D₃, ⁵D₂, ⁵Di and ⁵D₀ excited state, Tb³⁺ ions showing efficient emission from the ⁵D₃ and ⁵D₄ excited state, Dy³⁺ or Sm³⁺ ions. There may as well be incorporated Ce³⁺ - Eu³⁺ couples to produce energy transfer from Ce³⁺ to Eu³⁺.

According to the invention a LED (light emitting diode) device comprises a luminescent material according to one of the above-mentioned embodiments.

An essential feature of the present invention is therefore to provide activator ions or luminescent particles in photonic band gap materials by which optical absorption and/or energy transfer can be increased and to provide activator ions or luminescent particles in transparent luminescent ceramics by which optical absorption can be increased. This allows a larger mean distance between activator ions, showing energy transfer in case of application of photonic band gap materials as well as the use of unusual rare earth ions and transition metal ions in both cases.

By applying the activator ions in much smaller concentrations, the effects of concentration quenching or distribution of the excitation energy over two ions mediated by a process called cross relaxation, in some cases followed by luminescence quenching on each of the ions can be suppressed. As a result there is enough optical absorption either because the optical cross section has been increased, which can be done by incorporating the ions in a photonic band gap material or the optical pathway has to be increased, which can be done by incorporating these ions in a transparent material of sufficient thickness. In this way, a new class of phosphor materials can be obtained with rather unusual properties.

Claims

CLAIMS:

1. A luminescent material wherein luminescent ions or luminescent small particles are incorporated in a photonic band gap material or a luminescent ceramic material.

2. A luminescent material according to claim 1 that comprises phosphor particles doped with activator ions showing emission wherein the activator ions are arranged with a mean distance larger than 1 nm.

3. A luminescent material according to claim 2 that comprises phosphor particles doped with activator ions showing emission wherein the activator ions are arranged with a mean distance larger than 3.5 nm.

4. A luminescent material according to claim 2 or 3 that comprises very small phosphor particles with a mean distance larger than 3.5 nm.

5. A luminescent material as claimed by any of the claims 2 to 4 wherein the activator ions are excited by optical transitions involving electronic states with the same parity or a different spin.

6. A luminescent material as claimed by any of the claims 2 to 5 wherein the activator ions are transition metal ions.

7. A luminescent material as claimed in any of the claims 2 to 5 wherein the activator ions are rare earth ions.

8. A luminescent material as claimed in claim 7 wherein the rare earth ions are Eu³⁺ ions showing efficient emission from the ⁵D₃, ⁵D₂, ⁵Di and ⁵D₀ excited state.

9. A luminescent material as claimed in claim 7 wherein the rare earth ions are Tb³⁺ ions showing efficient emission from the ⁵D₃ and ⁵D₄ excited state.

10. A luminescent material as claimed in claim 7 wherein the rare earth ions are Dy³⁺ or Sm³⁺ ions.

11. A luminescent material as claimed in claim 7 in which Ce³⁺ - Eu³⁺ couples are incorporated.

12. A LED (light emitting diode) device comprising a luminescent material according to one of the foregoing claims.