KR20060112453A - Photo-luminescenct liquid crystal display - Google Patents

Abstract

A self-emission LCD is provided to reduce lowering of a contrast ratio caused by unnecessary light emission by preventing excitation of a light emission layer due to external light. Liquid crystals are provided between a front panel(18) and a rear panel(11). Electrodes are provided in respective inner surfaces of the front panel and the rear panel, and form an electric field to the liquid crystals. A light emission layer(17) is formed at the front panel, and generates visible light by ultraviolet rays. A UV light source unit(20) is formed at the rear of the rear surface, and generates ultraviolet rays required for stimulation of the light emission layer. A UV filter(19) blocks UV included in ambient light from a front side of the front panel.

Description

Photoluminescence LCC {Photo-Luminescenct Liquid Crystal Display}

1 is a cross-sectional view showing a schematic structure of an LCD according to a first embodiment of the present invention.

2 is a view for explaining an embodiment of the backlight unit of the LCD according to the present invention.

3 is a view for explaining another embodiment of the backlight unit of the LCD according to the present invention.

4 is a cross-sectional view showing a schematic structure of an LCD according to a second embodiment of the present invention.

5 is a cross-sectional view showing the structure of a switching element and a pixel electrode of the LCD according to the present invention.

6 to 8 are graphs showing changes in PL strength for each ND material.

9 is a graph showing emission intensity by external light of conventional UV-excited phosphors.

U.S. Patent 4,830,469

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to LCDs, and to light-emitting efficiency (PL) -photo-luminescenct liquid crystal displays (LCDs).

LCD is a non-active display, which requires a separate back light device to display the screen, and R (Red), G (Green), and B (Blue) color filters are used to display color images. Each must be prepared.

The R, G, and B color filters generate R, G, and B of white light incident from the backlight, and a color filter such as R, G, and B is used. Since the color filter passes only light of a specific wavelength, the light loss is large, and thus, a backlight device having a stronger luminance is required to realize an image of sufficient brightness.

PL LCDs having a structure of exciting phosphors by UV disclosed in US Pat. Nos. 4,822,144, 4,830,469 and the like have a high light utilization efficiency in LCDs using color filters. The UV used in the PL-LCD uses near beam UV and electron beam activated phosphor and other UV excited phosphors used in conventional CRTs.

These UV-excited phosphors can also be stimulated by ambient light because the ambient light contains UV. UV from this surrounding reduces the contrast ratio by stimulating the phosphor irrespective of the image display of the LCD.

An object of the present invention is to provide a PL-LCD capable of displaying a high quality image by suppressing a reduction in contrast ratio due to ambient light.

The LCD according to the invention is:

Front and back panels;

Liquid crystal provided between the front plate and the back plate;

Electrodes provided on respective inner surfaces of the front plate and the back plate to form an electric field in the liquid crystal;

A light emitting layer provided on the front plate to generate visible light by ultraviolet rays;

A UV light source unit provided at a rear side of the back plate to generate ultraviolet rays necessary for stimulation of the light emitting layer;

And a filter for blocking UV included in the ambient light entering from the front of the front plate.

According to a preferred embodiment of the present invention, the backlight unit includes a UV LED and a UV LAMP light source.

The light emitting layer is an inorganic dot or a nano dot made of a material such as CdSe, CdS, CdSeS.

The UV filter may use a chemical blocker that absorbs UV having a wavelength in the range of 350 to 420 nm or a physical blocker that reflects and disperses incident UV.

Chemical blocking agents include PABA (Aminobenzoic acid) derivatives, cinnamate derivatives, salicylic acid derivatives, benzophenone and derivatives thereof, anthranilate and derivatives thereof.

Physical barriers include zinc oxide, titanium oxide, iron oxide and magnesium oxide.

The filter may be selectively formed on the inner surface or the outer surface of the front plate.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Referring to FIG. 1, the LCD according to the first embodiment of the present invention includes a display panel 10 and a UV backlight 20.

First, referring to the display panel 10, the front plate 18 and the back plate 11 are spaced apart from each other by a predetermined interval, and the liquid crystal (LC) layer 14 is provided in a space therebetween.

R (Red), G (Green), and B (Blue) light emitting layers 17 are formed on the inner surface of the front plate 18, and the common electrode 16 and the upper alignment layer 15 are sequentially formed thereon. The switching element SW such as TFT and the pixel electrode 12 are formed on the inner surface of the back plate 11, and the lower alignment layer 13 is formed thereon. Here, the light emitting layer 17 is an ND made of a phosphor or a self-luminescent material which is generally known to absorb UV to express a given color light, and the self-emitting ND will be further described later. On the outer surface of the front plate 18, a polarizing plate 23 and a UV filter 19 characterizing the present invention are provided.

The UV filter 19 may use a chemical blocker that absorbs UV or a physical blocker that reflects and disperses incident UV. Chemical blocking agents include PABA (Aminobenzoic acid) derivatives, cinnamate derivatives, salicylic acid derivatives, benzophenone and derivatives thereof, anthranilate and derivatives thereof. Physical barriers include zinc oxide, titanium oxide, iron oxide, magnesium oxide and the like. The UV filter 19 stimulates the light emitting layer 17 and prevents UV from causing unnecessary light emission from entering the light emitting layer 17.

Meanwhile, the UV light source device 20 is provided near the outer surface of the back plate 11 on which the polarizer 24 is formed. The light source device 20 is provided with, for example, a UV lamp 21, for example a UV LED or a mercury lamp. A light guide / diffusion member 22 is provided between the lamp 21 and the back plate 11 to guide the UV from the lamp 21 toward the back plate 11 and to diffuse the UV light evenly. Here, the light guide / diffusion member 22 is optional, in which case the lamp 21 has a size corresponding to the front side of the back plate 11, for example, when the lamp is an LED, a plurality of LEDs are planar. Are arranged densely, and in the case of mercury lamps have a size corresponding to the back plate. As such, a light source that supplies UV across the front of the LCD is required for large LCD implementation.

In the case of the LED lamp, as shown in FIG. 2, a so-called edge lighting method may have a structure in which a plurality of light emitting / diffusing members are arranged side by side in a row. According to another embodiment, as shown in FIG. 3, the LED may be disposed in the entire plane of the light guide / diffusion member 22 over the entire surface of the back plate 11.

4 has a schematic cross-sectional structure of an LCD according to a second embodiment of the present invention.

The difference between the LCD of the second embodiment and the LCD of the first embodiment is the position of the UV filter 19. Referring to FIG. 4, the LCD according to the second embodiment of the present invention includes a display panel 10 and a UV light source unit 20.

First, referring to the display panel 10, the front panel 18 and the back panel 11 are spaced apart at predetermined intervals, and the liquid crystal (LC) layer 14 is provided in a space therebetween.

The common electrode 16 and the upper alignment layer 15 are sequentially formed on the inner surface of the front plate 18. The switching element SW such as TFT and the pixel electrode 12 are formed on the inner surface of the back plate 11, and the lower alignment layer 13 is formed thereon.

Polarizing plates 25 and 24 are provided on the outer surfaces of the front plate 18 and the back plate 11. The light emitting layer 17 which expresses the color light given by UV is formed on the polarizing plate 25 by the front plate 18 side. The light emitting layer 17 is an ND made of a phosphor or a self-luminescent material, which is generally known to absorb UV and express a given color light, which will be described later. The light emitting layer 17 is covered by the protective substrate 23, and the UV filter 19 having the function described above is formed on the surface of the protective substrate 23.

The UV filter 19 may use a chemical blocker that absorbs UV or a physical blocker that reflects and disperses incident UV. Chemical blocking agents include PABA (Aminobenzoic acid) derivatives, cinnamate derivatives, salicylic acid derivatives, benzophenone and derivatives thereof, anthranilate and derivatives thereof. Physical barriers include zinc oxide, titanium oxide, iron oxide, magnesium oxide and the like. The UV filter 19 stimulates the light emitting layer 17 and prevents UV from causing unnecessary light emission from entering the light emitting layer 17.

5 is a cross-sectional view showing a vertical structure of a TFT which is a switching element and a pixel electrode 12 connected thereto in the LCD of the present invention. The TFT shown in FIG. 5 has a structure in which the gate SWg is provided under the silicon channel SWc as a bottom gate method. Specifically, the gate SWg is formed on one side of the substrate 11, and the gate insulating layer SWi is formed on the entire substrate thereon. On the gate insulating layer SWi, the transparent pixel electrode 12 such as the silicon channel SWc immediately above the gate SWg and the ITO next to the silicon channel SWc are formed. Sources SWs and drains SWd are disposed on both sides of the silicon channel SWc, and a passivation layer SWp is formed thereon. The drain SWd extends to the pixel electrode 12 to electrically connect the drain SWd and the pixel electrode 12. The lower alignment layer 13, which contacts the liquid crystal LC and orients the liquid crystal, is covered on the TFT switching element SW and the pixel electrode 12.

As described above, the light emitting layer of the present invention may be formed of ND by an existing fluorescent material excited by ultraviolet light or a self-luminous material emitting by blue UV described below.

The fluorescent material for each color known as the fluorescent material is shown in Table 1 below.

Phosphor RED Y ₂ O ₂ S: Eu ³⁺ Y ₂ O ₂ S: Eu ³⁺ , Bi ³⁺ YVO ₄ : Eu ³⁺ , Bi ³⁺ Y ₂ O ₃ : Eu ³⁺ , Bi ³⁺ SrS: Eu ²⁺ (Ca, Sr) S: Eu ²⁺ SrY ₂ S ₄ : Eu ²⁺ CaLa ₂ S ₄ : Ce ³⁺ GREEN YBO ₃ : Ce ³⁺ , Tb ³⁺ BaMgAl ₁₀ O ₁₇ : Eu ²⁺ , Mn ²⁺ (Sr, Ca, Ba) (Al, Ga) ₂ S ₄ : Eu ²⁺ ZnS: Cu, Al Ca ₈ Mg (SiO ₄ ) ₄ Cl ₂ : Eu ²⁺ , Mn ²⁺ Ba ₂ SiO ₄ : Eu ²⁺ (Ba, Sr) ₂ SiO ₄ : Eu ²⁺ Ba ₂ (Mg, Zn) Si ₂ O ₇ : Eu ²⁺ (Ba, Sr) Al ₂ O ₄ : Eu ²⁺ Sr ₂ Si ₃ O ₈ .2 SrCl ₂ : Eu ²⁺ BLUE (Sr, Mg, Ca) ₁₀ (PO ₄ ) ₆ Cl ₂ : Eu ²⁺ BaMgAl ₁₀ O ₁₇ : Eu ²⁺ BaMg ₂ Al ₁₆ O ₂₇ : Eu ²⁺

On the other hand, the ND refers to a semiconductor particle of a predetermined size having a quantum confinement effect, the diameter of the quantum dot is in the range of 1 to 10nm. The quantum dots can be synthesized by chemical wet methods. Here, the chemical wet method is a method of growing particles by putting a precursor material in an organic solvent, a method of synthesizing quantum dots by a chemical wet method is a known technique. Examples of the quantum dots include II-VI compounds such as CdSe, CdTe, CdS, ZnSe, ZnTe, ZnS, HgTe or HgS. In addition, the quantum dot may have a core-shell structure. Here, the core includes any material selected from the group consisting of CdSe, CdTe, CdS, ZnSe, ZnTe, ZnS, HgTe and HgS, and the shell is CdSe, CdTe, CdS, ZnSe, ZnTe, ZnS, HgTe and It includes any one material selected from the group consisting of HgS. In addition, III-V compounds, such as InP, are also possible.

6 to 7 show changes in the intensity of photo-luminescence (PL) of CdSe, CdS and CdSeS, which are self-luminous materials.

First, referring to FIG. 6, CdSe ND, which is a G light emitting material, exhibits maximum PL intensity at a wavelength near 420 nm, and emits G (green) light having a center wavelength of 530 nm by UV of 400 nm.

Referring to FIG. 7, CdS ND, which is a B light emitting material, exhibits maximum PL intensity at a wavelength of about 400 nm, and emits B (blue) light having a center wavelength of about 480 nm by UV of 400 nm.

Meanwhile, referring to FIG. 8, CdSeS ND, which is an R light emitting material, exhibits maximum PL intensity at a wavelength near 465 nm, and emits R (red) light having a center wavelength of approximately 600 nm by UV of 400 nm wavelength.

Compiling the above PL characteristic graph, it can be seen that R, G, and B color light can be generated by UV of 400nm.

FIG. 9 shows the change in the luminescence intensity of a conventional phosphor due to 392 nm UV included in ambient light such as bright light or sunlight. As a result of FIG. 9, two phosphors of different manufacturers were used for each color as a conventional UV-excited phosphor, and a 392 nm LED was used as a light source for the experiment.

As shown in FIG. 9, UV having a wavelength of about 392 nm as external light stimulates red, green, and blue phosphors, and similar blue light is emitted from two kinds of blue phosphors having the shortest wavelength. Happens. In the case of green, strong and weak green light was expressed in the green phosphor, and in the case of red, relatively weak light emission appeared.

Considering this light emission, when the PL LCD is placed in an environment with strong ambient light, light emission irrelevant to the display of light occurs at the front of the display, and therefore the contrast by color is extremely low, especially blue and green are not very good compared to red. Contrast ratio appears.

Accordingly, the present invention applies the UV filter as one main element of the LCD to prevent the external light from entering the light emitter of the LCD. The UV filter uses chemical or physical means as described above, and thereby suppresses the decrease in contrast ratio due to external light.

In the present invention, most preferably the fluorescent material is to apply the ND by the aforementioned PL material. This is because the wavelength of 400 nm is less absorbed by the LC and therefore less deteriorated by the LC. That is, when CdSeS, CdS, and CdSe are used as the materials for the R, G, and B layers of the above-described PL layer 17, an LCD which emits light with UV light of 360 to 460 nm, preferably 400 nm, having low absorption by LC is obtained. It becomes possible. In the case of the LCD using the conventional phosphor, UV light having a wavelength of 400 nm or less, that is absorbed by the LC and deteriorating the LC, must be used. However, the light utilization efficiency is only about 70%. It is possible to extend the lifespan by preventing the damage and further increase the light utilization efficiency by more than 90%.

The cutoff wavelength of the UV filter is equal to or less than the blue visible light band including, for example, a wavelength band around 400 nm necessary for excitation of the light emitter, and does not include the visible light region required for image display.

When CdSeS, CdS, and CdSe are used as the materials for the R, G, and B layers of the above-described PL layer 17, it is possible to obtain an LCD which emits light by UV of 360 to 460 nm, preferably 400 nm, with little absorption by LC. do. In the case of the LCD using the existing phosphor, UV light having a wavelength of 400 nm or less, that is absorbed by the LC and deteriorating the LC, must be used, but the light utilization efficiency is only about 70%. However, the LCD according to the present invention can use UV of 400 nm or more together with the ND emitter, which can extend the lifespan by preventing the degradation of the LC and increase the light utilization efficiency by 90% or more.

According to the description of the above embodiment, the LCD according to the present invention has been described as an active driving type by TFT, but this does not limit the technical scope of the present invention. According to another embodiment of the present invention, a modification to a simple matrix type without switch elements is possible.

As described above, the present invention prevents excitation of the light emitting layer due to external light and consequent decrease of the contrast ratio, which may be a weak point of the PL LCD, thereby ensuring a high quality image having high luminance and light utilization efficiency.

While some exemplary embodiments have been described and illustrated in the accompanying drawings in order to facilitate understanding of the present invention, it should be understood that these embodiments merely illustrate the broad invention and do not limit it, and the invention is illustrated and described. It is to be understood that the invention is not limited to structured arrangements and arrangements, as various other modifications may occur to those skilled in the art.

Claims (8)

Front and back panels; Liquid crystal provided between the front plate and the back plate; Electrodes provided on respective inner surfaces of the front plate and the back plate to form an electric field in the liquid crystal; A light emitting layer provided on the front plate to generate visible light by ultraviolet rays; A UV light source unit provided at a rear side of the back plate to generate ultraviolet rays necessary for stimulation of the light emitting layer; And a UV filter for blocking UV contained in the ambient light entering from the front of the front plate. The method of claim 1, The UV filter is a self-luminous LCD, characterized in that formed with a chemical blocking agent that absorbs UV. The method of claim 2, The chemical blocking agent is PABA (Aminobenzoic acid) derivatives, cinnamate derivatives, salicylic acid derivatives, benzophenone and its derivatives, anthranilate and self-luminous LCD, characterized in that any one of its derivatives. The method of claim 1, The UV filter is a self-luminous LCD, characterized in that formed with a physical blocker that reflects and scatters UV. The method of claim 4, wherein  The physical blocking agent is a self-luminous LCD, characterized in that formed of any one of zinc oxide, titanium oxide, iron oxide, magnesium oxide. The method of claim 1, The light emitting layer is formed on the outer surface of the front plate, the protective glass is formed on the light emitting layer and the UV filter is characterized in that the UV filter is formed on the surface of the protective glass. The method according to any one of claims 2 to 6, The light emitting layer is a self-luminous LCD, characterized in that it comprises at least one material of CdSeS, CdS, CdS. The method of claim 7, wherein The light emitting layer comprises a CdSeS layer, a CdSe layer, CdSeS layer, self-luminous LCD, characterized in that it comprises a R, G, B layer.

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