CN1267526C - Preparation process of vacuum ultraviolet borate fluorescent material - Google Patents

Abstract

The invention discloses a hydrothermal preparation method of a vacuum ultraviolet borate fluorescent material (Y _1-xy Eu _x Gd _y )BO ₃ (0.05≤x≤0.3, 0.01≤y≤0.6). The preparation method of the present invention is a hydrothermal method, using yttrium nitrate, gadolinium nitrate, europium nitrate and organic reagents such as tributyl borate to react under the condition of acid or alkali as a hydrolysis catalyst. Compared with the prior art, the preparation method of the invention has low reaction temperature, simple operation, and controllable particle size and shape of the product. The spherical fluorescent powder of the present invention has good coating properties, can obtain high bulk density, and can better absorb vacuum ultraviolet light, can improve the luminous efficiency under vacuum ultraviolet excitation, is conducive to improving the brightness of the fluorescent screen, and can better meet Plasma displays require high brightness.

Description

A kind of preparation method of vacuum ultraviolet borate fluorescent material

technical field

The invention relates to a method for preparing a vacuum ultraviolet borate fluorescent material, more precisely, the invention relates to a method for preparing a (Y, Gd)BO ₃ :Eu fluorescent material.

Background technique

(Y, Gd)BO ₃ doped with Eu ³⁺ is a kind of red phosphor with excellent performance. Applied in plasma display (PDP). In the prior art, (Y, Gd)BO ₃ :Eu is generally synthesized by a solid phase method, and the reaction temperature is 1100°C-1400°C. Since B ₂ O ₃ will volatilize when the temperature is higher than 800°C, excess H ₃ BO ₃ or B ₂ O ₃ should be added to compensate for the loss of B during high temperature calcination. In addition, when (Y, Gd)BO ₃ :Eu is synthesized by a solid-state method, sintering of the fluorescent material will occur due to high-temperature calcination. In order to obtain phosphor powder with suitable particle size and uniform distribution, the prepared phosphor powder must be ground, but this will reduce the brightness of the phosphor powder. In recent years, many new synthetic methods have appeared, such as sol-gel method, microwave method, etc. Rao Ravilisetty first synthesized (Y, Gd) BO ₃ : Eu phosphors by sol-gel method. However, the preparation of (Y, Gd)BO ₃ :Eu by sol-gel method requires heat treatment above 900°C to obtain a single phase, which is essentially a solid-phase reaction and also has all the shortcomings of the solid-phase synthesis method. Synthesize (Y, Gd)BO ₃ :Eu phosphors by microwave method. Since the initial raw materials such as Y ₂ O ₃ and Eu ₂ O ₃ are oxides that rarely absorb microwaves, it is necessary to cover a layer of microwave-absorbing medium on the outside of the raw materials. In order to effectively use microwaves to react. Therefore, the purity and luminous efficiency of phosphor powder prepared by microwave method are relatively low. Moreover, the above methods have limited control over the morphology.

The hydrothermal method is an emerging method for studying the synthesis of inorganic materials in recent years. This method is to dissolve the soluble oxides or salts of metal and non-metal elements in the reaction medium (water or other liquids) and place them in a sealed pressure vessel. The product can be obtained by heating the reaction at a certain temperature. This method has the advantages of relatively mild reaction conditions, short reaction time, simple process, low synthesis temperature, controllable product morphology and particle size, and the powder prepared by the hydrothermal method does not require grinding, has no agglomeration, and has good dispersibility. Wang Yuhua, one of the inventors of the present invention, in "GdBO ₃ :Eu Phosphor Particles with Uniform Size, PlateMorphology, and Non-Aggregation" (Yuhua Wang, et al., Chem.Lett., 2001 (3): 206-207) The paper discloses the method of synthesizing flake GdBO ₃ :Eu phosphor with uniform particle size by hydrothermal method for the first time. The method is to dissolve gadolinium oxide, europium oxide and boron trioxide in nitric acid and evaporate to dryness, then place the residue after evaporation in a small stainless steel reaction kettle with polytetrafluoroethylene lining, add distilled water at 300 After the reaction at ℃, the flaky GdBO ₃ :Eu phosphor is obtained. However, the luminous efficiency of flake particles under 147nm excitation is very low, only 50% of the sample obtained by solid phase reaction.

The study found that spherical phosphors have high luminous efficiency and can better absorb vacuum ultraviolet light. Moreover, spherical phosphors have good coating properties and can obtain high packing density. For PDP phosphors, the optimal particle size range is 3- Between 5 microns, uniform distribution and no agglomeration are required ([1] R.P.Rao and D.J.Devine, Present Status of PDP Phosphors, p.152, International Conference on Luminescence and Optical Spectroscopy of Condensed Matter, Osaka, Japan (1999).[2 ] Y.C.Kang, I.W.Lenggoro, K.Okuyama and S.B.Park, J.Electrochem.Soc.1999.146 (3: 1227.). However, spherical particles cannot be obtained in the prior art.

Contents of the invention

The invention provides a hydrothermal preparation method capable of controlling the particle size and morphology of vacuum ultraviolet borate fluorescent material (Y _1-xy Eu _x Gd _y )BO ₃ (0.05≤x≤0.3, 0.01≤y≤0.6). In particular, it provides a method for preparing a spherical (Y, Gd)BO ₃ :Eu fluorescent material with uniform particle size distribution.

The method of the present invention is to dissolve yttrium nitrate, gadolinium nitrate, europium nitrate and boric acid ester with water and ethanol solution, then add acid or alkali hydrolysis catalyst to make the pH value of the solution range from 5 to 6, and transfer the mixed solution Put it in a small stainless steel reaction kettle with polytetrafluoroethylene lining, keep it warm at 240-280 ° C for 6 hours, wash with absolute ethanol and distilled water after the reaction is completed, and then filter and dry to obtain spherical (Y, Gd) BO ₃ : Eu phosphor. By controlling the ratio of water to ethanol in the reaction system, the types of hydrolysis catalysts, the types of different hydrolysis catalysts added, and the acidity of the system, it is possible to control the morphology and particle size of the product.

The sources of yttrium, gadolinium and europium used in the present invention may also be oxides of yttrium, gadolinium and europium, which are then treated with nitric acid to obtain salts of yttrium, gadolinium and europium.

The boric acid ester used in the present invention is trimethyl borate or tributyl borate.

In the present invention, when the volume ratio of water to ethanol is 1:1 to 1:3.5, a single-phase product can be obtained, impurities appear when it is less than 1:1, and an amorphous state is formed when it is greater than 1:3.5, as shown in Figure 2. The optimal volume ratio of water and ethanol in the present invention is 1:2.

The hydrolysis catalyst added in the reaction system of the present invention can be acid or alkali. Nitric acid or boric acid is preferably used when an acid is used as the hydrolysis catalyst. When using alkali, it is best to use ammonia water, because the use of other types of acid or alkali will increase the impurity content in the product. Relevant studies have shown that when nitric acid is used as the hydrolysis catalyst, the obtained phosphor is spherical and the particle surface is relatively rough. If boric acid is used as the hydrolysis catalyst, spherical phosphor with smooth surface can be obtained, but the particle size distribution may be uneven. If ammonia is used as a hydrolysis catalyst in the present invention, not only can a spherical fluorescent powder with a smooth surface be obtained, but also the particle size distribution of the obtained powder is more uniform.

The optimum reaction temperature range of the present invention is 240～280 ℃. For example, when the reaction temperature is low (below 180°C), the crystallization effect is poor, and when the reaction temperature is too high, although crystallization can be promoted, preferred orientation is prone to occur. Therefore, the optimum reaction temperature range of the present invention is 240-280°C.

The pH value of the solution of the present invention has a certain influence on the growth of the crystal. The pH value not only affects the solubility of the solute, but also may change the structure of the growth unit, and finally affect the structure, shape and size of the crystal. In the present invention, when 1≤PH<5, it is easy to produce non-spherical particles, and when the pH is 5≤PH≤6, spherical particles with different particle sizes can be obtained. Therefore the pH in the reaction of the present invention should be preferably 5～6.

Compared with the prior art, the present invention has the following advantages:

1. The reaction temperature is low, the preparation cost is low, and the obtained product has high purity, good dispersibility, no agglomeration phenomenon, and no need for later grinding treatment;

2. The shape of the obtained product is controllable, and it is easy to obtain a spherical product with a suitable particle size (about 3-5 microns) and uniform distribution. At the same time, a spherical product with an uneven particle size can also be formed to meet the needs of special applications;

3. (Y, Gd)BO ₃ :Eu fluorescent powder prepared by the method of the present invention, the quenching concentration of its activator (Eu ³⁺ ) is 20%, while the sample obtained by the solid phase reaction is only 10%, which shows that The product obtained in the present invention has more luminescent centers than solid-phase reaction, so the luminescent performance is better than that of the sample obtained by solid-phase reaction;

4. When (Y, Gd)BO ₃ :Eu is prepared by the method of the present invention, the reactants are mixed at the atomic or molecular level, so the activator (Eu ³⁺ ) can be more uniformly distributed in the lattice lattice ;

5. The raw materials for preparing (Y, Gd)BO ₃ :Eu by the method of the present invention are accurately weighed according to the stoichiometric ratio, and B ₂ O ₃ or H ₃ BO ₃ must be in excess of 5% to 15% in the solid phase reaction, so The defects of the product will increase, which will reduce the luminous intensity of the phosphor;

6. The intensity of the strongest emission peak of the spherical phosphor obtained by the present invention is more than 2 times higher than that of the sample prepared by solid-phase reaction under excitation at 254nm, and the intensity of the strongest emission peak under excitation at 147nm is higher than that of the sample prepared by solid-phase reaction more than 10% higher.

Description of drawings

Accompanying drawing 1 is the X-ray diffractogram of the product obtained in the present invention and related comparative experiments.

Accompanying drawing 2 is the figure of influence on product when water and ethanol are in different proportions in the present invention.

Accompanying drawing 3 is to use yttrium nitrate etc. and tributyl borate as raw material, use boric acid as hydrolysis catalyst, the scanning electron micrograph of the product obtained.

Accompanying drawing 4 is to use yttrium nitrate etc. and tributyl borate as raw material, use nitric acid as hydrolysis catalyst, the scanning electron micrograph of the product gained.

Accompanying drawing 5 is to use yttrium nitrate etc. and tributyl borate as raw material, use ammonia water as hydrolysis catalyst, the scanning electron micrograph of the product obtained.

Accompanying drawing 6 is the scanning electron micrograph of the product obtained by the disclosed hydrothermal method.

Accompanying drawing 7 is the scanning electron micrograph of the product obtained by solid phase reaction.

Accompanying drawing 8 is the excitation spectrum diagram (E _m =591nm) of the product obtained in the present invention.

Accompanying drawing 9 is the emission spectrogram (E _x =254nm) of the product obtained in the present invention.

Detailed ways

Several examples of the invention are provided below.

The initial raw material of the present invention is mainly composed of raw materials providing Y element, Eu element, Gd element and B element. The following two kinds of initial raw materials for providing Y, Eu, and Gd elements are selected: oxides and nitrates. When oxides are used, they should be reacted with dilute nitric acid to form nitrates in advance. The raw material that provides the B element is tributyl borate. In each embodiment, after Y, Eu, the raw material of Gd element and B element are mixed by stoichiometric ratio, join in the water and ethanol solution (volume ratio is 1: 2) as reaction solvent, then add the hydrolysis catalyst adjustment solution The pH value is 5 to 6. Transfer the mixed solution to a small stainless steel reaction kettle lined with polytetrafluoroethylene, and keep it warm at 240 to 280°C for 6 hours. Washed with distilled water, the product was filtered and dried at 100°C to obtain the target product.

In order to compare with the prior art, (Y, Gd)BO ₃ :Eu was prepared by the solid-state reaction method and the hydrothermal method disclosed in the prior art, respectively. When prepared by solid-phase _method , the initial raw _materials are _{Y2O3 , Gd2O3} , _H3BO3 , _{Eu2O3 ,} which are accurately weighed according to _the stoichiometric ratio (5%-15% excess of _H3BO3 ), mixed and ground evenly, heated at 500°C for 2.5 hours, taken out and ground again, and sintered at 1100°C for 2 hours to obtain the desired sample. When the hydrothermal method disclosed in the prior art is used to prepare (Y, Gd)BO ₃ :Eu, the raw materials used are yttrium nitrate, europium nitrate, gadolinium nitrate and boric acid, the reaction solvent is distilled water, and no other substances are used as hydrolysis catalysts.

The obtained product in the embodiment of the present invention has analyzed the phase of matter with the Rigaku D/MAX-2400 type X-ray diffractometer in Japan, observed the morphology of the sample with the JSM-5600LV low vacuum scanning electron microscope, and used the Hitachi F-4500 type fluorescence spectrometer UV excitation and emission spectra were measured at room temperature. The luminescence characteristics under vacuum ultraviolet excitation were measured by ARC Model VM-502 vacuum monochromator and corrected by sodium salicylate (sodium benzoate).

Example 1

Initial raw materials: yttrium nitrate, gadolinium nitrate, europium nitrate, tributyl borate; solvent: distilled water: ethanol = 1:2 (volume ratio); catalyst: boric acid.

Preparation process: Weigh yttrium nitrate, gadolinium nitrate, europium nitrate, and tributyl borate according to the stoichiometric ratio, and then add them to the mixed solution of water and ethanol (water: ethanol volume ratio is 1:2), the total volume of the solution is 18 ml. Under ultrasonic dispersion, dilute nitric acid is added dropwise to make the pH of the solution 5-6. Move the solution into a small stainless steel reaction kettle with polytetrafluoroethylene lining, and keep it warm at 260°C for 6 hours. dry. That is, a spherical (Y _1-xy Eu _x Gd _y )BO ₃ (0.05≤x≤0.3, 0.01≤y≤0.6) phosphor is obtained.

In this embodiment, boric acid is both a hydrolysis catalyst and an initial raw material for the reaction.

Measurement results: X-ray diffraction analysis shows that the obtained product is a single phase, see curve a in accompanying drawing 1. Scanning electron microscope analysis shows that the obtained powder is spherical and has a smooth surface, as shown in Figure 3. It can be seen from the figure that the particle size distribution is not uniform.

Example 2

Initial raw materials: yttrium nitrate, europium nitrate, gadolinium nitrate, tributyl borate; solvent: distilled water: ethanol = 1:2; catalyst: nitric acid.

Preparation process: Weigh yttrium nitrate, europium nitrate, gadolinium nitrate and tributyl borate according to the stoichiometric ratio, then add them to the mixed solution of water and ethanol (water: ethanol volume ratio is 1:2), the total volume of the solution is 18 ml. Under ultrasonic dispersion, dilute nitric acid was added dropwise to make the pH of the solution 5~6. Transfer the mixed solution into a small stainless steel reaction kettle lined with polytetrafluoroethylene, and keep it warm at 260°C for 6 hours. dry. That is, a spherical (Y _1-xy Eu _x Gd _y )BO ₃ (0.05≤x≤0.3, 0.01≤y≤0.6) phosphor is obtained.

Nitric acid must adopt dilute nitric acid in the present embodiment.

Measurement results: X-ray diffraction analysis shows that the obtained powder is a single phase, as shown in curve b in accompanying drawing 1. Scanning electron microscope analysis shows that the obtained powder is spherical, see accompanying drawing 4. It can be seen from the drawings that the surface of the particles is relatively rough, and there are traces of corrosion on the surface of the particles.

Example 3

Initial raw materials: yttrium nitrate, europium nitrate, gadolinium nitrate, tributyl borate; solvent: distilled water: ethanol = 1: 2 (volume ratio); catalyst: ammonia water.

Preparation process: Weigh yttrium nitrate, europium nitrate, gadolinium nitrate and tributyl borate according to the stoichiometric ratio, and then add them to the mixed solution of water and ethanol (water: ethanol volume ratio is 1:2), the total volume of the solution for 18 ml. Under ultrasonic dispersion, add ammonia water dropwise to the mixed solution to form a sol. Move the sol into a small stainless steel reaction kettle lined with polytetrafluoroethylene, and keep it warm at 260°C for 6 hours. After drying, spherical (Y _1-xy Eu _x Gd _y )BO ₃ (0.05≤x≤0.3, 0.01≤y≤0.6) fluorescent powder is obtained.

In this embodiment, the thinner the sol concentration, the easier it is to obtain the spherical phosphor.

Measurement results: X-ray diffraction analysis shows that the obtained powder is a single phase, as shown in curve c in accompanying drawing 1. Scanning electron microscope analysis shows that the obtained powder is uniform spherical, see accompanying drawing 3. It can be seen from the accompanying drawings that the product obtained in this example has a smooth surface and uniform particle size, and its size is about 2-3.5 microns. Under 254nm excitation, when x=0.2, the intensity of the strongest emission peak is twice that of the sample obtained by solid phase reaction. Under 147nm excitation, the luminous intensity is 10% higher than that of (Y, Gd)BO ₃ :Eu (KX-504A) commercial powder produced by Nippon Chemical Co., Ltd.

The experiment compared with the present invention is:

Comparative example 1

Starting materials: yttrium oxide, etc., boric acid; solvent: distilled water.

Preparation process: Weigh yttrium oxide, europium oxide, gadolinium oxide and boron oxide according to the stoichiometric ratio, add dilute nitric acid to dissolve and evaporate to dryness, add distilled water to the residue after evaporation to make the total volume of the solution 18 ml. The mixed solution was transferred to a small stainless steel reaction vessel lined with Teflon. Keep warm at 300°C for 3 hours. After the reaction, cool to room temperature with the furnace, wash with distilled water, filter and dry at 100°C. That is, flake (Y, Gd)BO ₃ :Eu powder was obtained.

Measurement results: X-ray diffraction analysis shows that the obtained powder is a single phase, which is consistent with the literature reports. Scanning electron microscope analysis shows that the obtained particles are in uniform sheet shape, see accompanying drawing 6.

Comparative example 2

(Y, Gd)BO ₃ :Eu was prepared by solid state reaction method, the initial raw materials were yttrium oxide, gadolinium oxide, boric acid, europium oxide, and they were accurately weighed according to the stoichiometric ratio (5%-15% excess of H ₃ BO ₃ ), mixed and ground evenly, heated at 500°C for 2.5 hours, taken out and ground again, and sintered at 1100°C for 2 hours to obtain the sample.

Measurement results: X-ray diffraction analysis shows that the obtained powder is a single phase, which is consistent with the literature reports. Scanning electron microscope analysis shows that the obtained particles are irregular, as shown in Figure 7. The excitation spectrum is shown in curve b of Fig. 8 . The emission spectrum is shown in curve b of Fig. 9 .

Claims (8)

1, a kind of (Y _1-x-yEu _xGd _y) BO ₃(0.05≤x≤0.3,0.01≤y≤0.6) Preparation of Fluorescent Material method, it is characterized in that Yttrium trinitrate, Gadolinium trinitrate, europium nitrate and boric acid ester are dissolved in water and the ethanolic soln, in system, add acid or ammoniacal liquor hydrolyst, system is heated to 200～300 ℃ reacts, the pH value of system with dehydrated alcohol and distilled water wash, carries out filtration drying again and handles after reaction is finished smaller or equal to 6 during reaction.

2, preparation method according to claim 1 is characterized in that described boric acid ester is trimethyl borate or tributyl borate.

3, preparation method according to claim 2 is characterized in that the system temperature of reaction is 240～280 ℃.

4, preparation method according to claim 3, the pH value of the system when it is characterized in that reacting is 5～6.

5, preparation method according to claim 4 is characterized in that water and ethanol volume ratio are 1: 1～1: 3.5 in the used solvent.

6, preparation method according to claim 5 is characterized in that water and ethanol volume ratio are 1: 2 in the used solvent.

7, according to described arbitrary preparation method among the claim 1 to 6, the hydrolyst that it is characterized in that in the system being added is nitric acid or boric acid.

8, according to described arbitrary preparation method among the claim 1 to 6, the hydrolyst that it is characterized in that in the system being added is an ammoniacal liquor.

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