Patent Application
20080081012
An electron beam-excited blue phosphor of the present invention is a rare earth-activated alkaline earth thiosilicate represented by a general formula M1xM22-xSi2OyS6-yRaz (where M1 and M2 each represent an alkaline earth metal, Ra represents a rare earth ion Ce3+ or Eu2+, and x, y, and z satisfy the relationships of 0≦x≦2, 0<y<6, and z≧0.005).
In the present invention, the body color of the phosphor measured with a D65 light source and a 2-degree field of view is preferably in the range of a*>0 and b*<0, and furthermore, an angle φ formed by the straight line connecting the point of the body color and the origin relative to an a* axis in an L*a*b* calorimetric chromaticity diagram preferably satisfies the relationship of 39°<φ<60°.
The electron beam-excited blue phosphor of the present invention shows sufficiently satisfactory color purity under low and medium acceleration voltages of about 15 kV or less, secures luminance linearity in a high current region, and stably emits light against the input of charge.
Hereinafter, an embodiment of the present invention will be described in detail.
An electron beam-excited blue phosphor of this embodiment is a phosphor represented by a formula M1xM22-xSi2OyS6-yRaz obtained by substituting part of the oxygen atoms of a rare earth-activated alkaline earth silicate phosphor represented by a general formula M1xM22-xSi2O6Raz with sulfur atoms. The substitution can be achieved by a reductive high-temperature annealing treatment in an H2S or S gas atmosphere. The substitution is mainly the capping of O atoms and O vacancies present in the surface of the phosphor. In other words, the substitution reduces the number of the O vacancies in the surface of the phosphor. The reduction leads to a suppressing effect on the diffusion of the O atoms, the O atoms each contributing as a donor of energy to a luminescent center metal in a bulk, to the surface of the phosphor as a non-light-emitting region, whereby a phenomenon in which the luminance of the phosphor deteriorates over time due to the input of charge can be reduced.
For example, a reduction in number of O vacancies can be observed as a result of annealing in the atmosphere, but the oxidation of Ce3+ or Eu2+ as a luminescent center metal represented by Ra in the general formula occurs, thereby causing the problem of a significant reduction in luminance of the phosphor. Although a reducing atmosphere is indispensable for annealing, a reducing atmosphere such as a CO atmosphere or an H2 atmosphere is not preferable because the atmosphere deprives the surface of the phosphor of oxygen atoms, with the result that an increase in number of O vacancies occurs.
The body color of the host material of the phosphor gradually changes from a bluish color to a reddish color depending on the degree of the substitution or capping of the above O vacancies with S atoms. In the case where the degree of the body color is observed with a D65 light source and a 2-degree field of view, the body color is in the region of b*<0 and a*>0. In the case where an angle formed by the straight line connecting the address point of the body color and the origin relative to an a* axis is represented by φ, a certain effect on the lifetime of the phosphor is observed for φ<60°. In addition, the case where φ satisfies the relationship of φ<39° is not preferable because the luminance of the phosphor reduces due to an excessively strong filter effect by the body color, though a sufficient effect on the lifetime of the phosphor can be observed. Therefore, φ desirably satisfies the relationship of 39°<φ<60°.
Here, the elements M1 and M2 each represent an alkaline earth metal such as magnesium, calcium, barium, or strontium, and the elements M1 and M2 are different from each other.
In addition, Si represents a silicon element, O represents an oxygen element, S represents a sulfur element, and Ra represents a rare earth element chosen from cerium and europium. x and y each representing a molar ratio in the general formula more suitably satisfy the relationships of 0≦x≦2 and 0<y<6.
In addition, z desirably satisfies the relationship of z≧0.005. The case where z satisfies the relationship of z<0.005 is not preferable because current saturation occurs at a relatively low current density.
The composition of the phosphor including those pieces of quantitative information can be identified by ICP, a glow discharge mass spectrum, or a combination such as a combustion-coulometric titration method or a combustion-infrared absorption method.
The element M1 most preferably represents Ca, and the element M2 most preferably represents Mg.
A rare earth-activated alkaline earth silicate phosphor having such constitution emits blue light having a good color purity and high luminous efficiency by being excited through irradiation with an electron beam.
In particular, when the phosphor is provided with a structure in which part of oxygen atoms are substituted with sulfur atoms, the number of oxygen vacancies in the surface of the phosphor is reduced by capping with sulfur atoms. Accordingly, the movement of an oxygen atom in a bulk, the oxygen atom providing a luminescent center metal with energy for light emission, to an oxygen vacancy in the surface of the phosphor by the input of excitation energy is suppressed. As a result, a phosphor which has a long lifetime, in other words, is stable against the input of charge can be obtained.
Meanwhile, the above structure in which part of oxygen atoms are substituted with sulfur atoms needs the steps of: synthesizing a structure corresponding to y=6 in the above general formula, that is, a silicate phosphor having two kinds of elements, that is, the elements M1 and M2 as alkaline earth metals at x=1; and annealing in an H2S or S atmosphere at high temperatures. In this case, the body color of the phosphor, which is bluish, changes to a reddish color. The extent to which the color changes depends on the temperature at the time of the annealing; the extent to which the color changes increases with increasing temperature.
The extent to which the color changes can be quantitatively estimated by the measurement of the diffuse reflectance of the phosphor. That is, a method of measuring the diffuse reflectance with a D65 light source or a C light source and with a 2-degree or 10-degree field of view can be employed. The color of the phosphor can be represented in an L*a*b* calorimetric system on the basis of the spectrum of the measured diffuse reflectance.
The color of the rare earth-activated alkaline earth thiosilicate phosphor presented in this proposal is in the range of a*>0 and b*<0. The L*a*b* values of the phosphor is calculated from the diffuse reflectance of the phosphor measured with a D65 light source and a 2-degree field of view, and is plotted in an L*a*b* calorimetric chromaticity diagram. In this case, when an angle formed by the straight line connecting the plotted point and the origin relative to an a* axis is represented by φ, an improving effect on the stability of the luminance of the phosphor against the input of charge is observed for φ<60°.
On the other hand, the case where φ satisfies the relationship of φ<39° is not preferable because the absorbing effect of the host material of the phosphor on light emitted from the phosphor strengthens, with the result that the luminance of the phosphor reduces.
Therefore, φ must satisfy the relationship of 39°<φ<60°.
Hereinafter, the present invention will be described in detail by way of comparative examples and specific examples.
The above compounds were each metered with a chemical balance, and were mixed. After that, the mixture mixed with acetone was sufficiently ground with an agate mortar, and then the whole was dried at 140° C. for 1 hour, whereby a precursor before calcination was prepared.
3 g of the precursor were packed in a 30-cc alumina crucible. The crucible was placed in a high-temperature atmosphere furnace in which a 5% H2/N2 mixed gas was caused to flow at a flow rate of 0.3 L/min, and the precursor was calcined at 1,250° C. for about 90 minutes. The gas was continuously caused to flow until the temperature of the precursor became 450° C. or lower. After having been slowly cooled to normal temperature, the calcined product was taken out.
The phosphor after the calcination was taken in 100 cc of pure water through a nylon 100 mesh lest a product peeled from the crucible should mix into the phosphor.
The suspension of the phosphor taken in pure water was sufficiently stirred with a magnetic stirrer. Next, the suspension was left standing so that the phosphor was precipitated, followed by the removal of the supernatant. The washing step was repeated 5 times, whereby an unnecessary calcination residue was removed.
The phosphor after the washing was filtrated with a Buchner funnel and an aspirator, and was dried at 140° C. for 5 hours.
Finally, the phosphor was subjected to vibration sorting with an SUS400 mesh, whereby a rare earth-activated alkaline earth silicate phosphor CaMgSi2O6Eu0.01 was obtained.
The phosphor thus obtained was placed in a sample chamber in a demountable reflection CL luminance evaluating apparatus shown in
The luminance and chromaticity of the emitted light were measured through an observation window made of Kovar with a BM7 luminance meter manufactured by TOPCON CORPORATION with a 1-degree field of view. It should be noted that the chromaticity were corrected in consideration of the transmittance of Kovar.
The measured luminance was 3.9×10−3 cd/m2, and the measured chromaticity coordinates (x, y) were (0.150, 0.042).
In addition, the phosphor was caused to emit light under the same excitation conditions. A time period required for the luminance under measurement to be reduced to 70% of the initial luminance was represented by t, and an input charge quantity τ70 was calculated. As a result, the quantity was 101 (C/cm2). It should be noted that the input charge quantity was calculated from the following equation by using an electron beam irradiation time t:
Q=Ie·t·Pw/f.
In the equation, Q represents an input charge quantity (C/cm2), Ie represents a current density (A/cm2), t represents a time (s), Pw represents the half width (s) of an applied current pulse, and f represents the frequency (Hz) of the pulse.
Meanwhile, 0.5 g of the phosphor was pelletized by pressure molding. The pellet was placed in a diffuse reflectance measurement unit having a structure shown in
A ZnS:Ag,Cl phosphor (manufactured by Kasei Optonix, Ltd., P22-B1 type) was placed in the same demountable reflection CL luminance evaluating apparatus as that of Comparative Example 1. The phosphor was caused to emit light by being excited through the application of a rectangular current pulse having an acceleration voltage of 10,000 V, a current density of 0.01 A/cm2, a frequency of 500 Hz, and a half width of 0.00002 s from an electron gun, and the luminance and chromaticity of the emitted light were measured. As a result, the measured luminance was 3.9×10−3 cd/m2, and the measured chromaticity (x, y) were (0.151, 0.052).
In addition, similarly to Comparative Example 1, a time period required for the luminance under measurement to be reduced to 70% of the initial luminance was represented by t, and an input charge quantity τ70 was calculated. As a result, the quantity was 99 (C/cm2)
In addition, the diffuse reflectance of the phosphor was measured in the same manner as in Comparative Example 1. Next, a value for L*a*b* under D65 light source/2-degree field of view conditions was determined by using data on the diffuse reflectance. As a result, coordinates (a*, b*) were (1.001, −7.039), and an angle φ formed by the straight line connecting the plotted point and the origin relative to an a* axis was 81.9°.
2 g of a CaMgSi2O6Eu0.01 phosphor obtained in the same manner as in Comparative Example 1 were mounted on a 50-cc quartz board. Next, the resultant was encapsulated in a quartz annular furnace, and the pressure in the furnace was reduced to about 10−2 Pa with a vacuum pump. After that, a 5% H2S/Ar mixed gas was caused to flow at a flow rate of about 0.1 L/min, and the phosphor was annealed at a temperature of 600° C. for 0.5 hour. Thus, a phosphor having a composition CaMgSi2O5.98S0.02Eu.0.01 was obtained.
In addition, the phosphor was placed in the same demountable reflection CL luminance evaluating apparatus as that of Comparative Example 1. The phosphor was caused to emit light by being excited through the application of a rectangular current pulse having an acceleration voltage of 10,000 V, a current density of 0.01 A/cm2, a frequency of 500 Hz, and a half width of 0.00002 s from an electron gun, and the luminance and chromaticity of the emitted light were measured. As a result, the measured luminance was 3.9×10−3 cd/m2, and the measured chromaticity (x, y) were (0.151, 0.041).
In addition, similarly to Comparative Example 1, a time period required for the luminance under measurement to be reduced to 70% of the initial luminance was represented by t, and an input charge quantity π70 was calculated. As a result, the quantity was 151 (C/cm2)
In addition, the diffuse reflectance of the phosphor was measured in the same manner as in Comparative Example 1. Next, a value for L*a*b* under D65 light source/2-degree field of view conditions was determined by using data on the diffuse reflectance. As a result, coordinates (a*, b*) were (2.851, −4.900), and an angle φ formed by the straight line connecting the plotted point and the origin relative to an a* axis was 59.8°.
2 g of a CaMgSi2O6Eu0.01 phosphor obtained in the same manner as in Comparative Example 1 were mounted on a 50-cc quartz board. Next, the resultant was encapsulated in a quartz annular furnace, and the pressure in the furnace was reduced to about 10−2 Pa with a vacuum pump. After that, a 5% H2S/Ar mixed gas was caused to flow at a flow rate of about 0.1 L/min, and the phosphor was annealed at a temperature of 700° C. for 1.0 hour. Thus, a phosphor having a composition CaMgSi2O5.0S1.0Eu0.01 was obtained.
In addition, the phosphor was placed in the same demountable reflection CL luminance evaluating apparatus as that of Comparative Example 1. The phosphor was caused to emit light by being excited through the application of a rectangular current pulse having an acceleration voltage of 10,000 V, a current density of 0.01 A/cm2, a frequency of 500 Hz, and a half width of 0.00002 s from an electron gun, and the luminance and chromaticity of the emitted light were measured. As a result, the measured luminance was 3.9×10−3 cd/m2, and the measured chromaticity (x, y) were (0.151, 0.041).
In addition, similarly to Comparative Example 1, a time period required for the luminance under measurement to be reduced to 70% of the initial luminance was represented by t, and an input charge quantity τ70 was calculated. As a result, the quantity was 175 (C/cm2)
In addition, the diffuse reflectance of the phosphor was measured in the same manner as in Comparative Example 1. Next, a value for L*a*b* under D65 light source/2-degree field of view conditions was determined by using data on the diffuse reflectance. As a result, coordinates (a*, b*) were (3.321, −4.521), and an angle φ formed by the straight line connecting the plotted point and the origin relative to an a* axis was 53.7°.
2 g of a CaMgSi2O6Eu0.01 phosphor obtained in the same manner as in Comparative Example 1 were mounted on a 50-cc quartz board. Next, the resultant was encapsulated in a quartz annular furnace, and the pressure in the furnace was reduced to about 10−2 Pa with a vacuum pump. After that, a 5% H2S/Ar mixed gas was caused to flow at a flow rate of about 0.1 L/min, and the phosphor was annealed at a temperature of 800° C. for 1.0 hour. Thus, a phosphor having a composition CaMgSi2O3.4S2.6Eu0.01 was obtained.
In addition, the phosphor was placed in the same demountable reflection CL luminance evaluating apparatus as that of Comparative Example 1. The phosphor was caused to emit light by being excited through the application of a rectangular current pulse having an acceleration voltage of 10,000 V, a current density of 0.01 A/cm2, a frequency of 500 Hz, and a half width of 0.00002 s from an electron gun, and the luminance and chromaticity of the emitted light were measured. As a result, the measured luminance was 3.9×10−3 cd/m2, and the measured chromaticity (x, y) were (0.151, 0.041).
In addition, similarly to Comparative Example 1, a time period required for the luminance under measurement to be reduced to 70% of the initial luminance was represented by t, and an input charge quantity τ70 was calculated. As a result, the quantity was 191 (C/cm2)
In addition, the diffuse reflectance of the phosphor was measured in the same manner as in Comparative Example 1. Next, a value for L*a*b* under D65 light source/2-degree field of view conditions was determined by using data on the diffuse reflectance. As a result, coordinates (a*, b*) were (3.670, −4.234), and an angle φ formed by the straight line connecting the plotted point and the origin relative to an a* axis was 49.1°.
2 g of a CaMgSi2O6Eu0.01 phosphor obtained in the same manner as in Comparative Example 1 were mounted on a 50-cc quartz board. Next, the resultant was encapsulated in a quartz annular furnace, and the pressure in the furnace was reduced to about 10−2 Pa with a vacuum pump. After that, a 5% H2S/Ar mixed gas was caused to flow at a flow rate of about 0.1 L/min, and the phosphor was annealed at a temperature of 900° C. for 1.0 hour. Thus, a phosphor having a composition CaMgSi2O2.2S3.8Eu0.01 was obtained.
In addition, the phosphor was placed in the same demountable reflection CL luminance evaluating apparatus as that of Comparative Example 1. The phosphor was caused to emit light by being excited through the application of a rectangular current pulse having an acceleration voltage of 10,000 V, a current density of 0.01 A/cm2, a frequency of 500 Hz, and a half width of 0.00002 s from an electron gun, and the luminance and chromaticity of the emitted light were measured. As a result, the measured luminance was 3.9×10−3 cd/m2, and the measured chromaticity (x, y) were (0.151, 0.041).
In addition, similarly to Comparative Example 1, a time period required for the luminance under measurement to be reduced to 70% of the initial luminance was represented by t, and an input charge quantity τ70 was calculated. As a result, the quantity was 205 (C/cm2)
In addition, the diffuse reflectance of the phosphor was measured in the same manner as in Comparative Example 1. Next, a value for L*a*b* under D65 light source/2-degree field of view conditions was determined by using data on the diffuse reflectance. As a result, coordinates (a*, b*) were (4.060, −3.915), and an angle φ formed by the straight line connecting the plotted point and the origin relative to an a* axis was 44.0°.
2 g of a CaMgSi2O6Eu0.01 phosphor obtained in the same manner as in Comparative Example 1 were mounted on a 50-cc quartz board. Next, the resultant was encapsulated in a quartz annular furnace, and the pressure in the furnace was reduced to about 10−2 Pa with a vacuum pump. After that, a 5% H2S/Ar mixed gas was caused to flow at a flow rate of about 0.1 L/min, and the phosphor was annealed at a temperature of 900° C. for 2.5 hours. Thus, a phosphor having a composition CaMgSi2O1.0S5.0Eu0.01 was obtained.
In addition, the phosphor was placed in the same demountable reflection CL luminance evaluating apparatus as that of Comparative Example 1. The phosphor was caused to emit light by being excited through the application of a rectangular current pulse having an acceleration voltage of 10,000 V, a current density of 0.01 A/cm2, a frequency of 500 Hz, and a half width of 0.00002 s from an electron gun, and the luminance and chromaticity of the emitted light were measured. As a result, the measured luminance was 3.9×10−3 cd/m2, and the measured chromaticity (x, y) were (0.151, 0.041).
In addition, similarly to Comparative Example 1, a time period required for the luminance under measurement to be reduced to 70% of the initial luminance was represented by t, and an input charge quantity τ70 was calculated. As a result, the quantity was 211 (C/cm2).
In addition, the diffuse reflectance of the phosphor was measured in the same manner as in Comparative Example 1. Next, a value for L*a*b* under D65 light source/2-degree field of view conditions was determined by using data on the diffuse reflectance. As a result, coordinates (a*, b*) were (4.360, −3.670), and an angle φ formed by the straight line connecting the plotted point and the origin relative to an a* axis was 40.1°.
2 g of a CaMgSi2O6Eu0.01 phosphor obtained in the same manner as in Comparative Example 1 were mounted on a 50-cc quartz board. Next, the resultant was encapsulated in a quartz annular furnace, and the pressure in the furnace was reduced to about 10−2 Pa with a vacuum pump. After that, a 5% H2S/Ar mixed gas was caused to flow at a flow rate of about 0.1 L/min, and the phosphor was annealed at a temperature of 950° C. for 4.0 hours. Thus, a phosphor having a composition CaMgSi2S6Eu0.01 was obtained.
In addition, the phosphor was placed in the same demountable reflection CL luminance evaluating apparatus as that of Comparative Example 1. The phosphor was caused to emit light by being excited through the application of a rectangular current pulse having an acceleration voltage of 10,000 V, a current density of 0.01 A/cm2, a frequency of 500 Hz, and a half width of 0.00002 s from an electron gun, and the luminance and chromaticity of the emitted light were measured. As a result, the measured luminance was 3.4×10−3 cd/m2, and the measured chromaticity (x, y) were (0.150, 0.040).
In addition, similarly to Comparative Example 1, a time period required for the luminance under measurement to be reduced to 70% of the initial luminance was represented by t, and an input charge quantity τ70 was calculated. As a result, the quantity was 239 (C/cm2)
In addition, the diffuse reflectance of the phosphor was measured in the same manner as in Comparative Example 1. Next, a value for L*a*b* under D65 light source/2-degree field of view conditions was determined by using data on the diffuse reflectance. As a result, coordinates (a*, b*) were (4.520, −3.540), and an angle φ formed by the straight line connecting the plotted point and the origin relative to an a* axis was 38.1°.
Table 1 summarizes the results of Comparative Examples 1 to 3 and Examples 1 to 5 described above. As can be seen from Table 1, in the range of 39°<φ<60°, the phosphors are identical to one another in luminance, and each have a high τ70. In addition, in this case, y satisfies the relationship of 0<y<6.
Eu0.01
S
Eu0.01
S1.0Eu0.01
S
Eu0.01
Eu0.01
Eu0.01
indicates data missing or illegible when filed
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2006-264090, filed on Sep. 28, 2006, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-264090 | Sep 2006 | JP | national |
