WO2012077042A1

WO2012077042A1 - Orange to red emitting silicion- oxyntirde luminescent materials

Info

Publication number: WO2012077042A1
Application number: PCT/IB2011/055475
Authority: WO
Inventors: Peter Josef Schmidt; Cora Sieglinde Hecht; Wolfgang Schnick
Original assignee: Koninklijke Philips Electronics N.V.; Philips Intellectual Property & Standards Gmbh
Priority date: 2010-12-08
Filing date: 2011-12-06
Publication date: 2012-06-14
Also published as: TW201241155A

Abstract

The invention relates to a novel red emitting material of composition M_4-xSi_9+yO_4-4yN_12+4y:Eu_x with M = Sr, Ba; 0.001 ≤ x ≤ 0.1, and 0 ≤ y < 0.8.

Description

ORANGE TO RED EMITTING SILICION- OXYNTIRDE LUMINESCENT MATERIALS

FIELD OF THE INVENTION

The present invention is directed to novel luminescent materials for light emitting devices, especially to the field of novel luminescent materials for LEDs. BACKGROUND OF THE INVENTION

Phosphors comprising silicates, phosphates (for example, apatite) and aluminates as host materials, with transition metals or rare earth metals added as activating materials to the host materials, are widely known. As blue LEDs, in particular, have become practical in recent years, the development of white light sources utilizing such blue LEDs in combination with such phosphor materials is being energetically pursued.

Especially red emitting luminescent materials have been in the focus of interest and several materials have been proposed, e.g. US patent 6680569(B2), " Red Deficiency Compensating Phosphor for a Light Emitting Device", or from WO patent application 2005/052087 Al .

However, there is still the continuing need for orange to red emitting luminescent materials which are usable within a wide range of applications and especially allow the fabrication of phosphor warm white pcLEDs with optimized luminous efficiency and color rendering. SUMMARY OF THE INVENTION

It is an object of the present invention to provide a material which is usable within a wide range of applications and especially allows the fabrication of phosphor warm white pcLEDs with optimized luminous efficiency and color rendering.

This object is solved by a phosphor material according to claim 1 of the present invention. Accordingly, a material M₄__xSi9₊y04_4yN₁2₊4_y:RE_x is provided, whereby

M is selected out of the group comprising Ba, Sr or mixtures thereof; RE is selected out of the group comprising rare earth metals or mixtures thereof;

and 0.001 < x < 0.1 and 0 < y < 0.8.

It should be noted that by the term„ M₄__xSi9₊y04_4yN₁2₊4y:RE_x" especially and/or additionally any material is meant and/or included, which has essentially this composition.

The term "essentially" means especially that > 95 %, preferably > 97 % and most preferred > 99 % wt-%. However, in some applications, trace amounts of additives may also be present in the bulk compositions. These additives particularly include such species known to the art as fluxes. Suitable fluxes include alkaline earth - or alkaline - metal oxides, borates, phosphates and halides such as fluorides, ammonium chloride, Si0₂ and the like and mixtures thereof.

Such a material has shown for a wide range of applications within the present invention to have at least one of the following advantages

Using the material as luminescent material, LEDs may be built which show improved lighting features, especially thermal stability.

The Material can be made in excellent purity due to the availability via a nitrification process (see below) using more-ready available oxygen precursor materials.

The Material for a wide range of applications only contains non-toxic and widely available constituents

Without being bound to any theory, the inventors believe that the improved properties of the inventive material arise at least partially out of the structure of the material.

The material has been found to crystallize in a new host lattice; said new host lattice formation can be explained and derived from the (known) M₂Si₅N8 structure by partial or complete removal of SiN₄ building blocks from the M₂Si₅N8 structure and introduction of terminal O atoms (see figs. 1 and 2 as described later on).

According to a preferred embodiment of the present invention, RE is Eu, i.e. Eu is the dopant material.

According to a preferred embodiment of the present invention, x is 0.005 < x < 0.02, i.e. the dopant level is somewhat around 1%. This has been shown to be advantageous for many applications within the present invention.

According to a preferred embodiment of the present invention, y is 0.2 < y < 0.6. By doing so it has been found that the high temperature efficiency of luminescence can be enhanced; it is believed (without being bound to any theory) that this results at least partially due to increasing the degree of condensation.

It is a further object of the present invention to provide a method for manufacture of a material according to the present invention. Accordingly a method for manufacture of a material according to the present invention is provided, comprising a oxonitride formation step from an oxygen-comprising precursor material.

By doing so it has been found that the material can be made on a large-scale basis with high purity and good material features.

Preferably the oxygen-comprising precursor material is a silicate material, e.g. Ba₂Si0_4> Sr₂Si0₄ or the like, mixtures thereof, which may also be doped with RE, especially Eu.

Alternatively the oxygen-comprising precursor material can be a oxonitridosilicate, e.g. BaSi₂0₂N₂, SrSi₂0₂N₂ or or the like.

According to a yet alternative embodiment of the method, the oxygen- comprising precursor material is an oxide, e.g. BaO, SrO or mixtures thereof and mixtures of these oxides with REO or RE₂0₃ (e.g. EuO or Eu₂0₃).

A preferred embodiment of the inventive method comprises a reduction step carried out simultaneously or prior to the oxonitride formation step. This has been shown to lead to a inventive material with enhanced purity.

Preferably the reduction step comprises a carbothermal reduction. In more detail, a preferred embodiment of the inventive method comprises a first oxonitride formation step from a silicate, e.g. according to the following equation:

M₂Si0₄:Eu + 3 SiN_4/3 -> 2 MSi₂0₂N₂:Eu

This material is then converted to the inventive material in a combined oxonitride formation step and reduction step using suitable precursor materials such as carbon and silicone nitride, e.g. according to the following equation:

4 MSi₂0₂N₂:Eu + (4+4x)C + (l+x)SiN_4/3 + (l+x)3/2 N₂ -> M₄Si_9+x0₄__4xNi_2+4x

Alternatively, the silicon nitride powder may be substituted by silicon powder in both above reactions. Other silicon sources like silicon diimide may also be used. Instead of nitrogen gas, also dry ammonia may be used for the oxonitride formation reaction and elemental carbon might be substituted by other sources of carbon like carbohydrates, saturated or non-saturated carbohydrates, and plastics and so on. A yet alternative reaction path to the inventive material comprises the oxonitride formation from a metal oxide, e.g. BaO:Eu or the like, following e.g. the following equation:

4 MO:Eu + 4.5 Si₂N₂(NH) -> Sr₄Si₉0₄Ni₂:Eu + 2.25 H₂ + 0.75 N₂

It has been shown in practice that this reaction is especially useful if the Sr:Ba ratio in the inventive material is >1, i.e. there is more Sr than Ba. It goes without saying that other suitable silicon and/or nitrogen precursore may be used (e.g. as described above).

It should be noted that the inventive method is to be understood in its broadest sense and also includes reations where e.g. the dopant is provided as a halogenide (which then also can serve as a flux aid etc.). A suitable reaction scheme is e.g.:

3.96 MN_2/3 + 0.04 EuF₃ + (7+3x) SiN_4/3 + (2-2x) Si0₂ -> M₄Si_9+x0₄__4xNi_2+4x:Eu,F

The present invention furthermore relates to a light emitting structure, especially a LED, comprising at least one material according to the present invention.

The present invention furthermore relates to as system comprising a material according to the present invention and/or materials made according to the inventive methods shown above, being used in one or more of the following applications:

Office lighting systems

- household application systems

shop lighting systems,

- home lighting systems,

accent lighting systems,

spot lighting systems,

- theater lighting systems,

- fiber-optics application systems,

- projection systems,

self-lit display systems,

- pixelated display systems,

segmented display systems,

- warning sign systems,

- medical lighting application systems,

- indicator sign systems, and

decorative lighting systems

portable systems automotive applications

green house lighting systems

The aforementioned components, as well as the claimed components and the components to be used in accordance with the invention in the described embodiments, are not subject to any special exceptions with respect to their size, shape, material selection and technical concept such that the selection criteria known in the pertinent field can be applied without limitations.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional details, features, characteristics and advantages of the object of the invention are disclosed in the subclaims, the figures and the following description of the respective figures and examples, which— in an exemplary fashion— show several embodiments and examples an inventive material according to the invention.

Fig. 1 shows a schematic perspective partial view of a structure of a host material according to a first example of the present invention;

Fig. 2 (background art) shows the (known) structure of M₂S1₅N₈

Fig. 3 shows an emission spectrum of the material of Example I

Fig. 4 shows an XRD pattern of the material of Example I

Fig. 5 shows an emission spectrum of the material of Example II; and

Fig. 6 shows an XRD pattern of the material of Example II

Fig. 1 shows a schematic perspective partial view of a structure of a host material according to a first example of the present invention. As described above, this structure can be explained and derived from the (known) M₂S1₅N₈ structure (Fig. 2) by partial or complete removal of S1N₄ building blocks from the M₂S1₅N₈ structure and introduction of terminal O atoms. Table 1 shows a comparision of crystallographic data of the host lattice for example M = Ba and x=0: TABLE I

crystallographic data Ba₄Si₉N₁₂0₄ Ba₂Si₅N, space group Cm (no. 8), twinned Pmn2_f (no. 31 ) lattice parameter / A a = 18.40 a = 5.78

b = 5.76 b = 6.96

c = 7.05 c = 9.39

A³ 747.78 377.9

Z 2 2 EXPERIMENTAL SECTION

The following invention will futhermore be understood by the following examples which are merely for illustration purposes and which are non- binding:

EXAMPLE I: Sr_4xSi_9+y0₄-_4yNi₂₊4_y:Eu(2%), y ~ 0.2

Figs 3 and 4 refer to the material according to Example I, which was made the following way:

4.088 g SrO:Eu(2%) is reacted with 3.001 g Si₂N₂(NH) for 2 hrs at 1550°C under steaming H₂/N₂ 5/95 gas with a dew point of -67°C, crushed, ball milled in

isopropanol, washed with 2N HCl solution, water and ethanol, and dried. The Sr to Si ratio of the powder was determined by EDX analysis.

The orange Sr₄Si_9+y0₄-_4yN₁₂ 4_y:Eu(2%), y ~ 0.2 powder shows emission in the orange - red spectral range with a peak at 623 nm (Fig. 3). The quantum efficiency of the phosphor was determined to be 80.7% (commercial YAG:Ce phosphor U728, Philips Lighting, used as a standard), 50% of the integral room temperature intensity has been reached at 218°C.

Fig. 4 shows the XRD pattern of Sr₄Si_9+y0₄__4yN_12+4y:Eu(2%), y ~ 0.2. It can be seen that this material crystallizes in the structure following Fig. 1, i. e. in a novel structure not described before. EXAMPLE II: Ba₄Si₉0₄N₁₂:Eu(l%).

Figs 5 and 6 refer to the material according to Example II, which was made the following way:

10 g BaO, 9.80 g Si(NH₂)₂ and 1.514 g EuF₃ are reacted for 2.5 hrs at 1400°C under a H₂/N₂ 5/95 gas atmosphere followed by cooling down to room temperature within 40 min.

Fig. 5 shows the emission spectrum of Ba₄Si₉0₄N₁₂:Eu(l%). CIE color coordinates are: x = 0.525, y = 0.469. Lumen equivalent of emission = 391 lm/W.

Fig. 6 shows the XRD pattern of Ba₄Sic)0₄N₁₂:Eu(l%). It can be seen that this material crystallizes in the structure following Fig. 1, i. e. in a novel structure not described before.

The particular combinations of elements and features in the above detailed embodiments are exemplary only; the interchanging and substitution of these teachings with other teachings in this and the patents/applications incorporated by reference are also expressly contemplated. As those skilled in the art will recognize, variations, modifications, and other implementations of what is described herein can occur to those of ordinary skill in the art without departing from the spirit and the scope of the invention as claimed.

Accordingly, the foregoing description is by way of example only and is not intended as limiting. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. The invention's scope is defined in the following claims and the equivalents thereto. Furthermore, reference signs used in the description and claims do not limit the scope of the invention as claimed.

Claims

CLAIMS:

M₄__xSi_9+y04-4yN 12+4y '■ RE_X, whereby

M is selected out of the group comprising Ba, Sr or mixtures thereof;

RE is selected out of the group comprising rare earth metals or mixtures thereof;

and 0.001 < x < 0.1 and 0 < y < 0.8.

The material of claim 1, whereby RE = Eu.

The material of claim 1 or 2, whereby x is 0.005 < x < 0.02.

The material of any of the claims 1 to 3, whereby y is 0.2 < y < 0.6.

5. A method of manufacturing a material according to any of the claims 1 to 4, whereby the method comprises a oxonitride formation step from an oxygen-comprising precursor material.

6. The method of claim 5, furthermore comprising a reduction step carried out simultaneously or prior to the oxonitride formation step 7. The method of any of the claims 5 or 6, whereby the reduction step comprises a carbothermal reduction.

8. A light-emitting structure, especially a LED, comprising a material according to any of the claims 1 to 4 or made according to any of the claims 5 to 7.

9. A system comprising a material according to any of the claims 1 to 4 and/or a material manufactured according to any of the Claims 4 to 7 and/or a structure according to claim 8, the system being used in one or more of the following applications: Office lighting systems