JP5403607B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a light-emitting device including a light-emitting element that emits primary light and a wavelength converter that absorbs primary light and emits secondary light, and further relates to a liquid crystal display device using the light-emitting device.

  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 nm 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 no method that satisfies both brightness and color reproducibility (NTSC ratio) at the same time has been developed.

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

By using _{Eu e Si f Al g O h} N i green light emitting phosphor consisting divalent europium-activated oxynitride is β type SIALON substantially represented to these technical problems, It is known that a light emitting device having good color reproducibility (NTSC ratio) and temperature characteristics can be obtained.

  On the other hand, the peak wavelength of light emission of the green light-emitting phosphor made of the above-described β-type SIALON, which is a divalent europium-activated oxynitride, is about 530 to 540 nm. Tend to be improved (compared to NTSC). Against this background, there is an urgent need to improve the color reproducibility (compared to NTSC) of backlights for large LCDs as well as small and medium-sized.

Conventionally, there is Patent Document 1 (Japanese Patent Laid-Open No. 2003-121838) that focuses on color reproducibility (NTSC ratio) in LCDs. Among them, as a backlight light source, it has a spectral peak in the range of 505 nm to 535 nm, and as an activator of a green phosphor used for the light source, any of europium, tungsten, tin, antimony, and manganese is used. In addition, the examples describe the use of MgGa ₂ O ₄ : Mn, Zn ₂ SiO ₄ : Mn as the green light-emitting phosphor. However, when the peak wavelength of the light emitting element is in the range of 430 nm 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 in the excitation light in the range of 430 nm to 480 nm, and are therefore suitable for use in the present invention. is not.

  In Patent Document 2 (Japanese Patent Application Laid-Open No. 2004-287323), 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, 3 It describes that there are wavelength-type fluorescent tubes, combinations of ultraviolet LEDs and RGB phosphors, organic EL light sources, and the like. However, there is no specific disclosure regarding an RG phosphor using blue light as an excitation source.

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

  Furthermore, Patent Document 4 (WO 2007/105631 A1) describes that SIALON (M, R) AlSiON belongs to an orthorhombic system and has a peak emission wavelength of 511 nm to 524 nm.

In Non-Patent Document 1 (Toshiba Review, Vol. 64 No. 4 pp60-63 (2009)), the peak wavelength of light emission is around 520 nm in SAL ₃ Sr ₃ Si ₁₃ Al ₃ O ₂ N ₂₁ , and this fluorescence It is described that the average color rendering index (Ra) is 82 to 88 when a body and a silicate red light emitting phosphor are combined. However, there is no description regarding color reproducibility (NTSC ratio).

  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, Patent Document 5 (Japanese Patent Publication No. 2004-529396) reports an example in which at least four primary colors such as RGB, Y (yellow), and C (cyan) are used as filters.

JP 2003-121838 A JP 2004-287323 A JP 2005-255895 A WO2007 / 105631 A1 publication JP-T-2004-529396

Toshiba Review (Vol.64 No.4 pp60-63 (2009))

  As a result of thorough investigation, examination, and development of the above technical problems, the present invention uses a specific phosphor that emits light with high efficiency by light in the range of 430 nm to 480 nm from a semiconductor light emitting device, thereby achieving color reproducibility. An object of the present invention is to provide a light-emitting device having excellent (NTSC ratio) and temperature characteristics, and a liquid crystal display device using the light-emitting device. Here, the NTSC ratio refers to red (0.670, 0.330), green (0.210, 0.710), blue, which are 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. This represents the ratio to the area of the triangle obtained by connecting the chromaticity coordinates of (0.140, 0.080).

The present invention provides a light emitting device including a light emitting element that emits primary light, and a wavelength conversion unit that absorbs part of the primary light and emits secondary light having a wavelength longer than the wavelength of the primary light. The peak wavelength of the light emitting element is in the range of 430 nm to 480 nm, the wavelength converter is made of one or more phosphors, and the one or more phosphors are a green light emitting phosphor and a red light emitting fluorescence. And the green light-emitting phosphor is represented by the following general formula (1)
(M1 _1-x Eu _x ) _a Si _b AlO _c N _d (1)
(In the formula, M1 is an alkaline earth metal element and represents at least one element selected from Ca, Sr and Ba, 0.001 ≦ x ≦ 0.3, 0.9 ≦ a ≦ 1.5, 4.0 ≦ b ≦ 6.0, 0.4 ≦ c ≦ 1.0, and 6.0 ≦ d ≦ 11.0.)
A divalent europium activated oxynitride phosphor substantially represented by:
The red light-emitting phosphor has the following general formula (2)
(M2 _1-y Eu _y ) M3SiN ₃ (2)
(Wherein M2 is an alkaline earth metal element and represents at least one element selected from Mg, Ca, Sr and Ba, M3 is composed of a trivalent metal element, and Al, Ga, In, Sc, Y represents at least one element selected from La, Gd, and Lu, and is a number satisfying 0.001 ≦ y ≦ 0.10)
Is a divalent europium activated nitride substantially represented by

In the green light-emitting phosphor composed of a divalent europium activated oxynitride substantially represented by the general formula (1): (M1 _1-x Eu _x ) _a Si _b AlO _c N _d When the europium concentration (x) is less than 0.001, sufficient brightness cannot be obtained. When the europium concentration (x) exceeds 0.3, the brightness is greatly lowered due to concentration quenching or the like. The range of 0.005 ≦ x ≦ 0.1 is preferable from the viewpoint of stability of characteristics and homogeneity of the matrix.

  The numbers a, b, c and d are 0.9 ≦ a ≦ 1.5, 4.0 ≦ b ≦ 6.0, 0.4 ≦ c ≦ 1.0 and 6.0 ≦ d ≦ 11, respectively. Within the range of 0.0, the influence of the impurity phase can be ignored and good light emission characteristics (brightness) can be obtained.

  Furthermore, the particle diameter of the green light-emitting phosphor is preferably in the range of 10 to 30 μm when expressed in terms of median diameter (50% D). When the thickness is less than 10 μm, crystal growth is not sufficient, and sufficient brightness cannot be obtained. When the thickness exceeds 30 μm, abnormally grown particles increase and it is not practical.

The green light-emitting phosphor made of divalent europium-activated oxynitride is merely an example in which the above general formula (1) has an Al index of 1, and (Sr _0.99 Eu _0.01 ) ₃ Si ₁₃ Al ₃ O ₂ N ₂₁ , (Sr _0.95 Eu _0.05 ) ₅ Si ₂₅ Al ₅ O ₄ N ₃₉ , (Sr _0.98 Eu _0.02 ) ₅ Si ₂₀ Al ₄ O ₃ N ₃₂ , (Sr _0.89 Ba _0.01 Eu _0.10 ) ₄ Si ₂₂ Al ₄ O ₃ N ₃₄ , (Sr _0.989 Ca _0.01 Eu _0.001 ) ₆ Si ₂₃ Al ₅ O ₄ N ₃₇ , (Sr _0.97 Eu _0.03 ) ₁₆ Si ₆₈ Al ₁₄ O ₁₁ N ₁₀₈ , (Sr _0.96 Ba _0.02 Eu _{0, 02} ) ₉₀ Si ₃₁₅ Al ₇₀ O ₆₃ N ₅₀₈ , (Sr _0.995 Eu _0.005 ) ₃ Si ₁₆ Al ₃ O ₂ N ₂₅ , (Sr _0.87 Ca _0.03 Eu _0.10 ) ₆ Si ₂₆ Al ₅ O ₄ N ₄₁ , (Sr _0.99 Eu _0.01 ) ₅ Si ₂₁ Al ₅ O ₂ N _{35 and the} like can be mentioned, but are not limited thereto.

In the red light-emitting phosphor made of a divalent europium activated nitride substantially represented by the general formula (2): (M2 _1-y Eu _y ) M3SiN ₃ , the europium concentration (y) is If it is less than 0.001, sufficient brightness cannot be obtained, and if it exceeds 0.10, the brightness is greatly reduced due to concentration quenching or the like. The range of 0.005 ≦ y ≦ 0.05 is preferable from the viewpoint of stability of characteristics and homogeneity of the matrix. Further, M3 is a trivalent metal element and represents at least one element selected from Al, Ga, In, Sc, Y, La, Gd, and Lu, and emits red light with higher efficiency. Therefore, M3 is preferably at least one element selected from Al, Ga and In.

  The particle diameter of the red light emitting phosphor is preferably in the range of 6 to 20 μm when expressed in terms of median diameter (50% D). If it is less than 6 μm, crystal growth is not sufficient and sufficient brightness cannot be obtained. If it exceeds 20 μm, abnormally grown particles increase, which is not practical.

Further, as red light emitting phosphors made of divalent europium activated nitride, (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 _{0.2 0 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 can be mentioned, but of course not limited thereto.

  Furthermore, a gallium nitride (GaN) based semiconductor is used as the light emitting element. As the primary light emitted from the light emitting element, one having a peak wavelength in the range of 430 nm to 480 nm is applied. Preferably, those in the range of 440 nm to 470 nm are used.

  Another embodiment of the present invention is a liquid crystal display device including a backlight and a filter, and the backlight absorbs primary light emitted from the light emitting element and the light emitting element and emits first secondary light. A light emitting device including a wavelength conversion unit including a first phosphor and a second phosphor that emits second secondary light, wherein the light emitting element has a peak wavelength in blue, and the first phosphor Secondary light emitted from the second phosphor has a peak wavelength at a wavelength of 630 nm to 680 nm, and the filter includes the liquid crystal display device. For each of the subpixels, a filter for each color of red (R), green (G), blue (B) and yellow (Y) is arranged on a plane, The filter of 490nm to 530nm It has a peak wavelength of the transmittance to a liquid crystal display device comprising a.

In the liquid crystal display device, the first phosphor has the following general formula (1):
(M1 _1-x Eu _x ) _a Si _b AlO _c N _d (1)
(In the formula, M1 is an alkaline earth metal element and represents at least one element selected from Ca, Sr and Ba, 0.001 ≦ x ≦ 0.3, 0.9 ≦ a ≦ 1.5, 4.0 ≦ b ≦ 6.0, 0.4 ≦ c ≦ 1.0, 6.0 ≦ d ≦ 11.0)
And a divalent europium-activated green light-emitting oxynitride phosphor substantially represented by

Furthermore, in the liquid crystal display device, the second phosphor has the following general formula (2):
(M2 _1-y Eu _y ) M3SiN ₃ (2)
(Wherein M2 is an alkaline earth metal element and represents at least one element selected from Mg, Ca, Sr and Ba, M3 is composed of a trivalent metal element, and Al, Ga, In, Sc, Y represents at least one element selected from La, Gd, and Lu, and is a number satisfying 0.001 ≦ y ≦ 0.10)
It is desirable to consist of the bivalent europium activated red light emitting nitride phosphor substantially represented by

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

  The light-emitting device of the present invention as described above efficiently absorbs light emitted from the light-emitting element to emit high-efficiency white light and has extremely good temperature characteristics. In addition, an LCD using it has a high color reproducibility (NTSC ratio) and can provide a high-definition image. In particular, when the phosphor is combined with a liquid crystal display device having four sub-pixels of RGBY, a liquid crystal display device with higher color reproducibility (NTSC ratio) and a bright display image can be obtained.

It is a side view of the principal part in the light-emitting device of one Embodiment of this invention. It is an emission spectrum distribution map in the light-emitting device of one Embodiment of this invention. It is an emission spectrum distribution map in a light emitting device using a β-type SIALON green light emitting phosphor. It is a chromaticity diagram showing the color reproducibility of an LCD incorporating a light emitting device as an embodiment of the present invention as a backlight light source. It is a schematic diagram which shows the principal part of LCD provided with the sub pixel of R (red), G (green), B (blue), and Y (yellow). It is a schematic diagram of the transmission spectrum characteristic of each filter of R (red), G (green), B (blue), and Y (yellow). The color which shows the color reproducibility of LCD provided with the sub pixel of R (red), G (green), B (blue), Y (yellow) which incorporated the light-emitting device as one embodiment of this invention as a backlight light source FIG. An LCD including R (red), G (green), B (blue), and Y (yellow) subpixels 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.

Hereinafter, the present invention will be described according to examples.
(Example 1)
A cross-sectional view of the light emitting device of the present invention is shown in FIG. In the light emitting device 10, a light emitting element 12 is mounted on a package 11. As the light-emitting element 12, a gallium nitride (GaN) -based semiconductor having a peak wavelength of 450 nm which is blue is used. The wavelength conversion unit 13 includes (Sr _0.99 Eu _0.01 ) ₃ Si ₁₃ Al ₃ O ₂ N ₂₁ (peak wavelength around 520 nm) as the green light-emitting phosphor 14 and (Ca _0.99 Eu _0.01 ) AlSiN as the red light-emitting phosphor 15. _A composition having a composition of ₃ and a mixture of these green light-emitting phosphor and red light-emitting phosphor in a ratio of 1: 0.35 dispersed in the silicone resin 16 was used.

  The characteristics of the light emitting device 10 incorporating the wavelength conversion unit 13 and the LCD using the light emitting device as a backlight were evaluated. The results are shown in Table 1. In addition, FIG. 2 shows an emission spectrum characteristic of the light-emitting device of Example 1.

(Comparative Example 1)
In Comparative Example 1, (Sr _0.48 Ba _0.47 Eu _0.05 ) ₂ SiO ₄ (peak wavelength around 520 nm) was used as the green light-emitting phosphor, and (Ca _0.99 Eu _0.01 ) AlSiN ₃ was used as the red light-emitting phosphor. . The characteristics of the LCD using this light emitting device as a backlight were evaluated, and the results are shown in Table 1.

  As can be seen from Table 1, the temperature characteristics of the light emitting device of Example 1 are remarkably improved as compared with Comparative Example 1, and the LCD using the light emitting device of Example 1 as a backlight is compared with Comparative Example 1. It can be seen that the color reproducibility (NTSC ratio) is further improved. As described above, the light emitting device of the present invention has characteristics suitable as backlights for various (particularly large) LCDs.

(Example 2)
A gallium nitride (GaN) -based semiconductor having a peak wavelength at 440 nm, which is blue, was used as the light-emitting element. In the wavelength conversion part, a composition of (Sr _0.95 Eu _0.05 ) ₅ Si ₂₁ Al ₅ O ₂ N ₃₅ (peak wavelength around 525 nm) as a green light emitting phosphor and (Ca _0.980 Eu _0.020 ) AlSiN ₃ as a red light emitting phosphor. The thing of was used. Using these green light emitting phosphors and red light emitting phosphors, a wavelength conversion unit was prepared in the same manner as in Example 1, and a light emitting device incorporating this wavelength conversion unit and this light emitting device were used as a backlight. The characteristics of the LCD were evaluated. The results are shown in Table 2.

(Comparative Example 2)
In Comparative Example 2, a green light emitting phosphor having a composition of (Sr _0.53 Ba _0.42 Eu _0.05 ) ₂ SiO ₄ (peak wavelength around 525 nm) was used. The characteristics of the LCD using this light emitting device as a backlight were evaluated, and the results are shown in Table 2.

  As can be seen from Table 2, the temperature characteristics of the light emitting device of Example 2 are significantly improved as compared with Comparative Example 2, and the color reproducibility (NTSC ratio) of the LCD using the light emitting device is further improved. I know that. That is, it has characteristics suitable for various (especially large-size) LCD backlights.

(Examples 3-5, Comparative Examples 3-5)
Tables 3 and 4 show the results of fabricating a light emitting device and an LCD by the same method as in Example 1 and evaluating various characteristics.

  As can be seen from Tables 3 and 4, the LCDs using the light emitting devices of Examples 3 to 5 have further improved color reproducibility (NTSC ratio) and remarkably temperature characteristics as compared with those of Comparative Examples 3 to 5. It turns out that it improves. This has characteristics suitable as backlights for various (particularly large) LCDs.

  In addition, with respect to this type of light emitting device, a green light-emitting phosphor made of the above-described β-type SIALON, which is a divalent europium-activated oxynitride, has been improved. It is known that an LCD having good color reproducibility (NTSC ratio) and temperature characteristics can be obtained by using it. However, the emission peak wavelength of the green light-emitting phosphor made of the above-described β-type SIALON, which is a divalent europium-activated oxynitride, is approximately 530 to 540 nm, and the reproducibility of the green region in particular is still not sufficient. .

  On the other hand, since the phosphor of the present invention can emit light with a shorter wavelength, that is, 515 to 525 nm, an LCD incorporating a light emitting device using the phosphor of the present invention as a wavelength conversion unit as a backlight light source has a color Reproducibility (NTSC ratio) is higher.

  FIG. 3 shows an emission spectrum distribution diagram of a light emitting device using a β-type SIALON green light emitting phosphor. In this example, the wavelength conversion unit is prepared by adjusting the emission chromaticity to be substantially the same as that of the first embodiment shown in FIG. In FIG. 3, the emission peak of the green band is approximately 530 to 540 nm, the emission of the green band is closer to the longer wavelength compared to FIG. 2, and at the same time, the emission of the red band is suppressed and balanced, The emission chromaticity is the same as in Example 1.

  FIG. 4 is a chromaticity diagram showing the color reproducibility region of the backlight of Example 1. In the figure, 41 is a color gamut of an LCD incorporating a light emitting device using a europium-activated oxynitride β-type SIALON green light emitting phosphor as a backlight source, and 40 in the figure is a back of the light emitting device of Example 1. The color gamut of an LCD incorporated as a light source is shown. It can be seen that the color reproduction range 40 of Example 1 is particularly improved in the reproducibility of the green range as compared with the color reproduction range 41 of the light emitting device using the β-type SIALON green light emitting phosphor.

(Example 6)
In this embodiment, the same phosphor as that in Embodiment 1 is used, but the subpixels in the LCD are four colors of R (red), G (green), B (blue), and Y (yellow). We used what is. FIG. 5 is a schematic view showing the main part of the LCD 50 according to the present embodiment (the LCD element members normally used such as the inside of the liquid crystal cell, the polarizing plate, and the optical sheet attached to the light guide plate are not shown). The light emitted from the light emitting device 10 using the phosphor of the first embodiment is introduced into the light guide plate 51, and the light emitted upward from the light guide plate passes through each pixel 53 of the liquid crystal cell 52. One pixel 53 includes four sub-pixels R (red), G (green), B (blue), and Y (yellow), and each sub-pixel is driven individually. One pixel has four subpixels arranged in the vertical and horizontal directions, but other arrangements such as arranging four subpixels in parallel in one pixel may be used.

  FIG. 6 is a diagram schematically showing transmission spectrum characteristics of the R (red), G (green), B (blue), and Y (yellow) filters used in this example. A light emitting device using a blue LED and a phosphor has a relatively broad spectrum. Therefore, if only three filters of R (red), G (green), and B (blue) are used to cover the region, each filter Therefore, it is necessary to use a material having a wide transmission band, so that the color purity is lowered and the color reproduction range is lowered. By using the Y (yellow) filter, it is possible to improve the luminance by capturing the entire broad spectrum of a light emitting device using a blue LED and a phosphor.

  FIG. 7 is a chromaticity diagram showing the color gamut 70 of the LCD according to the present embodiment and the color gamut 40 of the first embodiment. In addition to simply adding a yellow sub-pixel, the center transmission wavelength of the green sub-pixel, which is an adjacent color, can be shifted to a short wavelength away from yellow, thereby expanding the color reproducibility of the LCD. That is, in this embodiment, by using a Y (yellow) filter, a G (green) filter having a short wavelength and a narrow band can be used. In this embodiment, the center wavelength of the G (green) filter is 520 nm. In order to widen the color reproduction range, the center wavelength of the G (green) filter is 530 nm or less, preferably 520 nm or less. However, in order to reduce the overlap with blue, it is 490 nm or more, preferably 500 nm or more.

  The peak wavelength of the red phosphor suitable for combination with the R (red), G (green), B (blue), and Y (yellow) filters is as follows. Considering that the tail is drawn on the long wavelength side, the wavelength may be 590 nm or more, and the wavelength is more preferably 610 nm or more. On the other hand, the upper limit is preferably 680 nm or less because of poor visibility at long wavelengths, and more preferably 660 nm or less. The peak wavelength of the green phosphor is preferably from 510 nm to 530 nm, more preferably from 515 nm to 525 nm, considering that the color reproduction range can be improved by making the green filter shorter.

  In this embodiment, an edge light type LCD using a light guide plate is used. However, a back irradiation type LCD in which the light emitting device is arranged on the back surface of the LCD and no light guide plate is used. The back-illuminated LCD 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.

In Example 6, the phosphor used in Example 1 is used, but the phosphor used in Examples other than Example 1 may be used, and R (red), G (green), B ( As long as the phosphor has a wavelength excellent in matching with the blue and Y (yellow) filters, the phosphor of each comparative example and other phosphors may be used.
(Example 7)
FIG. 8 incorporates the light emitting device of the present invention as a backlight light source and includes an LCD including R (red), G (green), B (blue), and Y (yellow) subpixels and a circuit for driving the LCD. The block diagram of the liquid crystal television 80 is shown. Here, a light-emitting device using the phosphor of Example 1 (but not a side-emitting type but a top-emitting type) is arranged in a matrix on the back side of the LCD panel, and is an area active type (local type) that emits LED light from the back side. A liquid crystal television with a screen size of 46 inches using an LCD 81 which is a liquid crystal panel of a dimming type) was manufactured. In the LCD 81, each pixel 82 is composed of R (red), G (green), B (blue), and Y (yellow) sub-pixels.

Based on the broadcast signal obtained from the external antenna 83, a circuit 84 for generating R ₀ (red), G ₀ (green), B ₀ (blue) signals, and R ₀ (red), G ₀ (green) , B ₀ (blue) signals, a circuit 85 for generating RGBY (red, green, blue, yellow) signals, a liquid crystal drive circuit 86 for generating LCD drive signals based on video signals, an LCD 81, an LCD 81, and A casing 87 that supports each circuit is provided. 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 only full green is displayed, the yellow signal is 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 (Sr _0.99 Eu _0.01 ) ₃ Si ₁₃ Al ₃ O ₂ N ₂₁ (peak wavelength around 520 nm) has a 1 / e fluorescence lifetime of about 1 μsec, and the red phosphor (Ca _0.99 Eu _0.01 ) AlSiN ₃ is also 1 / e e Since the fluorescence lifetime is as high as about 1 μsec, it was possible to follow area active drive even at a refresh rate of 240 Hz.

As the LCD, R (red), G (green), B (blue), and Y (yellow) subpixels are used, but other subpixels such as W (white), C (cyan), Adding one or more sub-pixels of M (magenta) has the same 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 liquid crystal television is used in the seventh embodiment, a computer 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. For chromaticity (x, y), the light emitted from the light emitting device was measured with MCPD-2000 manufactured by Otsuka Electronics, and the value was obtained. Further, the color reproducibility (NTSC ratio) was determined by measuring the value of Bm5 manufactured by Topcon Co., Ltd. by incorporating the produced light emitting device as a backlight source of a liquid crystal display device.

  The light emitting device having a wavelength conversion part in the present invention absorbs light emitted from the light emitting element with high efficiency and emits high efficiency white light, and further has excellent temperature characteristics. Furthermore, LCDs using it have high color reproducibility (NTSC ratio) and can provide high-definition images. In particular, in the present invention, a specific phosphor is combined with a liquid crystal display device having four sub-pixels of RGBY, and has high color reproducibility (NTSC ratio) and a bright display image. It can be applied to a liquid crystal display device.

DESCRIPTION OF SYMBOLS 10 Light-emitting device, 11 Package, 12 Light-emitting element, 13 Wavelength conversion part, 14 Green light-emitting fluorescent substance, 15 Red light-emitting fluorescent substance, 16 Silicone resin, 40 Color of LCD which incorporated the light-emitting device of this invention as a backlight light source Reproduction area, color reproduction area of LCD incorporating light emitting device using 41 β-type SIALON green light emitting phosphor as a backlight light source, 504 color LCD, 51 light guide plate, 52 liquid crystal cell, 53 pixels, 70 Color gamut of a 4-color LCD incorporating a light-emitting device as a backlight source, 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.

Claims (6)

A liquid crystal display device having a backlight and a filter,
The backlight includes a light emitting element, a first phosphor that absorbs primary light emitted from the light emitting element and emits first secondary light, and a second phosphor that emits second secondary light. A light emitting device including a wavelength conversion unit;
The light emitting element has a peak wavelength in blue,
The first phosphor has the following general formula (1)
(M1 _1-x Eu _x ) _a Si _b AlO _c N _d (1)
(In the formula, M1 is an alkaline earth metal element and represents at least one element selected from Ca, Sr and Ba, 0.001 ≦ x ≦ 0.3, 0.9 ≦ a ≦ 1.5, 4.0 ≦ b ≦ 6.0, 0.4 ≦ c ≦ 1.0, 6.0 ≦ d ≦ 11.0)
A divalent europium activated green light-emitting oxynitride phosphor represented by:
The secondary light emitted from the first phosphor has a peak wavelength in the range of 515 nm to 525 nm,
The second phosphor has the following general formula (2)
(M2 _1-y Eu _y ) M3SiN ₃ (2)
(Wherein M2 is an alkaline earth metal element and represents at least one element selected from Mg, Ca, Sr and Ba, M3 is composed of a trivalent metal element, and Al, Ga, In, Sc, Y represents at least one element selected from La, Gd, and Lu, and is a number satisfying 0.005 ≦ y ≦ 0.05 )
A divalent europium-activated red light-emitting nitride phosphor represented by:
The secondary light emitted from the second phosphor has a peak wavelength at a wavelength of 630 nm to 660 nm,
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. And
The green filter has a transmittance peak wavelength in a wavelength range of 490 nm to 530 nm.   2. The liquid crystal display device according to claim 1, wherein M1 is Sr. 3. The liquid crystal display device according to claim 1, wherein M3 is at least one element selected from Al, Ga, and In. The light emitting element is gallium nitride (GaN) based semiconductor, the primary light emitted from the light emitting element is Pi - claim 1-3 in which peak wavelength is equal to or in the range of 480nm from 430nm A liquid crystal display device according to 1. The liquid crystal display device according to any one of claims 1 to 4, characterized in that together with a circuit for converting the RGB signals into RGBY signal is held in the housing. 6. The liquid crystal display device according to claim 5 , wherein the area active drive has a refresh rate of 120 Hz or more, and the brightness is changed by the area active drive following the refresh rate.

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