JPH0673376A - Red-or infrared-emitting phosphor and liquid crystal light bulb crt using the same - Google Patents

Abstract

PURPOSE:To improve the luminance and life of a phosphor by forming a red- or infrared-emitting phosphor represented by a specific formula. CONSTITUTION:Y2O3, Gd2O3, Cr2O3, Al2O3, and Ga2O3 in a specified ratio, if necessary together with one or more kinds of alkaline earth metal, are mixed, baked in air at a specified temp., ground, washed with water, and dried to give a red- or infrared-emitting phosphor, which is represented by the formula: (Y1-x-yCrxGdy)3(Al1-zGaz)5O12 (wherein 0.0005<=x<=0.05, 0<=y<=1, and 0<=z<=1), contains 10ppm to 0.5% alkaline earth metal, emits in a wavelength range of 600-800nm, and has an emission peak in a range of 707-730nm. A liq. crystal light bulb CRT with a high resolution is obtd. by combining a liq. crystal light bulb having a photosensitive layer comprising a hydrogenated alpha-silicon photoconductor with a cathode ray tube having a fluorescent panel contg. this red- or infrared-emitting phosphor.

Description

Detailed Description of the Invention

[0001]

The present invention has a main emission wavelength of 650n.
More specifically, the present invention relates to a phosphor for a cathode ray tube which is excited by an electron beam and emits light mainly in an infrared band, particularly yttrium aluminum garnet (hereinafter referred to as YAG) -based phosphor, gadolinium gallium garnet (hereinafter referred to as GGG) -based phosphor. The present invention relates to a phosphor, a yttrium gallium garnet (hereinafter referred to as YGG) -based phosphor, and a liquid crystal light valve CRT using the phosphor.

[0002]

2. Description of the Related Art A silver-activated cadmium sulfide phosphor (CdS: Ag) has long been known as a phosphor for a cathode ray tube that emits light in the red band of 650 nm or more. Although this phosphor has a main emission peak in the infrared band around 710 to 740 nm, it has a practical red band of 610 nm.
Luminous efficiency in the vicinity is low. Therefore, it has never been used as a red-emitting phosphor for general television.

Such a red-emitting phosphor should be used as a mixture with other red-emitting phosphors in a cathode ray tube used with a light pen, as described in, for example, JP-A-60-190488. You can This light pen is
It has the ability to provide a feedback signal to the display control unit. When using the light pen, what is important is to give a trigger signal in response to a light irradiation portion of a display image designated by the light pen at an arbitrary time. To reliably trigger such a light pen, it is necessary to have a fast transient response. This is an important problem especially for red light emitting phosphors. This is because the emission intensity of a normal red light emitting phosphor such as P22R is
It is not enough to give the diode a fast response. Although the CdS: Ag phosphor does not have high luminous efficiency near 610 nm, the overall luminous efficiency is more than twice as high as other red-emitting phosphors such as P22R phosphor. Japanese Unexamined Patent Publication No. 61-190488 discloses that this Cd
By mixing the S: Ag phosphor with a red-emitting phosphor having a main emission wavelength in the red band near 610 nm, the decrease in the brightness of the red-emitting phosphor layer of the cathode ray tube can be suppressed within an allowable range, and the radiation sensitivity can be reduced. It is stated that can be increased.

The CdS: Ag can be used in a cathode ray tube used together with a liquid crystal light valve (hereinafter referred to as LCLV). This liquid crystal light valve can basically be composed of a liquid crystal panel and a multi-layer provided on one glass surface of the panel, the photoconductive layer, a light blocking layer, and a dielectric mirror. This multi-layer has a role of amplifying optical information. When light is applied to this multi-layer, the resistance of the light-exposed portion of the photoconductor layer decreases, and a voltage is applied to the liquid crystal layer. As a result, this portion is turned on. In this case, applying light is also referred to as writing with light. This cathode ray tube is used as a light source for this writing.

When light whose polarization direction is aligned is incident from the other surface of this panel, the polarization state of the reflected light changes between the ON state portion and the OFF state portion. An image can be displayed by projecting this reflected light on a screen after passing through the polarized beam splitter.

In this LCLV, silicon amorphous is usually used as the photoconductor layer. When the sensitivity of the silicon amorphous to the wavelength of light is graphed, the sensitivity curve of the silicon amorphous has a broad peak in the range of about 650 to 800 nm. The maximum value of the peak is around 740 nm. Therefore, a CdS: Ag phosphor that emits light in this range can be used.

However, the CdS: Ag phosphor has a drawback that it is easily deteriorated by electron beam excitation for a long period of time and a decrease in luminance is likely to occur. Also, as the current density increases,
There is a drawback that the emission wavelength changes. FIG. 8 shows C
It is the figure which showed a mode that the emission spectrum of dS: Ag fluorescent substance was changed, when current density was changed and it excited sequentially under the acceleration voltage of 18 kV. In FIG.
Curves 101, 102, 103, and 104 have current densities of 0.05, 0.5, 5.0, and 50 μA / c, respectively.
The emission wavelength at m ² is shown. Cd as shown in this figure
The main emission wavelength of the S: Ag phosphor shifts to the short wavelength side as the current density increases. This phenomenon is of course the same when the acceleration voltage is increased. Therefore, the CdS: Ag phosphor is not practical as a phosphor having a main emission peak in the wavelength region of 650 nm or more in the high current density region.

Further, from the viewpoint of environmental pollution, CdS: A
Since the cadmium contained in the g phosphor is a harmful substance, the use of this phosphor is not preferable. In addition, a cathode ray tube using YAG: Eu, Cr phosphors (Eu 1 to 5%, Cr 0.1 to 1%) has been proposed as a writing source for LCLV in recent years. The emission spectrum of this phosphor is 700 or It has two peaks in the vicinity of 705 nm and does not sufficiently correspond to the sensitivity curve of silicon amorphous. Therefore, sufficient emission brightness cannot be obtained with respect to the sensitivity of silicon amorphous. Also, the overall emission brightness and the emission brightness around 740 nm are not sufficient.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and there is no change in the emission wavelength even when the current density or the accelerating voltage is increased, and the deterioration is less likely to occur. Also, it contains no harmful substances, 650
An object of the present invention is to provide a phosphor that emits light in the band of nm or more and a display device using the phosphor.

[0010]

The present inventors have found that 650n
A number of experiments were repeated on a phosphor containing a matrix having a main emission wavelength of m or more and containing no harmful cadmium. As a result, the garnet-type composition containing at least one of yttrium and gadolinium is used as the phosphor, and by replacing the yttrium or gadolinium in the composition with a specific amount of chromium, the drawbacks of the prior art are overcome. The inventors have newly discovered what can be done and have completed the present invention.

The phosphor of the present invention is excited by an electron beam, emits light in the wavelength range of red emission to the infrared wavelength range, and has the general formula (Y _1-xy Cr _x Gd _y ) ₃ (Al _1-z Ga
_z ) ₅ O ₁₂ (where M is selected from the group consisting of Gd, La and Lu, and 0.0005 ≦ x ≦ 0.05, 0 ≦ y ≦
1, 0 ≦ z ≦ 1).

This phosphor has a single-phase garnet structure, and its body color is white to light green. To obtain a single phase of the composition of the garnet structure, for example, as a raw material, yttrium, gadolinium, aluminum, oxides of the respective component elements such as chromium, are mixed in a predetermined composition ratio,
Then, it can be obtained by firing in an air atmosphere at a temperature of 1500 ° C. or higher for 20 hours or longer.

Further, the hydroxides, chlorides and the like of the above-mentioned respective component elements mixed in a predetermined composition ratio may be fired at a temperature of around 1500 ° C. for ten hours or more. The liquid crystal light valve CRT of the present invention includes a liquid crystal light valve comprising a photosensitive layer consisting essentially of hydrogenated α- silicon photoconductor, the general formula _{(Y 1-xy Cr x Gd} y) 3 (Al 1 _-z Ga
_z ) ₅ O ₁₂ (however, 0.0005 ≦ x ≦ 0.05, 0 ≦
y ≦ 1, 0 ≦ z ≦ 1), and a cathode ray tube having a phosphor screen containing a red or infrared emitting phosphor.

[0014]

Next, the characteristics of the phosphor of the present invention will be described. The X value of the phosphor of the present invention is limited to the range of 0.0005 to 0.05 as shown in the above general formula.
FIG. 2 shows (Y _1-X Cr _X ) ₃ Al ₅ O _{12 according} to the present invention.
The graph which shows the relationship between the X value in a fluorescent substance and the luminance of a fluorescent substance is shown. This relative brightness is (Y _1-X Cr _X ) ₃ Al
₅ O ₁₂ phosphor is applied to a glass plate and the acceleration voltage is 18 kV,
The emission intensity at a wavelength of about 708 nm, which shows the main emission peak when excited at a current density of 0.5 μA, was measured by CdS: A
The g phosphor is represented as 100.

As shown in this figure, (Y _1-X Cr _X ) ₃
When the X value of the Al ₅ O ₁₂ phosphor is in the range of 0.0005 to 0.05, its brightness is superior to that of the conventional CdS: Ag phosphor. The X value is preferably in the range of 0.001 to 0.03, at this time the relative luminance is 120% or more, more preferably in the range of 0.003 to 0.015, and at this time, the relative luminance is 145% or more. Is.

FIG. 1 shows an emission spectrum of the (Y _1-X Cr _X ) ₃ Al ₅ O ₁₂ phosphor (x = 0.0065). This phosphor has a main emission peak of about 707 nm and a peak of about 650 nm.
It emitted over a wavelength range of nm to 800 nm and had a half-value width of about 35 nm. Such light emitting characteristics are suitable for a photoconductor using silicon amorphous, for example. Unlike the CdS: Ag phosphor, even if the phosphor is excited by increasing the current density, the phosphor does not shift its emission peak due to deterioration. Also, within the above range, Y is C
Even if it is replaced with r, the light emitting peak does not shift due to deterioration. However, when this phosphor does not have a YAG single phase, for example, when it contains YAP having a perovskite structure, a light emission peak appears near 750 nm.

In this phosphor, in order to obtain a desired red light emitting region, part or all of Y can be replaced with Gd and part of Al can be replaced with Ga within respective predetermined ranges. Even if these substitutions are performed, there is no problem with the above-mentioned relative luminance and phosphor characteristics at high current densities.

The composition ratio y of Gd and the composition ratio z of Ga are 0 ≦ y ≦ 1 and 0 ≦ z ≦ 1, respectively. Preferably 0 for each
Or 1. When y is higher than 0 or lower than 1, the brightness tends to decrease. There is a similar tendency for z.

3 and 4, as examples of substituted phosphors, (Y _1-X Cr _X ) ₃ Ga ₅ O ₁₂ phosphors and (Gd _1-X Cr _X ) ₃ Ga ₅ O ₁₂ phosphors, respectively. The emission spectrum of a fluorescent substance is shown. Each phosphor has a main light emission peak in the vicinity of about 707 to 730 nm, and emits light in the wavelength range of about 650 nm to 800 nm. In addition, the half-width is about 7 each.
5 nm and 110 nm.

The relationship between the X value of these phosphors and the brightness of the phosphors is almost the same as in the graph of FIG. As described above, the phosphor of the present invention does not change the emission wavelength even when the current density or the accelerating voltage is increased, is not easily deteriorated, and sufficiently emits light in the wavelength range of 650 to 800 nm. The full width at half maximum of the main emission peak of the emission spectrum is 35 nm or more, preferably 35 to 110 nm.

Further, the phosphor according to the present invention preferably contains at least one additive selected from the group consisting of Ba, Sr, Mg and Ca based on the total amount of the phosphor.
It can be contained in the range of ppm to 0.5%.

By including these elements, it is possible to further improve the characteristic (γ characteristic) of increase in luminance with respect to increase in current density in the phosphor. Even if more than 0.5% of the alkaline earth metal is added to the phosphor in order to prevent the phosphor from burning, no significant improvement in γ characteristics over that of the phosphor containing 0.5% is observed. On the contrary, the alkaline earth metal added in an amount of more than 0.5% tends to act as a killer for the phosphor and reduce the brightness of the phosphor itself.

FIG. 5 is a graph showing the relationship between the content of alkaline earth metal and the relative brightness of the phosphor. In this relative luminance, the luminance of the phosphor according to the present invention containing no alkaline earth metal was set to 100%. In FIG. 5, curves 601, 602, 603 and 604 are graphs relating to phosphors containing Ba, Sr, Mg and Ca as additive components, respectively. As is clear from FIG. 5, when the alkaline earth metal is added and the added amount exceeds about 0.5%, the relative luminance decreases to around 80%. Phosphors having a relative brightness of less than about 80% are not preferable in practice, and therefore the content of alkaline earth metal is preferably 0.5% or less.

Further, it can be seen from FIG. 5 that when Ba is used as an additive, the decrease in brightness is particularly small. From this, a particularly preferable additive is Ba. Another disadvantage when the content of this additive is more than 0.5% is that the alkaline earth metal doped in the phosphor is exposed to the outside of the phosphor by long-time electron beam excitation. There is a tendency that the cathode ray tube is adversely affected by coming out and adhering to the electron gun.

The alkaline earth metal is preferably introduced into the phosphor by using its halide as a flux.
For this reason, the lower limit of the content of alkaline earth metal is limited by the lower limit which is sufficient for the halide to act as a flux. The method of adding an alkaline earth metal and the lower limit thereof will be briefly described below.

The alkaline earth metal is added, for example, by adding its halide together with the phosphor raw material at the time of firing.
It can be doped into the phosphor. The added alkaline earth metal halide has an advantage that it acts as a flux, assists in the sintering of the phosphor, and can lower the firing temperature. During firing, the firing temperature is as high as 1400 ° C or higher,
This causes the alkaline earth metal halide added to the phosphor to scatter. In order to prevent this, the firing is preferably performed in a closed crucible. Alkaline earth metal halides that are attached to the surface of the phosphor without being doped are
Usually, the phosphor obtained after the completion of firing can be removed by washing with acid. If the phosphor is used for the cathode ray tube with the oxide of the alkaline earth metal adhered to the surface, the vacuum degree of the cathode ray tube is lowered, or the alkaline earth metal scatters due to the irradiation of the electron beam and the electron gun. Adverse effects such as adherence to.

The amount of the alkaline earth metal halide added is usually adjusted to the range of about 0.5% to 20% with respect to the phosphor raw material. If the amount of the alkaline earth metal halide added is less than 0.5%, it tends to be difficult to act as a flux. When 0.5% of the alkaline earth metal halide is added, the alkaline earth metal content in the final phosphor will be about 10 ppm, considering the amount removed by acid washing. As described above, it is understood that the addition amount of the alkaline earth metal is preferably 10 ppm to 0.5%. Further, a particularly preferable range of this addition amount is 550 ppm to 0.1% in consideration of the relationship between the luminance characteristic and the γ characteristic.

In the phosphor of the present invention, the ratio of Y and / or Gd to Al is changed, or the ratio of Y and / or Gd to Cr is changed to change the ratio of the phosphor. Afterglow can be adjusted. For example,
The afterglow can be lengthened by increasing the amount of Al in the ratio of Y and / or Gd to Al.
Alternatively, the afterglow can be similarly lengthened by increasing the amount of Cr in the ratio of Gd and Cr. Thus, the phosphor of the present invention has an advantage that a desired afterglow time can be adjusted by their composition ratio.

As explained above, even if the phosphor of the present invention is excited in a high current density region, the emission peak does not shift, and the brightness is improved as the current density is increased. When such a phosphor is used in a cathode ray tube for projection, it is possible to achieve excellent life and brightness. Further, it is much less likely to deteriorate than a cathode ray tube using a conventional CdS: Ag phosphor, and the characteristics can be maintained for a long time.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings. The phosphor of the present invention can be applied to a cathode ray tube alone or in combination with other red-emitting phosphors.

Such a cathode ray tube has, for example, the following structure. FIG. 6 shows an example of a cathode ray tube using the phosphor of the present invention. As shown in FIG. 6, the cathode ray tube 1 has a sealed vacuum envelope 2 made of a vacuum glass bulb.
The vacuum envelope 2 has an integrated neck 3 and cone 4. The envelope 2 has a face plate 5 hermetically attached to the cone 4 with frit glass.
An explosion-proof metal tension band 6 is provided around the side wall of the face plate 5. An electron gun 7 for irradiating an electron beam is provided on the neck 3. The fluorescent screen 8 is formed on the inner surface of the face plate 5. The phosphor screen 8 has a phosphor layer having a predetermined shape and regularly arranged. This phosphor layer has the general formula (Y _1-xy Cr _x Gd _y ) ₃ (A
_{l 1-z Ga z) 5} O 12 ( where, 0.0005 ≦ x ≦ 0.
05, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1). A reflective layer is provided outside the cone 4 (not shown).

In this cathode ray tube, the phosphor used for the phosphor screen has a high luminous efficiency, is not easily deteriorated even if it is used for a long time, and is resistant to an increase in current density or accelerating voltage. The emission wavelength of the phosphor does not change.

FIG. 7 shows an LCLV CRT according to the present invention.
It is a schematic diagram showing an example. This LCLV CRT 1
0 has a cathode ray tube (CRT) 12 and this CRT 1
2 is combined with the LCVC 14 to provide the input image, typically through a glass fiber optic face plate (not shown). The xenon arc lamp 16 provides output light, which is linearly polarized by the pre-polarization filter 20 through the UV filter 18 and before reaching the liquid crystal light valve 14. This image is then projected through polarizing mirror 22, through a prism wedge window and then projection lens 26, where it is projected onto a screen (not shown).

This LCLV uses a hydrogenated α-silicon photoconductor. The inner surface of the face plate is coated with the phosphor according to the present invention to form a phosphor surface (not shown).

Preferably, the phosphor used for LCLV emits light in the range of 650 to 800 nm, and its main emission peak appears at 707 to 730 nm. Examples of the phosphor according to the present invention will be shown below. [Example 1] Y ₂ O ₃ ... 200 g Al ₂ O ₃ ... 150.4 g Cr ₂ O ₃ ... 0.177 g The above raw materials were sufficiently mixed and filled in an alumina crucible,
Cover and bake at 1800 ° C. for 30 hours.

After firing, the fired product is taken out, milled with a ball mill and crushed. After crushing, the phosphor is sufficiently washed with water and dried to obtain (Y _0.9987 Cr _0.0013 ) ₃ A
An l ₅ O ₁₂ phosphor was obtained. [Example 2] Y ₂ O ₃ ... 200 g Al ₂ O ₃ ... 150.4 g Cr ₂ O ₃ ... 0.885 g The same as in Example 1 except that the above raw materials were used.
A (Y _0.9935 Cr _0.0065 ) ₃ Al ₅ O ₁₂ phosphor was obtained. [Example 3] Y ₂ O ₃ ... 200 g Al ₂ O ₃ ... 150.4 g Cr ₂ O ₃ ... 1.15 g In the same manner as in Example 1 except that the above raw materials were used.
A (Y _0.9915 Cr _0.0085 ) ₃ Al ₅ O ₁₂ phosphor was obtained. [Example 4] Y ₂ O ₃ ... 200 g Al ₂ O ₃ ... 150.4 g Cr ₂ O ₃ ... 1.15 g BaF ₂ ... 14 g The above raw materials were sufficiently mixed and filled into an alumina crucible,
After covering the lid and bonding the gap of the lid with ceramic adhesive,
Bake at 1450 ° C. for 3 hours.

After firing, the fired product is taken out, milled with a ball mill and crushed. After crushing, the phosphor was washed with 10% nitric acid to remove the flux remaining on the surface, sufficiently washed with water and dried to obtain (Y _0.9915 Cr) of the present invention.
_{A 0.0085} ) ₃ Al ₅ O ₁₂ phosphor was obtained. When this phosphor was dissolved in acid and the Ba remaining in the phosphor was analyzed by ICP-AES, it was 250 ppm. [Example 5] Y ₂ O ₃ ... 200 g Al ₂ O ₃ ... 150.4 g Cr ₂ O ₃ ... 1.15 g MgCl ₂ ... 2 g BaF ₂ ... 14 g Example 4 except that the above raw materials were used. Similarly, Mg
Of 200 ppm and Ba of 250 ppm (Y
_{A 0.9915} Cr _0.0085 ) ₃ Al ₅ O ₁₂ phosphor was obtained. [Example 6] Y ₂ O ₃ ...... 200 g Ga ₂ O ₃・ ・ ・ 285.2 g Cr ₂ O ₃・ ・ ・ 1.36 g BaF ₂・ ・ ・ 14 g NH ₄ Cl ・ ・ ・ 1.8 g A (Y _0.9900 Cr _0.0100 ) ₃ Ga ₅ O ₁₂ phosphor containing 250 ppm of Ba was obtained in the same manner as in Example 4 except that the calcination was carried out for a period of time. [Example _{7] Gd 2 O 3 ...... 108.7g} Ga 2 O 3 ... 93.7g Cr (NO 3) 3 9H 2 O ... 1.6g MgF 2 ... 3.0g NH 4 Cl ... 0.5g material In the same manner as in Example 6 except that the above amounts were used, Mg
Of 250 ppm (Gd _0.9933 Cr _0.0067 )
_{A 3} Ga ₅ O ₁₂ phosphor was obtained. [Example 8] Gd ₂ O ₃ ... 200.0 g Ga ₂ O ₃ ... 177.7 g Cr ₂ O ₃ ... 0.85 g SrF ₂ ... 7.0 g CaF ₂ ... 7.0 g NH ₄ Cl ... 1.8 g Sr is the same as in Example 6 except that the above amounts are used.
Containing 180 ppm of Ca and 180 ppm of Ca (Gd
_{A 0.9900} Cr _0.0100 ) ₃ Ga ₅ O ₁₂ phosphor was obtained.

The phosphors obtained in Examples 1 to 8 were coated on a glass plate to form a phosphor film, and the characteristics of the phosphor were measured as follows. The results are shown in Table 1. 1) Electron beam deterioration Acceleration voltage of 27 kV, current density of 50 μA / cm ²
Continuous excitation is performed for 1 hour, and the luminance retention rate is measured. 2) γ characteristic The fluorescent film was accelerated at an acceleration voltage of 27 kV, a current density of 0.05,
Excitation at 5, ⁵ and 50 μA / cm ² respectively, 0.05
Assuming that the brightness when excited with μA / cm ² is 100%,
The relative brightness of each is shown. 3) Afterglow Fluorescent film with acceleration voltage 10 kV, current density 0.5 μA / cm
Excitation is performed at ² , and after the excitation is stopped, the time when the brightness is reduced to 10% is measured. The unit is millisecond.

Table 1 Example 1) Deterioration 2) γ characteristic 3) Afterglow (%) 0.05 0.5 5.0 50 1 98.1 100 113.6 147.2 171.5 6 2 98.3 100 116.8 152.3 180.5 18 3 98.0 100 117.2 153.7 183.2 72 4 99.2 100 130.3 162.4 198.3 72 5 99.0 100 132.6 165.5 200.7 72 6 97.1 100 119.7 162.2 240.8 8 7 96.9 100 117.1 164.0 260.9 8 8 96.0 100 121.2 169.7 270.9 15 In addition, any of the phosphors will increase its accelerating voltage and current density. The emission wavelength did not change at all.

[0040]

EFFECTS OF THE INVENTION The phosphor of the present invention does not change the emission wavelength even when the current density or the acceleration voltage is increased, is not easily deteriorated, and sufficiently emits light in the wavelength range of 650 to 800 nm.

In the cathode ray tube using such a phosphor, the phosphor used does not change its emission wavelength even when the current density or the accelerating voltage is increased, and is not easily deteriorated. Since sufficient light emission is performed in the wavelength range of 650 to 800 nm, a good image that does not change with time can be obtained.

Further, this cathode ray tube can be sufficiently used as a writing light source of a liquid crystal light valve, and it is possible to improve the response speed of the photoconductor layer and the resolution.

[Brief description of drawings]

FIG. 1 is a graph showing an emission spectrum of a phosphor according to the present invention.

FIG. 2 is a graph showing the relationship between the Cr composition ratio and the relative luminance of the phosphor according to the present invention.

FIG. 3 is a graph showing an emission spectrum of another phosphor according to the present invention.

FIG. 4 is a graph showing an emission spectrum of still another phosphor according to the present invention.

FIG. 5 is a graph showing the relationship between the content of alkaline earth metal and the relative brightness of the phosphor.

FIG. 6 is a partially cutaway schematic view showing an example of a cathode ray tube according to the present invention.

FIG. 7 is a schematic cutaway view of a liquid crystal light valve CRT according to the present invention.

FIG. 8 is a graph showing an emission spectrum of a conventional phosphor.

[Explanation of symbols]

1 ... Cathode ray tube, 8 ... Phosphor screen, 10 ... LCLV CRT,
12 ... Cathode ray tube, 14 ... LCLV, 16 ... Xenon arc lamp

Claims (4)

[Claims] 1. The general formula (Y _1-xy Cr _x Gd _y ) ₃ (A
_{l 1-z Ga z) 5} O 12 ( where, 0.0005 ≦ x ≦ 0.
05, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1)). 2. At least one alkaline earth metal selected from the group consisting of Ba, Sr, Mg, and Ca,
The phosphor according to claim 1, further containing 10 ppm to 0.5% of the total amount of the phosphor. 3. The phosphor according to claim 1, which emits light in the wavelength region of 650 to 800 nm and has a main emission peak in the range of 707 to 730 nm. And the liquid crystal light valve comprising a photosensitive layer consisting essentially of wherein hydrogenated α- silicon photoconductor, the general formula _{(Y 1-xy Cr x Gd} y) 3 (Al 1-z Ga
_z ) ₅ O ₁₂ (however, 0.0005 ≦ x ≦ 0.05, 0 ≦
y ≦ 1, 0 ≦ z ≦ 1), and a cathode ray tube having a phosphor screen containing a red or infrared emitting phosphor, represented by the formula: y ≦ 1, 0 ≦ z ≦ 1.