Compositions – Inorganic luminescent compositions – Compositions containing halogen; e.g. – halides and oxyhalides
Reexamination Certificate
2002-03-01
2003-09-30
Koslow, C. Melissa (Department: 1755)
Compositions
Inorganic luminescent compositions
Compositions containing halogen; e.g., halides and oxyhalides
C252S30140P, C428S403000, C428S404000, C313S582000, C313S584000, C313S643000
Reexamination Certificate
active
06627114
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rare earth oxide type phosphor which is excited by vacuum ultraviolet rays (VUV) having a wavelength of at most 200 nm and emits light highly efficiently, a phosphor paste containing said phosphor, and a light-emitting device comprising a phosphor layer containing said phosphor. Particularly, it relates to a rare earth oxide type phosphor for VUV excitation, with which a decrease of brightness with time is small, suitable for a vacuum ultraviolet ray excitation type light-emitting device (VUV excitation type light-emitting device) such as a plasma display panel (PDP) or a rare gas discharge lamp.
2. Discussion of Background
A VUV excitation type light-emitting device represented by e.g. PDP or a rare gas discharge lamp, comprises a transparent envelope and a phosphor layer containing a phosphor for VUV formed inside of the envelope, so that the phosphor layer is excited by VUV having a wavelength of at most 200 nm, radiated by discharge of a rare gas sealed in the envelope, such as Ar, Xe, He, Ne, He—Xe or Ne—Xe, to emit visible light.
With respect to the phosphor for VUV to be used for the phosphor layer for the VUV excitation type light-emitting device, it undergoes baking deterioration due to heat in a baking treatment at the time of the phosphor layer formation, and further, it undergoes deterioration due to VUV irradiation or ion impact at the time of discharge of a rare gas, thus leading to a decrease of luminescence brightness. Accordingly, it is required for the phosphor for VUV that the baking deterioration is small (baking resistance) and the deterioration due to VUV or ion impact is small (VUV resistance, ion impact resistance).
Here, as the phosphor for VUV, a red color-emitting phosphor such as (Y,Gd)BO
3
:Eu, Y
2
O
3
:Eu or (Y,Gd)
2
O
3
:Eu, a green color-emitting phosphor such as Zn
2
SiO
4
:Mn, LaPO
4
:Ce, Tb or (Ba, Sr, Mg)O.aAl
2
O
3
:Mn, or a blue color or blue green color-emitting phosphor such as BaMgAl
10
O
17
:Eu, BaMgAl
10
O
17
:Eu or Mn, may, for example, be used.
Among these phosphors for VUV, particularly with respect to a rare earth oxide type phosphor for VUV excitation represented by the formula (Y
1-x-y
, Ln
x
, Re
y
)
2
O
3
wherein Ln is at least one rare earth element selected from the group consisting of Gd, La and Lu, Re is at least one rare earth element selected from the group consisting of Eu, Tm, Sm and Pr, and x and y are numbers which satisfy conditions 0≦x≦1−y and 0.001≦y≦0.1, such as Y
2
O
3
:Eu or (Y,Gd)
2
O
3
:Eu, when continuously used as a phosphor layer for a VUV excitation type light-emitting device, a decrease of brightness with time tends to be significant, and improvement has been desired.
SUMMARY OF THE INVENTION
The present invention has been made to overcome the above problems, and it is an object of the present invention to provide a rare earth oxide type phosphor with which a decrease of luminescence brightness with time is small, and which is excellent in VUV resistance with less deterioration due to VUV or ion impact, when used under excitation by VUV having a wavelength of at most 200 nm for a long period of time, a phosphor paste composition and a VUV excitation type light-emitting device.
The present inventors have conducted extensive studies on improvement of the VUV resistance of a phosphor by subjecting the phosphor to surface treatment, and as a result, have found that by coating the surface of a rare earth oxide type phosphor with a compound containing Mg and P in its composition such as magnesium phosphate, the VUV resistance improves, and the decrease of luminescence brightness with time can be suppressed when the phosphor is irradiated with VUV to emit light, and the present invention has been accomplished.
Namely, the present invention provides:
(1) A phosphor for vacuum ultraviolet ray excitation, which comprises a rare earth oxide type phosphor, wherein at least part of the surface of the rare earth oxide type phosphor is coated with a compound containing at least a magnesium element and a phosphorus element.
(2) The phosphor for vacuum ultraviolet ray excitation according to the above (1), wherein the vacuum ultraviolet rays for excitation have a wavelength of at most 160 nm.
(3) The phosphor for vacuum ultraviolet ray excitation according to the above (1) and (2), wherein the rare earth oxide type phosphor is represented by the following formula:
(Y
1-x-y
, Ln
x
, Re
y
)
2
O
3
wherein Ln is at lease one rare earth element selected from the group consisting of Gd, La and Lu, Re is at least one rare earth element selected from the group consisting of Eu, Tm, Sm and Pr, and x and y are numbers which satisfy conditions 0≦x≦1−y and 0.001≦y≦0.2.
(4) The phosphor for vacuum ultraviolet ray excitation according to the above (3), wherein Re is Eu.
(5) The phosphor for vacuum ultraviolet ray excitation according to any one of the above (1) to (4), wherein the compound containing at least a magnesium element and a phosphorus element is a magnesium phosphate type compound.
(6) The phosphor for vacuum ultraviolet ray excitation according to any one of the above (1) to (5), wherein the content of magnesium is within a range of from 0.001 to 2 wt %, preferably from 0.01 to 0.5 wt %, on the basis of the weight of the rare earth oxide type phosphor.
(7) The phosphor for vacuum ultraviolet ray excitation according to any one of the above (1) to (6), wherein the content of phosphorus is within a range of from 0.001 to 2 wt %, preferably from 0.01 to 0.4 wt %, on the basis of the weight of the rare earth oxide type phosphor.
(8) A phosphor paste composition comprising a binder solution and the phosphor for vacuum ultraviolet ray excitation as defined in any one of the above (1) to (7), dispersed in the solution.
(9) A vacuum ultraviolet ray excitation type light-emitting device comprising an envelope and a phosphor layer formed inside of the envelope, so that the phosphor layer is excited by vacuum ultraviolet rays generated by discharge of a rare gas sealed in the envelope, to emit light, wherein the phosphor layer comprises the phosphor for vacuum ultraviolet ray excitation as defined in any one of the above (1) to (7).
(10) The vacuum ultraviolet ray excitation type light-emitting device according to the above (9), wherein the vacuum ultraviolet rays include at least vacuum ultraviolet rays having wavelengths of from 160 to 120 nm.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
According to the present invention, there is provided a rare earth oxide type phosphor which highly efficiently emits light under excitation with vacuum ultraviolet rays (VUV) having a wavelength of at most 200 nm, particularly at most 160 nm, and which has an excellent brightness maintenance ratio, by coating at least part of the surface of a rare earth oxide type phosphor with a magnesium phosphate type compound containing at least a Mg element and a P element as constituents in its composition, such as magnesium phosphate.
The rare earth oxide type phosphor for VUV excitation may be a phosphor which emits light with high brightness under irradiation with VUV having a wavelength of at most 200 nm, and a phosphor represented by the following formula may, for example, be used:
(Y
1-x-y
, Ln
x
, Re
y
)
2
O
3
wherein Ln is at least one rare earth element selected from the group consisting of Gd, La and Lu, Re is at least one rare earth element selected from the group consisting of Eu, Tm, Sm and Pr, and x and y are numbers which satisfy conditions 0≦x≦1−y and 0.001≦y≦0.2, preferably 0≦x≦0.4−y and 0.02≦y≦0.1. Specifically, a Y
2
O
3
:Eu phosphor and (Y,Gd)
2
O
3
:Eu phosphor may, for example, be mentioned.
The magnesium phosphate type compound to be used for coating of the surface of the rare earth oxide type phosphor of the present invention is not particularly limited so long as it is a compound containing at least a Mg element and a P element in its composition, and examples of whi
Kasei Optonix Ltd.
Koslow C. Melissa
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