JP2012003073A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device with excellent color reproductivity (NTSC ratio) and with high light emission luminance.SOLUTION: In a liquid crystal display device with a backlight and a filter, the backlight includes a light generating device provided with a light generating element which generates blue light, a green phosphor which absorbs a part of primary light generated from the light generating element to generate first secondary light, and a red phosphor which generates second secondary light. The filter is constructed such that each filter for red (R), green (G), blue (B), and yellow (Y) is placed on the flat plane for each sub pixel arranged in each pixel of the liquid crystal display device.

Description

  The present invention relates to a liquid crystal display device using a light emitting device including a light emitting element that emits primary light and a wavelength conversion unit that absorbs primary light and emits secondary light as a backlight.

  Light-emitting devices combining semiconductor light-emitting elements and phosphors are attracting attention as next-generation light-emitting devices that are expected to have low power consumption, small size, high brightness, and wide color reproducibility, and are actively researched and developed. .

  The primary light emitted from the light emitting element is usually in the range of long wavelength ultraviolet to blue, that is, 380 to 480 nm. In addition, wavelength converters using various phosphors suitable for this application have been proposed. Furthermore, in recent years, competition for development of backlights for large-sized LCDs as well as small-sized and medium-sized has intensified. Various methods have been proposed in this field, but a method that satisfies both brightness and color reproducibility (NTSC ratio) at the same time has not been developed.

Currently, as a white light emitting device, a blue light emitting element (peak wavelength, around 450 nm) and (Y, Gd) ₃ (Al, Ga) activated by trivalent cerium excited by the blue and emitting yellow light are used. A combination with ₅ O ₁₂ phosphor or (Sr, Ba) ₂ SiO ₄ phosphor activated with divalent europium is mainly used.

  However, an LCD (liquid crystal display device) using these light emitting devices as a backlight has a color reproducibility (NTSC ratio) of around 70%. On the other hand, in recent years, various types of LCDs with better color reproducibility have been demanded.

  Furthermore, recently, attempts have been made to increase not only the conversion efficiency (brightness) but also the input energy to make this type of light emitting device brighter. When the input energy is increased, efficient heat dissipation of the entire light emitting device including the wavelength conversion unit is required. For this reason, development of the structure and material of the entire light emitting device is also underway, but the current situation is that an increase in the temperature of the light emitting element and the wavelength conversion unit during operation is unavoidable.

However, in the case of (Y, Gd) ₃ (Al, Ga) ₅ O ₁₂ phosphor activated by trivalent cerium, the luminance (brightness) at 25 ° C. is assumed to be 100%. In this case, the luminance decreases to about 85%. In addition, the (Sr, Ba) ₂ SiO ₄ phosphor activated by divalent europium also has a technical problem that the input energy cannot be set high because it similarly decreases. Therefore, it is urgent to improve the temperature characteristics of the phosphor used for this type of light emitting device.

Green light-emitting consisting These technical problems with respect to _{Eu e Si f Al g O h} N i with (also referred to as β-sialon) substantially represented by β-type SiAlON 2 divalent europium-activated oxynitride is It is known that a light emitting device having good color reproducibility (NTSC ratio) and temperature characteristics can be obtained by using a phosphor.

Conventionally, Japanese Patent Application Laid-Open No. 2003-121838 (Patent Document 1) has focused on color reproducibility (NTSC ratio) in LCDs. Among them, it has a spectrum peak in the range of 505 to 535 nm as a backlight light source, and contains any of europium, tungsten, tin, antimony, and manganese as an activator of the green phosphor used for the light source. Furthermore, in the examples, it is described that MgGa ₂ O ₄ : Mn, Zn ₂ SiO ₄ : Mn is used as the green light emitting phosphor. However, when the peak wavelength of the light-emitting element is in the range of 430 to 480 nm, not all phosphors containing any of europium, tungsten, tin, antimony, and manganese are applied. That is, MgGa ₂ O ₄ : Mn and Zn ₂ SiO ₄ : Mn described in the examples have remarkably low luminous efficiency with excitation light in the range of 430 to 480 nm, and are therefore suitable for use in the present invention. is not.

  In Japanese Patent Application Laid-Open No. 2004-287323 (Patent Document 2), a three-wavelength type is used as a backlight, in addition to an RGB-LED in which a red light emitting LED chip, a green light emitting LED chip, and a blue light emitting LED chip are packaged. It is described that there are a fluorescent tube, a combination of an ultraviolet LED and an RGB phosphor, an organic EL light source, and the like. However, there is no specific disclosure regarding an RG phosphor using blue light as an excitation source.

  Japanese Patent Laying-Open No. 2005-255895 (Patent Document 3) describes that β-type SiAlON belongs to the hexagonal system and has an emission peak wavelength of 525 to 546 nm. However, there is no disclosure regarding color reproducibility (NTSC ratio).

  Furthermore, in International Publication No. 2007/066673 (Patent Document 4), Japanese Unexamined Patent Application Publication No. 2008-303331 (Patent Document 5) and Japanese Unexamined Patent Application Publication No. 2009-010315 (Patent Document 6), the crystal composition of β-type SiAlON Although a method for controlling an emission spectrum is described and it is described that the color reproducibility (NTSC ratio) of the liquid crystal display device can be improved thereby, there is no specific disclosure regarding the luminance of the display device.

  A normal LCD uses a CCFL (Cold Cathode Fluorescent Lamp) as a backlight and transmits the light for each pixel of the liquid crystal. Each pixel has three sub-pixels that transmit RGB (red, green, and blue), which are the three primary colors of light, and each sub-pixel is provided with a filter corresponding to RGB (red, green, and blue). Yes. Therefore, the color reproducibility (NTSC ratio) of the LCD is determined by the combination of the spectral characteristics of the light source and the transmission spectral characteristics of the filter. For the purpose of improving color reproducibility or improving luminance, there is an example in which light of RGB and other colors is used as a filter. For example, in Japanese translations of PCT publication No. 2004-529396 (patent document 7) and JP-A-2006-162706 (patent document 8), at least four primary colors such as RGB, Y (yellow) and C (cyan) are used as filters. Examples have been reported.

JP 2003-121838 A JP 2004-287323 A JP 2005-255895 A International Publication No. 2007/066673 JP 2008-303331 A JP 2009-010315 A JP-T-2004-529396 JP 2006-162706 A

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a liquid crystal display device having excellent color reproducibility (NTSC ratio) and high emission luminance.

  The present invention is a liquid crystal display device including a backlight and a filter, wherein the backlight absorbs part of the primary light emitted from the light emitting element emitting blue light and the first secondary light. A light emitting device including a green phosphor that emits red light and a red phosphor that emits second secondary light, and the filter includes red (R), green for each subpixel arranged in each pixel of the liquid crystal display device. The filter for each color of (G), blue (B), and yellow (Y) is arrange | positioned on the plane, It is characterized by the above-mentioned.

  In the liquid crystal display device of the present invention, the light emitting element is preferably a gallium nitride (GaN) based semiconductor that emits primary light having a peak of 430 to 480 nm.

  In the liquid crystal display device of the present invention, the emission peak wavelength of the green phosphor is preferably in the range of 510 to 545 nm, and more preferably in the range of 520 to 530 nm.

  In the liquid crystal display device of the present invention, the full width at half maximum of the emission spectrum of the green phosphor is preferably in the range of 40 to 55 nm, and more preferably in the range of 40 to 52 nm.

In the liquid crystal display device of the present invention, the green phosphor is a β-type SiAlON phosphor in which Eu and Al are dissolved in a nitride or oxynitride crystal having a β-type Si ₃ N ₄ crystal structure, The red phosphor is represented by the general formula (1)
(M1 _1-x Eu _x ) M2SiN ₃ (1)
(In general formula (1), M1 is at least one alkaline earth metal element selected from Mg, Ca, Sr and Ba, and M2 is Al, Ga, In, Sc, Y, La, Gd and It is at least one trivalent metal element selected from Lu, and x is a number satisfying 0.001 ≦ x ≦ 0.10.) preferable.

  In the liquid crystal display device of the present invention, it is preferable that the oxygen concentration contained in the crystal of the green phosphor is 0.1% by mass or more and 0.6% by mass or less.

  In the liquid crystal display device of the present invention, the Al concentration in the green phosphor crystal is preferably 0.13% by mass or more and 0.8% by mass or less.

  In the liquid crystal display device of the present invention, it is preferable that the Eu concentration in the crystal of the green phosphor is 0.5% by mass or more and 4% by mass or less.

  ADVANTAGE OF THE INVENTION According to this invention, the liquid crystal display device which can obtain a high-definition image with high color reproducibility (NTSC ratio) can be provided. Further, according to the liquid crystal display device of the present invention, an unprecedented bright display image can be obtained by matching the phosphor with the transmission characteristics of the RGBY four-color sub-pixels and the emission spectrum of the light-emitting device.

It is a figure which shows typically the principal part of the liquid crystal display device 1 of a preferable example of this invention. It is sectional drawing which shows typically an example of the light-emitting device 10 used as the backlight 2 to the liquid crystal display device 1 shown in FIG. It is a graph which shows the emission spectrum of the light-emitting device 10 obtained in Example 1, a vertical axis | shaft is intensity | strength (arbitrary unit) and a horizontal axis is a wavelength (nm). It is a graph which shows the transmission spectrum of the subpixel red (R), green (G), blue (B), and yellow (Y) filter used for Example 1, a vertical axis | shaft is intensity | strength (arbitrary unit) and a horizontal axis is a wavelength. (Nm). 4 is a graph showing color gamuts of liquid crystal display devices manufactured in Example 1 and Comparative Example 1, respectively. It is a figure which shows typically the principal part of the liquid crystal display device 50 of the other preferable example of this invention. It is a graph which shows the emission spectrum characteristic of the light-emitting device used for the comparative example 1, a vertical axis | shaft is intensity | strength (arbitrary unit) and a horizontal axis is a wavelength (nm). It is a graph which shows the emission spectrum of the light-emitting device used for Example 2, a vertical axis | shaft is intensity | strength (arbitrary unit) and a horizontal axis is a wavelength (nm). 6 is a graph showing color gamuts of liquid crystal display devices manufactured in Example 2 and Comparative Example 1, respectively. 6 is an enlarged view of an emission spectrum distribution of the light emitting device used in Example 2. FIG. An LCD including a red (R), green (G), blue (B), and yellow (Y) subpixel incorporating a light emitting device as an embodiment of the present invention as a backlight light source, and a circuit for driving the LCD It is a block diagram of the liquid crystal television provided.

  FIG. 1 is a perspective view schematically showing a main part of a liquid crystal display device 1 as a preferred example of the present invention, and FIG. 2 shows a light emitting device 10 used as a backlight 2 in the liquid crystal display device 1 shown in FIG. It is sectional drawing which shows an example typically. The liquid crystal display device 1 of the present invention basically includes a backlight 2 and a filter, and the backlight 2 absorbs part of the primary light emitted from the light emitting element 12 that emits blue light and the light emitting element 12. One feature is that a light emitting device including a green phosphor 14 and a red phosphor 15 that emit one secondary light is provided.

  A light-emitting device 10 preferably used in the present invention includes a light-emitting element 12 mounted on a package 11, for example, as shown in FIG. A light emitting element that emits blue light is used as the light emitting element 12 used in the light emitting device 10, and a gallium nitride (GaN) system that emits primary light having a peak of 430 to 480 nm (more preferably, a peak of 440 to 470 nm). A semiconductor is particularly preferred, but is not limited thereto. This is because when the primary light peak of the light-emitting element 12 is less than 430 nm, the human visual sensitivity tends to be low, and the light emission luminance tends to decrease, and when it exceeds 480 nm, the color of the blue region This is because the reproduction range tends to be narrow.

  The light emitting device 10 according to the present invention includes a wavelength conversion unit 13 in which a green phosphor 14 and a red phosphor 15 are dispersed in a medium 16. As the green phosphor 14 in the present invention, one having an emission peak wavelength in the range of 510 to 545 nm is preferably used. This is because when the emission peak wavelength of the green phosphor 14 is less than 510 nm, there is a tendency that the spectral valley between the blue peak and the color reproduction range of the green region tends to be narrow, and when it exceeds 545 nm. This is because the color reproduction range of the green region tends to be narrowed because the chromaticity point of the green peak approaches the yellow side. Further, as shown in Example 2 to be described later, from the viewpoint of dramatically increasing the green color reproduction range and obtaining good backlight characteristics, the green phosphor 14 has an emission peak wavelength of 520 to 530 nm. It is more preferable to use those within the range. When the emission peak is less than 520 nm, the emission intensity on the long wavelength side is weak, so the yellow emission intensity is low and the white luminance is low. In addition, when the emission peak exceeds 530 nm, not only the green color purity is poorly improved, but also it is necessary to suppress the spectrum of the red phosphor in order to achieve white balance, so the red emission luminance is lowered.

  The green phosphor 14 according to the present invention preferably has a full width at half maximum of the emission spectrum in the range of 40 to 55 nm, and more preferably in the range of 40 to 52 nm. When the full width at half maximum of the emission spectrum of the green phosphor 14 is less than 40 nm, the emission intensity on the long wavelength side is weak, so the yellow emission intensity tends to be low and the white luminance tends to be low. This is because when the wavelength exceeds 55 nm, the chromaticity point of the green peak approaches the white point, and the color reproduction range of the green region tends to be narrowed.

The green phosphor 14 in the present invention is preferably a β-type SiAlON phosphor in which Eu and Al are dissolved in a nitride or oxynitride crystal having a β-type Si ₃ N ₄ crystal structure. Since β-type SiAlON has a very narrow spectral line width among general rare-earth activated phosphors, in a liquid crystal display device using a light-emitting device using the same as described later, matching with a backlight filter is good. Wide color reproduction range.

  Further, the oxygen concentration in the green phosphor 14 is preferably 0.1% by mass or more and 0.6% by mass or less, and more preferably 0.2% by mass or more and 0.4% by mass or less. . When the oxygen concentration is less than 0.2% by mass, the phosphor particles are not sufficiently grown and the emission intensity tends to be weak. Further, by setting the oxygen concentration to 0.4 mass% or less, the uniformity of the coordination structure in the vicinity of the divalent Eu which is a luminescent ion is increased, and the spectral half width can be narrowed. The oxygen concentration in the green phosphor indicates a value obtained by measuring the oxygen concentration using, for example, an infrared absorption method.

  Further, the Al concentration in the green phosphor 14 is preferably 0.13% by mass or more and 0.8% by mass or less, more preferably 0.2% by mass or more and 0.7% by mass or less. preferable. By setting the Al concentration to be 0.2% by mass or more and 0.7% by mass or less, the peak intensity in the vicinity of 527 nm among the sub-peaks can be maximized. The Al concentration in the green phosphor indicates a value measured by, for example, ICP emission analysis.

  In the green phosphor 14 of the present invention, the Eu concentration is preferably 0.5% by mass or more and 4% by mass or less, and more preferably 0.5% by mass or more and 1% by mass. When the Eu concentration is 0.5% by mass or more and 1% by mass, the charge balance around the Eu ions can be optimized. If the charge balance around the Eu ions is not appropriate, the concentration of trivalent Eu ions that do not contribute to light emission increases and the concentration of divalent Eu ions that contribute to green light emission decreases. The Eu concentration in the green phosphor indicates a value measured by, for example, ICP emission analysis.

  The particle diameter of the green phosphor 14 is not particularly limited. For example, when expressed by the median diameter (50% D), it is preferably in the range of 5 to 25 nm, and more preferably in the range of 8 to 20 nm. . This is because when the particle size of the green phosphor 14 is less than 5 nm, the crystal growth is not sufficient and not only the light emission efficiency is low, but also the scattering / absorption loss due to Mie scattering tends to increase. This is because when the particle size of the phosphor 14 exceeds 25 nm, the grain boundary phase due to abnormal crystal growth or sintering increases and the light emission efficiency tends to decrease.

  As the red phosphor 15 in the present invention, a phosphor having an emission peak wavelength in the range of 630 to 680 nm is preferably used, and a phosphor in the range of 640 to 660 nm is more preferably used. This is because when the emission peak wavelength of the red phosphor 15 is less than 630 nm, the color reproduction range of the red region tends to be narrow, and when it exceeds 680 nm, the human visibility becomes low. This is because the emission luminance tends to decrease.

  Further, as the red phosphor 15 in the present invention, it is preferable to use a divalent europium activated phosphor represented by the following general formula (1).

(M1 _1-x Eu _x ) M2SiN ₃ (1)
In the general formula (1), M1 is at least one alkaline earth metal element selected from Mg, Ca, Sr and Ba, and among these, Ca or Sr is preferable. In the general formula (1), M2 is at least one trivalent metal element selected from Al, Ga, In, Sc, Y, La, Gd, and Lu. Since it can emit light, it is preferably at least one selected from Al, Ga and In.

  In the general formula (1), x indicating the europium (Eu) concentration is a number satisfying 0.001 ≦ x ≦ 0.10. When x is less than 0.001, sufficient brightness cannot be obtained, and when it exceeds 0.10, the brightness is greatly reduced due to concentration quenching or the like. The range of 0.005 ≦ x ≦ 0.05 is preferable from the viewpoint of stability of characteristics and homogeneity of the base material.

Specific examples of such a red phosphor 15 include (Ca _0.99 Eu _0.01 ) AlSiN ₃ , (Ca _0.97 Mg _0.02 Eu _0.01 ) (Al _0.99 Ga _0.01 ) SiN ₃ , (Ca _0.98 Eu _0.02 ) AlSiN ₃ , (Ca _0.58 Sr _0.40 Eu _0.02 ) (Al _0.98 In _0.02 ) SiN ₃ , (Ca _0.999 Eu _0.001 ) AlSiN ₃ , (Ca _0.895 Sr _0.100 Eu _0.005 ) AlSiN ₃ , (Ca _0.79 Sr _0.20 Eu _0.01 ) AlSiN ₃ , (Ca _0.98 Eu _0.02 ) (Al _0.95 Ga _0.05 ) SiN ₃ , (Ca _0.20 Sr _0.79 Eu _0.01 ) AlSiN _{3, and the} like, of course, but are not limited thereto.

  Further, the particle diameter of the red phosphor 15 is not particularly limited, but when expressed in terms of median diameter (50% D), a range of 6 to 20 μm is preferable. This is because when the particle diameter of the red phosphor 15 is less than 6 μm, the crystal growth is not sufficient and sufficient brightness tends not to be obtained, and when the particle diameter of the red phosphor 15 exceeds 20 μm, there is an abnormality. This is because the number of grown particles increases and is not practical.

  In the light emitting device 10 according to the present invention, the wavelength conversion unit 13 is manufactured by dispersing the green phosphor 14 and the red phosphor 15 as described above in the medium 16. Although it does not restrict | limit especially as the medium 16, The epoxy resin, silicone resin, urea resin etc. which are the resin material which has translucency can be used.

  The liquid crystal display device 1 of the present invention uses such a light emitting device 10 as the backlight 2. Here, FIG. 3 is a graph showing an emission spectrum of the light-emitting device 10 obtained in Example 1 described later, where the vertical axis represents intensity (arbitrary unit) and the horizontal axis represents wavelength (nm). Thus, in the present invention, the spectrum adjusted in accordance with the transmission characteristics of the liquid crystal display device 1 by using a specific phosphor that emits light with high efficiency by light in the range of 430 to 480 nm from the semiconductor light emitting element. By using the light emitting device 10 having the characteristics, a liquid crystal display device having excellent color reproducibility (NTSC ratio) and high emission luminance can be realized. Here, the NTSC ratio refers to red (0.670, 0.330), green (0...) Defined by the NTSC (National Television System Committee) of the color reproduction range in the XYZ color system chromaticity diagram of the liquid crystal display device. 210, 0.710) and blue (0.140, 0.080) chromaticity coordinates are represented by the ratio to the area of the triangle obtained.

  In the liquid crystal display device 1 of the present invention, a filter for each color of red (R), green (G), blue (B), and yellow (Y) is flat for each subpixel arranged in each pixel of the liquid crystal display device. It is also characterized by having a filter arranged above. As described above, FIG. 1 schematically shows the main part of the liquid crystal display device 1 (edge light type LCD) of the present invention (the optical sheet associated with the inside of the liquid crystal cell, the polarizing plate, and the light guide plate). The light emitted from the backlight 2 is introduced into the light guide plate 3, and the light emitted upward from the light guide plate 3 passes through each pixel 5 of the liquid crystal cell 4. One pixel 5 includes four sub-pixels red (R), green (G), blue (B), and yellow (Y), and each sub-pixel is driven individually. Although FIG. 1 shows an example in which four subpixels are arranged vertically and horizontally to form one pixel, other arrangements such as arranging four subpixels in parallel in one pixel may of course be used.

  FIG. 4 is a graph showing transmission spectra of sub-pixel red (R), green (G), blue (B), and yellow (Y) filters used in Example 1 described later, and the vertical axis represents intensity (arbitrary unit). ), The horizontal axis is the wavelength (nm). As can be seen from FIG. 4, since the light emitting device using the light emitting element and the phosphor emitting blue light has a relatively broad spectrum, only three filters of red (R), green (G), and blue (B) are used. In order to cover the area, it is necessary to use a filter having a wide transmission band as each filter, so that the color purity is lowered and the color reproduction area is lowered. For this reason, in the liquid crystal display device 1 of the present invention, by using the yellow (Y) filter, it is possible to improve the luminance by capturing the entire broad spectrum of the light emitting device that uses blue light emitting elements and phosphors. .

  FIG. 5 is a graph showing the color gamut of the liquid crystal display devices produced in Example 1 and Comparative Example 1 described later. As can be seen from FIG. 5, in the color gamut of Example 1, the enlargement of the yellow region important in the LCD was successfully realized by using the Y filter. In general, when the transmittance of the yellow region is increased, it is necessary to lower the peak values of the green phosphor and the red phosphor of the light emitting device in order to achieve white balance. For this reason, the green color gamut tends to be reduced. However, when β-type SiAlON is used as the green phosphor 14, the matching with the filter is good and the spectral separation between blue and green is particularly strong. Compared to Example 1, the color reproducibility in the green region is sufficiently secured. Since the peak intensity of the light emitting element that emits blue light relatively increases, the blue color reproduction range also increases. As a result, the NTSC ratio of Example 1 is improved compared to the comparative example, and in particular, the brightness of the screen is improved by expanding the yellow color reproduction region (region 100 in FIG. 5) with high human visibility. The white brightness was also improved. This is presumably because the combination of the phosphors used in the present invention has a moderately yellow emission intensity.

  FIG. 6 is a diagram schematically showing a main part of a liquid crystal display device 50 of another preferred example of the present invention. FIG. 1 shows an example of an edge light type liquid crystal display device using a light guide plate. However, as shown in FIG. 6, a light emitting device 10 is arranged on the back surface, and a back-illuminated liquid crystal without using a light guide plate. The display device 50 may be used. In FIG. 6, parts having the same configuration as in the example shown in FIG. In FIG. 6, the light emitting device 10 is mounted on a mounting substrate 51. The back-illuminated liquid crystal display device is excellent in energy saving because it can modulate the brightness of the backlight for each pixel, and can increase the contrast ratio between light and dark.

  The liquid crystal display device of the present invention can be held in a housing together with a circuit that converts RGB signals into RGBY signals. Preferably, the liquid crystal display device is area active drive with a refresh rate of 120 Hz or more, and the light emitting device is realized so as to change brightness by the area active drive following the refresh rate.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

<Example 1>
First, the light emitting device 10 as shown in FIG. 2 including the light emitting element 12 mounted on the package 11 and the wavelength conversion unit 13 in which the green phosphor 14 and the red phosphor 15 are dispersed in the medium 16 was manufactured. . In the light emitting device 10, a gallium nitride (GaN) -based semiconductor having a peak wavelength of 450 nm, which is blue, is used as the light emitting element 12, and an Eu-activated β-type SiAlON phosphor (crystal) having a peak wavelength of about 540 nm is used as the green phosphor 14. Eu concentration in the crystal: 0.6% by mass, Al concentration in the crystal: 2% by mass, acidity concentration in the crystal: 1.1% by mass), and the red phosphor 15 has a composition of (Ca _0.99 Eu _0.01 ) AlSiN ₃ The thing of was used. A mixture of these green phosphor 14 and red phosphor 15 at a ratio of 1: 0.25 was dispersed in a silicone resin as a medium 16 to produce a wavelength conversion section. FIG. 3 is a graph showing the emission spectrum of the light-emitting device 10 obtained in this way, where the vertical axis represents intensity (arbitrary unit) and the horizontal axis represents wavelength (nm). As shown in FIG. 3, the light emitting device 10 obtained in Example 1 has a spectral characteristic adjusted in accordance with the transmission characteristic of the liquid crystal display device 1 to be manufactured. In addition, this emission spectrum characteristic is shown as a characteristic normalized by the peak intensity of blue light, including the examples described in the following description.

  Using the obtained light emitting device 10 as the backlight 2, the liquid crystal display device 1 as shown in FIG. The four sub-pixels red (R), green (G), blue (B), and yellow (Y) are configured to be individually driven, and four subpixels are arranged vertically and horizontally to form one pixel. FIG. 4 is a graph showing transmission spectra of the subpixel red (R), green (G), blue (B), and yellow (Y) filters used in Example 1, and the vertical axis represents intensity (arbitrary unit), The horizontal axis is the wavelength (nm). As described above, it can be seen that by using the yellow (Y) filter, the luminance can be improved by capturing the entire broad spectrum of the light emitting device 10 using the light emitting element and the phosphor emitting blue light.

<Comparative Example 1>
Only the conventional three filters of red (R), green (G), and blue (B) are used, and the ratio of the green phosphor to the red phosphor in the light emitting device is set to 1: 0.35 in accordance with the filter characteristics. A liquid crystal display device was produced in the same manner as in Example 1 except that. FIG. 7 is a graph showing emission spectrum characteristics of the light emitting device used in Comparative Example 1. The vertical axis represents intensity (arbitrary unit) and the horizontal axis represents wavelength (nm).

  FIG. 5 is a graph showing the color gamut of the liquid crystal display devices produced in Example 1 and Comparative Example 1 described above. As can be seen from FIG. 5, in the color gamut of Example 1, the enlargement of the yellow region important in the LCD was successfully realized by using the Y filter. In Example 1, since β-type SiAlON was used, the matching with the filter was good, and the spectral separation of blue and green was particularly strong, and the color reproducibility in the green region was sufficiently ensured as compared with Comparative Example 1. Since the peak intensity of the light emitting element that emits blue light relatively increases, the blue color reproduction range also increases. As a result, the NTSC ratio of Example 1 was 85.8%, which was improved from 83.4% of Comparative Example 1. In particular, the brightness of the screen has been improved due to the enlargement of the yellow color reproduction region (the region indicated by reference numeral 100 in the figure) with high human visibility. White brightness was also improved by about 10%. In this example, the Eu, Al, and oxygen concentrations in the green phosphor crystal were 0.6 mass%, 2 mass%, and 1.1 mass%, respectively, but the Eu concentration was 0.5 mass% or more. Equivalent light emission characteristics were obtained when 1.0 mass% or less, Al concentration was 1.5 mass% or more and 2.5 mass% or less, and acidity concentration was 0.8 mass% or more and 2.0 mass% or less.

<Example 2>
Eu-activated β-type SiAlON phosphor having a peak wavelength of 520 to 530 nm as the green phosphor 14 (Eu concentration in the crystal: 0.5% by mass, Al concentration in the crystal: 0.6% by mass, oxygen concentration in the crystal: 0.3 mass%), a red phosphor 15 having a composition of (Ca _0.99 Eu _0.01 ) AlSiN ₃ , and the green phosphor 14 and the red phosphor 15 were mixed at a ratio of 1: 0.33. A light emitting device 10 was produced in the same manner as in Example 1 except for the above. FIG. 8 is a graph showing an emission spectrum of the light emitting device obtained in Example 2, where the vertical axis represents intensity (arbitrary unit) and the horizontal axis represents wavelength (nm). As shown in FIG. 8, the light emitting device obtained in Example 2 has a spectral characteristic adjusted in accordance with the transmission characteristic of the LCD described below. A liquid crystal display device was produced in the same manner as in Example 1 using the light-emitting device thus obtained as a backlight.

  FIG. 9 is a graph showing the color gamut of the liquid crystal display devices produced in Example 2 and Comparative Example 1 described above. Also in Example 2, it can be seen that, by using the Y filter, enlargement of an important yellow region can be realized in the LCD as in Example 1. Furthermore, in Example 2, the green color reproduction range could be dramatically increased by using β-type SiAlON having a peak wavelength of 520 to 530 nm as the green phosphor in the light emitting device. As described above, the β-type SiAlON phosphor has a very narrow spectral line width among general rare-earth activated phosphors, so that the matching with the backlight filter is good and the color reproduction range is widened. By adopting a composition having a shorter peak wavelength and a narrower spectral line width as described above, the green color reproduction region (region indicated by reference numeral 101 in the figure) could be further expanded. This makes it possible to reproduce intermediate colors in the blue-green region, which has heretofore been difficult to reproduce on LCDs. In general, when the peak wavelength of the green phosphor is shortened, the separation from the blue peak tends to deteriorate and the blue color reproducibility tends to decrease. In Example 2, the wavelength of the green phosphor is shortened. As a result, the spectrum is narrowed, so that the spectral separation of blue and green does not deteriorate, so that a blue color reproduction range can be secured. As a result, the NTSC ratio of Example 2 was 92.5%, which was significantly improved from 83.4% of Comparative Example 1. White brightness was also improved by about 5% compared to Comparative Example 1. Furthermore, in Example 2, since the emission intensity of the red phosphor was higher than that in Example 1, the display luminance in the red region was improved by about 10%. This is because the mixing ratio of the red phosphor can be increased to achieve white balance as the wavelength of the green phosphor is shortened. For the same reason, the color reproducibility in the red region was also improved from that in Example 1.

  Note that the oxygen concentration in the crystal of the Eu-activated β-type SiAlON phosphor is 0.1% by mass or more and 0.6% by mass or less, the Al concentration is 0.13% by mass or more and 0.8% by mass or less, and the Eu concentration. Is 0.5 mass% or more and 4 mass% or less, the emission peak wavelength is shortened in the range of 520 to 530 nm, high luminous efficiency is exhibited, and the spectral line width is narrowed. When the oxygen concentration in the crystal of the Eu-activated β-type SiAlON phosphor is larger than 0.6% by mass, the full width at half maximum of the emission spectrum is about 53 to 55 nm, whereas the oxygen concentration is 0. In the case of .6 mass% or less, the value is 45 to 52 nm, and the lower the oxygen concentration, the narrower the tendency is seen. For this reason, when the subpixel in the liquid crystal display device is used for four colors of red (R), green (G), blue (B), and yellow (Y), as described later, the color purity of green As a result, the color reproduction area is greatly improved.

  This is due to the emission spectrum unique to the Eu-activated β-type SiAlON phosphor having the above composition. As shown in FIG. 8, the green emission spectrum of the Eu-activated β-type SiAlON phosphor having the above composition is obtained by superimposing several emission peaks when viewed in detail. An enlarged view of this part is shown in FIG. The emission peak has three sub-peaks around 514 nm, 527 nm and 537 nm. The Eu-activated β-type SiAlON phosphor forms an emission spectrum by superimposing such a plurality of emission peaks, but when it has a special composition as described above, the entire emission spectrum half-value width decreases, Sub-peak becomes clear. For this reason, compared with the case of Example 1, a half value width is narrow, an emission peak becomes short wavelength, and light emission with high green color purity is obtained. The emission peak wavelength at this time is a case where the peak at 527 nm of the above peaks becomes the main peak. Actually, a peak appears at 520 to 530 nm due to other compositional differences and competition with other peaks due to thermal energy. In this case, the best backlight characteristics can be obtained.

  The emission spectrum as described above is such that the oxygen concentration contained in the crystal of the Eu-activated β-type SiAlON phosphor is 0.1 mass% or more and 0.6 mass% or less, and the Al concentration is 0.13 mass% or more. And 0.8% by mass or less, and the Eu concentration is 0.5% by mass or more and 4% by mass or less, but the oxygen concentration is 0.2% by mass or more and 0.4% by mass or less, and the Al concentration is More preferably, the content is 0.2% by mass or more and 0.7% by mass or less, and the Eu concentration is 0.5% by mass or more and 1% by mass. When the oxygen concentration is less than 0.2% by mass, the phosphor particles are not sufficiently grown and the emission intensity is weak. Further, by setting the oxygen concentration to 0.4% by mass or less, the uniformity of the coordination structure in the vicinity of the divalent Eu which is a luminescent ion is increased, and the spectral half width can be narrowed. Moreover, the intensity | strength of the peak of 527 nm vicinity can be maximized by making Al concentration into 0.2 mass% or more and 0.7 mass% or less. Moreover, the charge balance around Eu ions can be optimized by setting the Eu concentration to 0.5 mass% or more and 1 mass%. If the charge balance around the Eu ions is not appropriate, the concentration of trivalent Eu ions that do not contribute to light emission increases and the concentration of divalent Eu ions that contribute to green light emission decreases.

  In addition, although the fluorescent substance suitable for this invention was illustrated in the said Example, fluorescent substance other than description may be sufficient, and a red (R), green (G), blue (B), yellow (Y) filter and Other phosphors may be used as long as the phosphor has a wavelength excellent in matching.

<Example 3>
In FIG. 11, the light emitting device of the present invention is incorporated as a backlight light source, and includes an LCD including red (R), green (G), blue (B), and yellow (Y) subpixels and a circuit for driving the LCD. The block diagram of the liquid crystal television 80 is shown. Here, an area active type in which light emitting devices similar to those used in Example 1 are arranged in a matrix on the back surface of the LCD panel except that the top light emitting type is used instead of the side light emitting type, and LED light is irradiated from the back side. A liquid crystal television having a screen size of 46 inches using an LCD 81 which is a (local dimming type) liquid crystal panel was produced. In the LCD 81, each pixel 82 includes red (R), green (G), blue (B), and yellow (Y) sub-pixels.

The liquid crystal television 80 in the example shown in FIG. 11 includes a circuit 84 that generates R ₀ (red), G ₀ (green), and B ₀ (blue) signals based on a broadcast signal obtained from the external antenna 83. , R ₀ (red), G ₀ (green), B ₀ (blue) signals from the circuit 85 for generating RGBY (red, green, blue, yellow) signals, and LCD drive signals based on the video signals Liquid crystal driving circuit 86, LCD 81, LCD 81, and a housing 87 for supporting each circuit. In the circuit 86, the Y (yellow) signal is in principle calculated from the G (green) signal and the R (red) signal, but the addition ratio is adjusted according to each signal level in order to optimize the overall display color. (For example, if you display only full green, the yellow light will be zero).

  Sample images were displayed on this television for subjective evaluation by humans. In particular, regarding sample images containing many green and yellow components such as fruits and skin colors, good evaluation results were obtained due to improved color reproducibility.

  In order to display a moving image smoothly, the refresh rate of the liquid crystal screen was set to 120 Hz or 240 Hz. In order to perform image display at such a high refresh rate by area active drive, a drive signal to the light emitting device that handles each area is set in accordance with the necessary luminance information for each area generated for each refresh. The drive signal was a PWM (Pulse width modulation) signal of 600 Hz, which is a frequency higher than the refresh rate.

The response speed of the phosphor used in the light emitting device does not necessarily follow the PWM signal, but needs to follow the refresh rate. The green phosphor β-type SiAlON has a 1 / e fluorescence lifetime of about 1 μsec, and the red phosphor (Ca _0.99 Eu _0.01 ) AlSiN ₃ also has a 1 / e fluorescence lifetime of about 1 μsec, so the refresh rate is 240 Hz. But I was able to follow the area active drive.

The LCD uses red (R), green (G), blue (B), and yellow (Y) subpixels, but other subpixels such as white (W), cyan (C), Adding one or more sub-pixels of magenta (M) has a similar effect. When another color is added, it is necessary to generate a signal of that color from the signals of R ₀ , G ₀ and B ₀ .

  Although the third embodiment is a liquid crystal television, a computer liquid crystal monitor having a wide color reproduction range can be obtained. Further, since the overall power consumption is relatively low even at a high NTSC ratio, it is suitable as an AC power cordless type liquid crystal monitor / liquid crystal television.

  In the evaluation of the light emitting device in each of the above examples, the brightness was turned on at a forward current (IF) of 20 mA, and the light output (photocurrent) from the light emitting device was measured. Moreover, about chromaticity (x, y), the light radiated | emitted from the light-emitting device was measured in MCPD-2000 made from Otsuka Electronics, and the value was calculated | required. Further, the color reproducibility (NTSC ratio) was determined by measuring the value of the produced light emitting device as a backlight source of a liquid crystal display device using Bm5 manufactured by Topcon Co., Ltd.

  The LCD according to the present invention has a high color reproducibility (NTSC ratio) and can provide a high brightness and high definition image. In particular, in the present invention, a specific phosphor is combined with a liquid crystal display device having RGBY four-color sub-pixels to provide high color reproducibility (NTSC ratio) and a bright display image. It can be applied to a liquid crystal display device.

DESCRIPTION OF SYMBOLS 1 Liquid crystal display device, 2 Backlight, 3 Light guide plate, 4 Liquid crystal cell, 5 pixels, 10 Light emitting device, 11 Package, 12 Light emitting element, 13 Wavelength conversion part, 14 Green fluorescent substance, 15 Red fluorescent substance, 16 Medium, 50 Liquid crystal display device, 51 mounting substrate, 80 4-color area active liquid crystal television, 81 4-color LCD, 82 pixels, 83 external antenna, 84 R ₀ G ₀ B ₀ signal generation circuit, 85 RGBY signal generation circuit, 86 liquid crystal Drive circuit, 87 housing, 100 enlarged yellow color gamut, 101 enlarged green color gamut.

Claims (10)

A liquid crystal display device having a backlight and a filter,
The backlight includes a light emitting element that emits blue light, a green phosphor that emits first secondary light by absorbing a part of the primary light emitted from the light emitting element, and a red phosphor that emits second secondary light. Including a light emitting device including
In the filter, a filter for each color of red (R), green (G), blue (B), and yellow (Y) is arranged on a plane for each sub-pixel arranged in each pixel of the liquid crystal display device. A liquid crystal display device characterized by that.   The liquid crystal display device according to claim 1, wherein the light emitting element is a gallium nitride (GaN) -based semiconductor that emits primary light having a peak of 430 to 480 nm.   3. The liquid crystal display device according to claim 1, wherein an emission peak wavelength of the green phosphor is in a range of 510 to 545 nm.   4. The liquid crystal display device according to claim 3, wherein the emission peak wavelength of the green phosphor is in the range of 520 to 530 nm.   5. The liquid crystal display device according to claim 1, wherein the full width at half maximum of the emission spectrum of the green phosphor is in the range of 40 to 55 nm.   6. The liquid crystal display device according to claim 5, wherein the full width at half maximum of the emission spectrum of the green phosphor is in the range of 40 to 52 nm. The green phosphor is a β-type SiAlON phosphor in which Eu and Al are dissolved in a nitride or oxynitride crystal having a β-type Si ₃ N ₄ crystal structure,
The red phosphor has the general formula (1)
(M1 _1-x Eu _x ) M2SiN ₃ (1)
(In general formula (1), M1 is at least one alkaline earth metal element selected from Mg, Ca, Sr and Ba, and M2 is Al, Ga, In, Sc, Y, La, Gd and (At least one trivalent metal element selected from Lu, and x is a number satisfying 0.001 ≦ x ≦ 0.10.)
The liquid crystal display device according to claim 1, wherein the liquid crystal display device is a divalent europium activated phosphor represented by the formula:   The liquid crystal display device according to any one of claims 1 to 7, wherein the concentration of oxygen contained in the crystal of the green phosphor is 0.1 mass% or more and 0.6 mass% or less.   The liquid crystal display device according to any one of claims 1 to 8, wherein an Al concentration in the crystal of the green phosphor is 0.13 mass% or more and 0.8 mass% or less.   The liquid crystal display device according to claim 1, wherein an Eu concentration in the crystal of the green phosphor is 0.5 mass% or more and 4 mass% or less.

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