KR950008655B1 - Fat-red emitting phosphor for cathode ray tube - Google Patents

Abstract

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Description

Far Infrared Emission Phosphor for Cathode Ray Tubes

1 is a schematic diagram of a liquid crystal light valve projector system using a cathode ray tube.

2 is a plot of the spectral response of an amorphous silicon (α-Si) photoconductor, expressed in coordinates of normalized emissivity and wavelength in nanometers.

3-10 show Y _3-y Gd _y Al _5-x Ga _x O ₁₂ : Cr [(a) y = 0 and x = 0 as a function of the composition, expressed as coordinates of normalized emissivity and wavelength in nanometers. (FIG. 3), 1 (FIG. 4, 2 (FIG.), 3 (FIG. 6), 4 (FIG. 7) and 5 (FIG. 8), (b) y = 3 and x = 5 (Figure 9) and (c) y = 3 and x = 0 (Figure 10).

Figures 11 to 15 are plots of Y _3-y Gd _y Al _5-x Ga _x O ₁₂ : Cr [y = 0 and x = 0 as a function of the processing conditions, expressed as coordinates of normalized emissivity and wavelength in nanometers. 11 degrees to 13 degrees) and y = 3 and x = 5 (FIGS. 14 and 15).

16 and 17 are plots of particle size distributions for representative methods of making phosphorous of the present invention, expressed in percentiles and coordinates of particle size in micrometers.

* Explanation of symbols for main parts of the drawings

10 LCLV Projector 12 Cathode Ray Tube (CRT)

14 liquid crystal light valve 16 xenon discharge lamp

18: UV filter 20: pre-polarized filter

22: polarized mirror 24: prism V-shaped window

26: projection lens

The present invention relates to phosphorus used in cathode ray tubes (CRTs) for liquid crystal displays, and more particularly to a new group of phosphorus having a yttrium aluminum garnet crystal structure.

The phosphorus used to address amorphous silicon in the fuse liquid crystal light valve (LCLV) must meet the following conditions:

Spectral output matched as closely as possible to the amorphous silicon (α-Si) reaction; Maximum radiant energy output in the target spectral range; Decay time less than about 10 milliseconds measured from 100% to 10%; Average particle size suitable for high resolution of less than about 6 μm; And high resistance to thermal or lifetime induced degradation.

The spectral reactivity of α-silicon used in LCLV is maximum at about 740 nm. As a result, the light incident used to activate the α-silicon photosensitive layer for optimum sensitivity should be matched as closely as possible to the reaction curve.

Many phosphors have been studied to find phosphors with the correct properties regarding spectral emission, decay time, efficiency and small particle size. Examples of such phosphorus include aluminum oxide: Cr, cadmium sulfide: Ag, zinc cadmium sulfide: Ag, zinc phosphate: Mn, yttrium oxysulfide: Eu, yttrium aluminum oxide: Eu, and the like.

One far-infrared ("far-infrared" means about 600-800 nm) used in luminescent lamps has been found to be very closely matched to the α-silicon reaction, which is iron-activated lithium aluminum oxide (LiAlO ₂ : Fe). In commercially available materials, the iron content is about 0.5%, however, such phosphorus, when used in CRTs, has a decay time of about 30 milliseconds longer than the acceptable decay time.

Yttrium aluminum garnet (YAG) phosphorus is known in the art. They have various active factors such as terbium, cerium, europium and the like. In YAG: Eu the energy is distributed between 591, 608, 630 and 710 nm lines but weaker at about 649 and 692 nm. Because of this spectral output, this phosphorus does not effectively stimulate the light valve.

None of the commercially available phosphorus was found to satisfy the α-silicon LCLV requirement.

According to the present invention, a new group of phosphorus having an yttrium aluminum garnet crystal structure is provided. The general formula of phosphorus of the present invention is Y _3-y Gd _y Al _5-x Ga _x O ₁₂ : A, where x is 0 to 5, y is 0 to 3, A is chromium, iron, vanadium, neodymium, Dysprosium, cobalt, nickel, titanium or mixtures thereof.

Phosphorus of the said general formula shows the change of their spectral output, emissivity, and a permanent characteristic in the conditions required by the need of the (alpha)-silicon photosensitive layer in a liquid crystal light valve.

Liquid crystal light valves (LCLV) are described in SID International Symposium, Digest of Technical Papers, "Video-Rate Liquid Crystal Light-Valve Using an Amorphous Silicon Photoconductor", R.D. Sterling et al., Volume XXI, pp. 327-328 (1990). Figure 1 obtained from the above reference shows a basic LCLV projector 10 consisting of a cathode ray tube (CRT) 12 which provides an input image coupled to a liquid crystal light valve 14 via a molten fiber optical faceplate (not shown). Schematic diagram. The xenon discharge lamp 16 provides output light that is filtered by the UV filter 18 and is constantly polarized by the preliminary polarization filter 20 before reaching the LCLV 14. The image passes through a polarizing mirror 22, a prism V-shaped window 24, and then passes through a projection lens 26 to be projected onto a screen (not shown).

The projector is an example of a device that uses a combination of LCLV and CRT. Other combinations of LCLVs and CRTs are also known. While such combinations are known to those skilled in the art, there is no example of using the phosphorus of the invention as phosphorus in CRTs.

LCLV utilizes hydrogenated amorphous silicon photoconductors (α-Si: H) as known in the art and as indicated in the references above. The spectral response of the α-Si photoconductor is shown in FIG. This curve indicates that phosphorus should be matched as closely as possible for efficient energy coupling.

The phosphorus composition of the present invention is represented by the general formula Y _3-y Gd _y Al _5-x Ga _x O ₁₂ : A, wherein x is 0 to 5, y is 0 to 3, A is chromium, iron, Vanadium, neodymium, dysprosium, cobalt, nickel, titanium or mixtures thereof.

Preference is given to using at least one of chromium, neodymium and iron. Most preferably, chromium is used, particularly preferably in the range of about 0.33 to 2 at%. Outside this range, the light output is undesirably attenuated.

Preferred compositions depend on the specific properties. For example, the highest luminance composition (highest relative power) consists of chromium-activated yttrium aluminum garnet, Y ₃ Al ₅ O ₁₂ : Cr (YAG1: Cr), and the shortest decay time is chromium activated gadolinium gallium garnet , Gd ₃ Ga ₅ O ₁₂ : Cr (GGG: Cr). The most preferred composition for achieving the highest brightness and shortest decay time is Y ₃ Al ₂ Ga ₃ O ₁₂ : Cr. This result is shown below.

Composition Relative Output Decay Time

YAG: Cr 100 5-6 milliseconds

GGG: Cr 45 1 millisecond

Y ₃ Al ₂ Ga ₃ O ₁₂ : Cr 76 2 milliseconds

The manufacturing method of the garnet group of phosphorus of this invention is based on the conventional method used in the industrial field. The starting material consists of an oxide of each element. Mix in stoichiometric ratio and ball mill grind to produce a well mixed homogeneous mixture. After the reaction is pulverized and dried, after the first processing, it is heated in the first processing step at about 1500 ° to 1600 ° C. for about 2 to 8 hours under an oxidizing atmosphere such as air.

Alternatively, the oxide is heated in the second processing step at about 1200 ° C. for 1 to 4 hours under an oxidizing atmosphere such as air and at about 1500 ° to 1600 ° C. for about 2 to 8 hours.

Alternatively, heating was performed at about 1200 ° C. for 1 to 4 hours, at about 1550 ° C. for 1 to 4 hours, and at about 1590 ° C. for about 1 to 4 hours in the third processing step.

Such methods are known in the art and do not form part of the invention.

Since the light emission properties of phosphorus are improved by small particle size, it is necessary to control the production of particles having an average particle size of less than about 6 μm as heating.

Sol-gel processing can also be used for the production of phosphorus. In this case the starting material component consists of nitrates or chlorides of Y, Al and Cr. These components are dissolved in deionized water in stoichiometric proportions. The next step is to add a solution of ammonium hydroxide in excess of the stoichiometric requirement to precipitate out the hydroxides of all metals. After the precipitate has been properly decomposed and stabilized, it is filtered, washed thoroughly and dried. The heating process can be used for this starting material to obtain the desired phosphorus. Such procedures are known and do not form part of the invention.

Alternatively, the starting material may consist of stoichiometric amounts of yttrium, gadolinium, aluminum and gallium nitrate. The starting material is dissolved in aqueous solution and the hydroxide is precipitated with ammonium hydroxide. After washing, a proportion of the activated oxide can be mixed into the material by a ball mill. After ball mill grinding as described above, the mixture was dried and heated under the same conditions as above. Such methods are known and do not form part of the present invention.

Another known alternative is to start with yttrium, aluminum, gadolinium and gallium and as activating factors and precipitate the hydroxide with ammonium hydroxide as treated above.

Conventional methods for producing garnet forming phosphorus according to the techniques of the present invention have been described. These two step methods are not considered novel and do not form part of the present invention.

Assuming that it is desirable to produce 10 g of phosphorus using the oxide component as a starting material, the required amount of oxide (see formula below) is placed in a 2-ounce ball mill with about 30 g of sintered alumina balls having a diameter of about 9 mm. 15 ml of deionized water was added and the mill was sealed and placed on a roller. As is known, in order to produce higher amounts of phosphorus it is necessary to increase it in an appropriate ratio.

After rolling for 2 hours, the mills are removed from the rolls while the oxides are intimately mixed and their size is somewhat reduced, and the ingredients are placed in a clean receptacle. Rinse water from the mill was mainly added to the dump charge. After drying in an oven at about 110 ° C., the powder was passed through a 70 stainless steel mesh. This was placed in a sintered alumina boat and placed in a furnace at 400 ° C. The temperature was raised to 1200 ° C. and maintained for 2 hours. Eventually the temperature was lowered to 400 ° C. at which point the boat was removed from the furnace. The atmosphere in the furnace during heating is preferably air. The material was sifted again and the particle size was measured. After the material was placed back in the furnace, the temperature was raised to 1600 ° C. and maintained for 2 hours. The furnace was cooled to 400 ° C. and the boat was removed. The final material was ground in mortar with a pestle, sieved and particle size was measured for immediate use.

Many compositions were prepared using the above method. The effects of some compositions on various properties are shown in Table 1 below. Relative power was calculated by measuring emissivity with spectroradiometer in the wavelength range of 600-800 nm. This data is converted to relative power by dividing each value by the highest emissivity value. Decay time was measured in milliseconds. The heating temperature in each case was 1200 degreeC and then 1600 degreeC. The spectral distribution as a function of composition is shown in the figures shown.

TABLE 1

The effect of heating temperature on the properties is shown in Table 2 below. In all cases, the heating time at the indicated temperature is 2 hours. The effect of heating temperature on the spectral distribution is shown in the figures shown.

TABLE 2

The effect of the various additional compositions on the relative power is shown in Table 3 below. Spectral distributions for the two compositions are shown in FIGS. 16 and 17.

TABLE 3

Particle size distributions of phosphorus having the preferred composition prepared as described above are shown in FIGS. 18 and 19. Figure 18 is for GGG with a Cr activating factor of 1.0%. The average particle size is 6.31 μm, with 10% of the particles being less than 1.32 μm and greater than 21.15 μm of the 10% of the particles. 19 is for YAG with a Cr activating factor of 0.5%. The average particle size is 6.54 μm, with 10% of the particles being less than 1.76 μm and 10% of the particles exceeding 14.12 μm.

Thus, the present invention is essentially Y _3-y Gd _y Al _5-x Ga _x O ₁₂ : A (where x is 0 to 5, y is 0 to 3, A is chromium, iron, vanadium, neodymium, Far infrared emitting phosphorus) selected from the group consisting of dysprosium, cobalt, nickel, titanium, or mixtures thereof. Various changes and modifications to the apparent nature may be readily made by those skilled in the art and all such changes and modifications should be made within the scope of the present invention as defined by the appended claims.

Claims (12)

In a liquid crystal light valve comprising a photosensitive layer consisting essentially of α-silicon and far-infrared emitting phosphorus functionally combined therewith, the phosphorus is essentially Y _3-y Gd _y Al _5-x Ga _x O ₁₂ : A Wherein x is 0 to 5, y is 0 to 3, and A is selected from the group consisting of chromium, iron, vanadium, neodymium, dysprosium, cobalt, nickel, titanium, or mixtures thereof. Combination. The combination of claim 1, wherein x is 0, y is 0 and A is chromium. The combination of claim 1, wherein x is 5, y is 3 and A is chromium. The combination of claim 1, wherein x is 2, y is 0 and A is chromium. In a method of coupling energy from light emitted from red phosphorus to a hydrogenated amorphous silicon photoconductor, essentially Y _3-y Gd _y Al _5-x Ga _x O ₁₂ : A, where x is 0 Has a value in the range of 5 to 5, y has a value in the range of 0 to 3, A is selected from the group consisting of chromium and neodymium, chromium has a value in the range of about 0.33 to 2 at%, and neodymium is about 1 at Having a value of%) as a red phosphorus. 6. The method of claim 5 wherein x is 0, y is 0 and A is chromium. 6. The method of claim 5 wherein x is 5, y is 3 and A is chromium. 6. The method of claim 5 wherein x is 2, y is 0 and A is chromium. In a method for producing a cathode ray tube in which a hydrogenated amorphous silicon photoconductor contains a screen having red phosphorus thereon for kerring energy from light emitted from red phosphorus, essentially Y _3-y Gd _y Al _5-x Ga _x O ₁₂ : A, where x has a value in the range of 0 to 5, y has a value in the range of 0 to 3, A is selected from the group consisting of chromium and neodymium, and chromium Is in the range of about 0.33 to 2 at%, and neodymium has a value of about 1 at%). 10. The method of claim 9 wherein x is 0, y is 0 and A is chromium. 10. The method of claim 9, wherein x is 5, y is 3 and A is chromium. 6. The method of claim 5 wherein x is 2, y is 0 and A is chromium.