KR19980059076A - Red phosphor for active light emitting liquid crystal display - Google Patents

Abstract

Potassium, europium and tungsten oxide are combined in an appropriate ratio and sodium is placed in place of potassium to provide a new high-brightness red-emitting phosphor that can realize the structure of an active light-emitting liquid crystal display. Phosphors with a composition such as (K _5-x Na _x ) Eu _2.5 (WO ₄ ) _6.25 (x = 0.5 to 1.5) synthesized by a solid chemical reaction with an appropriate amount of sodium) ion are excited at a high luminance of 380 to 420 nm. It is a red light emitting phosphor of which the brightness is increased by more than 20% compared with the conventional phosphor, and it is possible to realize the device of an active light emitting liquid crystal display by improving the brightness of the phosphor.

Description

Red phosphor for active light emitting liquid crystal display

[Industrial use]

The present invention relates to a red phosphor for an active light emitting liquid crystal display, and more particularly, a novel sodium europium by developing and optimizing a new red phosphor that emits light in the near ultraviolet region that can be used for an active light emitting liquid crystal display. It is used in forming a desired device by providing a mother light emitting phosphor with tungsten salt as a phase, and can be used to form a film by controlling the appropriate particle size as well as red phosphor for an active light emitting liquid crystal display which improves luminance. It is about.

[Prior art]

All information displays perform their functions by utilizing the ability to control the light. Regardless of the complexity of the display, the basic operating principle of the display is to control the light in the pixels of the display. This is done by two methods, one type that gives each pixel the ability to generate light, called an active display, and a good example is a cathode ray tube. The screen of the cathode ray tube has a phosphor that emits light when the electron beam collides. Each pixel is made to generate light only by impinging on an electron beam.

In addition, the second form of the display does not generate light, but controls the amount of light reflected or transmitted by the display, called a passive display. Representative examples of passive displays include liquid crystal displays. The liquid crystal display is extremely thin and thin. It does not consume much power to generate light and use the light that exists around it, so it is operated at low cost and low power consumption. It is also well integrated with integrated circuits. Its size can be arbitrarily used for battery-powered devices such as wristwatches, portable radios and tape players, and portable computers. Is expanding. Such a liquid crystal display has already been put to practical use in the size of 2 to 12.1 inches and is currently being studied for the enlargement of 12.1 inches or more.

The liquid crystal display is generally configured to control the arrangement of liquid crystal molecules by applying an electric field through a driving integrated circuit by making a liquid crystal layer having a thickness of several micrometers to several tens of micrometers between glass plates coated with two thin conductive films. have. When the electric field is applied, the arrangement state of the liquid crystal molecules is parallel to the electric field or rearranged in the vertical direction. When the electric field is removed or weakened, the liquid crystal molecules are returned to the original state by the thinly oriented alignment layer on the conductive film.

The method of applying an electric field to the liquid crystal layer is classified into an active driving method in which liquid crystal display pixels are actively driven and a passive driving method in which a liquid crystal display pixel is driven individually, which is a reaction speed of liquid crystal molecules and interference between neighboring pixels ( It is closely related to the display characteristics of the liquid crystal display such as crosstalk, contrast, flickering of the screen, view angle, and large screen.

The reason why the thin liquid crystal layer can electrically control the amount of light transmitted is that the liquid crystal molecules have optical anisotropy, that is, the refractive index is not constant or different depending on the difference between the light propagation direction and the liquid crystal molecule direction. The advantage of a liquid crystal display is that such optical properties can be obtained sufficiently with a liquid crystal layer only a few μm thick and the corresponding electric field strength is very low, with only a few volts of voltage.

Currently, the liquid crystal display which is put into practical use is a red, green on a lower substrate, which is a thin film transistor (TFT), which is an individual switching element, that is, a TFT substrate and a liquid crystal layer and a black matrix layer having a predetermined repetitive pattern. ), And a blue colored layer is composed of an upper substrate, that is, a color filter substrate, which is repeatedly arranged to colorize.

When manufacturing the conventional color filter substrate for liquid crystal displays, it generally goes through the following processes.

First, a light blocking black matrix layer for preventing deterioration of a thin film transistor is formed on a glass substrate by using a sputtering method of chromium (Cr) to a thickness of 1000 to 2000 GPa. Subsequently, a negative photoresist having optimized spectral characteristics such as pigmented photosensitive resist resin in which pigments were dispersed was applied onto a glass substrate on which a black matrix layer was formed, and for a predetermined time on a hot plate at 60 to 120 ° C. After soft bake, the solution is developed for 2 to 3 minutes with a developer and then rinsed with deionized water for 1 to 2 minutes to form a red pattern, which is a first color filter layer having optimized red spectroscopic characteristics. . In the same manner as the first color filter layer, the pattern is formed such that the green pattern, which is the second color filter layer, and the blue pattern, which is the third color filter layer, are sequentially overlapped with the black matrix between each black matrix. Next, when the indium tin oxide (ITO) transparent electrode film having a thickness of about 500 to 1800 kPa is applied on the black matrix and the color filter layer, a color filter substrate as an upper substrate is completed.

However, when manufacturing a liquid crystal display using a conventional color filter substrate manufactured as described above, the common electrode of the color filter substrate should be connected to the thin film transistor array substrate at several short points. In this case, the transparent conductive material used as the common electrode has a high specific resistance of the sheet resistance of several hundred ohms, and thus it is difficult to maintain a uniform voltage, and the common signal may be distorted, thereby causing interference. In order to prevent this, four or more short-circuit points are required, and therefore, an additional process is required and a complicated process must be added.

In order to solve the problem of the color substrate described above, an active light emitting liquid crystal display as shown in FIG. 1 has been developed. As shown in FIG. 1, this active light-emitting liquid crystal display is an electrode including liquid crystals 15 in which ultraviolet rays scanned from the rear light source pass between two polarizing plates 13 and pass through ultraviolet rays scanned from the rear light source 11. When the ultraviolet rays passed through collide with the ultraviolet-excited phosphors R, G, and B of the black matrix film 19 formed on the windshield 17, the phosphors emit light to reproduce colors. This active light emitting liquid crystal display improves the narrow viewing angle of the conventional liquid crystal display.

In order to realize an active light emitting liquid crystal display illustrated in FIG. 1, a red phosphor having high luminance is required, and development of a red phosphor emitting light in the near ultraviolet region has emerged as a key issue. In general, however, in the case of green and blue phosphors, even if the excitation source moves to a longer wavelength, the excitation spectrum may move to a longer side, but in the case of the red phosphors, there is a problem that such a substance is not easy to find.

As the phosphor used in the active light-emitting liquid crystal display, commercial phosphors capable of emitting light at 380 nm to 420 nm, which are the excitation region of the back light, are now widely used. However, there are not many kinds of commercial phosphors excited in the near ultraviolet excitation region. In the case of green and blue phosphors, the excitation region extends to a longer wavelength region, but in the case of red phosphors, the limitation is particularly severe. Magnesium series emits red light, but it is not suitable for the purpose because it shows a region longer than a desired wavelength, that is, deep red. An example is a 3.5MgO0.5MgF ₂ GeO ₂ : Mn deep red phosphor developed for a five wavelength lamp. Since the phosphor emits deep red light at 650 nm, the phosphor has excellent color purity but low luminance.

In the meantime, the invention is a tungsten-based phosphor that emits light from europium trivalent ions. The phosphor is suitable for the present purpose and emits light in the 394 nm region, so it meets the desired conditions, but there is room for improvement in luminance. .

That is, Na ₅ Eu (Wo ₄ ) ₄ , a self-luminous phosphor, has a problem of low luminance due to insufficient light emission in the region of 380 to 420 nm, and K ₅ Eu _2.5 (WO ₄ ) _6.25 red phosphor has a particle size. It has a large size, which does not meet the film forming conditions, and has a weak weakness in luminance.

Therefore, it is essential to develop a red phosphor in which the emission position where the luminance is not reduced while maintaining the color purity moves toward the shorter wavelength than 3.5MgO0.5MgF ₂ GeO ₂ : Mn and is excited in the wavelength range of 380 to 420 nm.

The present invention has been made to solve the above problems of the prior art, an object of the present invention is to produce a new high-luminance red light-emitting phosphor for an active light-emitting liquid crystal display having a color CRT-level image quality and to control the appropriate particle size Through this, it is possible to realize deviceization of an active light-emitting liquid crystal display which helps in forming a film.

1 is a cross-sectional view showing the structure of an active light emitting liquid crystal display.

2 is an emission spectrum of the K ₅ Eu _2.5 (WO ₄ ) _6.25 phosphor prepared in Example 1 of the present invention at a wavelength of 394 nm in an excitation source.

Figure 3 is an emission spectrum of the (K _5-x Na _x ) Eu _2.5 (WO ₄ ) _6.25 phosphor prepared in Example 1 of the present invention according to the wavelength at an excitation source of 394 nm.

Explanation of symbols on the main parts of the drawings

11 back light source 13 polarizing plate

15 liquid crystal 17 front glass

19: black matrix film

R, G, B: UV-excited RGB phosphor

The present invention has the following configuration to achieve the above object of the present invention.

In the present invention, there is provided a red phosphor for an active light emitting liquid crystal display represented by the following formula (1).

(K _5-x Na _x ) Eu _2.5 (WO ₄ ) _6.25

Wherein x is a value ranging from 0.5 to 1.5.

The phosphor is preferably prepared through a solid chemical reaction.

In addition, in the present invention, the phosphor raw material mixed with K ₂ CO ₃ , Eu ₂ O ₃ , WO ₃ and Na ₂ CO ₃ phosphor raw materials is mixed and calcined at a temperature of 800 to 1100 ° C. for 2 to 6 hours, followed by potassium site. The present invention provides a method of manufacturing a red phosphor for an active light-emitting liquid crystal display, including a process of preparing a phosphor by controlling a flux thereof to replace sodium ions, and cleaning the phosphor.

It is preferred that K ₂ CO ₃ is 10 to 25% by weight, Eu ₂ O ₃ is 10 to 25% by weight, WO ₃ is 60 to 70% by weight and Na ₂ CO ₃ is 1 to 5% by weight.

The present invention is intended to facilitate the formation of an active light emitting liquid crystal display device by manufacturing a phosphor by optimizing a phosphor suitable for use in a conventional tungstate system and using it for device formation.

While having the self-absorption spectrum through the same europium trivalent ions, the characteristics are improved by changing the appropriate composition, and the device of FIG.

It also controls the size of the particles through the adoption of a new composition, thereby forming particles to help form the film. The changing composition improves its properties as it changes these factors, as it is important to change the amount of potassium that acts as a self flux.

The present invention basically used potassium, europium, and tungsten oxide, which are basically used to develop a phosphor having a new structure including self-emitting europium ions as a high-brightness red phosphor, and such a composition solves the overall problem. Since it can not replace the site of potassium, which acts as a self-flux, it is possible to replace the sodium ions among the alkali metal series, which is thought to be possible, to improve properties.

Tungsten-based potassium carbonate (potassium carbonate) acts as a self-flux to improve the characteristics by trying to change the appropriate composition for this.

The following presents a preferred embodiment to aid the understanding of the present invention. However, the following examples are merely provided to more easily understand the present invention, and the present invention is not limited to the following examples.

EXAMPLE

Example

(K _5-x Na _x ) Eu _2.5 (WO ₄ ) _6.25 (x = 0.5 to 1.5) Phosphor synthesis in the case of x = 1, that is, (K ₄ Na) Eu _2.5 (WO ₄ ) _6.25 The method was prepared using solid state reaction of solid chemistry. Each composition ratio suitable for stoichiometry results in 12.46 g K ₂ CO _3, 19.83 g Eu ₂ O _3, 65.32 g WO ₃ and 2.39 g Na ₂ CO ₃ to replace the potassium site with sodium ions. Mix well using a mortar and pestle. After putting this mixture in an alumina container, the process of baking at 800-1100 degreeC for about 2 to 6 hours was implemented. The obtained phosphor was washed 2 to 3 times with warm water, and filtered to prepare a finished phosphor.

Comparative example

12.76 g K ₂ CO _3, 20.32 g Eu ₂ O _{3 and} 66.92 g WO ₃ were mixed well using mortar or mortar. The mixture was placed in an alumina container and calcined at 800 to 1100 ° C. for 2 to 6 hours. The phosphor obtained after firing was washed 2 to 3 times with warm water, and filtered to prepare a finished product of K ₅ Eu _2.5 (WO ₄ ) _6.25 red phosphor.

The emission spectrum according to the wavelength of 300 to 750 nm of the phosphor of (K ₄ Na) Eu _2.5 (WO ₄ ) _6.25 synthesized in the comparative example of the present invention is shown in FIG. 2 and the (K ₄ Na) Eu synthesized in Examples. The emission spectrum of the phosphor having a composition of _2.5 (WO ₄ ) _6.25 is shown in FIG. 3. 2 and 3 it can be confirmed that the red light emitting phosphor by observing that there is a very strong light emitting band at a wavelength near 612nm. Therefore, the phosphor according to the present invention can be said to be a phosphor suitable for realizing the active light emitting liquid crystal display of FIG. 1 even in the emission spectrum.

Table 1 shows the color coordinate values of the phosphors prepared in Examples and Comparative Examples.

1: wavelength of highest peak

As described above, the phosphor of the present invention emits red color and has excellent brightness as compared with the conventional phosphor of Comparative Example, thereby obtaining a desired display color.

This red phosphor is a tungsten-based high-brightness red phosphor that is excited in the near-ultraviolet region of 380 to 420 nm to realize the desired device structure, and is replaced by about 20% by replacing an appropriate amount of sodium ions in the place of potassium. There is an effect of improving the brightness of, which is because the properties were changed by substituting a homologous substance having a similar ionic radius, and it is thought that the properties were changed in the same phase without changing the phase.

Claims (4)

Red phosphor for an active light emitting liquid crystal display represented by the following formula (1). [Formula 1] (K _5-x Na _x ) Eu _2.5 (WO ₄ ) _6.25 Wherein x is a value ranging from 0.5 to 1.5. The red phosphor of claim 1, wherein the phosphor is prepared through a solid chemical reaction. K ₂ CO ₃ , Eu ₂ O ₃ , WO ₃ and Na ₂ CO ₃ phosphor raw materials were mixed, and the mixed phosphor raw materials were calcined at a temperature of 800 to 1100 ° C. for 2 to 6 hours, and sodium ions were substituted in place of potassium. The method of manufacturing a red phosphor for an active light-emitting liquid crystal display comprising the step of adjusting the flux to produce a phosphor and cleaning the phosphor. The active light emitting device according to claim 4, wherein K ₂ CO ₃ is 10-25 wt%, Eu ₂ O ₃ is 10-25 wt%, WO ₃ is 60-70 wt% and Na ₂ CO ₃ is 1-5 wt%. The manufacturing method of the red fluorescent substance for type | mold liquid crystal display.