JP2002012862A - Zinc sulfide phosphor and method for evaluating luminance of the phosphor. - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zinc sulfide phosphor having high luminance and a method for evaluating the luminance of the zinc sulfide phosphor. SOLUTION: The objective zinc sulfide phosphor is characterized by the near infrared Raman spectrum obtained by irradiating a zinc sulfide fluorescent material with monochromatic near infrared ray and spectroscoping the scattered rays and having an intensity ratio (ILO/IS) of >=0.7 wherein ILO is the intensity of Raman line at a Raman shift value σLO of 330-354 cm-1 and IS is the intensity of Raman line on a silicon wafer surface of the face index 100 at a Raman shift value σS of 521 cm-1 and measured under the condition the same as the measuring condition of the Raman intensity ILO.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zinc sulfide-based phosphor having zinc sulfide as a matrix and a method for evaluating the luminance of the phosphor, and more particularly to a zinc sulfide-based phosphor which emits light with high luminance under electron beam excitation. And a method for evaluating the emission luminance of the phosphor.

[0002]

2. Description of the Related Art Zinc sulfide-based phosphors are widely used mainly as blue or green component phosphors for color cathode ray tubes (CRTs). This phosphor has zinc sulfide as a host crystal, which is activated by an activator element such as copper (Cu), silver (Ag), and gold (Au).
It is obtained by co-activation with an element such as aluminum (Al). In order to further improve the performance of a display such as a CRT, there is a strong demand in the market for a phosphor having higher luminance.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the conventional problems and to provide a zinc sulfide-based phosphor having higher luminance. It is another object of the present invention to provide an alternative method for evaluating the emission luminance of a zinc sulfide-based phosphor.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted various analyzes mainly by an optical method on the relationship between the microscopic structure of a crystal of a zinc sulfide-based phosphor and the emission luminance of the phosphor. Thus, it was found that a product having a higher luminance than that of the conventional device could be obtained. In other words, the near-infrared Raman spectrum obtained by irradiating the zinc sulfide-based phosphor with monochromatic light in the near-infrared region and dispersing the scattered light at that time shows a specific pattern. I found something.

[0005] That is, the present invention has succeeded in solving the above-mentioned problems by employing the following configuration. (1) The Raman shift value (σ _LO ) of the near-infrared Raman spectrum obtained by irradiating near-infrared monochromatic light to the zinc sulfide-based phosphor and dispersing the scattered light at that time has a wave number of 330 to 354.
Raman peak intensity in the range of cm ^-1 (I _LO )
And the Raman shift value (σ _s ) of the near-infrared Raman spectrum obtained under the same conditions as described above for a plane index of 100 of a silicon wafer as a standard sample has a wave number of 521 cm ^−1.
Ratio to the intensity of the Raman line (I _S ) at (I _LO / I _S )
Is 0.7 or more. (2) The Raman shift value (σ _LO ) has a wave number of 348 to 354.
The zinc sulfide-based phosphor according to the above (1), which is in the range of cm ^-1 .

(3) The Raman shift value (σ _HEX ) of the near-infrared Raman spectrum obtained by irradiating the zinc sulfide-based phosphor with near-infrared monochromatic light and dispersing the scattered light at that time has a wave number of 290 to 290. Raman peak intensity (I _HEX ) in the range of 310 cm ⁻¹ and Raman peak intensity (I _LO ) in the range of Raman shift value (σ _LO ) of near-infrared Raman spectroscopy spectrum of 330 to 354 cm ^−1. And the ratio (I _HEX /
(I _LO ) 0.014 or less.

(4) The zinc sulfide-based material according to any one of (1) to (3), wherein the monochromatic light is a laser beam of 752.5 nm oscillated from krypton (Kr) gas. Phosphor. (5) The sulfide according to any one of (1) to (4), wherein the zinc sulfide-based phosphor is a copper and aluminum co-activated zinc sulfide phosphor (ZnS: Cu, Al). Zinc-based phosphor.

(6) The monochromatic light in the near infrared region is irradiated to the zinc sulfide based phosphor, and the Raman shift value (σ _LO ) of the near infrared Raman spectrum obtained by dispersing the scattered light at that time has a wave number of 3
The peak intensity of the Raman line in the range of 30 to 354 cm ^-1 (I
_LO ), and the emission luminance of the zinc sulfide-based phosphor is evaluated based on the measured intensity.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS When light having a specific frequency (ν) is applied to a substance, the frequencies (ν ₁ , ν ₂ , ν ₃ ) specific to the substance are applied.
...) and scattered light (ν ± ν ₁ , ν ± ν ₂ , ν ±
ν ₃ ...) appears. This is due to Raman scattering. FIG. 1 shows one of the zinc sulfide-based phosphors, ZnS:
Each of the Cu and Al phosphors has a wavelength (λ) of 488n.
m, 514.5 nm, 647.1 nm and 752.5 n
FIG. 4 shows a Raman spectral spectrum obtained by spectrally separating Raman scattered light when monochromatic light of m is irradiated. FIG.
FIG. 3 shows a Raman spectrum of a ZnS: Cu, Al phosphor different from the phosphor of FIG. 1 when irradiated with a Kr laser beam having a wavelength of 752.5 nm. FIG.
Raman shift value is wave number 330-370c in the upper right part of
Only at a point near m ^−1, a spectrum obtained by further increasing the measurement resolution is also shown.

When observing the Raman spectrum spectrum of the ZnS: Cu, Al phosphor shown in FIGS. 1 and 2, when the three types of long-wavelength monochromatic light other than 488 nm are irradiated, the Raman shift value becomes near the wave number of 350 cm ^-1 . Although a remarkable peak appears, it is considered that the peak of the Raman light appearing in the vicinity of the wave number of 350 cm ^-1 is a peak caused by the longitudinal wave optical mode (LO mode) of cubic zinc sulfide. Then, assuming that the shape of the curve near the peak of the Raman spectrum spectrum curve drawn directly from the spectroscope approximates the Lorentz function, and fitting and rewriting this, the curve of the Raman spectrum spectrum, The Raman shift value (hereinafter, this wave number is referred to as σ _LO ) due to the longitudinal wave optical mode (LO mode) of cubic zinc sulfide has a wave number of 350.
The cm ^-1 centered, the peak intensity of the Raman light appears in the range of 330~354cm ^-1 (hereinafter, the intensity I _LO
Surprisingly found to be proportional to the emission intensity of the ZnS: Cu, Al phosphor under electron beam excitation.

The longitudinal wave optical mode (LO mode)
The Raman shift value (σ _LO ) due to the difference in wave number of 35 depending on the sample, such as the difference in crystallinity and particle diameter of the zinc sulfide-based phosphor.
Centered at 0 cm ^-1, vary in the range of 330～354Cm ^-1, in particular, near the infrared Raman spectrum, the longitudinal wave optical mode (LO mode) wave number peak in the resulting Raman light 348～354Cm ^- It was found that the phosphor appearing near ¹ had better crystallinity and higher emission luminance.

In the measurement of Raman spectroscopy, if ultraviolet light or visible light is used as irradiation light for irradiating the phosphor, the irradiation light excites the phosphor to emit light, and the emitted light is converted into Raman scattered light. It is more preferable to use near-infrared light as the irradiation light to the phosphor, since it may overlap and hinder the measurement of the Raman shift.

FIG. 3 shows that a plurality of ZnS: Cu, Al phosphors are irradiated with a Kr laser beam having a wavelength of 752.5 nm to measure near-infrared Raman spectroscopy under the same conditions, and the Raman shift value (σ _LO 4 is a graph in which the relationship between the peak intensity (I _LO ) of the Raman line in (1) and the luminous efficiency of the phosphor is plotted. The vertical axis Raman line intensity (I _LO ) is approximately 330 wavenumbers in the near-infrared Raman spectrum.
The peak intensity after performing a process of fitting a spectrum near a Raman light peak appearing around 付 近 354 cm ⁻¹ with a Lorentz function is shown. In the present specification, the peak intensity of Raman light in the Raman spectrum refers to the peak intensity after performing a process of fitting the vicinity of the peak of the spectrum obtained from the spectroscope with the Lorentz function.

The luminous efficiency on the horizontal axis is represented by the luminous brightness when the phosphor is excited by an electron beam at an accelerating voltage of 12 kV. In addition, the point R in FIG.
S: The measurement points of the Cu and Al phosphors, and points A, B and C are the measurement points of the ZnS: Cu and Al phosphors of the present invention, respectively. In the figure, the measured values of each sample were measured by changing the irradiation position of the laser beam by 5 points for each sample, and displayed including the maximum value and the minimum value of the measured values of the same sample.

As can be seen from FIG. 3, the ZnS of the present invention:
The Cu and Al phosphors have a Raman shift value (σ _LO ) due to the longitudinal wave optical mode (LO mode) in the Raman spectroscopy spectrum which is higher than that of the conventional phosphors.
Raman light intensity peak value at 354 cm ^-1 (I _LO )
However, it is stronger than that of the conventional ZnS: Cu, Al phosphor, and at the same time, has a high luminous efficiency under cathode ray excitation.

Therefore, the Raman shift value (σ _LO ) of the near-infrared Raman spectrum obtained by irradiating the zinc sulfide-based phosphor with monochromatic light in the near-infrared region, which is obtained by dispersing the scattered light, has a wave number of 330 to 354 cm ^{−. 1} range, preferably wavenumber 348-
Raman peak intensity in the range of 354 cm ^-1 (I
_LO ) was measured, and the Raman shift value (σ _s ) of the near-infrared Raman spectroscopy spectrum obtained under the same conditions as above for 100 plane indices of the silicon wafer was Raman line intensity (I _s ) at a wave number of 521 cm ⁻¹ . Is used as a standard value, and a zinc sulfide-based phosphor having high emission luminance can be obtained by selecting a phosphor having a ratio (I _LO / I _S ) of 0.7 or more. Note that a preferable range of the ratio (I _LO / I _S ) is 0.85 or more.

Further, the sulfide-based phosphor of the present invention comprises Zn
S: In the near-infrared Raman spectrum of the Cu, Al phosphor, the peak intensity of the Raman line (I _LO ) in which the Raman shift value (σ _LO ) due to the LO mode of cubic zinc sulfide is in the wave number range of 330 to 354 cm ^−1. _The higher the _LO ), the higher the emission luminance of the phosphor. In addition, the peak intensity (I _HEX ) of the Raman line attributable to the hexagonal zinc sulfide crystal having a Raman shift value (σ _HEX ) of the Raman spectrum of 290 to 310 cm ^-1 upon irradiation with near infrared rays. Is relatively small, and the Raman shift value (σ _LO ) has a wave number of 330 to 354c.
For Raman peak intensity (I _LO ) in the range of m ⁻¹ ,
Raman shift value (σ _HEX ) ratio to peak intensity (I _HEX ) of Raman line in the range of 290 to 310 cm ⁻¹ (I _HEX /
By setting I _LO ) to 0.014 or less, a phosphor having high emission luminance can be obtained.

Further, by observing the half-value width of the peak caused by the LO mode in the near-infrared Raman spectrum of the ZnS: Cu, Al phosphor, it was also confirmed that a phosphor having a smaller width had higher emission luminance. The LO mode shift of the LO mode of the cubic zinc sulfide crystal is sensitive to the disorder of the crystal structure, and the peak intensity of the Raman ray increases as the disorder of the crystal structure decreases. It is believed that the body has less disorder in the crystal structure than the conventional one, and as a result, the emission luminance of the phosphor is higher than the conventional one.

Based on the above findings, the present invention provides a Raman shift value (σ _LO ) of the near-infrared Raman spectrum.
By measuring the peak intensity (I _LO ) of the Raman line in the wave number range of 330 to 354 cm ⁻¹ , the emission luminance of the zinc sulfide-based phosphor can be easily evaluated.

The near-infrared monochromatic light used in the present invention is, for example, 752.5 oscillated from krypton (Kr) gas.
nm laser light is particularly preferable in terms of efficiency and the like, but other than that, a Kr laser having a wavelength of 799.3 nm, a Ti-sapphire laser excited by Ar (700 to 1000 nm).
And a near-infrared semiconductor laser (780 nm). The zinc sulfide-based phosphor of the present invention is, for example, Zn co-activated with copper and aluminum.
Phosphors using zinc sulfide as a base crystal, such as S: Cu, Al phosphor, ZnS: Cu, Al, Au phosphor, ZnS: Ag, Cl phosphor, and ZnS: Mn phosphor, are suitable. The reason why the plane index of the silicon wafer was 100 was used as the standard sample of the Raman line of the near-infrared Raman spectrum, because the Lo mode was strong and stable.

The ZnS: Cu, Al phosphor used in the present invention is obtained by adding a compound of copper and aluminum to 1 g of zinc sulfide and a compound of 3 × 10 ⁻⁵ to 1 g of zinc sulfide, respectively, as an activator material for zinc sulfide powder as a base material. 1 × 10 ⁻³ g (30 to 1000
ppm), and combined with a plurality of fluxes comprising low-melting compounds such as sodium chloride, potassium chloride, zinc chloride, zinc iodide, bismuth iodide, bismuth nitrate, and a total amount of 3 to 5% by weight. Add and mix well and place in electric furnace. H ₂ S, CS ₂ , SO ₂
And a sulfur-containing gas such as nitrogen gas and a neutral gas such as an argon gas are passed through under a sulfide atmosphere for 800 to
1100 ° C., more preferably 1 to 900 to 1000 ° C.
It can be manufactured by firing for 5 hours. The obtained phosphor is washed with water and, if necessary, further subjected to a dispersion treatment such as coating the phosphor surface with an inorganic compound such as silica, alumina, titania and zinc hydroxide by a conventional method and then sieving. Obtainable.

Although the ZnS: Cu, Al phosphor has been described in detail above, the present invention is not limited to the case of co-activating with Cu and Al.
The zinc sulfide-based phosphor of the present invention may be any phosphor having zinc sulfide as a host crystal, and the phosphor activated with Ag, Au, or the like, or a phosphor activated with a halogen element such as Cl, Br, or I. Phosphor may be used. Regarding the correlation between the emission intensity of the phosphor and the peak intensity I _LO of the Raman line at the Raman shift value σ _LO due to the LO mode of cubic zinc sulfide in the Raman spectrum when this phosphor is irradiated with near infrared rays , ZnS: Cu, Al phosphors have substantially the same correlation.

[0023]

[Example 1]

Zinc sulfide (ZnS) 1000 g of copper nitrate _{[Cu (N0 3) 2 · 6H} 2 0 ] 0.70g of aluminum nitrate _{[Al (N0 3) 3 · 9H} 2 0 ] 2.09g of bismuth nitrate [Bi (N0 _{3) 3} · 5H ₂ 0] 1.0 g Zinc chloride (ZnCl ₂ ) 2.0 g Potassium iodide (KI) 2.0 g The above phosphor material is sufficiently kneaded with water, dried at 100 ° C., and then quartz. Fill the crucible and put it in the electric furnace,
After baking at 980 ° C. for 1 hour while passing a nitrogen gas containing about 20% by volume of carbon disulfide gas into the electric furnace, the baking material is taken out of the furnace, washed with water and dehydrated, and then heated at 110 ° C.
And dried sufficiently for 16 hours.
The concentration of Cu and Al is 1.5 × 10 ⁻⁴ per g.
g of ZnS: Cu, Al phosphor of Example 1 was obtained.

Example 2 The fired product of Example 1 was taken out of the furnace, washed with water, and before the dehydration, water was added thereto and subjected to a wet ball mill treatment to disintegrate the fired product. And phosphor was prepared by adding water to the mixture. Colloidal silica was added to the slurry, the slurry was stirred, and a silica film was formed on the surface of the phosphor.
After heating at 0 ° C. for 16 hours and drying, the concentration of Cu and Al were both 1.5 × 10 ^{−4 /} g of zinc sulfide matrix.
g of ZnS of Example 2 coated on the surface with silica:
Cu and Al phosphors were manufactured.

[0025] Example 3 Zinc sulfide (ZnS) 1000 g of copper nitrate _{[Cu (N0 3) 2 · 6H} 2 0 ] 0.70g of aluminum nitrate _{[Al (N0 3) 3 · 9H} 2 0 ] 2.09g iodide Bismuth (BiI ₃ ) 2.0 g Zinc chloride (ZnCl ₂ ) 2.0 g The above phosphor material was sufficiently kneaded with water, dried at 100 ° C., filled in a quartz crucible, and placed in an electric furnace. It was charged and fired at 980 ° C. for 1 hour while passing a nitrogen gas containing about 10% by volume of carbon disulfide gas into the electric furnace.
After that, take it out of the furnace and wash and dehydrate the fired material,
After heating at 110 ° C. for 16 hours and drying sufficiently, the concentration of Cu and Al was 1.5
A ZnS: Cu, Al phosphor of Example 3 weighing × 10 ⁻⁴ g was produced.

[0026] Comparative Example 1 Zinc sulfide (ZnS) 1000 g of copper nitrate _{[Cu (N0 3) 2 · 6H} 2 0 ] 0.70g of aluminum nitrate _{[Al (N0 3) 3 · 9H} 2 0 ] 2.09g of bismuth nitrate _{[Bi (N0 3) 3 · 5H} 2 0 ] 2.0 g potassium iodide (KI) 2.0 g the above phosphor raw materials were sufficiently kneaded together with water, dried at 100 ° C., which quartz crucible And fired at 980 ° C. for 1 hour while passing hydrogen sulfide gas through the furnace, then taken out of the furnace, washed and dehydrated, and heated at 110 ° C. for 16 hours. And fully dried, and ZnS: Cu, of Comparative Example 1 in which the concentrations of Cu and Al were 1.5 × 10 ⁻⁴ g / g of zinc sulfide matrix, respectively.
An Al phosphor was manufactured.

(Evaluation) Next, using a micro Raman spectroscopy system (R64000, manufactured by Atago Bussan Co., Ltd.), the ZnS: Cu, Al phosphors of Examples 1 to 3 and Comparative Example 1 described above were subjected to an Ar spot having a spot diameter of 2 μm. A near-infrared Raman spectrum was measured by irradiating a monochromatic light of 752.5 nm with a / Kr laser (output: 3 mW on the sample), and the Raman shift value (σ _LO )
Table 1 shows the relative values of the peak intensity (I _LO ) of the Raman line in the range of 330 to 354 cm ^-1 . These relative values are the primary Raman line intensity (I _S ) at the Raman shift value (σ _S = 521 cm ⁻¹ ) of the vibration mode of the F _2g symmetry in the Raman spectroscopy spectrum with respect to the plane index (100) of the silicon wafer measured under the same conditions. ) To (I _LO / I _S )
It was expressed by. The emission luminance when each phosphor was irradiated with an electron beam was shown as a relative value to the emission luminance of the phosphor of Comparative Example 1, which is a conventional phosphor.

[0028]

[Table 1]

As is clear from Table 1, the peak intensity (I) of the Raman lines of the ZnS: Cu, Al phosphors of Examples 1 to 3 is shown.
_LO ) is a Raman shift value (σ _s ) at least 0.7 times the primary Raman line intensity (I _s ) at a wave number of 521 cm ⁻¹ due to the vibration mode of F _2g symmetry of a silicon wafer as a standard sample. , Ie, the ratio (I _LO / I _S ) is 0.7 or more, and the relative luminous intensity is the same as that of the conventional ZnS: C
The luminous brightness was higher than that of the phosphor of Comparative Example 1 which was a u, Al phosphor.

Further, each of Zn in Examples 1 to 3 and Comparative Example 1
As for the S: Cu, Al phosphor, 752.
The near-infrared Raman spectrum was measured by irradiating monochromatic light of 5 nm, and the Raman shift value (σ _LO ) was 330 to 354c.
The relative value (I _HEX / I) of the peak intensity (I _LO ) of the Raman line in the range of m ⁻¹ and the peak intensity (I _HEX ) of the Raman line in the range of the Raman shift value (σ _HEX ) of 290 to 310 cm ^−1.
I _LO ) is shown in Table 2. The emission luminance when each phosphor was irradiated with an electron beam was the same as that of the conventional phosphor.
And the relative value to the light emission luminance of the phosphor.

[0031]

[Table 2]

As is clear from Table 2, the relative values (I _HEX / I _LO ) of the peak intensity of the Raman line of the ZnS: Cu, Al phosphors of Examples 1 to 3 are all 0.014 or less. The relative light emission luminance showed a higher light emission luminance than the phosphor of Comparative Example 1, which is a conventional ZnS: Cu, Al phosphor.

[0033]

According to the present invention, by adopting the above structure, the Raman light intensity due to the longitudinal wave optical mode (LO mode) of the Raman spectroscopy spectrum by near infrared rays is higher than that of the conventional zinc sulfide-based phosphor. Accordingly, it has become possible to obtain a phosphor having high luminous efficiency. In addition, Raman shift value (σ _LO ) of Raman spectrum by near infrared ray
The emission intensity can be evaluated based on the peak intensity (I _LO ) of the Raman line in the wave number range of 330 to 354 cm ⁻¹ , and the evaluation can be performed extremely easily.

[Brief description of the drawings]

FIG. 1 is a graph illustrating Raman spectroscopy spectra of ZnS: Cu, Al phosphors when irradiated with light having different wavelengths.

FIG. 2 is a graph illustrating a Raman spectrum when ZnS: Cu, Al phosphor is irradiated with near infrared rays.

FIG. 3 is a graph showing a correlation between the luminous efficiency of a ZnS: Cu, Al phosphor and the intensity of a Raman ray at a Raman shift value of 330 to 354 cm ⁻¹ in a Raman spectroscopic spectrum upon irradiation with near infrared rays.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Ryuji Adachi 1060 Narita, Odawara City, Kanagawa Prefecture Inside Kasei Optonics Co., Ltd. (72) Inventor Takashi Ichihara 1060 Narita, Odawara City, Kanagawa Prefecture Inside Kasei Optonics Co., Ltd. (72) Inventor Naoto Kijima 1000 Kamoshita-cho, Aoba-ku, Yokohama-shi, Kanagawa Prefecture F-term in Yokohama Research Laboratory, Mitsubishi Chemical Corporation 2G043 AA06 BA11 CA05 EA03 FA02 KA01 KA09 4H001 CA06 XA16 XA30 YA13 YA29

Claims (6)

[Claims] 1. A near-infrared monochromatic light is irradiated to a zinc sulfide-based phosphor, and a Raman shift value (σ _LO ) of a near-infrared Raman spectrum obtained by dispersing the scattered light at that time has a wave number of 33.
The peak intensity (I _LO ) of the Raman line in the range of ⁰ to 354 cm ⁻¹ and the Raman shift value of the near-infrared Raman spectrum obtained under the same conditions as described above for a plane index of 100 of a silicon wafer as a standard sample ( σ _S ) has a wave number of 52
The ratio (I _LO ) to the Raman line intensity (I _S ) at 1 cm ⁻¹
/ I _s ) is 0.7 or more. 2. The method according to claim 1, wherein the Raman shift value (σ _LO ) is a wave number of 34.
2. The zinc sulfide-based phosphor according to claim 1, wherein the phosphor is in a range of 8 to 354 cm ^-1 . 3. A Raman shift value (σ _HEX ) of a near-infrared Raman spectrum obtained by irradiating near-infrared monochromatic light to a zinc sulfide-based phosphor and dispersing the scattered light at that time has a wave number of 2.
The peak intensity (I _HEX ) of the Raman line in the range of 90 to 310 cm ⁻¹ and the peak intensity (I _HEX ) of the Raman line in the range where the Raman shift value (σ _LO ) of the near-infrared Raman spectroscopy spectrum is in the wave number range of 330 to 354 cm ^−1. _LO ) ratio (I _HEX / I
_LO ) is 0.014 or less. 4. The zinc sulfide-based phosphor according to claim 1, wherein the monochromatic light is a laser beam of 752.5 nm oscillated from krypton (Kr) gas. 5. The zinc sulfide according to claim 1, wherein the zinc sulfide-based phosphor is a copper and aluminum co-activated zinc sulfide phosphor (ZnS: Cu, Al). System phosphor. 6. A Raman shift value (σ _LO ) of a near-infrared Raman spectrum obtained by irradiating a zinc sulfide-based phosphor with near-infrared monochromatic light and dispersing the scattered light at that time has a wave number of 33.
A method for evaluating the emission luminance of a zinc sulfide-based phosphor, comprising measuring a peak intensity (I _LO ) of a Raman line in a range of ⁰ to 354 cm ⁻¹ and evaluating the emission luminance of the phosphor based on the intensity.