JP2001228809A - Display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image with high sharpness, high efficiency, high luminance and high contrast in a display device, such as a PL-LCD in which a fluorescent film is irradiated with excitation light on its back face to emit light from its front face. SOLUTION: The device is equipped with a light source part 40 to generate excitation light having specified wavelength, an optical device 50 to modulate the excitation light emitted from the light source 40 for each pixel in a two-dimensional plane, and a fluorescent screen 60, which accepts the excitation light modulated by the optical device 50 on a first face of the screen and generates visible rays to emit outside from a second face which is on a side opposite to the first face. The fluorescent screen 60 has a phosphor layer of 1×102 cm-1 or higher absorption coefficient to the excitation light having prescribed wavelength.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device, and more particularly to a display device in which an image formed by modulating excitation light such as ultraviolet light generated from a light source section with a liquid crystal panel or the like is visualized on a phosphor screen. The present invention relates to a photoluminescent display device.

[0002]

2. Description of the Related Art In recent years, liquid crystal displays (LCDs) have been increasingly used in place of CRTs (cathode-ray tubes) as displays for thin televisions and computers. In addition, the use of LCDs as a display for diagnosis and monitoring of medical equipment such as an ultrasonic apparatus, a CT apparatus, an MRI apparatus, and a CR apparatus, as well as for art appreciation, and for displaying large-scale information such as at airports is being considered. ing.

A conventional LCD has advantages such as small size and light weight, but has a disadvantage that it has a large viewing angle dependency. That is, the brightness is maximum when the viewing direction is perpendicular to the display surface, and when deviated from the perpendicular direction, the brightness and contrast are sharply reduced, and further, the inversion of gradation occurs. It changes depending on the angle.

In recent years, a photoluminescent liquid crystal display (PL-LCD) has been developed in order to eliminate the viewing angle dependence and increase the luminance. The basic principle is that an image formed by modulating excitation light such as ultraviolet light generated from a light source section with a liquid crystal panel or the like is visualized and displayed on a phosphor screen. Since the image displayed by the PL-LCD is a fluorescent image similar to that of a CRT, there is no viewing angle dependency. Also, in the case of a color image, since phosphors of three colors may be separately applied similarly to the CRT, a color filter is not required, and it is expected that the efficiency is excellent. However, it is known that if the excitation light incident on the liquid crystal cell is directed in a random direction, the image will be blurred and the contrast will be reduced. For example, see Japanese Patent Application Publication No. 9-511588. Discloses a display screen in which a light-condensing member is provided inside a cell of a liquid crystal layer in order to improve this.

[0005] By the way, as a criterion for selecting a phosphor used in a photoluminescent display device, conventionally, only high excitation efficiency by ultraviolet or blue light has been considered. For example, in U.S. Pat. No. 5,608,554, three types of red, green, and blue (RGB) light are emitted instead of white light emitted from a light source being incident on a color filter and split into three colors of red, green, and blue (RGB). Display devices using phosphors are posted,
As these phosphors, those having a favorable emission spectrum when exposed to deep blue excitation light from a backlight having a main emission peak in the wavelength range of 380 to 420 nm are selected. Also, J.I. Appl. Phys
s. 88.4660 (2000) has a wavelength of 365 nm.
And a phosphor having high excitation efficiency at 394 nm.

[0006]

The excitation efficiency by ultraviolet rays as used herein is a concept used in the evaluation of phosphors. Generally, the excitation light is applied from the surface to a phosphor layer having a thickness enough to absorb the excitation light. It is measured under the condition that irradiation is performed and light emission from the same surface is observed. However,
The excitation efficiency measured by this method is significantly different from the practical efficiency when light emission is observed from the surface of the phosphor layer opposite to the excitation light irradiation surface. In this arrangement, the relationship between the sharpness and the film thickness is also different, and the film thickness for realizing the high sharpness required for the diagnosis of the CR device will be described in detail later. is there.

[0007] Phosphors for PL-LCD, which have been conventionally used, have high excitation efficiency by ultraviolet rays or the like, but most of them do not absorb excitation light sufficiently. Therefore, if the thickness of the phosphor layer is made relatively thin in order to achieve high sharpness, the energy efficiency when observed from the surface opposite to the surface irradiated with the excitation light is low, which poses a problem for practical use. Further, when the film thickness is increased to increase the energy efficiency, the sharpness is reduced, so that both high luminance and high definition cannot be achieved. Conversely, if the absorption of the excitation light is too large, only the very surface of the phosphor will be excited, which also lowers the energy efficiency.

On the other hand, US Pat. No. 4,822,144 discloses that
By providing an interference filter layer that reflects visible light through ultraviolet light between the excitation backlight unit and the phosphor layer,
A display device in which visible light loss generated in a phosphor layer is reduced is described.

In view of the above, the present invention provides a PL
-In display devices, such as LCDs, which irradiate excitation light from the back to the fluorescent film and extract emission light from the front, with the aim of realizing images with high sharpness, high efficiency, high brightness, and high contrast. I do.

[0010]

In order to solve the above problems, a contact type display device according to the present invention has a light source section for generating excitation light having a predetermined wavelength, and a light source section generated by the light source section. An optical element that modulates the excitation light for each pixel in a two-dimensional plane, and a second surface that receives the excitation light modulated by the optical element on a first surface and that is opposite to the surface.
And a fluorescent screen that emits visible light from the surface of the device to the outside.

A rear projection type display device according to the present invention comprises a light source unit for generating excitation light having a predetermined wavelength, and modulating the excitation light generated by the light source unit for each pixel on a two-dimensional plane. Optical element, a projection lens for projecting the excitation light modulated by the optical element, and a second surface on the opposite side of the first surface receiving the excitation light projected by the projection lens. A fluorescent screen that emits visible light from the surface to the outside.

According to a first aspect of the present invention, a fluorescent screen includes a phosphor layer having an absorption coefficient of 1 × 10 ² cm ⁻¹ or more for excitation light having a predetermined wavelength. Here, in order to increase the brightness and the sharpness, the thickness of the phosphor layer is desirably 120 μm or less. In the present application, the absorption coefficient refers to an apparent absorption coefficient,
The evaluation method will be described later in detail.

According to a second aspect of the present invention, the fluorescent screen includes a phosphor layer having a film thickness of 120 μm or less that gives maximum luminance to excitation light having a predetermined wavelength. More preferably, the film thickness giving the maximum luminance is 80 μm.
m or less.

Further, according to a third aspect of the present invention, the fluorescent screen includes a phosphor layer having a product of an absorption coefficient for excitation light having a predetermined wavelength and a film thickness of 1.2 to 8. . More preferably, the product of the absorption coefficient and the film thickness is 2 to 4. Here, in order to increase the brightness and the sharpness, the thickness of the phosphor layer is desirably 120 μm or less.

The materials of the phosphor include ZnO: Zn,
_{(Sr, Ca, Ba) 5} (PO 4) 3 Cl: Eu and, Zn
S: Ag, Al, ZnS: Au, Ag, Al, Zn
S: Cu, Au, Al, (Zn, Cd) S: Ag,
(Zn, Cd) S: Cu, Y ₂ O ₃ : Bi, Eu, L
iEuW ₂ O ₈ and Ca ₈ Mg (SiO ₄ ) ₄ Cl ₂ : Eu,
Mn, Ba ₂ ZnS ₃ : Mn, Y ₂ O ₂ S: Eu, B
aMg ₂ Al ₁₆ O ₂₇ : Eu, BaMg ₂ Al ₁₆ O ₂₇ : E
u, Mn, BaMgAl ₁₀ O ₁₇ : Eu, BaMgA
l ₁₀ O _17: Eu, and _{Mn, Sr 5 (PO 4)} 3 Cl: Eu
, (Sr, Ba) SiO ₄ : Eu, and SrGa ₂ S ₄ :
Eu, K ₅ Eu _2.5 (WO ₄ ) _6.75 , ZnS: Cu,
Al and 3.5MgO.0.5MgF ₂ .GeO ₂ : Mn
And at least one of the group consisting of Note that the fluorescent screen may be configured to further include a phosphor different from the phosphor that emits visible light upon receiving light emission from the phosphor. As a material of a phosphor different from the above-mentioned phosphor, Y ₃ Al ₅ O ₁₂ : Ce and Y
_{3 (Al, Ga) 5 O} 12: may include at least one of the group consisting of Ce.

According to the above arrangement, in a system in which the phosphor layer is irradiated with excitation light from the back and the emitted light is extracted from the front, the excitation light is appropriately absorbed in the phosphor layer to obtain visible light. Therefore, an image with high sharpness, high efficiency, high brightness, and high contrast can be obtained.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing a display device (contact type) according to a first embodiment of the present invention in principle. This display device has a light source unit (backlight) 40 for generating excitation light. The excitation light generated by the light source unit 40 enters the optical element 50.
The optical element 50 has a large number of pixels in a two-dimensional plane, and modulates the excitation light for each pixel. The excitation light modulated by the optical element 50 is incident on the first surface (back surface 60a) of the fluorescent screen 60. The fluorescent screen 60 is
Visible light is generated to the outside from a second surface (front surface 60b) opposite to the first surface. Such a display device,
Since the optical element 50 and the fluorescent screen 60 are in close contact, it is called a contact type.

The light source section 40 has a housing 10, a fluorescent lamp 20 as a light source disposed in the housing 10, and a bead collimator 30 disposed on a side of the housing 10 on the optical element 50 side. This bead collimator 3
0 converts the excitation light emitted from the fluorescent lamp 20 into light having directivity (also referred to as collimated light). As the light source, an LED (light emitting diode) or an ultra-high pressure mercury lamp can be used instead of the fluorescent lamp.

A wavelength of 36 is suitable as excitation light.
UV rays of about 0 to 380 nm or wavelengths of 380 to 420
It is a purple or deep blue light beam of about nm. Particularly suitable is a light beam having a wavelength in the range of 360 to 410 nm, and preferably has a peak near the wavelength of 390 nm. If the wavelength is too short, the excitation light may be absorbed by an optical element for modulating the excitation light or the optical element may be damaged. On the other hand, if the wavelength is too long, the excitation efficiency of the phosphor decreases. It is also desirable to use a bead collimator, a multilayer filter, or the like to convert the diffused excitation light into sufficiently collimated light. In the present embodiment, a bead collimator 30 is used.

FIG. 2 is a diagram showing the structure of the bead collimator 30. As shown in FIG.
Has a light-transmitting support sheet 31 and a light-transmitting sphere (hereinafter referred to as a bead) 32 partially fixed to and in contact with the support sheet 31. In order to fix the beads 32 to the support sheet 31, a light reflecting adhesive 33 is filled between them. The light reflection adhesive 33 also has a role of preventing light from passing through a region other than the contact portion between the support sheet 31 and the beads 32 and the vicinity thereof. The bead collimator 30
The beads are arranged with the bead side facing the optical element 50. Fluorescent light 2
The scattered light emitted from 0 enters the bead 32 only from the contact portion between the support sheet and the bead and the vicinity thereof, is refracted by the action of the spherical bead, and is condensed to be collimated light.

The light reflecting adhesive 33 is formed by dispersing a light diffusing substance in the adhesive. Including fine voids results in stronger light scattering. As the light diffusing substance, a substance having a refractive index of 1.6 or more is preferable.
Fine particles such as ₂ O ₃ ), barium sulfate (BaSO ₄ ), and titanium oxide (TiO ₂ ) are suitable. By using such a substance, efficient light diffusion (reflection) can be performed. Instead of using a binder, a light reflecting film may be formed by using a metal thin film or the like, except in the vicinity of the contact portion between the beads 32 and the support sheet 31. In this case, the efficiency is reduced due to multiple reflection.

Further, when a light absorbing agent is used in place of the light diffusing substance, the light collecting effect can be obtained although the efficiency is reduced.
Alternatively, using a photosensitive developing material or a heat-sensitive ablation material, a black mask may be formed in a portion other than the vicinity of the contact portion between the beads 32 and the support sheet 31. Combination with a light reflecting film is also effective.

In the present embodiment, a combination of a fluorescent lamp and a bead collimator is used as the light source unit 40, but the present invention is not limited to this. Various light sources used in known LCDs, such as a combination of an LED and a microlens array or a combination of an ultra-high pressure mercury lamp, an optical filter (which cuts most of visible light) and a lens, can be used.

Next, the fluorescent screen 60 included in the display device according to the present embodiment will be described in detail with reference to FIG. The fluorescent screen 60 is mounted on the substrate 7.
0 and a phosphor layer 80 formed thereon. The substrate 70 is a substrate that transmits visible light generated by the phosphor, and for example, a glass substrate can be used. Preferably, an optical filter that absorbs or reflects the excitation light emitted from the light source unit 40 and transmits only the emission light emitted from the phosphor layer 80 is provided on the rear surface or the front surface of the substrate 70. Further, it is desirable to provide an external light antireflection film on the front surface of the substrate 70.

In the case of a color display device, FIG.
As shown in (1), red, green and blue (RGB) correspond to one pixel.
The three phosphor dots 81, 82, and 83 of the phosphor layer 80
include. A black matrix 84 fills the space between the dots. 1 for monochrome display devices
It is sufficient that one phosphor dot corresponds to one pixel, or a uniform screen having no structure corresponding to the pixel may be used.

The phosphor layer 80 is formed by dispersing and applying a phosphor in an acrylic resin binder dissolved using an organic solvent such as MEK / toluene. Or CR
Similarly to the method of manufacturing the T fluorescent film, the phosphor dots may be formed using a photoresist. Alternatively, the phosphor dots may be formed in the same manner as in the method of manufacturing a color filter used for a liquid crystal display. This manufacturing method includes a method using a transer, a method using an inkjet, a screen printing method, and the like.

Here, as the phosphor, it is not sufficient to simply have high excitation efficiency with ultraviolet light or blue light. When the thickness of the phosphor layer 80 is a thickness for realizing high sharpness, practical energy efficiency when observing from the surface opposite to the excitation light irradiation surface must be large. For that purpose, the ability to absorb the excitation light emitted from the light source unit 40 needs to be large to some extent. on the other hand,
If the ability to absorb the excitation light is too large, only the very surface of the phosphor layer 80 will be excited, and the emitted light will be attenuated inside the phosphor layer 80, so that the energy efficiency will also decrease. Therefore, the absorption coefficient representing the ability to absorb the excitation light needs to be within a certain range.

FIG. 4 shows that various kinds of phosphor layers were prepared by changing the material, binder ratio, and film thickness of the phosphor.
The results of measuring the brightness and sharpness are shown. In this measurement, excitation light having a peak at a wavelength of 390 nm was used, but it is presumed that similar results can be obtained by using excitation light having a wavelength in the range of 350 to 420 nm. Light having a wavelength in the range of 360 to 410 nm is particularly suitable as the excitation light. The particle size of the phosphor is 5 to 5 in median diameter.
An acrylic resin was used as a binder.
In FIG. 4, the luminance indicates a relative luminance when the sample that gives the highest luminance among the samples in each group is 100. Further, the sharpness was evaluated only for samples having a film thickness giving the highest luminance among the samples of each group. Some thinner samples have good sharpness, but thinner samples have lower energy efficiency. Therefore, samples having a film thickness that gives the highest luminance among the samples in each group are representative.

The absorption coefficient referred to here means an apparent absorption coefficient, and its evaluation method is defined as follows. The phosphor layer is regarded as a uniform layer having a thickness of d, and the reflectance and the transmittance of the phosphor layer when placed in isolation in a space are represented by r and t, respectively. The reflectance measurement is obtained by relative comparison with a standard white plate.
As shown in FIG. 5, a white plate (reflectance r
If you place a _w) (a) and a black plate (if put r _b) reflectance (b), respectively the measured values of the reflectance of the entire system R _w
And _Rb . However, since fluorescent light is generated when the incident light I ₀ is incident on the phosphor layer, by using a fluorescence spectrophotometer, the wavelength on the measurement side is made to match the wavelength of the incident light, and the reflected light I ₀ R _w Measure I _{0 Rb} .

The reflection of the whole system includes reflection by the phosphor layer and
Since it is the sum of the reflection by the white plate or the black plate, it is expressed by the following equation. R _w = r + r _w × t ² (1) R _b = r + r _b × t ² (2) The apparent absorption coefficient of the phosphor layer is K, and the absorption is related to the thickness d of the phosphor layer. Assuming exponential decay,
According to the law of conservation of energy, the sum of reflection, absorption and transmission is 1
Therefore, the following equation is established.

(Equation 1) Ｒ r + (1-r) (1-e^-Kd) + T = 1 (3) From equations (1) and (2), the following is obtained. R_w-R_b= (R_w-R_b) × t^Two Ｔ t = ｛(R_w-R_b) / (R_w-R_b)｝^1/2 (4) From equations (1) and (4), the following is obtained. r = R_w-R_w(R_w-R_b) / (R_w-R_bFrom the formulas (5), (3), (4) and (5), the apparent absorption coefficient K is
Is required. K = − (1 / d) × ln [t / (1-r)] = − (1 / d) × ln [｛(R_w-R_b) / (R_w-R_b)｝^1/2 / ｛1-R_w+ R_w(R_w-R_b) / (R_w-R_bHere, for example, r_w= 1, r_b= 0 and d = 1
0^-3R under the condition of cm_w= 0.5, R_b= 0.1 measurement
If a fixed result is obtained, K = 3.5 × 10 ^Twocm^-1
Is required.

The point of this evaluation method is that the measurement is performed by setting the thickness d of the phosphor layer so as to have appropriate values of R _w and R _b . If the values of R _w and R _b are approximately the same,
An accurate apparent absorption coefficient cannot be determined. If scattering is large, it can be dealt with by reducing the film thickness. Also,
In the case of a phosphor having a very large apparent absorption coefficient, there is a possibility that R _w ≒ R _b even at a thickness of about the particle size.
In such a case, instead of reducing the film thickness, measurement is performed with the filling rate of the phosphor in the binder lowered, and the apparent absorption coefficient is calculated from the value. For example, when the filling rate is halved, the calculation is performed assuming that the film thickness is halved.

In FIG. 4, the group of Examples 1-1 to 1-3 is
The film thickness is changed by using ZnO: Zn as the phosphor and setting the ratio of the phosphor to the binder (phosphor / binder) to 5/1. The absorption coefficient is 1600 cm ^-1 ,
Very high values were obtained. In this group, the film thickness 13
The highest luminance was obtained at μm, and the sharpness at that time was also extremely excellent (marked with ◎).

Further, the group of Examples 2-1～5 as phosphor _{(Sr, Ca, Ba) 5} (PO 4) 3 Cl: with Eu, the ratio of the phosphor and the binder as 1/1, The film thickness was changed. The absorption coefficient is 300 cm ^-1 ,
A slightly lower value was obtained. In this group, the film thickness is 80 μm.
m, the highest luminance was obtained, and the sharpness at that time was also excellent (○). The group of Examples 3-1 to 3 is a group of Examples 2-1 to 5
The same phosphor was used, and the thickness of the film was changed with the ratio of the phosphor to the binder being 5/1. The absorption coefficient is 70
0 cm ⁻¹ , which was a higher value than the binder ratio of 1/1. In this group, the highest luminance was obtained at a film thickness of 57 μm, and the sharpness at that time was also excellent (印).
The groups of Examples 4-1 to 3 use the same phosphors as in Examples 2-1 to 5 and change the film thickness with the ratio of the phosphor to the binder being 20/1. Absorption coefficient is 1000cm
^{It was -1} and was even higher. In this group,
The highest luminance was obtained with a film thickness of 40 μm, and the sharpness at that time was also extremely excellent (marked with ◎).

The group of Examples 5-1 to 4 used phosphors having a ratio of ZnS: Ag, Al / ZnS: Au, Ag, Al of 1/1, and a ratio of the phosphor to the binder. Is set to 5/1, and the film thickness is changed. The absorption coefficient was 600 cm ^-1 . In this group, a film thickness of 5
The highest brightness was obtained at 2 or 64 μm, and the sharpness at that time was also excellent (○).

The group of Examples 6-1 to -4 is a group in which
nS: Ag, Al / ZnS: The ratio of Cu, Au, Al was set to 8.5 / 1.5, and the ratio of the phosphor to the binder was set to 5/1, and the film thickness was changed. . The absorption coefficient was 600 cm ^-1 . In this group, the highest brightness was obtained at a film thickness of 55 μm, and the sharpness at that time was also excellent (印).

On the other hand, the group of Comparative Examples 1-1 to 6 used Y ₂ O ₃ : Eu as a phosphor and the ratio of the phosphor to the binder was 5/5.
1, the film thickness was changed. The absorption coefficient is
It was less than 100 cm ⁻¹ , which was a low value. In this group, the highest luminance was obtained at a film thickness of 164 μm, but the sharpness at that time was inferior (x mark).

In the comparative example, the absorption coefficient of the phosphor was
Is 1 × 10^Twocm^-1Less than the film thickness to obtain the brightness
High sharpness cannot be obtained because
No. Therefore, in order to obtain high sharpness, the absorption coefficient is 1 ×
10^Twocm^-1It is necessary to be above. Preferably, absorption
The coefficient is 2 × 10^Twocm^-1That is all. In particular, Example 2-
3, the absorption coefficient is 3 × 10^Twocm^-1If
In this case, excellent sharpness was obtained. Furthermore, Example 4-2 and
As in Example 1-2, the absorption coefficient was 1 × 10 ^Three~ 1.6
× 10^Threecm^-1Is very good sharpness
Obtained. On the other hand, when the absorption coefficient is large, the excitation light
Do not reduce the film thickness to some extent because it does not penetrate deeply
The emitted light is less likely to exit from the surface opposite the excitation surface
Is disadvantageous in terms of luminance.

When examining the results of FIG. 4 with respect to the thickness of the phosphor layer, it can be seen that considerable luminance can be obtained even with a film thickness of about 120 μm as in Example 2-4 (the highest luminance of 9).
9%). However, as in Comparative Example 1-6, the film thickness was 120
When it is larger than μm (film thickness 164 μm), the sharpness decreases. On the other hand, when the film thickness was 120 μm or less (film thickness 80 μm) as in Example 2-3, excellent sharpness was obtained. Therefore, under the above conditions of the absorption coefficient of the phosphor, the thickness of the phosphor layer is appropriately 120 μm or less, preferably 80 μm or less.

Actually, the apparent absorption coefficient and the optimum film thickness are not determined only by the kind of the phosphor, and vary depending on the binder ratio and the particle size. Therefore, the maximum luminance is determined according to the phosphor material and the binder ratio. It is appropriate to select a given film thickness. Therefore, the above conditions of the absorption coefficient and the film thickness can be limited using the concept of the film thickness giving the highest luminance. That is, as the film thickness giving the highest luminance, 120 μm
m or less is appropriate, and preferably 80 μm or less.

By using the phosphor layer having the absorption coefficient within the predetermined range, the excitation light is sufficiently absorbed by the phosphor layer having a thickness of several tens μm or less. Image can be realized.

Further, appropriate conditions for the phosphor layer can be limited by the product of the absorption coefficient and the film thickness. When the absorption coefficient has a minimum value of 1 × 10 ² cm ⁻¹ , the film thickness is 120 μm.
m, the value of the product of the absorption coefficient and the film thickness is 1.2 (dimensionless). On the other hand, the absorption coefficient is 1 ×
When it is as large as 10 ³ cm ⁻¹ , a certain degree of luminance can be obtained even when the film thickness is 80 μm as in Example 4-3 (72% of the maximum luminance). In this case, the product of the absorption coefficient and the film thickness is 8 When the absorption coefficient is 1.6 × 10 ³ cm ⁻¹ ,
Even when the film thickness is 7 μm as in Example 1-1, the highest luminance of 94 is obtained.
%, In which case the value of the product of the absorption coefficient and the film thickness is 1.1. Therefore, the product of the absorption coefficient and the film thickness is
It can be said that the range of 1 to 8 is appropriate. Actually, when extremely excellent sharpness is obtained (marked by ◎ in FIG. 4), the product of the absorption coefficient and the film thickness is in the range of 2 to 4.

As the material of the phosphor, a part of which is shown in the above embodiment, ZnO: Zn and (Sr, Ca,
Ba) ₅ (PO ₄ ) ₃ Cl: Eu, ZnS: Ag, Al
And ZnS: Au, Ag, Al and ZnS: Cu, A
u, Al, (Zn, Cd) S: Ag, and (Zn, C
d) S: Cu, Y ₂ O ₃ : Bi, Eu and LiEuW ₂
O ₈ , Ca ₈ Mg (SiO ₄ ) ₄ Cl ₂ : Eu, Mn,
Ba ₂ ZnS ₃ : Mn, Y ₂ O ₂ S: Eu, BaMg ₂
Al ₁₆ O ₂₇ : Eu, BaMg ₂ Al ₁₆ O ₂₇ : Eu, M
n, BaMgAl ₁₀ O ₁₇ : Eu, BaMgAl ₁₀ O
_17: Eu, and _{Mn, Sr 5 (PO 4)} 3 Cl: and Eu,
(Sr, Ba) SiO ₄ : Eu and SrGa ₂ S ₄ : Eu
, K ₅ Eu _2.5 (WO ₄ ) _6.75 , ZnS: Cu, Al
And 3.5MgO.0.5MgF ₂ .GeO ₂ : Mn can be used alone or in combination of one or more. In addition, the fluorescent screen 60 may be configured to further include a phosphor different from the phosphor that emits visible light by receiving light emission of the phosphor. This phosphor may be used as a mixture with the phosphor, or may be provided as a separate layer on the opposite side of the phosphor layer from the excitation light. As a material of a phosphor different from the above-mentioned phosphor, Y ₃ Al ₅ O ₁₂ :
Ce and Y ₃ (Al, Ga) ₅ O ₁₂ : Ce are suitable.

Next, the optical element 50 included in the display device according to the present embodiment will be described in detail with reference to FIG. 3 again. In the present embodiment, a transmission type liquid crystal panel is used as the optical element 50. In this liquid crystal panel, a liquid crystal layer 56 is formed between cell walls 54 and 58 on both sides. Inside of cell wall 54 (right side in the figure)
, A first address line 55 is provided in a direction perpendicular to the paper surface, and a second address line 57 is provided inside the cell wall 58 (left side in the figure) in a direction parallel to the paper surface. These address lines are transparent but conductive. By applying a voltage by designating the first address and the second address, the light transmittance of the liquid crystal located at each pixel on the two-dimensional plane in the liquid crystal layer is changed, and the light is incident on the optical element 50. The excitation light can be modulated. In the case of a color display device, three dots of RGB correspond to one pixel.

Polarizing plates 53 and 59 are arranged outside the cell walls 54 and 58. In order to remove crosstalk between dots, a light-shielding film 52 having a predetermined grid opening corresponding to the dots may be formed. Further, the optical element 50
A multi-layer filter that efficiently transmits excitation light when the light is substantially perpendicular to the fluorescent screen 60 and between the fluorescent screen 60 and the fluorescent screen 60, and efficiently reflects emitted light from the fluorescent screen 60. Is desirably provided. Note that, although different from the structure shown in FIG. 3, an active matrix liquid crystal panel using TFTs can be used.

Next, a display device according to a second embodiment of the present invention will be described with reference to FIG.
The second embodiment is a rear projection type display device using an optical element such as a transmissive liquid crystal cell, and the other points are almost the same as the first embodiment. This display device has a light source unit 110 for generating excitation light. The excitation light generated by the light source unit 110 is transmitted by the condenser lens 120 to the optical element 13 disposed immediately after the condenser lens 120.
The light is condensed on the stop of the projection lens 140 through 0. The optical element 130 has a large number of pixels in a two-dimensional plane,
The excitation light is modulated for each pixel. The excitation light that has passed through the optical element 130 is projected by the projection lens 140,
The light enters the first surface of the fluorescent screen 150. The fluorescent screen 150 emits visible light from a second surface opposite to the first surface.

As the light source of the light source unit 110, for example, an ultra-high pressure mercury lamp can be used. A filter that cuts visible light and extra ultraviolet light components is required before the optical element 130. As the optical element 130, a transmission type liquid crystal panel as used in the first embodiment can be used. The fluorescent screen 150 is composed of, for example, a glass substrate and a phosphor layer formed thereon. Appropriate phosphor layer conditions and phosphor materials are the same as in the first embodiment. In order to reduce the size of the optical system, the optical path may be folded by using a reflection mirror.

Next, a display device according to a third embodiment of the present invention will be described with reference to FIG.
The third embodiment is a rear projection type display device using an optical element such as a reflection type liquid crystal cell, and the other points are almost the same as the second embodiment. This display device has a light source unit 210 for generating excitation light. The excitation light generated by the light source 210 enters the polarization beam splitter 220 from a first direction (upper side in the figure). Inside the polarization beam splitter 220, a polarization separation film is formed at an angle of approximately 45 ° with the incident light, and this polarization separation film reflects only S waves and transmits P waves. Therefore, the polarization beam splitter 220 reflects the S-wave excitation light in a direction (left side in the figure) at an angle of substantially 90 ° with the incident direction. The excitation light reflected by the polarization beam splitter 220 enters the optical element 230. The optical element 230 has a large number of pixels in a two-dimensional plane, modulates and reflects the excitation light for each pixel, and makes the excitation light enter the polarization beam splitter 220 again from the second direction. Here, when the image is all white, the S wave becomes a P wave in the liquid crystal unit and is guided to the projection lens 240. On the other hand, when the image is all black, the S wave returns to the light source unit 210 by the polarization beam splitter 220. The excitation light that has passed through the polarizing beam splitter 220 is projected by the projection lens 240 and enters the first surface of the fluorescent screen 250. Fluorescent screen 25
0 generates visible light outside from the second surface opposite to the first surface.

As the optical element 230, for example, a reflection type liquid crystal panel in which a liquid crystal layer is formed on a silicon substrate can be used. In this liquid crystal panel, an arrangement direction of liquid crystal molecules located at each pixel on a two-dimensional plane in the liquid crystal layer is changed by specifying a first address and a second address and applying a voltage. Along with that,
The excitation light passing through the polarizing beam splitter 220 is modulated. Appropriate phosphor layer conditions and phosphor materials are as follows:
This is the same as the embodiment.

Next, a display device according to a fourth embodiment of the present invention will be described with reference to FIG.
In the fourth embodiment, a light modulation element is used as an optical element instead of a liquid crystal panel, and the structures of a light source unit and a fluorescent screen are changed correspondingly. The display device includes a light source unit 310 for generating excitation light.
Having. The excitation light generated by the light source 310 enters the optical element 320. The optical element 320 has a large number of pixels in a two-dimensional plane, and modulates the excitation light for each pixel. The excitation light modulated by the optical element 320 is incident on the first surface of the fluorescent screen 330. The fluorescent screen 330 emits visible light from the second surface opposite to the first surface.

As a light source of the light source section 310, for example, a low-pressure mercury lamp is used. Light from the light source unit 310 is guided to the light guide plate 321 that forms the optical element 320. A plurality of strip-shaped transparent lower electrodes 323 are provided on the light guide plate 321.
Are provided in parallel with a predetermined interval. A column 325 is formed between adjacent lower electrodes. The support 325 can be formed by, for example, etching a material of the same quality as the light guide plate 321.

A plurality of strip-shaped transparent flexible thin films 327 are formed on the upper end surface of the column 325 at a predetermined interval in parallel with a direction perpendicular to the lower electrode 323. The flexible thin film 327 is located at a position away from the lower electrode 323 and has an insulating property. On its upper surface, a plurality of strip-shaped transparent upper electrodes 329 are provided. That is, the plurality of lower electrodes 323 and the plurality of upper electrodes 329 are arranged orthogonally in a lattice. By selecting a desired electrode among them and applying a voltage, the flexible thin film 327 is bent downward in the figure by Coulomb force. Flexible thin film 3
In a portion where 27 contacts the lower electrode 323 or approaches a predetermined distance, the excitation light emitted from the light source 310 passes through the flexible thin film 327 and the upper electrode 329. On the other hand, at a portion where the flexible thin film 327 is sufficiently separated from the lower electrode 323, the excitation light is reflected by the lower electrode 323. Thus, the excitation light emitted from the light source unit 310 can be modulated in the optical element 320.

Further, when the excitation light is vertically incident on the phosphor layer between the optical element 320 and the fluorescent screen 330 or as a part thereof, the excitation light is efficiently transmitted, and the non-perpendicular component of the excitation light and It is desirable to provide a multilayer filter that efficiently reflects light emitted from the phosphor layer.

As a material of the light guide plate 321, a transparent glass, a resin such as acrylic, polyethylene terephthalate, polycarbonate and the like can be used. Lower electrode 3
As the material of the upper electrode 329 or the upper electrode 329, a metal oxide such as ITO having a high electron density, a very thin metal or metal compound, a thin film in which metal fine particles are dispersed in a transparent insulator, a wide band gap which is highly doped, A semiconductor or the like can be used. Suitable metals include gold, silver, palladium, zinc, and aluminum, and suitable metal compounds include indium oxide, zinc oxide, and aluminum-added zinc oxide (commonly known as AZO). In addition, as a material of the flexible thin film 327, silicon oxide, silicon nitride, ceramic, resin, or the like can be used.

A fluorescent screen 330 is provided above the optical element 320. The fluorescent screen 330 is
It has a transparent front plate 334 and a phosphor layer including phosphor dots 331 to 333 formed on the front plate 334. In the case of a color display device, as shown in FIG. 7, three phosphor dots 331, 332, 333 of RGB are formed corresponding to one pixel. A black matrix may be provided around these phosphor dots. In the case of a monochrome display device, it is sufficient if one phosphor dot corresponds to one pixel,
A uniform screen having no structure corresponding to pixels may be used. Appropriate phosphor layer conditions and phosphor materials are as follows:
This is the same as the embodiment.

As the front plate 334, for example, a glass plate can be used. Preferably, an optical filter that absorbs or reflects excitation light emitted from the light source unit 310 and transmits only emission light emitted from the phosphor layer is provided. Further, it is desirable to provide an anti-reflection film for external light.

In the display device configured as above, Fabry-Perot interference can be used to modulate the excitation light emitted from the light source section 310. That is, in a state where the two planes are arranged in parallel to face each other, the incident light beam is repeatedly transmitted and reflected to be divided into a number of light beams, which are parallel to each other and cause interference. The angle between the perpendicular of the surface and the incident light is θ, and 2
Assuming that the interval between the two planes is t, the optical path difference x between the transmitted light and the light reflected twice between the two planes is given by x = 2 nt · cos θ if there is no phase change at the time of reflection. .
Here, n is the refractive index between the two planes. When the optical path difference x is an integral multiple of the wavelength λ, the transmitted light beams intensify each other, and when the optical path difference x is an odd multiple of a half wavelength, the transmitted light beams weaken each other. Therefore, the transmitted light becomes maximum when 2 nt · cos θ = mλ, and 2 nt · cos θ = (2m + 1) λ /
At 2, the transmitted light is minimized. Here, m is an integer greater than or equal to zero. When utilizing the Fabry-Perot interference, the excitation light emitted from the light source 310 passes through the flexible thin film 327 and the upper electrode 329, so that it is not necessary to bring the flexible thin film 327 into contact with the lower electrode 323. Is sufficient.

Next, a display device according to a fifth embodiment of the present invention will be described with reference to FIG.
The fifth embodiment is a modification of the fourth embodiment, in that the flexible thin film has conductivity and also serves as the upper electrode, and that the forming directions of the lower electrode and the upper electrode are reversed. The fourth embodiment differs from the fourth embodiment in that a phosphor layer is formed on the upper electrode. The other points are almost the same as the fourth embodiment.

In this embodiment, for example, an LED array can be used as a light source. Light from the LED array is guided to the light guide plate 421. On the light guide plate 421, a plurality of strip-shaped transparent lower electrodes 423 are provided in parallel with a predetermined interval, and a transparent insulating layer 427 is formed thereon. Although not shown, columns are formed between adjacent lower electrodes.

A plurality of strip-shaped transparent flexible thin films 429 having conductivity and also serving as an upper electrode are provided on the upper end surface of the support column in a direction orthogonal to the lower electrode 423 at a predetermined interval in parallel. Is formed. This flexible thin film 429 is
27. That is, the plurality of lower electrodes 42
3 and a plurality of upper electrodes (flexible thin films 429) are arranged in a grid at right angles. By selecting a desired electrode among them and applying a voltage, the flexible thin film 429 is bent downward in the figure by Coulomb force. In a portion where the flexible thin film 429 is in contact with or close to a predetermined distance from the insulating layer 427, excitation light emitted from a light source passes through the flexible thin film 429. On the other hand, at a portion where the flexible thin film 429 is sufficiently separated from the insulating layer 427, the excitation light is reflected by the insulating layer 427. Thereby, the excitation light can be modulated.

As the material of the flexible thin film 429, a semiconductor such as polysilicon or the like, or the same electrode material as in the third embodiment can be used. On the flexible thin film 429, a phosphor layer 431 is formed. Appropriate conditions for the phosphor layer and the material of the phosphor are the same as in the first embodiment. Further, a transparent front plate may be provided above the phosphor layer 431.

Next, an example of the operation principle of the display device according to the present embodiment will be described. When a cavity (for example, air) exists between the flexible thin film 429 and the insulating layer 427, the refractive index of the cavity is set to 1 and the insulating layer 4
Assuming that the refractive index of 27 is n _W , the critical angle for total reflection (the angle formed with the perpendicular) θ _{C at} the interface with air is θ _C = sin ⁻¹ (1
/ N _W ). Therefore, when the incident angle θ to the interface (the angle formed with the perpendicular) is θ> θ _C , the incident light travels while being totally reflected in the light guide plate 421 or the insulating layer 427. On the other hand, when the flexible thin film 429 and the insulating layer 427 come into contact with each other or approach a predetermined distance, θ <θ _C , and the incident light becomes
The light is guided to the side, propagates and transmits, and is emitted from the upper side of the flexible thin film 429 to excite the phosphor layer 431.

Next, a display device according to a sixth embodiment of the present invention will be described with reference to FIG. The tenth embodiment uses a DMD as the optical element 510.
(Digital Micromirror Device).
The excitation light is incident at an angle of about 20 ° with respect to the perpendicular of the substrate 512 on which the DMD element is formed. The DMD element has a minute reflecting surface 511 formed on a substrate 512. When the minute reflecting surface is tilted by about ± 10 °, the excitation light enters the projection lens 520 or the light absorber 530. The excitation light incident on the projection lens 520 is projected on the first surface of the fluorescent screen 540. The fluorescent screen 540 includes a transparent front plate 544,
Phosphor dots 541-5 formed on front plate 544
43, and a phosphor layer. The phosphor dots onto which the excitation light has been projected emit visible light to the outside from a second surface of the fluorescent screen 540 opposite to the first surface. Appropriate phosphor layer conditions and phosphor materials in the phosphor screen 540 are the same as in the first embodiment.

[0063]

As described above, according to the present invention, in a display device in which a phosphor film is irradiated with excitation light from the back surface and emitted light from the front surface, high sharpness and high efficiency are obtained.
High brightness and high contrast images can be realized. Therefore,
Since it is not limited to a display for a flat-screen television or a computer, but has no viewing angle dependence, it is most suitable as a display for diagnosis and monitoring of medical equipment, an art appreciation, and a display for large information such as an airport.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a display device according to a first embodiment of the present invention in principle.

FIG. 2 is a diagram showing a structure of a bead collimator 30 in the display device of FIG.

FIG. 3 is an optical element 50 in the display device of FIG.
FIG. 3 is a cross-sectional view showing a structure of a fluorescent screen 60.

FIG. 4 is a table showing the results of preparing various kinds of phosphor layers by changing the material, binder ratio, and film thickness of the phosphor, and measuring the absorption coefficient, luminance, and sharpness thereof.

FIG. 5 is a diagram for explaining a reflectance measuring method when obtaining an apparent absorption coefficient of a phosphor.

FIG. 6 is a diagram illustrating a display device according to a second embodiment of the present invention.

FIG. 7 is a diagram illustrating a display device according to a third embodiment of the present invention.

FIG. 8 is a sectional view showing a display device according to a fourth embodiment of the present invention.

FIG. 9 is a cross-sectional view illustrating a display device according to a fifth embodiment of the present invention.

FIG. 10 is a diagram illustrating a display device according to a sixth embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Housing 20 Fluorescent lamp 30 Bead collimator 31 Support sheet 32 Bead 33 Binder 40, 110, 210, 310 Light source part 50, 130, 230, 320, 510 Optical element 52 Light shielding film 53, 59
Polarizing plates 54, 58 Cell wall 55 First address line 56 Liquid crystal layer 57 Second
Address line 60, 150, 250, 330, 540 phosphor screen 70 substrate 80, 431 phosphor layer 81-83, 331-333, 541-543 phosphor dot 84 black matrix 120 condenser lens 220 polarizing beam splitter 140, 240,
520 Projection lens 321,421 Light guide plate 323,423
Lower electrode 325 Post 327, 4
29 Flexible thin film 329 Upper electrode 334, 544
Front plate 427 Insulating layer 511 Micro-reflection surface 512 Substrate on which DMD element is formed 530 Light absorber

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) C09K 11/61 CPS C09K 11/61 CPS CPX CPX 11/64 CPM 11/64 CPM 11/66 CPT 11/66 CPT 11/78 CPB 11/78 CPB CQC CQC 11/80 CPM 11/80 CPM CPP CPP 11/84 CPD 11/84 CPD G02F 1/13 505 G02F 1/13 505

Claims (12)

[Claims] A light source section for generating excitation light having a predetermined wavelength; an optical element for modulating the excitation light generated by the light source section for each pixel on a two-dimensional plane; and an optical element modulated by the optical element. A fluorescent screen that receives the excitation light on the first surface and emits visible light to the outside from a second surface opposite to the surface, wherein the fluorescent screen has an absorption coefficient of 1 × for the excitation light. A display device comprising a phosphor layer of 10 ² cm ^-1 or more. 2. A light source unit for generating excitation light having a predetermined wavelength, an optical element for modulating the excitation light generated by the light source unit for each pixel on a two-dimensional plane, and an optical element modulated by the optical element. A fluorescent screen that receives the excitation light on the first surface and emits visible light to the outside from a second surface opposite to the surface, the fluorescent screen having a maximum luminance with respect to the excitation light. A display device comprising a phosphor layer whose applied film thickness is 120 μm or less. 3. A light source unit for generating excitation light having a predetermined wavelength, an optical element for modulating the excitation light generated by the light source unit for each pixel on a two-dimensional plane, and modulated by the optical element. A fluorescent screen that receives the excitation light on the first surface and emits visible light to the outside from a second surface opposite to the first surface, wherein the fluorescent screen has an absorption coefficient and a film thickness for the excitation light. A phosphor layer whose product is 1 to 8. 4. A light source unit for generating excitation light having a predetermined wavelength, an optical element for modulating the excitation light generated by the light source unit for each pixel on a two-dimensional plane, and modulated by the optical element A projection lens for projecting excitation light, a fluorescent screen that receives the excitation light projected by the projection lens on a first surface, and emits visible light from a second surface opposite to the surface to the outside, The display device, comprising: a phosphor screen having an absorption coefficient of 1 × 10 ² cm ⁻¹ or more for the excitation light. 5. A light source unit for generating excitation light having a predetermined wavelength, an optical element for modulating the excitation light generated by the light source unit for each pixel on a two-dimensional plane, and modulated by the optical element A projection lens for projecting excitation light, a fluorescent screen that receives the excitation light projected by the projection lens on a first surface, and emits visible light from a second surface opposite to the surface to the outside, The display device, comprising: a phosphor layer having a film thickness that gives a maximum luminance to the excitation light and having a thickness of 120 μm or less. 6. A light source unit for generating excitation light having a predetermined wavelength, an optical element for modulating the excitation light generated by the light source unit for each pixel on a two-dimensional plane, and modulated by the optical element A projection lens for projecting excitation light, a fluorescent screen that receives the excitation light projected by the projection lens on a first surface, and emits visible light from a second surface opposite to the surface to the outside, The display device, comprising: a phosphor screen, wherein the phosphor screen has a product of an absorption coefficient for the excitation light and a film thickness of 1 to 8. 7. The display device according to claim 1, wherein the thickness of the phosphor layer is 120 μm or less. 8. The display device according to claim 2, wherein the thickness of the phosphor layer that gives maximum luminance to the excitation light is 80 μm or less. 9. The display device according to claim 3, wherein the phosphor layer has a product of an absorption coefficient for the excitation light and a film thickness of 2 to 4. 10. The phosphor according to claim 1, wherein the phosphor is ZnO: Zn.
_{r, Ca, Ba) 5 (} PO 4) 3 Cl: Eu and, ZnS:
Ag, Al and ZnS: Au, Ag, Al and ZnS:
Cu, Au, Al, (Zn, Cd) S: Ag, and (Z
n, Cd) S: Cu, Y ₂ O ₃ : Bi, Eu, and LiE
uW ₂ O ₈ and Ca ₈ Mg (SiO ₄ ) ₄ Cl ₂ : Eu, Mn
, Ba ₂ ZnS ₃ : Mn, Y ₂ O ₂ S: Eu, and BaM
g ₂ Al ₁₆ O ₂₇ : Eu, BaMg ₂ Al ₁₆ O ₂₇ : Eu,
Mn, BaMgAl ₁₀ O ₁₇ : Eu, BaMgAl ₁₀
O ₁₇ : Eu, Mn, Sr ₅ (PO ₄ ) ₃ Cl: Eu,
(Sr, Ba) SiO ₄ : Eu and SrGa ₂ S ₄ : Eu
, K ₅ Eu _2.5 (WO ₄ ) _6.75 , ZnS: Cu, Al
The display device according to claim 1, further comprising at least one of a group consisting of: 3.5MgO.0.5MgF ₂ .GeO ₂ : Mn. 11. The phosphor screen according to claim 1, wherein the phosphor screen further includes a phosphor different from the phosphor that emits visible light upon receiving light emitted from the phosphor. Display device. 12. A phosphor different from said phosphor, Y ₃
Al ₅ O _12: Ce _{and, Y 3 (Al, Ga)} 5 O 12: display device according to claim 11, characterized in that it comprises at least one of the group consisting of Ce.