Illumination unit having at least one LED as light source

Details Illumination unit having at least one LED as light source Illumination unit having at least one LED as light source

2002-07-26

2003-12-30

Patel, Ashok (Department: 2879)

Electric lamp and discharge devices

With luminescent solid or liquid material

Solid-state type

C313S502000, C313S483000, C313S485000, C313S512000, C252S30140F

Reexamination Certificate

active

06670748

ABSTRACT:

TECHNICAL FIELD
The invention is based on an illumination unit having at least one LED as light source in accordance with the preamble of claim 1. This is in particular an LED which emits in the visible or white region and is based on an LED which emits primarily UV/blue.
BACKGROUND ART
An illumination unit which emits, for example, white light is currently obtained predominantly by combining a Ga(In)N-LED, which emits in the blue at approximately 460 nm, and a yellow-emitting YAG:Ce
3+
phosphor (U.S. Pat. No. 5,998,925 and WO 98/12757). For good color rendering, two different yellow phosphors are often used, as described in WO-A 01/08453. A problem in this case is that the two phosphors often have different temperature characteristics, even if their structures are similar. A known example is the yellow-luminescent Ce-doped Y garnet (YAG:Ce) and the (Y,Gd) garnet which, by comparison, is luminescent at a longer wavelength. This leads to fluctuations in the color locus and changes in the color rendering at different operating temperatures.
The publication “On new rare-earth doped M-Si—Al—O—N materials” by van Krevel, TU Eindhoven 2000, ISBN 90-386-2711-4, Chapter 11 has disclosed a number of classes of phosphor materials which have the structure of nitrides or oxynitrides or are known as sialons (in particular (&agr;-sialons), which represent a contraction of their composition. An emission in a wide optical spectral region with excitation at 365 nm or 254 nm is achieved by means of doping with Eu, Tb or Ce.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide an illumination unit having at least one LED as light source,the LED emitting primary radiation in the range from 300 to 570 nm, this radiation being partially or completely converted into the longer-wave radiation by phosphors which are exposed to the primary radiation of the LED and the structure of which is based on nitrides or derivatives thereof, which is distinguished by a high level of constancy at fluctuating operating temperatures. A further object is to provide an illumination unit which emits white light and in particular has a good color rendering and a high output. A further object is to provide a new daylight fluorescent pigment.
This object is achieved by the following features: the conversion takes place with the aid of at least one phosphor which is derived from a cation M and a silicon nitride or a derivative of a nitride which emits with a peak emission wavelength at 430 to 670 nm, the cation being partially replaced by a dopant D, namely Eu
2+
or Ce
3+
, at least one of the divalent metals Ba, Ca, Sr and/or at least one of the trivalent metals Lu, La, Gd, Y being used as cation M, the phosphor originating from one of the following classes which provide as such new daylight fluorescent pigments:
nitrides of the structure MSi
3
N
5
, M
2
Si
4
N
7
, M
4
Si
6
N
11
and M
9
Si
11
N
23
,
oxynitrides of the structure M
16
Si
15
O
6
N
32
sialons of the structure MSiAl
2
O
3
N
2
, M
13
Si
18
Al
12
O
18
N
36
, MSi
5
Al
2
ON
9
and M
3
Si
5
AlON
10
.
Particularly advantageous configurations are given in the dependent claims.
According to the invention, the phosphor used for the LEDs is a phosphor from one of a number of nitride-based phosphor classes.
These are certain classes of nitrides and their derivatives oxynitrides and sialons. The phosphor which is derived from a cation M and a silicon nitride or a derivative of a nitride emits with a peak emission wavelength of 430 to 670 nm, the cation being partially replaced by a dopant D, namely Eu
2+
or Ce
3+
, the cation M used being at least one of the divalent metals Ba, Ca, Sr and/or at least one of the trivalent metals Lu, La, Gd, Y, the phosphor originating from one of the following classes:
nitrides of the structure MSi
3
N
5
, M
2
Si
4
N
7
, M
4
Si
6
N
11
, and M
9
Si
11
N
23
,
oxynitrides of the structure M
16
Si
15
O
6
N
32
;
sialons of the structure MSiAl
2
O
3
N
2
, M
13
Si
18
Al
12
O
18
N
36
, MSi
5
Al
2
ON
9
and M
3
Si
5
AlON
10
.
The following specific phosphors are particularly preferred:
M′M″Si
4
N
7
:D  1.
where
M′=Sr or Ba, in each case alone or in combination, and in particular M′ is partially (up to 20 mol %) replaced by Ca; M′ is a divalent ion.
M″=Lu alone or in combination with Gd and/or La; M″ is a trivalent ion.
A specific example is SrLuSi
4
N
7
:Eu
2+
.
M′M″Si
6
N
11
:D  2.
where M′=Ba
x
Sr
3−x
, preferably x=1.5; M′ is divalent;
where M″=Lu alone or in combination with Gd and/or La and/or Y; M″ is trivalent;
To a certain extent, the quantities of Ba
2+
and Sr
2+
may vary (the value for x may fluctuate between 1.3 and 1.7), and these components may be partially (up to 20 mol % of the total quantity of M′) replaced by Ca
2+
.
A specific example is BaLuSi
6
N
11
:Eu.
M″
3
Si
6
N
11
:D  3.
Where M″=La alone or in combination with Gd and/or Y and/or Lu; M″ is a trivalent ion.
Preferably, D=Ce
3+
.
A specific example is La
3
Si
6
N
11
:Ce.
M′
2
M″
7
Si
11
N
23
:D  4.
Where M′=Ba alone or in combination with Sr (up to 50 mol %)
M″=La alone or in combination with Gd and/or Lu;
A specific example is Ba
2
La
7
Si
11
N
23
:Eu
M″Si
3
N
5
:D  5.
Where M″=La alone or in combination with Gd and/or Lu;
Where D=Ce.
A specific example is LaSi
3
N
5
:Ce.
Furthermore, they may be certain classes of oxynitrides, namely those of type M″
16
Si
15
O
6
N
32
:D. As trivalent cation M″, these oxynitrides use at least one of the metals La, Gd, Lu or Y. The cation is partially replaced by a dopant D, namely Eu
2+
or Ce
3+
. The following specific phosphors are particularly preferred:
M″
16
Si
15
O
6
N
32
:Ce  6.
where M″=La alone or in combination with Gd and/or Lu;
a specific example is La
16
Si
15
O
6
N
32
:Ce.
Furthermore, they are certain classes of sialons, i.e. those of type MSiAlON:D. As divalent or trivalent cation M″, these sialons use at least one of the metals Ba, Sr, Ca, La, Gd, Lu or Y. The cation is partially replaced by a dopant D, namely Eu
2+
or Ce
3+
. The following specific phosphors are particularly preferred:
M′SiAl
2
O
3
N
2
:D  7.
where M′=Sr alone or in combination with Ba and/or Ca
2+
; the proportion of Ba may be up to 50 mol %, and the proportion of Ca may be up to 20 mol %.
A specific example is SrSiAl
2
O
3
N
2
:Eu.
M′
3
M″
10
Si
18
Al
12
O
18
N
36
:D  8.
where M′=Sr alone or in combination with Ba and/or Ca; the proportion of Ba may be up to 50 mol %, and the proportion of Ca may be up to 20 mol %;
where M″=La alone or in combination with Gd and/or Lu;
preferably, M′=Sr
2+
and/or M″=La
3+
;
a specific example is Sr
3
La
10
Si
18
Al
12
O
18
N
36
:Eu.
M″Si
5
Al
2
ON
9
:Ce
3+
  9.
where M″=La alone or in combination with Gd and/or Lu;
A specific example is LaAl
2
Si
5
ON
9
:Ce.
M″
3
Si
5
AlON
10
:Ce
3+
  10.
where M″=La alone or in combination with Gd and/or Lu;
Preferably, M″=La
3+
.
A specific example is La
3
Si
5
AlON
10
:Ce.
The proportion of the dopant (i.e. the Eu or Ce content) which replaces some of the cation M should be 0.5 to 15%, preferably 1 to 10%, of the M cation, so that the emission wavelength can be selected accurately and the light efficiency can be optimized. An increasing dopant content generally shifts the peak emission toward longer wavelengths. Surprisingly, it has been found that a changing concentration of the cation M also shifts the peak emission wavelength. At a low concentration of the M cation, good absorption by the dopant can be obtained by selecting the amount of this dopant to be 5 to 10

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