# Patent

## Title
Fluorescent material and illumination device

## Abstract

A fluorescent material represented by the following formula (I):

M1yM2nOzCx:M3w  (I);

    
    
        wherein M1 is selected from Sc3+, Y3+, La3+, Sm3+, Gd3+, Tb3+, Pm3+, Er3+, Lu3+, and combinations thereof; M2 is selected from Al3+, In3+, Ga3+, and combinations thereof; M3 is selected from Tm3+, Bi3+, Tb+, Ce3+, Eu3+, Mn3+, Er3+, Yb3+, Ho3+, Gd3+, Pr3+, Dy3+, Nd3+, and combinations thereof; and 0.45≦x/n≦0.75, 0.54≦y/n≦0.6, 0.002<w/n≦0.06, and 0.9≦z/n≦1.5. An illumination device including a light emitting element and the aforesaid fluorescent material is also disclosed.

## Background
CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority of Taiwanese patent application no. 102101132, filed on Jan. 11, 2013.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a fluorescent material and an illumination device using the fluorescent material.
2. Description of the Related Art
Nichia Corporation started to produce white light emitting diodes (white LEDs) since 1996. U.S. Pat. No. 5,998,925 discloses a light emitting device that generates white light and that comprises a blue light emitting diode (blue LED) having a wavelength ranging from 450 nm to 470 nm as an illuminating unit, and a Cerium-doped fluorescent material (Y3Al5O12:Ce3+, also known as YAG:Ce3+), wherein Cerium is used as an activator. Part of blue light emitted from the illuminating unit is absorbed by YAG:Ce3+ and converted into yellowish light with a relatively broader emission spectrum (the peak wavelength being around 580 nm). Because massive yellow light irradiated by YAG:Ce3+ is capable of stimulating both red light and green light photoreceptors in human eyes, and the rest of blue light emitted from the blue light LED stimulates blue light photoreceptors, white light could be seen my human eyes.
However, such combination of blue LED and YAG fluorescent material has several drawbacks including low color rendering index (Ra) owing to lack of red light, lower light emitting efficiency with increasing operating temperature, and poor thermal stability of illuminated light induced by high power light sources.
In order to alleviate the aforesaid drawbacks, many researchers have focused on adding silicon (Si) element into the composition of YAG. Silicon compound fluorescent materials, in which Al3+ is replaced by Si4+, have drawn more attention due to higher thermal and chemical stabilities, stronger absorption in UV zone, high purity and low cost, and abundant supply with respect to silicon or silicate materials.
US Patent Application Publication No. 2010/0142182 discloses an illumination system, comprising a light emitting device which includes a first phosphor layer, and a second phosphor layer which is separated from the light emitting device. The first phosphor layer includes a fluorescent material which contains silicon and nitrogen elements and which is represented by the following formula:

(Y1-α-β-a-bLuαGdβ)3(Al5-u-νGawSiv)O12-yNw:Cea3+Prb3+);

wherein 0≦α<1, 0≦β<1, 0<(α+β+a+b)≦1, 0≦u<2, 0≦ν<2, 0<a<0.25, and 0<b<0.25.

This fluorescent material has been modified based on the YAG structure. However, drawbacks of this silicon-containing fluorescent material include low bearing temperature, low stability, and relatively high brightness which causes over stimulation and results in fatigue of human eyes after exposure over a long period of time. Also, although nitrogen element has also been added to raise the sintering temperature, the fluorescent material still only has a sintering temperature of approximately 1500° C. Besides, the bearing temperature and stability are still insufficient and the color rendering index (Ra) of the modified fluorescent material is about 80%. Moreover, higher quantity of the fluorescent material is needed in the illumination system.
Therefore, there is a need in the art to provide a fluorescent material that has high bearing temperature, high color rendering index, good thermal stability, and more natural light emission to avoid over stimulation of human eyes.
SUMMARY OF THE INVENTION
Therefore, the object of the present invention is to provide a fluorescent material with desirably high bearing temperature and high color rendering index (Ra), and an illumination device including the aforesaid fluorescent material.
According to one aspect of this invention, a fluorescent material is represented by the following formula (I):

M1yM2nOzCx:M3w  (I);

wherein M1 is selected from the group consisting of Sc3+, Y3+, La3+, Sm3+, Gd3+, Tb3+, Pm3+, Er3+, Lu3+, and combinations thereof; M2 is selected from the group consisting of Al3+, In3+, Ga3+, and combinations thereof; M3 is selected from the group consisting of Tm3+, Bi3+, Tb3+, Ce3+, Eu3+, Mn3+, Er3+, Yb3+, Ho3+, Gd3+, Pr3+, Dy3+, Nd3+, and combinations thereof; and 0.45≦x/n≦0.75, 0.54≦y/n≦0.6, 0.002<w/n≦0.06, and 0.9≦z/n≦1.5
According to another aspect of the invention, an illumination device comprises a light emitting element, and a fluorescent layer that is formed on the light emitting element. The fluorescent layer includes the fluorescent material mentioned above, and is capable of absorbing light emitting from the light emitting element.
This invention has the following effects:
a) the fluorescent material is capable of emitting specific light in desired ranges of wavelengths by altering different elements in the fluorescent material;
b) the fluorescent material does not comprise silicon elements, and part of the oxygen elements in the fluorescent material have been replaced by carbon elements, whereby thermal stability and bearing temperature are increased accordingly via covalent bonding structure of the carbon atoms; and
c) light emitted from the illumination device of this invention is more natural and has higher color rendering index (Ra).



BRIEF DESCRIPTION OF THE DRAWINGS
Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments of this invention, with reference to the accompanying drawings, in which:
FIG. 1 is a partly cross-sectional view of a preferred embodiment of a fluorescent material and an illuminating device according to this invention;
FIG. 2 is a graph illustrating relative emission spectra of Example 12 and Comparative Example 2;
FIG. 3 is a spectrum of Example 14 and Comparative Example 3;
FIG. 4 is a chromaticity coordinate diagram of Example 4;
FIG. 5 is a chromaticity coordinate diagram of Comparative Example 4; and
FIG. 6 is a graph describing degradation of light emission intensity of Example 5 and Comparative example 1.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, a preferred embodiment of an illumination device 1 according to the present invention is shown to include a light emitting element 11, and a fluorescent layer 12 that is formed on the light emitting element 11. The fluorescent layer 12 includes a fluorescent material, and is capable of absorbing light emitted from the light emitting element 11 and emits light by photoluminescence effect.
Preferably, the light emitting element 11 includes a chip containing, for example, aluminum (Al), gallium (Ga), nitrogen (N), phosphorus (P), and combinations thereof. More preferably, the light emitting element 11 is a LED chip emitting purple, blue, or green light.
Preferably, light emission spectrum of the light emitting element 11 has a peak wavelength ranging from 350 nm to 500 nm.
Preferably, the fluorescent material of the fluorescent layer 12 is formed on the light emitting element 11 via vapor deposition method. More preferably, the fluorescent material forms a thin film on the light emitting element 11, and the thin film has a smooth surface.
According to the present invention, a fluorescent material of the fluorescent layer 12 is represented by the following formula (I):

M1yM2nOzCx:M3w  (I);

wherein M1 is selected from the group consisting of Sc3+, Y3+, La3+, Sm3+, Gd3+, Tb3+, Pm3+, Er3+, Lu3+, and combinations thereof; M2 is selected from the group consisting of Al3+, In3+, Ga3+, and combinations thereof; M3 is selected from the group consisting of Tm3+, Bi3+, Tb+, Ce3+, Eu3+, Mn3+, Er3+, Yb3+, Ho3+, Gd3+, Pr3+, Dy3+, Nd3+, and combinations thereof; and 0.45≦x/n≦0.75, 0.54≦y/n≦0.6, 0.002<w/n≦0.06, and 0.9≦z/n≦1.5.
Therefore, when n=5, 2.25≦x≦3.75, 2.7≦y≦3, 0.01<w≦0.3, and 4.5≦z≦7.5.
Preferably, M1 and M3 are different, i.e., they cannot be the same.
When the activator M3 of the fluorescent material comprises Tm3+ or Bi3+, the fluorescent material illuminates blue light. When the activator M3+ comprises Tb3+ or Ce3+, the fluorescent material illuminates yellow-green light. When the activator M3 comprises Eu3+ or Mn3+, the fluorescent material illuminates red light. The activator (M3+) of the fluorescent material not only correlates to the wavelength of emitted light but also intensifies the luminescence effect of the fluorescent material.
Preferably, w/n ranges from 0.002 to 0.06. When w/n is less than 0.002, the luminous intensity is insufficient. On the other hand, when w/n is greater than 0.06, the wavelength of emission light would be increased, which results in lower luminous intensity.
Preferably, the fluorescent material is selected from the group consisting of Y2.98Al5O7.5C2.25:Tm0.02, Y2.95Al5O6C3:Bi0.05, Y2.94Al5O6C3:Tb0.06, Y2.95Al5O7.5C2.25:Ce0.05, Y2.95Al5O6C3:Ce0.05, Y2.95Al5O4.5C3.75:Ce0.05, Y2.95Al5O6C3:Mn0.05, Y2.75GaAl4O6C3:Mn0.25, Y2.94Al5O4.5C3.75:Bi0.06, Y2.94Al5O4.5C3.75:Tm0.06, Y2.94Al5O4.5C3.75:Ce0.04Tb0.02, Y2.95Al5O4.5C3.75:Mn0.05, Y2.95Ga5O4.5C3.75:Mn0.05, Y2.94Al5O6C3:Bi0.06, Y2.94Al5O6C3:Mn0.06, Y2.94Al5O6C3:Ce0.06, Lu1.72Gd1.2Al5O6C3:Ce0.05Pr0.03, Lu1.72Er1Ga5O4.5C3.75:Mn0.25Dy0.03, Lu1.92Sc1Al5O6C3:Ce0.05Yb0.03, Sm1.92La1Al5O6C3:Ce0.05Ho0.03, Y2.32Gd0.6In1Al4O6C3:Ce0.05Nd0.03, and Lu1.95Pm1Al5O6C3:Ce0.05.
Preferably, the emission wavelength for the fluorescent material ranges from 380 nm to 700 nm. When M3+ comprises Tb3+, Er3+, Yb3+ or Ho3+, the emission wavelength ranges from 380 nm to 535 nm. When M3+0 comprises Gd3+, Pr3+, Dy3+, or Nd3+, the emission wavelength ranges from 535 nm to 700 nm.
Preferably, the fluorescent material has an excitation wavelength ranging from 250 nm to 500 nm.
Preferably, the fluorescent material has a particle size ranging from 5 nm to 20 μm.
The fluorescent material can be produced by, but is not limited to, solid-state reaction method, sol-gel reaction method, or co-precipitation method.
Preferably, the fluorescent material is produced by the solid-state reaction method. Because of its relatively simple process, it may be easily applied in manufacturing large quantities of the fluorescent material. More preferably, the sintering temperature used in the solid-state reaction method is 1800° C., and temperature of reduction is 1500° C.
EXAMPLES
Source of Chemicals
1. Bismuth (III) oxide (Bi2O3): commercially available from ACROS Organics, 99.9% of purity, reagent grade.
2. Barium fluoride (BaF2): commercially available from ACROS Organics, 99.9% of purity, reagent grade.
3. Thulium (III) oxide (Tm2O3): commercially available from ACROS Organics, 99.9% of purity, reagent grade.
4. Cerium (IV) oxide (CeO2): commercially available from ACROS Organics, 99.9% of purity, reagent grade.
5. Ammonium bicarbonate (NH4HCO3): commercially available from ACROS Organics, 99.9% of purity, reagent grade.
6. Manganese dioxide (MnO2): commercially available from ACROS Organics, 99.9% of purity, reagent grade.
7. Yttrium (III) oxide (Y2O3): commercially available from ACROSS Organics, 99.9% of purity, reagent grade.
8. Aluminum oxide (Al2O3): commercially available from ACROS Organics, 99.9% of purity, reagent grade.
9. Bismuth (IV) oxide (BiO2): commercially available from ACROS Organics, 99.9% of purity, reagent grade.
10. Terbium (III, IV) oxide (Tb4O7): commercially available from ACROS Organics, 99.9% of purity, reagent grade.
11. Gallium (III) oxide (Ga2O3): commercially available from ACROS Organics, 99.9% of purity, reagent grade.
12. Gadolinium (III) oxide (Gd2O3): commercially available from ACROS Organics, 99.9% of purity, reagent grade.
13. Lutetium (III) oxide (Lu2O3): commercially available from ACROS Organics, 99.9% of purity, reagent grade.
14. Erbium (III) oxide (Er2O3): commercially available from ACROS Organics, 99.9% of purity, reagent grade.
15. Dysprosium (III) oxide (Dy2O3): commercially available from ACROS Organics, 99.9% of purity, reagent grade.
16. Praseodymium (III, IV) oxide (Pr6O11): commercially available from ACROS Organics, 99.9% of purity, reagent grade.
17. Scandium (III) oxide (Sc2O3) commercially available from ACROS Organics, 99.9% of purity, reagent grade.
18. Ytterbium (III) oxide (Yb2O3): commercially available from ACROS Organics, 99.9% of purity, reagent grade.
19. Samarium (III) oxide (Sm2O3): commercially available from ACROS Organics, 99.9% of purity, reagent grade.
20. Holmium (III) oxide (Ho2O3): commercially available from ACROS Organics, 99.9% of purity, reagent grade.
21. Neodymium (III) oxide (Nd2O3): commercially available from ACROS Organics, 99.9% of purity, reagent grade.
22. Promethium (III) oxide (Pm2O3): commercially available from ACROS Organics, 99.9% of purity, reagent grade.
23. Barium magnesium aluminate (BaMgAl10O17, also known as BAM): commercially available from Nemoto & Co. Ltd.
24. Yttrium aluminum garnet (also known as YAG): commercially available from Nemoto & Co. Ltd.
25. Europium (III)-doped Yttrium aluminum garnet (also known as YAG:Eu): commercially available from Nemoto & Co. Ltd.
26. Yttrium carbide (Y4C3): synthesized from Y2O3 and C under an argon gas atmosphere ranging from 1200° C. to 1800° C.
27. Aluminum carbide (Al4C3): synthesized from Al2O3 and C under an argon gas atmosphere ranging from 1200° C. to 1800° C.
28. Cerium carbide (Ce4C3): synthesized from CeO2 and C under an argon gas atmosphere ranging from 1200° C. to 1800° C.
28. Gallium carbide (Ga4C3): synthesized from Ga2O3 and C under an argon gas atmosphere ranging from 1200° C. to 1800° C.
EXAMPLE
Example 1 (E1)
Preparation of fluorescent material: 33.65 grams of Y2O3 (precursor for M1), 0.39 grams of Tm2O3 (precursor for M3), 20.39 grams of Al2O3 (precursor for M2), 5.4 grams of Al4C3 (precursor for M2), and 2.9 grams of BaF2 as a flux agent were mixed together to form a mixture. The mixture was disposed in a crucible, followed by heating to 1650° C. with 5° C./min increasing rate and calcining for 24 hours under a nitrogen gas atmosphere. The reaction product was then cooled to room temperature with 5° C./min decreasing rate, followed by pulverizing, washing, drying, and sieving using a #400 mesh sieve. After reducing at 1500° C. for 12 hours under a reducing atmosphere of nitrogen gas and hydrogen gas (85%/15% by volume), a fluorescent powder of Example 1 was obtained. The ingredients and the amounts of the ingredients for Examples 1 are shown in Table 1.
Example 2 ̃22 (E2 ̃E22)
The methods for preparing fluorescent materials of Examples 2 to 22 were the same as that of Example 1, except for the ingredients and the amounts of the ingredients. The ingredients and the amounts of the ingredients for Examples 2 to 22 are shown in Table 1.
Comparative Example 1 ̃4 (CE1 ̃CE4)
Fluorescent powders for Comparative Examples 1 to 3 were commercially available and were Y2.95Ce0.05Al5O12, Y2.9Eu0.1Al5O12, and BAM, respectively. A fluorescent powder of Comparative Example 4, Y3Al2O7.5:Ce, was obtained using the same method as that of Example 1. Ingredients and amounts of the ingredients for Comparative Example 4 can also be found in Table 1.
[Photoluminescence Test]
The fluorescent powder of Example 1 was excited by purple light with a 400 nm peak wavelength, and emission spectrum thereof was measured by virtue of photoluminescence effect. The fluorescent powder of Example 1 emits blue light with a 460 nm peak wavelength (shown in Table 2). Photoluminescence tests for Examples 2 to 22 and Comparative Examples 1 to 4 were performed as well. The colors and peak wavelengths of excitation light and emission light for Examples 2 to 22 and Comparative Examples 1 to 4 are also found in Table 2.








TABLE 1








Ingredient (g)










Precursor compound















M1
M2
M3
flux



Formula
(g)
(g)
(g)
agent





Exp.







E1
Y2.98Al5O7.6C2.26:Tm0.02
Y2O3
Al2O3
Tm2O3
BaF2




33.65 g
15.29 g
0.39 g
2~3 g





Al4C3







10.8 g




E2
Y2.95Al5O6C3:Bi0.06
Y2O3
Al2O3
Bi2O3
BaF2




33.31 g
5.1 g
1.16 g
2~3 g





Al4C3







14.4 g




E3
Y2.94Al5O6C3:Tb0.06
Y2O3
Al2O3
Tb4O7
BaF2




33.19 g
5.1 g
1.12 g
2~3 g





Al4C3







14.4 g




E4
Y2.95Al5O7.5C2.25:Ce0.06
Y2O3
Al2O3
CeO2
BaF2




33.31g
15.29 g
0.87 g
2~3 g





Al4C3







10.8 g




E5
Y2.95Al5O6C3:Ce0.06
Y2O3
Al2O3
CeO2
BaF2




33.31 g
5.1 g
0.87 g
2~3 g





Al4C3







14.4 g




E6
Y2.95Al5O4.5C3.76:Ce0.06
Y2O3
Al4C3
CeO2
BaF2




33.31 g
18 g
0.87 g
2~3 g


E7
Y2.95Al5O6C3:Mn0.05
Y2O3
Al2O3
MnO2
BaF2




33.31 g
5.1 g
0.43 g
2~3 g





Al4C3







14.1 g




E8
Y2.75GaAl4O6C3:Mn0.26
Y2O3
Ga2O3
MnO2
BaF2




31.06 g
9.37 g
2.17 g
2~3 g





Al4C3







14.4 g




E9
Y2.94Al5O4.5C3.75:Bi0.06
Y2O3
Al4C3
Bi2O3
BaF2




33.19 g
18 g
1.4 g
2~3 g


E10
Y2.94Al5O4.5C3.75:Tm0.06
Y2O3
Al4C3
Tm2O3
BaF2




33.19 g
18 g
1.16 g
2~3 g


E11
Y2.95Al5O4.5C3.75:Ce0.06
Y2O3
Al4C3
CeO2
BaF2




33.31 g
18 g
0.87 g
2~3 g


E12
Y2.95Al5O4.5C3.75:Mn0.06
Y2O3
Al4C3
MnO2
BaF2




33.31 g
18 g
0.43 g
2~3 g


E13
Y2.95Ga5O4.5C3.75:Mn0.05
Y2O3
Ga4C3
MnO2
BaF2




33.31 g
40.8 g
0.43 g
2~3 g


E14
Y2.94Al5O6C3:Bi0.06
Y2O3
Al4C3
Bi2O3
BaF2




33.19 g
18 g
1.4 g
2~3 g


E15
Y2.94Al5O6C3:Mn0.06
Y2O3
Al4C3
MnO2
BaF2




33.19 g
18 g
0.52 g
2~3 g


E16
Y2.94Al5O6C3:Ce0.06
Y2O3
Al4C3
CeO2
BaF2




33.19 g
18 g
1.04 g
2~3 g


E17
Lu1.72Gd1.2Al5O6C3:
Lu2O3
Al2O3
CeO2
BaF2



Ce0.05Pr0.03
34.22 g
5.1 g
0.87 g
2~3 g




Gd2O3
Al4C3
Pr6O11





21.75 g
14.4 g
0.51 g



E18
Lu1.72Er1Ga3O4.5C3.75:
Lu2O3
Al4C3
Mn2O3
BaF2



Mn0.25Dy0.03
34.22 g
18 g
2.17 g
2~3 g




Er2O3

Dy2O3





19.13 g

0.56 g



E19
Lu1.92Sc1Al5O6C3:
Lu2O3
Al4C3
CeO2
BaF2



Ce0.05Yb0.03
38.2 g
14.4 g
0.87 g
2~3 g




Sc2O3
Al2O3
Yb2O3





7.57 g
5.1 g
0.59 g



E20
Sm1.92La1Al5O6C3:
La2O3
Al4C3
CeO2
BaF2



Ce0.05Ho0.03
16.29 g
14.4 g
0.87 g
2~3 g




Sm2O3
Al2O3
Ho2O3





33.48 g
5.1 g
0.57 g



E21
Y2.32Gd0.6In1Al4O6C3:
Y2O3
In2O3
CeO2
BaF2



Ce0.05Nd0.03
26.19 g
13.88 g
0.87 g
2~3 g




Gd2O3
Al4C3
Nd2O3





10.88 g
14.4 g
0.51 g



E22
Lu1.96Pm1Al5O6C3:Ce0.05
Lu2O3
Al2O3
CeO2
BaF2




38.8 g
5.1 g
0.87 g
2~3 g




Pm2O3
Al4C3






16.89 g
14.4 g




Comparative Example














CE1
Y2.95Ce0.05Al5O12
Commercial Product


CE2
Y2.9Eu0.1Al5O12
Commercial Product


CE3
BAM
Commercial Product












CE4
Y3Al2O7.5:Ce
Y2O3
Al2O3
CeO2
BaF2




33.3 g
10.2 g
0.87 g
2~3 g





Note:


“—” represents “none”
















TABLE 2







Excitation
Emission




Wavelength
Wavelength




(nm)
(nm)



Formula
Color
color







Exp.





E1
Y2.98Al5O7.5C2.25:Tm0.02
~400
460




Purple
Blue


E2
Y2.98Al5O6C3:Bi0.05
~400
450




Purple
Blue


E3
Y2.94Al5O6C3:Tb0.06
~400
520




Purple
Green


E4
Y2.93Al5O7.5C2.25:Ce0.05
440~480
530




Blue
Yellow-Green


E5
Y2.85Al5O6C3:Ce0.05
440~480
530




Blue
Yellow-Green


E6
Y2.95Al5O4.5C3.75:Ce0.05
440~480
530




Blue
Yellow-Green


E7
Y2.95Al5O6C3:Mn0.05
440~480
650




Blue
Red


E8
Y2.75GaAl4O6C3:Mn0.25
440~480
675




Blue
Red


E9
Y2.94Al5O4.5C3.75:Bi0.06
~400
455




Purple
Blue


E10
Y2.94Al5O4.5C3.75:Tm0.06
~400
450




Purple
Blue


E11
Y2.35Al5O4.5C3.75:Ce0.06
440~480
530




Blue
Yellow-Green


E12
Y2.95Al5O4.5C3.75:Mn0.05
440~480
650




Blue
Red


E13
Y2.95Ga5O4.5C3.75:Mn0.05
440~480
673




Blue
Red


E14
Y2.94Al5O6C3:Bi0.06
~400
450




Purple
Blue


E15
Y2.94Al5O8C3:Mn0.06
440~480
650




Blue
Red


E16
Y2.94Al5O8C3:Ce0.06
440~480
530




Blue
Yellow-Green


E17
Lu1.72Gd1.2Al5O6C3:
450~490
540



Ce0.06Pr0.83
Blue
Yellow-Green


E18
Lu1.72Er1Ga5O4.5C3.76:
450~490
675



Mn0.25Dy0.03
Blue
Red


E19
Lu1.92Sc1Al5O6C3:
450~490
525



Ce0.05Yb0.03
Blue
Yellow-Green


E20
Sm1.92La1Al5O6C3:
450~490
535



Ce0.85Ho0.03
Blue
Yellow-Green


E21
Y2.32Gd0.6In2Al4O6C3:
450~490
550



Ce0.05Nd0.03
Blue
Yellow


E22
Lu1.95Pm1Al5O6C3:Ce0.05
440~480
530




Blue
Yellow-Green


Comparative





Example





CE1
Y2.95Ce0.05Al5O12
450~490
530




Blue
Yellow-Green


CE2
Y2.9Eu0.1Al5O12
400
620




Purple
Red


CE3
BAM
400
450




Purple
Blue


CE4
Y3Al2O7.5:Ce
400~490
N/A




Purple AND





Blue









As shown in Table 2, the fluorescent powder of Comparative Example 1, Y2.95Ce0.05Al5O12, is excited by blue light and emits yellow light with 530 nm peak wavelength; Y2.9Eu0.1Al5O12 of Comparative Example 2 is excited by purple light and emits red light with 620 nm peak wavelength. This reveals that different co-activators (M3) in the fluorescent powders result in different excitation and emission peak wavelengths.
From Examples 4 to 6, it is shown that an increase in carbon content and a decrease in oxygen content in the fluorescent powders do not affect peak wavelength of emission spectrum. The peak wavelengths of emission spectrum are primarily related to the species of activators M3 in fluorescent materials. In these examples, when M3 comprises Tm3+ or Bi3+, the fluorescent material emits blue light. When M3 comprises Tb3+ or Ce3+, the fluorescent material emits green, yellow, or yellow-green light. When M3 comprises Mn3+, the fluorescent material emits red light. When M3 in the fluorescent material comprises Tb+, Yb3+ or Ho3+, the peak wavelength of emission spectrum of the fluorescent material ranges from 520 nm to 535 nm. When M3 of fluorescent material comprises Pr3+, Dy3+, or Nd3+, the peak wavelength of emission spectrum of the fluorescent material ranges from 540 nm to 675 nm.
FIG. 2 shows relative emission spectra of the fluorescent powders of Example 12 (Y2.95Al5O4.5C3.75:Mn0.05) and Comparative Example 2 (YAG:Eu3+), each of which is excited by purple light with 400 nm peak wavelength. The results show that the fluorescent powder of Example 12 has stronger photoluminescence intensity as compared to that of Comparative Example 2.
FIG. 3 shows the spectra of the fluorescent powders of Comparative Example 3 (BAM) and Example 14 (Y2.94Al5O6C3:Bi0.06). When the fluorescent powder of Comparative Example 3 is excited by purple light with a 400 nm peak wavelength, the emission peak wavelength is around 450 nm (blue light), and the average number of photons emitted per frequency in spectrum is 446.9. When the fluorescent powder of Example 14 is excited by purple light with a 400 nm peak wavelength, the emission peak wavelength is around 450 nm (blue light), and the average number of photons emitted per frequency in the spectrum is 701.1. The results show that the fluorescent powder of Example 14 has better illuminating efficiency than that of Comparative Example 3.
It is noted that the fluorescent powder of Comparative Example 4 (Y3Al2O7.5:Ce) is a white powder, and has different structure from other conventional YAG phosphors (Y3Al3 ̃5O9 ̃12). FIG. 4 is a CIE chromaticity coordinate diagram for Comparative Example 4, which shows a blue light output when the fluorescent material of Comparative Example 4 is excited by blue light with a peak emission wavelength of 450 nm. This indicates that the fluorescent material of Comparative Example 4 cannot be excited by blue light.
As shown in FIG. 5, when the fluorescent powder of Example 4 is excited by blue light with a peak emission wavelength of 450 nm, the chromaticity coordinates of Example 4 are located in zone of white color. This indicates that the fluorescent powder of Example 4 emits yellow-greenish light, and the emitted yellow-greenish light mixes with part of blue light to form white light. The major difference in formula between the fluorescent powder of Example 4 and the fluorescent powder of Comparative Example 4 resides in the atom numbers of aluminum (Al) and carbon (C). The difference in the atom numbers of aluminum and carbon between Example 4 and Comparative Example 4 is (Al4C3)0.75, which causes phosphor emission for the fluorescent powder of Example 4. Based on formula (I), the difference in the atom numbers of aluminum and carbon between the fluorescent materials of this invention and conventional materials could range from 2.25 to 3.75.
FIG. 6 is a graph showing degradation of light emission intensity with change of temperature for the fluorescent powders of Example 5 (Y2.95Al5O6C3:Ce0.05) and of Comparative Example 1 (Y2.95Ce0.05Al5O12). FIG. 6 shows that degradation level of light emission intensity for Example 5 is less than that of Comparative Example 1. It is suggested that the less degradation might be attributed to the covalent bond of carbon elements, which improves thermal resistance for the fluorescent powder of Example 5.
In the aspect of color rendering index, the conventional YAG fluorescent materials have color rendering index (Ra) of around 80%. Some other conventional fluorescent materials, which are modified by substituting aluminum element of YAG with silicon element, have similar color rendering index (Ra) of around 80% since the structures thereof are similar to that of YAG. However, the color rendering index of the fluorescent materials of this invention might be greater than 85%, which is better than that of the conventional YAG or YAG-modified materials.
To sum up, by altering the species and the amounts of elements in the fluorescent material of this invention, the fluorescent materials irradiating different colors of light can be obtained. Also, substitution of part of oxygen (O) atoms with carbon (C) atoms in the fluorescent material of this invention would enhance the bonding strength through covalent bonds of carbon atoms. The fluorescent material of this invention has a sintering temperature of around 1800° C. and has good thermal resistance. Moreover, superior color rendering index can be achieved in this invention.
While the present invention has been described in connection with what are considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation and equivalent arrangements.

## Claims

1. A fluorescent material
wherein said fluorescent material is selected from the group consisting of
Y2.98Al5O7.5C2.25:Tm0.02, Y2.95Al5O6C3:Bi0.05, Y2.94Al5O6C3:Tb0.06, Y2.95Al5O7.5C2.25:Ce0.05,
Y2.95Al5O6C3:Ce0.05, Y2.95Al5O4.5C3.75:Ce0.05,
Y2.95Al5O6C3:Mn0.05, Y2.75GaAl4O6C3:Mn0.25,
Y2.94Al5O4.5C3.75:Bi0.06, Y2.94Al5O4.5C3.75:Tm0.06,
Y2.94Al5O4.5C3.75:Ce0.04Tb0.02, Y2.95Al5O4.5C3.75:Mn0.05,
Y2.95Ga5O4.5C3.75:Mn0.05, Y2.94Al5O6C3:Bi0.06,
Y2.94Al5O6C3:Mn0.06, Y2.94Al5O6C3:Ce0.06,
Lu1.72Gd1.2Al5O6C3:Ce0.05Pr0.03,
Lu1.72Er1Ga5O4.5C3.75:Mn0.25Dy0.03,
Lu1.92Sc1Al5O6C3:Ce0.05Yb0.03,
Sm1.92La1Al5O6C3:Ce0.05Ho0.03,
Y2.32Gd0.6In1Al4O6C3:Ce0.05Nd0.03, and
Lu1.95Pm1Al5O6C3:Ce0.05.

2. The fluorescent material of claim 1, wherein said fluorescent material has an emission wavelength ranging from 380 nm to 700 nm.

3. The fluorescent material of claim 1, wherein said fluorescent material has an excitation wavelength ranging from 250 nm to 500 nm.

4. An illumination device, comprising:
a light emitting element; and
a fluorescent layer that is formed on said light emitting element, that includes a fluorescent material of claim 1, and that is capable of absorbing light emitting from said light emitting element.

5. The illumination device of claim 4, wherein said fluorescent material has an emission wavelength ranging from 380 nm to 700 nm.

6. The illumination device of claim 4, wherein said fluorescent material has an excitation wavelength ranging from 250 nm to 500 nm.