Fluorescent substance
A green fluorescent substance of the invention is higher in luminance of green than a conventional rare-earth activated sialon fluorescent substance and more excellent in durability than a conventional oxide fluorescent substance. The fluorescent substance is obtained by solid-dissolving Eu into a nitride or oxy-nitride crystal having a β-type Si 3 N 4 crystal structure, and emits a fluorescent light having a peak within a range of 500 nm to 600 nm in wavelength by being irradiated with an excitation source.
1. A fluorescent substance comprising a crystal of nitride or oxy-nitride having a β-type Si 3 N 4 crystal structure having Eu +2 solid-dissolved into it and emitting a fluorescent light having a peak within a range of 500 nm to 600 nm in wavelength by being irradiated with an excitation source.
2. A fluorescent substance according to claim 1 , wherein said crystal having a β-type Si 3 N 4 crystal structure comprises a β-type sialon (Si 6-z Al z O z N 8-z , where 0≦z≦4.2).
3. A fluorescent substance according to claim 2 , wherein the value of said z is 0≦z≦0.5.
4. A fluorescent substance according to claim 1 , wherein in case of representing Eu, A (where A is one, two or more kinds of elements selected from C, Si, Ge, Sn, B, Al, Ga and In) and X (where X is one or two kinds of elements selected from O and N) which are contained in said nitride or oxy-nitride crystal with a composition formula Eu a A b X c (where a+b+c=1), a, b and c in this formula meet the following relations (i) to (iii):
0.00001≦a≦0.1 (i)
0.38≦b≦0.46 (ii)
0.54≦c≦0.62 (iii).
5. A fluorescent substance according to claim 1 , wherein in case of representing said nitride or oxy-nitride crystal with a composition formula Eu a Si b1 Al b2 O c1 N c2 (where a +b 1 +b 2 +c 1 +c 2 =1), a, b 1 , b 2 , c 1 and c 2 in this formula meet the following relations (i) to (v):
0.00001≦a≦0.1 (i)
0.28≦b 1 ≦0.46 (ii)
0.001≦b 2 ≦0.3 (iii)
0.001≦c 1 ≦0.3 (iv)
0.4≦c 2 ≦0.62 (v).
6. A fluorescent substance according to claim 5 , wherein in said composition formula Eu a Si b1 Al b2 O c1 N c2 , the relation between b 1 and b 2 and the relation between c 1 and c 2 respectively meet the following relations:
0.41 ≦b 1 +b 2 ≦0.44, and
0.56 ≦c 1 +c 2 ≦0.59.
7. A fluorescent substance according to claim 1 , wherein said excitation source is an ultraviolet light or a visible light of 100 nm to 500 nm in wavelength.
8. A fluorescent substance according to claim 7 , wherein said excitation source is a violet light or a blue light of 400 nm to 500 nm in wavelength.
9. A fluorescent substance according to claim 1 , wherein said excitation source is an electron beam or an X ray.
10. A fluorescent substance according to claim 1 , wherein said peak is within a range of 500 nm to 550 nm in wavelength.
11. A fluorescent substance according to claim 1 , wherein x and y of a value (x, y) on a CIE chromaticity coordinates of a color of light emitted at a time of being irradiated with said excitation source meet the followinq relations (i) and (ii):
0≦x≦0.3 (i)
0.5≦y≦0.83 (ii).
12. A fluorescent substance according to claim 1 , wherein said nitride or oxy-nitride crystal comprises a single crystal of 50 nm to 20 μm in average grain diameter.
13. A fluorescent substance according to claim 1 , wherein said nitride or oxy-nitride crystal is a single crystal of 1.5 to 20 in average aspect ratio.
14. A fluorescent substance according to claim 1 , wherein a total of impurity elements Fe, Co and Ni contained in said nitride or oxy-nitride crystal is not more than 500 ppm.