(19)
(11)EP 1 849 192 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
22.06.2011 Bulletin 2011/25

(21)Application number: 05738295.4

(22)Date of filing:  12.04.2005
(51)International Patent Classification (IPC): 
H01L 33/00(2010.01)
C09K 11/80(2006.01)
(86)International application number:
PCT/KR2005/001046
(87)International publication number:
WO 2006/041249 (20.04.2006 Gazette  2006/16)

(54)

WHITE LIGHT EMITTING DEVICE

WEISSES LICHT EMITTIERENDES BAUELEMENT

DISPOSITIF A DEL BLANCHE


(84)Designated Contracting States:
AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HU IE IS IT LI LT LU MC NL PL PT RO SE SI SK TR

(30)Priority: 11.10.2004 KR 20040080982

(43)Date of publication of application:
31.10.2007 Bulletin 2007/44

(73)Proprietor: NANOCMS Co., Ltd.
Seobuk-gu, Cheonan-si Chungcheongnam-do 330-814 (KR)

(72)Inventors:
  • KIM, Shi-surk
    Namdong-gu, Incheon 405-782 (KR)
  • JEON, Duk-young
    Yuseong-gu, Daejeon 305-761 (KR)
  • JANG, Ho-seong
    Nam-gu, Incheon 402-023 (KR)

(74)Representative: Grünecker, Kinkeldey, Stockmair & Schwanhäusser Anwaltssozietät 
Leopoldstrasse 4
80802 München
80802 München (DE)


(56)References cited: : 
WO-A1-01/08452
DE-A1- 19 913 358
JP-A- 2004 115 304
KR-Y1- 200 364 708
US-A1- 2003 006 469
US-A1- 2004 188 655
WO-A1-02/099902
JP-A- 2003 535 478
JP-A- 2004 250 705
US-A- 4 755 715
US-A1- 2004 072 106
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description

    BACKGROUND OF THE INVENTION


    Field of the Invention



    [0001] The present invention relates to a TAG phosphor and a White Light Emitting Diode (White LED) using the same. More specifically, the present invention relates to a phosphor having excellent emission brightness by inclusion of Si or Fe in the phosphor having a TbAG:Ce composition, and a white LED utilizing the same.

    Description of the Related Art



    [0002] The white LED is a next generation light emitting device potential capable of replacing conventionally used general lighting means. The white LED has advantages such as very low power consumption compared to conventional light sources, high photoluminescence efficiency and high brightness, long-term service life and rapid response time.

    [0003] Methods of manufacturing white LEDs may be broadly divided into the following 3 types: the first method is to use a combination of high-brightness red, green and blue LEDs, the second method is to coat red, green and blue light-emitting phosphors on a UV LED and finally, and the third method is to coat a blue LED with light-emitting phosphors.

    [0004] The first method using a combination of red, green and blue LEDs suffers from problems in that three diodes should be used in the form of one chip, thus resulting in an increase in volume.

    [0005] The second method involving coating red, green and blue light-emitting phosphors on the UV LED is disclosed in W09839805. This method is the most ideal method of producing three-wavelength white light by transmission of UV light into three primary color phosphors. However, phosphors having good photoluminescence efficiency of UV light have yet to be developed.

    [0006] The last method of manufacturing the white LED by coating light-emitting phosphors on the blue LED is currently undergoing the most wide and extensive study. This method has advantages in that it is possible to achieve easy production due to the simplified structure of the white LED and it is also possible to obtain high-brightness white light. Such a method is disclosed in detail in WO9805078, filed by Nichia, a Japanese company. This method is also detailed in S. Nakamura, "The Blue Laser Diode", Springer-Verlag, P. 216-219, 1997. According to this method, white light is produced by the combination of blue and yellow light such that the blue light emitted from the LED is absorbed by yttrium-aluminum garnet (Y2Al5O12:Ce3+; YAG) phosphor which then emits yellow light. However, YAG-based light-emitting phosphors, due to unique properties of their light-emitting wavelengths, exhibit relatively weak photoluminescence intensity in a red light region, thereby making it difficult to obtain superior color rendering characteristics, and are susceptible to color temperature. Therefore, YAG-based light-emitting phosphors are disadvantageously not suitable for use in environmental illumination or as an LCD color backlight source.

    [0007] WO 01/08452 discloses TbAG:Ce phosphors, having the formula (Tb0.96 Ce0.04)3Al5O12, for a white light emitting device.

    SUMMARY OF THE INVENTION



    [0008] Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a TAG phosphor having high photoluminescence intensity in a red light region, good color rendering properties, and high-brightness pure light emitting characteristics, and a white light emitting diode (white LED) utilizing the same.

    [0009] In accordance with the present invention, the above and other objects can be accomplished by the provision of a phosphor having a composition of TbAG:Ce, wherein the phosphor having a composition of TbAG:Ce is composed of a compositional formula of (Tb1-xCex)3(Al1-yMy)5O12, wherein x is between 0.01 and 0.4, y is between 0.0 and 0.1, and M is selected from the group consisting of Si and Fe.

    [0010] In the above formula, if M is Si, y is preferably between 0.01 and 0.04, whereas if M is Fe, y is preferably between 0.01 and 0.02.

    [0011] In addition, the white photoluminescent device in accordance with the present invention comprises at least one light-emitting diode emitting light with a wavelength of 430 to 470 nm and a phosphor having a composition of TbAG:Ce, wherein the phosphor having a composition of TbAG:Ce is composed of a compositional formula of (Tb1-xCex)3(Al1-yMy)5O12, wherein x is between 0.01 and 0.4, y is between 0.0 and 0.1, and M is selected from the group consisting of Si and Fe.

    [0012] In the formula, if M is Si, y is preferably between 0.01 and 0.04, whereas if M is Fe, y is preferably between 0.01 and 0.02.

    [0013] The phosphor in accordance with the present invention is primarily made of Tb and Al as a mother body, and Ce3+ functions as an activator. Where the amount of cerium is less than 0.01, it is not sufficient to serve as the activator. In contrast, where the amount of cerium is greater than 0.4, this may undesirably cause lowering in brightness due to concentration quenching effects.

    [0014] As raw materials for the phosphor in accordance with the present invention, mention may be made of Tb4O7, Al2O3 and CeO2, for example. As an additive, SiO2 or Fe2O3 may be utilized. These materials are quantified within an optimal molar ratio, and are sufficiently mixed to obtain a uniform composition using a mixer. The resulting mixture is placed in a crucible, which is covered with a lid. Then, the mixture is introduced into an electric furnace and calcined by heating the mixture at a temperature of 1400 to 1600° C for 1 to 4 hours. If the calcination temperature is less than 1400° C, single-phase crystals are not completely formed and unreacted reactants or by-products are produced. In addition, if the calcination temperature is above 1600° C, irregularly shaped particles are formed, thus sharply lowering brightness.

    [0015] Further, fluoride flux may be added to a calcination process. The quantity of fluoride used is preferably in the range of 7 to 15 wt%, relative to (Tb1-xCex)3(Al1-yMy)3O12. More preferred is 8 wt%. The fluoride utilized in the present invention may include, for example, barium fluoride, ammonium fluoride, sodium fluoride and alumina fluoride. Use of such fluorides in the calcination process enables easy attainment of single-phase phosphors and makes it possible to obtain high-brightness superior phosphors even at low synthesis temperatures.

    [0016] After completion of the calcination process, the calcined materials are cooled to room temperature and milled in vacuo or under water using a ball mill to obtain powdered phosphors having a diameter of 0.5 to 20 µm size. The thus-obtained phosphors having a stable phase of (Tb1-xCex)3(Al1-ySiy)3O12 or (Tb1-cCex)3 (Al1-yFey)3O12 are coated on a blue light-emitting diode chip with an emission wavelength near 460 nm made up of GaN or the like. Preferably, 1 to 40 wt% of phosphors are mixed with epoxy resins or silicon based resins and the resulting mixture is coated on the blue LED chip which is then cured at a temperature of 130 to 200° C to fabricate a white light-emitting diode.

    [0017] As such, it is possible to obtain a white light source that achieves high quantum efficiency, desired color temperature (4500K to 8000K) and good color rendering characteristics by use of the single phosphor material in accordance with the present invention alone, and is suited to mass production.

    BRIEF DESCRIPTION OF THE DRAWINGS



    [0018] The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

    Fig. 1 is an XRD result of a TAG phosphor in accordance with the present invention;

    Fig. 2 is an excitation spectrum of a TAG phosphor in accordance with the present invention;

    Fig. 3 is a photoluminescence spectrum of a TAG phosphor in accordance with the present invention;

    Fig. 4 is a photoluminescence spectrum result of a TAG phosphor based light-emitting diode in accordance with the present invention; and

    Fig. 5 is a color coordinate of a TAG phosphor based light-emitting diode in accordance with the present invention.


    DESCRIPTION OF THE PREFERRED EMBODIMENTS



    [0019] The following is a comparative analysis of properties of the TAG phosphor and white light-emitting diode prepared according to various examples of the present invention

    EXAMPLES



    [0020] Now, the present invention will be described in more detail with reference to the following Examples. These examples are provided only for illustrating the present invention and should not be construed as limiting the scope and spirit of the present invention.

    Example 1



    [0021] Comparative analysis between the TAG phosphor prepared according to the present invention and a conventional phosphor is given as follows.

    [0022] Fig. 1 shows the results of X-ray diffraction (XRD) of (Tb0.9Ce0.1)3(Al1-ySiy)5O12 phosphors prepared in accordance with the present invention. As can be seen from Fig. 1, the TAG phosphors prepared in accordance with the process of the present invention show formation of a stable garnet structure (TAG).

    [0023] Fig. 2 shows an excitation spectrum of (Tb0.9Ce0.1)3 (Al1-ySiy)5O12 phosphors prepared according to the present invention. Fig. 3 shows comparison between photoluminescence spectra measured under an excitation wavelength of 465 nm, with respect to Si concentrations in (Tb0.9Ce0.1)3(Al1-ySiy)5O12 phosphors. As can be seen from Fig. 3, the red-band photoluminescence intensity is stronger in phosphors containing Si, as in the present invention, than in conventional Tb3Al5O12 : Ce phosphors.

    [0024] Table 1 summarizes photoluminescence intensity of Tb3Al5O12:Ce0.1 (sample #0) phosphors prepared according to a conventional method and the (Tb0.9Ce0.1)3(Al1-ySly)5O12 phosphors prepared according to the present invention measured under an excitation wavelength of 465 nm, based on the molar ratio of Si.
    Table 1
    Sample #TbCeAlSiPL Intensity (arbitrary)PL increase (%)Remarks
    0 0.9 0.1 1.0 0.000 22.5 - Comp. Ex.
    1 0.9 0.1 0.9975 0.0025 22.6 -  
    2 0.9 0.1 0.9950 0.0050 23.8 -  
    3 0.9 0.1 0.9925 0.0075 29.0 28.9  
    4 0.9 0.1 0.99 0.01 42.0 86.7  
    5 0.9 0.1 0.98 0.02 40.0 77.8  
    6 0.9 0.1 0.96 0.04 35.0 55.6  
    7 0.9 0.1 0.94 0.06 31.0 37.7  
    8 0.9 0.1 0.92 0.08 27.5 22.2  
    9 0.9 0.1 0.90 0.1 23.8 5.8  


    [0025] Photoluminescence intensity (PL) was remarkably excellent in the range of 0.01 to 0.04 of the Si molar ratio. In particular, when the Si molar ratio was 0.01, it showed about 87% improvement in PL, as compared to a comparative example.

    [0026] Table 2 summarizes photoluminescence intensity of Tb3Al5O12:Ce0.1 (sample #0) phosphors prepared according to a conventional method and the (Tb0.9Ce0.1) 3 (Al1-yFey) 5O12 phosphors prepared according to the present invention measured under an excitation wavelength of 465 nm, based on the molar ratio of Fe.
    Table 2
    Sample #TbCeAlFePL Intensity (arbitrary)PL increase (%)Remarks
    0 0.9 0.1 1.0 0.000 22.5 - Comp. Ex.
    10 0.9 0.1 0.9975 0.0025 22.6 -  
    11 0.9 0.1 0.9950 0.0050 23.8 -  
    12 0.9 0.1 0.9925 0.0075 26.2 16.4  
    13 0.9 0.1 0.99 0.01 34.0 51.1  
    14 0.9 0.1 0.98 0.02 32.0 42.2  
    15 0.9 0.1 0.96 0.04 29.5 31.1  
    16 0.9 0.1 0.94 0.06 27.0 30.0  
    17 0.9 0.1 0.92 0.08 25.5 13.3  
    18 0.9 0.1 0.90 0.1 22.6 -  


    [0027] As can be seen from table 2, photoluminescence intensity was remarkably excellent in the range of 0.01 to 0.02 of the Fe molar ratio. When the Fe molar ratio was 0.01, it showed about 51% improvement in photoluminescence intensity, as compared to a comparative example. Fe has lower excitation intensity than Si, but the phosphors having a Fe molar ratio of 0.01 mol exhibited better results than the comparative example.

    Example 2



    [0028] The following evaluation results illustrate properties of a white LED prepared by applying a mixture of the TAG phosphor prepared according to the present invention and a light-transmissive silicon resin to a 460 nm (In)GaN blue light-emitting diode chip, followed by curing and drying.

    [0029] Table 3 summarizes characteristics of Tb3Al5O12:Ce0.1 (sample #0) phosphors prepared according to a conventional method and the (Tb0.9Ce0.1) 3 (Al1-ySiy)5O12 phosphors with replacement of Si content with the range of 0.0 < y < 0.1, prepared according to the present invention, on the basis of the molar ratio.
    Table 3
    Sample #TbCeAlSiBrightness (1m)Brightness increase (%)Reliability (%)
    0 0.9 0.1 1.0 0.000 1.64 - 92.80
    19 0.9 0.1 0.9975 0.0025 1.73 - -
    20 0.9 0.1 0.9950 0.0050 1.73 - -
    21 0.9 0.1 0.9925 0.0075 1.92 17.1 93.90
    22 0.9 0.1 0.99 0.01 2.41 47.0 97.70
    23 0.9 0.1 0.98 0.02 2.35 43.3 95.24
    24 0.9 0.1 0.96 0.04 2.19 33.5 94.56
    25 0.9 0.1 0.94 0.06 1.98 20.7 94.60
    26 0.9 0.1 0.92 0.08 1.85 12.8 93.81
    27 0.9 0.1 0.90 0.1 1.70 3.7 93.00


    [0030] Reliability data is a proportion of sample with characteristics equal to or higher than given criteria, after heat treatment at 85° C for 500 hours. At a Si molar ratio of 0.01 to 0.04, remarkably excellent results were obtained, ;as compared to the conventional art. In particular, when the Si molar ratio was 0.01, brightness increased by 47% and reliability was improved to 97.7%.

    [0031] Fig. 4 is a photoluminescence spectrum result of a light-emitting diode fabricated using (Tb0.9Ce0.1) 3 (Al0.99Si0.01) 5O12 phosphors prepared according to the present invention.

    [0032] Table 4 summarizes characteristics of Tb3Al5O12:Ce0.1 (sample # 0) phosphors prepared according to a conventional method and the (Tb0.9Ce0.1) 3 (Al1-yFey) 5O12 with replacement of Fe content with the range of 0.0 < y < 0.1, prepared according to the present invention, on the basis of molar ratio.
    Table 4
    Sample #TbCeAlFeBrightness (lm)Brightness increase (%)Reliability (%)
    0 0.9 0.1 1.0 0.000 1.64 - 92.80
    28 0.9 0.1 0.9975 0.0025 1.73 - -
    29 0.9 0.1 0.9950 0.0050 1.89 15.2 94.50
    30 0.9 0.1 0.9925 0.0075 1.95 18.9 93.85
    31 0.9 0.1 0.99 0.01 2.17 32.3 95.20
    32 0.9 0.1 0.98 0.02 1.97 20.7 94.84
    33 0.9 0.1 0.96 0.04 1.80 9.8 94.60
    34 0.9 0.1 0.94 0.06 1.78 8.5 93.28
    35 0.9 0.1 0.92 0.08 1.70 3.7 93.11
    36 0.9 0.1 0.90 0.1 1.64 - 92.90


    [0033] Reliability data is a proportion of sample with characteristics equal to or higher than given criteria, after heat treatment at 85° C for 500 hours. The Fe molar ratio of 0.01 to 0.02 exhibited remarkably excellent results, as compared to the conventional art. In particular, when the Fe molar ratio was 0.01, brightness increased by 37% and reliability was improved to 95.2%.

    [0034] Fig. 5 shows the measured result of a CIE (Commission international de l'Eclairage) color coordinate (X, Y) on a photoluminescence spectrum of a light-emitting diode fabricated using a TAG phosphor in accordance with the present invention. As can be seen from Fig. 5, X and Y coordinates exhibited excellent color rendering within the range of pure white color, high brightness and excellent reliability.

    [0035] The white LED fabricated using (Tb0.9Ce0.1) 3 (Al0.95Si0.05) 5O12 phosphors had a chromaticity point XY=(0.298,0.32), and photoluminescence efficiency of 1.77 ml/w. In addition, the white LED fabricated using (Tb0.95Ce0.05) 3 (Al0.99Fe0.01) 5O12 phosphors had a chromaticity point XY=(0.31,0.29), and photoluminescence efficiency of 1.779 ml/w.

    [0036] As apparent from the above description, in accordance with the present invention, it is possible to obtain a white LED having high brightness and excellent color rendering characteristics. Further, it is possible to obtain a TAG based white LED having strong photoluminescence intensity in a red light region and excellent chip color characteristics.


    Claims

    1. A phosphor having a composition of TbAG:Ce, wherein the phosphor having a composition of TbAG:Ce is composed of a compositional formula of:

    (Tb1-xCex)3(Al1-yFey)5O12, wherein x is between 0.01 and 0.4, and y is between 0.01 and 0.02
    or

    (Tb1-xCex)3(A)1-ySiy)5O12, wherein x is between 0.01 and 0.4, and y is between 0.01 and 0.04.


     
    2. A white photoluminescent device comprising at least one light-emitting diode emitting light with a wavelength of 430 to 470 nm and a phosphor according to claim 1.
     


    Ansprüche

    1. Leuchtstoff, der eine Zusammensetzung aus TbAG:Ce hat, wobei der Leuchtstoff, der eine Zusammensetzung aus TbAG:Ce hat, aus einer Zusammensetzungsformel aus:

    (Tb1-xCex)3(Al1-yFey)5O12, wobei x zwischen 0,01 und 0,4 liegt und y zwischen 0,01 und 0,02 liegt,
    oder

    (Tb1-xCex)3(Al1-ySiy)5O12, wobei x zwischen 0,01 und 0,4 liegt und y zwischen 0,01 und 0,04 liegt,
    zusammengesetzt ist.


     
    2. Weiße Fotolumineszenzvorrichtung, die wenigstens eine Leuchtdiode, die Licht mit einer Wellenlänge von 430 bis 470 nm emittiert, und einen Leuchtstoff nach Anspruch 1 umfasst.
     


    Revendications

    1. Phosphore ayant une composition de TbAG:Ce, où le phosphore ayant une composition de TbAG:Ce est composé d'une formule de composition de :

    (Tb1-xCex)3(Al1-yFey)5O12, où x est entre 0,01 et 0,4 et y est entre 0,01 et 0,02
    ou

    (Tb1-xCex)3(Al1-ySiy)5O12, où x est entre 0,01 et 0,4 et y est entre 0,01 et 0,04.


     
    2. Dispositif à photoluminescence blanche comprenant au moins une diode électroluminescente émettant une lumière d'une longueur d'onde de 430 à 470 nm et un phosphore selon la revendication 1.
     




    Drawing




















    Cited references

    REFERENCES CITED IN THE DESCRIPTION



    This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

    Patent documents cited in the description




    Non-patent literature cited in the description