CN104927856A - Method for preparing red phosphors of tungstate based on sol-gel combustion method - Google Patents

Abstract

The method for preparing tungstate red fluorescent powder based on the sol-gel combustion method disclosed by the present invention, the specific method is: 1) first weigh sodium nitrate, magnesium nitrate, gadolinium nitrate, europium nitrate and ammonium tungstate, and then weigh The five kinds of salts taken are dissolved in deionized water respectively to form five kinds of salt solutions, and finally the five kinds of salt solutions are mixed together to form a mixed solution; the liquids are mixed together to form a mixed solution; 2) Weigh citric acid and add In the mixed solution, the sol is formed by stirring; the sol is placed in a constant temperature water bath and heated to form a wet gel; the xerogel is obtained by drying; 3) the xerogel obtained in 2) is put into a muffle furnace for calcination, Prepare tungstate NaGd _1-x Eu _x MgWO ₆ red phosphor. The method for preparing tungstate red fluorescent powder based on a sol-gel combustion method in the present invention can prepare tungstate red fluorescent powder with good stability, high color purity and high luminous efficiency, which is very suitable for white LEDs.

Description

Method for preparing tungstate red phosphor based on sol-gel combustion method

technical field

The invention belongs to the technical field of fluorescent material preparation methods, and in particular relates to a method for preparing tungstate red fluorescent powder based on a sol-gel combustion method.

Background technique

In 1993, the advent of blue-emitting GaN light-emitting diodes (LEDs) brought a significant revolution in the field of lighting, followed by the use of GaN-LED chips in combination with YAG:Ce ³⁺ phosphors to emit white light in 1996, Developed the first white LED solid light source. Since then, white LEDs have attracted great attention for their advantages of small size, low calorific value, low power consumption, long life, fast response, environmental protection and planar packaging. The fourth generation lighting source of fluorescent lamps and HID (High Intensity Discharge) lamps has a very broad application prospect.

At present, there are three main ways to realize white light LED: one is to use the light emitted by the LED chip to excite the phosphor, and the light emitted by the chip and the phosphor is mixed to form white light, that is, the phosphor coating light conversion method; the other is to use red light, green light, The blue light LED is used to prepare LED white light components, that is, the multi-color LED combination method; the third is to use multiple active layers to make the LED directly emit white light, that is, the multi-quantum well method. Among them, the phototransition method of phosphor coating is one of the main ways to manufacture white light LEDs. Most of the products that have been commercialized are manufactured by this method; in this method, phosphors are used as light conversion substances The role it plays is crucial, and it directly affects the main indicators such as luminous efficiency, service life, color rendering index and color temperature of white LED products. Therefore, how to prepare red, green and blue phosphors with high luminous efficiency and good thermal stability is the key to improving the luminous quality of white LEDs.

In terms of research on phosphor powder for white LEDs, the preparation of green powder and yellow powder and their luminous properties have reached a mature stage. However, the luminous efficiency and stability of red powder cannot be compared with other powders. For a long time, red phosphors for white LEDs have been limited to alkaline earth metal sulfide series. The physical and chemical properties of this type of phosphors are extremely unstable, and their thermal stability is poor, and the light decay is large, which seriously damages the quality of white LED products. Therefore, it is very important to develop red fluorescent materials with high stability, high color purity and effective excitation by near-ultraviolet and blue light.

In recent years, many new red phosphors for LED have been developed successively, such as: alkaline earth metal polyaluminate, silicate, titanate, germanate, arsenate, molybdate, tungstate and other red phosphors. Phosphor powder; compared with other systems, the red phosphor powder of the tungstate system shows outstanding features: (1) It can effectively absorb the excitation light around 400nm; (2) It is different from the commonly used Y ₂ O ₂ S:Eu ³⁺ Compared with fluorescent powder, the relative brightness is higher, about 1.5 times that of the former; (3) It can be sintered in the air, and the sintering temperature (700 ° C ~ 900 ° C) is significantly lower than that of silicate and aluminate systems (1200 ° C above); (4) stable in nature, green and non-toxic, and will not produce toxic gases such as sulfides under ultraviolet radiation; (5) its strongest emission peak is located near 615nm, and its luminous color is pure.

The red phosphor powder based on tungstate system has the above-mentioned remarkable characteristics, and has attracted more and more attention in recent years, and has become a hot spot in the current research of red phosphor powder for LEDs.

Contents of the invention

The purpose of the present invention is to provide a method for preparing tungstate red fluorescent powder based on sol-gel combustion method, which can prepare tungstate red fluorescent powder with good stability, high color purity and high luminous efficiency, which is very Suitable for white LED.

The technical scheme adopted in the present invention is, based on the sol-gel combustion method, the method for preparing tungstate red phosphor, specifically implemented according to the following steps:

Step 1. First weigh sodium nitrate NaNO ₃ , magnesium nitrate Mg(NO ₃ ) ₂ ·6H ₂ O, gadolinium nitrate Gd(NO ₃ ) ₃ ·6H ₂ O, europium nitrate Eu(NO ₃ ) ₃ ·6H ₂ O and ammonium tungstate (NH ₄ ) ₅ H ₅ [H ₂ (WO ₄ ) ₆ ]·H ₂ O; then the five salts weighed were dissolved in deionized water to form five salt solutions, and finally the five The salt solutions are mixed together to form a mixed solution;

Step 2, first weigh citric acid and add it to the mixed solution obtained in step 1, and stir to form a sol; then place the sol in a constant temperature water bath and heat to form a wet gel; finally, dry it to obtain a dry gel;

Step 3. Put the xerogel obtained in step 2 into a muffle furnace for calcination to prepare tungstate NaGd _1-x Eu _x MgWO ₆ red phosphor.

The present invention is also characterized in that:

Step 1 is specifically implemented according to the following steps:

Step 1.1, the molar ratio is n _NaNO3 : n _{Mg(NO3)2 6H2O} : n _{Gd(NO3)3 6H2O} : n _{Eu(NO3)3 6H2O} : n _{(NH4)5H5[H2(WO4)6] H2O} = 1～1.2: 1～1.2: 0.95～0.8: 0.05～0.2: 0.17～0.2 Weigh sodium nitrate NaNO ₃ , magnesium nitrate Mg(NO ₃ ) ₂ 6H ₂ O, gadolinium nitrate Gd(NO ₃ ) ₃ ·6H ₂ O, europium nitrate Eu(NO ₃ ) ₃ ·6H ₂ O and ammonium tungstate (NH ₄ ) ₅ H ₅ [H ₂ (WO ₄ ) ₆ ]·H ₂ O;

Step 1.2, sodium nitrate NaNO ₃ , magnesium nitrate Mg(NO ₃ ) ₂ ·6H ₂ O, gadolinium nitrate Gd(NO ₃ ) ₃ ·6H ₂ O, europium nitrate Eu(NO ₃ ) ₃ · 6H ₂ O and ammonium tungstate (NH ₄ ) ₅ H ₅ [H ₂ (WO ₄ ) ₆ ]·H ₂ O were respectively dissolved in deionized water to form sodium nitrate solution and 1mol/L molar volume concentration respectively. /L magnesium nitrate solution, 1mol/L gadolinium nitrate solution, 1mol/L europium nitrate solution, 1mol/L ammonium tungstate solution;

Step 1.3: Mix the sodium nitrate solution, magnesium nitrate solution, gadolinium nitrate solution, europium nitrate solution and ammonium tungstate solution formed in step 1.2 together, and prepare a mixed solution after stirring.

Sodium nitrate NaNO ₃ , magnesium nitrate Mg(NO ₃ ) ₂ ·6H ₂ O, gadolinium nitrate Gd(NO ₃ ) ₃ ·6H ₂ O, europium nitrate Eu(NO ₃ ) ₃ ·6H ₂ O and ammonium tungstate in step 1.1 The molar ratio of (NH ₄ ) ₅ H ₅ [H ₂ (WO ₄ ) ₆ ]·H ₂ O is preferably n _NaNO3 : n _{Mg(NO3)2·6H2O} : n _{Gd(NO3)3·6H2O} : n _{Eu(NO3 )3·6H2O} : n _{(NH4)5H5[H2(WO4)6]·H2O} =1.1:1:0.85:0.15:0.17.

Step 2 is specifically implemented according to the following steps:

Step 2.1, weigh citric acid, the molar ratio of citric acid to metal ions is n _{citric acid} : n _{metal ions} = 1-2:1;

Step 2.2, adding the citric acid weighed in step 2.1 to the mixed solution prepared in step 1, and mixing the citric acid and the mixed solution evenly by stirring to form a transparent sol;

Step 2.3. Place the sol obtained in step 2.2 in a constant temperature water bath at 80°C to 100°C, and use a magnetic stirrer to heat and stir the sol for 10h to 20h to form a wet gel;

Step 2.4, place the wet gel prepared in step 2.3 in an oven, and perform aging and drying treatment at 100° C. to 130° C. After 10 hours to 18 hours, a dry gel is obtained.

Step 3 is specifically implemented according to the following steps:

Step 3.1, placing the xerogel obtained in step 2 in a crucible;

Step 3.2, put the crucible containing the xerogel in step 3.1 into a muffle furnace, and perform calcination in the temperature range of 800°C to 1000°C to prepare tungstate NaGd _1-x Eu _x MgWO ₆ red phosphor ;

Wherein x=0.05, 0.10, 0.15, 0.20; the preferred value of x is 0.15.

The calcining process in step 3.2 is carried out according to the following method:

First, heat up to 400-500°C at a rate of 2°C/min-5°C/min, and keep warm for 1h-3h;

Then heat up to 800-1000°C at a rate of 2°C/min-5°C/min;

Finally keep warm for 4h~6h and then cool down to room temperature with the furnace.

The beneficial effects of the present invention are:

(1) In the method for preparing tungstate red phosphor based on the sol-gel combustion method of the present invention, the sol-gel combustion method is a novel chemical synthesis method, which takes into account the sol-gel method and low-temperature self-combustion The advantage of the method is that it is easy to operate, safe and fast; in addition, the tungstate red phosphor (NaGd _1-x Eu _x MgWO ₆ red phosphor) prepared by this method has a good microscopic appearance, that is, it has crystal Good state, small and uniform particle size.

(2) Utilize the method for preparing tungstate red fluorescent powder based on the sol-gel combustion method of the present invention to obtain a kind of europium-doped novel NaGd _1-x Eu _x MgWO ₆ red fluorescent powder, which has calcium titanium In this structure, the site occupied by Eu ³⁺ ions does not have inversion symmetry. According to the transition selection rule, Eu ³⁺ ions emit light under the excitation of near ultraviolet (393nm) and blue light (466nm). The spectrum is dominated by the electric dipole transition at 616nm; in addition, by adjusting the doping amount of rare earth europium ions and process parameters, high-purity, uniform doping, and controllable particle size monodisperse spherical powder can be prepared, making it highly stable It is a red fluorescent material with high color purity and can be effectively excited by near-ultraviolet and blue light. It can meet the requirements of white LEDs for red phosphors, improve the main indicators of white LED products such as luminous efficiency and color rendering index, and has certain economic and social benefits.

Description of drawings

Fig. 1 is the XRD figure of the tungstate red phosphor prepared by the method for preparing tungstate red phosphor based on the sol-gel combustion method of the present invention;

Fig. 2 is the SEM picture of the tungstate red phosphor prepared by the method for preparing tungstate red phosphor based on the sol-gel combustion method of the present invention;

Fig. 3 is the excitation spectrogram of the tungstate red phosphor prepared by the method for preparing tungstate red phosphor based on the sol-gel combustion method of the present invention;

Fig. 4 is the emission spectrogram of the tungstate red phosphor prepared by the method for preparing tungstate red phosphor based on the sol-gel combustion method of the present invention;

Fig. 5 is the relationship between the luminous intensity and the amount of citric acid of the tungstate red phosphor prepared by the method for preparing the tungstate red phosphor based on the sol-gel combustion method of the present invention;

Fig. 6 is the luminous intensity and sintering temperature relationship diagram of the tungstate red phosphor prepared by the method of preparing tungstate red phosphor based on the sol-gel combustion method of the present invention;

Fig. 7 is a graph showing the relationship between the luminous intensity and the Eu ³⁺ concentration of the tungstate red phosphor prepared by the method of preparing the tungstate red phosphor based on the sol-gel combustion method of the present invention.

detailed description

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

The present invention prepares the method for tungstate red fluorescent powder based on sol-gel combustion method, specifically implements according to the following steps:

Step 1. First weigh sodium nitrate NaNO ₃ , magnesium nitrate Mg(NO ₃ ) ₂ ·6H ₂ O, gadolinium nitrate Gd(NO ₃ ) ₃ ·6H ₂ O, europium nitrate Eu(NO ₃ ) ₃ ·6H ₂ O and ammonium tungstate (NH ₄ ) ₅ H ₅ [H ₂ (WO ₄ ) ₆ ]·H ₂ O; then the five salts weighed were dissolved in deionized water to form five salt solutions, and finally the five The salt solutions are mixed together to form a mixed solution, which is implemented according to the following steps:

Step 1.1, the molar ratio is n _NaNO3 : n _{Mg(NO3)2 6H2O} : n _{Gd(NO3)3 6H2O} : n _{Eu(NO3)3 6H2O} : n _{(NH4)5H5[H2(WO4)6] H2O} = 1～1.2: 1～1.2: 0.95～0.8: 0.05～0.2: 0.17～0.2 Weigh sodium nitrate NaNO ₃ , magnesium nitrate Mg(NO ₃ ) ₂ 6H ₂ O, gadolinium nitrate Gd(NO ₃ ) ₃ ·6H ₂ O, europium nitrate Eu(NO ₃ ) ₃ ·6H ₂ O and ammonium tungstate (NH ₄ ) ₅ H ₅ [H ₂ (WO ₄ ) ₆ ]·H ₂ O;

Among them, sodium nitrate NaNO ₃ , magnesium nitrate Mg(NO ₃ ) ₂ ·6H ₂ O, gadolinium nitrate Gd(NO ₃ ) ₃ ·6H ₂ O, europium nitrate Eu(NO ₃ ) ₃ ·6H ₂ O and ammonium tungstate ( The molar ratio of NH ₄ ) ₅ H ₅ [H ₂ (WO ₄ ) ₆ ]·H ₂ O is preferably n _NaNO3 :n _{Mg(NO3)2·6H2O} :n _{Gd(NO3)3·6H2O} :n _{Eu(NO3) 3.6H2O} : n _{(NH4)5H5[H2(WO4)6] H2O} = 1.1:1:0.85:0.15:0.17;

Sodium nitrate NaNO ₃ , magnesium nitrate Mg(NO ₃ ) ₂ 6H ₂ O, gadolinium nitrate Gd(NO ₃ ) ₃ 6H ₂ O, europium nitrate Eu(NO ₃ ) ₃ 6H ₂ O and ammonium tungstate (NH ₄ ) ₅ H ₅ [H ₂ (WO ₄ ) ₆ ]·H ₂ O were respectively dissolved in deionized water to form sodium nitrate solution, 1 mol/L magnesium nitrate solution, 1 mol/L gadolinium nitrate solution, 1mol/L europium nitrate solution, 1mol/L ammonium tungstate solution;

Step 1.3: Mix the sodium nitrate solution, magnesium nitrate solution, gadolinium nitrate solution, europium nitrate solution and ammonium tungstate solution formed in step 1.2 together, and prepare a mixed solution after stirring.

Step 2. First weigh citric acid and add it to the mixed solution obtained in step 1, and stir to form a sol; then heat the sol in a constant temperature water bath to form a wet gel; finally dry to obtain a loose light yellow dry gel Glue, specifically follow the steps below:

Step 2.1, weigh citric acid, the molar ratio of citric acid to metal ions is n _{citric acid} : n _{metal ions} = 1-2:1;

Step 2.2, adding the citric acid weighed in step 2.1 to the mixed solution prepared in step 1, and mixing the citric acid and the mixed solution evenly by stirring to form a transparent sol;

Step 2.3. Place the sol obtained in step 2.2 in a constant temperature water bath at 80°C to 100°C, and use a magnetic stirrer to heat and stir the sol for 10h to 20h to form a wet gel;

Step 2.4, place the wet gel prepared in step 2.3 in an oven, and perform aging and drying treatment at 100°C to 130°C. After 10h to 18h, a light yellow xerogel with a loose texture is obtained.

Step 3. Put the xerogel obtained in step 2 into a muffle furnace for calcination to prepare tungstate NaGd _1-x Eu _x MgWO ₆ red phosphor, specifically follow the steps below:

Step 3.1, placing the xerogel obtained in step 2 in a crucible;

Step 3.2, put the crucible containing the xerogel in step 3.1 into a muffle furnace, and perform calcination in the temperature range of 800°C to 1000°C to prepare tungstate NaGd _1-x Eu _x MgWO ₆ red phosphor ;

Wherein x=0.05, 0.10, 0.15, 0.20; the preferred value of x is 0.15.

In step 3.2, the calcination process is carried out in the following manner:

First, heat up to 400°C to 500°C at a rate of 2°C/min to 5°C/min, and keep warm for 1h to 3h; then heat up to 800°C to 1000°C at a rate of 2°C/min to 5°C/min; finally keep hold for 4h After ~6h, it was cooled to room temperature with the furnace.

Among them, the XRD spectrum of NaGd _0.85 Eu _0.15 MgWO ₆ red phosphor is shown in Figure 1, as can be seen from Figure 1: the X-ray diffraction peaks of NaGd _0.85 Eu _0.15 MgWO ₆ red phosphor and the international standard diffraction card JCPDS 37- 0243 are completely consistent, without any other diffraction peaks of impurity phases, which shows that the prepared NaGd _0.85 Eu _0.15 MgWO ₆ red phosphor has a single-phase perovskite structure, that is, Eu ³⁺ replacing Gd ³⁺ does not change the crystal structure, and is a complete solid solution.

The SEM image of the NaGd _0.85 Eu _0.15 MgWO ₆ red phosphor is shown in Figure 2. It can be seen from Figure 2 that the prepared NaGd _0.85 Eu _0.15 MgWO ₆ red phosphor has good powder dispersion and the boundary between the particles Obvious, and the particle size distribution range is narrow, with an average particle size of about 1 μm.

Figure 3 and Figure 4 are the excitation spectrum and emission spectrum of the NaGd _0.85 Eu _0.15 MgWO ₆ red phosphor measured by the fluorescence spectrophotometer F-7100, respectively. It can be seen from Figure 3: NaGd _0.85 Eu _0.15 MgWO ₆ red phosphor has a series of sharp fronts at 360nm~550nm, which belong to the 4f-4f transition of Eu ³⁺ , and the main peaks are located at 393nm ( ⁷ F ₀ → ⁵ L ₆ ) and 466nm ( ⁷ F ₀ → ⁵ D ₂ ), which is consistent with the emission spectrum of the currently widely used near-ultraviolet LED chips and blue-light LED chips, so it can be used as a three-color phosphor composition white LED excited by near-ultraviolet and blue light of red phosphor. It can be seen from Figure 4 that the main peak of the emission spectrum of NaGd _0.85 Eu _0.15 MgWO ₆ red phosphor is located at 616nm under excitation at 393nm, which belongs to the ⁵ D ₀ → ⁷ F ₂ electric dipole transition of Eu ³⁺ .

Found in the preparation process, the consumption of citric acid is different, and the emission spectrum figure of the NaGd _0.85 Eu _0.15 MgWO ₆ red fluorescent powder that it makes is different to some extent, as shown in Figure 5, although the emission spectrum main peak under 393nm excitation is still located at 616nm, but the emission intensity of the sample obtained when the ratio of citric acid to metal ion is 1:1.5 is the strongest.

In the final calcination process, different calcination temperatures have an impact on the luminous intensity of the obtained NaGd _0.85 Eu _0.15 MgWO ₆ red phosphor, as shown in Figure 6, the luminous intensity of NaGd _0.85 Eu _0.15 MgWO ₆ first increases with the increase of sintering temperature After that, the optimum sintering temperature is 950°C.

In addition, XRD analysis was performed on the NaGd _1-x Eu _x MgWO ₆ phosphors obtained when x=0.05, 0.1, 0.15, and 0.20, respectively, and it was confirmed that each product was the target product. The relative luminescence intensity of NaGd _1-x Eu _x MgWO ₆ samples with different Eu doping amounts varies with the Eu ³⁺ doping concentration, as shown in Figure 7, the emission spectra of samples with different Eu ³⁺ doping concentrations Similar to the figure, under the excitation of near-ultraviolet light at 393nm, the main emission peaks are all located at 616nm, which belongs to the electric dipole transition of ⁵ D ₀ → ⁷ F ₂ . However, the emission intensity of the sample increases first and then decreases with the increase of the doping concentration of Eu ³⁺ ions, and the optimum doping concentration is x=0.15.

Example 1

Molar ratio is n _NaNO3 : n _{Mg(NO3)2 6H2O} : n _{Gd(NO3)3 6H2O} : n _{Eu(NO3)3 6H2O} : n _{(NH4)5H5[H2(WO4)6] H2O} = 1.1 : ₁ : 0.85: 0.15: 0.17 Weigh _sodium nitrate, magnesium nitrate, gadolinium nitrate, _europium nitrate and ammonium tungstate respectively _; Gd(NO ₃ ) ₃ ·6H ₂ O, europium nitrate Eu(NO ₃ ) ₃ ·6H ₂ O and ammonium tungstate (NH ₄ ) ₅ H ₅ [H ₂ (WO ₄ ) ₆ ]·H ₂ O were dissolved in In deionized water, respectively form sodium nitrate solution, 1mol/L magnesium nitrate solution, 1mol/L gadolinium nitrate solution, 1mol/L europium nitrate solution, 1mol/L ammonium tungstate solution with molar volume ratio concentration of 1mol/L ; Mix sodium nitrate solution, magnesium nitrate solution, gadolinium nitrate solution, europium nitrate solution and ammonium tungstate solution together, after stirring, prepare a mixed solution;

Weigh citric acid, the molar ratio of citric acid and metal ions is n _{citric acid} : n _{metal ions} = 1.5: 1; add citric acid to the mixed solution, and mix the citric acid and the mixed solution evenly by stirring to form a transparent sol; The obtained sol was placed in a constant temperature water bath at 80°C, and the sol was heated and stirred with a magnetic stirrer for 20 hours to form a wet gel; the prepared wet gel was placed in an oven at 130°C for Aging and drying treatment, after 10 hours, a light yellow xerogel with loose texture is obtained;

Put the dry gel in the crucible, put the crucible containing the dry gel into the muffle furnace, and start calcining under the air atmosphere, firstly raise the temperature to 500°C at a rate of 2°C/min, and keep it for 2h; then The temperature was raised to 900°C at a rate of 2°C/min; the final temperature was kept for 4 hours and then cooled to room temperature with the furnace; the NaGd _0.85 Eu _0.15 MgWO ₆ red phosphor was prepared.

Example 2

Molar ratio is n _NaNO3 : n _{Mg(NO3)2 6H2O} : n _{Gd(NO3)3 6H2O} : n _{Eu(NO3)3 6H2O} : n _{(NH4)5H5[H2(WO4)6] H2O} = 1.2 : _1.2 : 0.8: 0.2: 0.2 Weigh _sodium nitrate, magnesium nitrate, _gadolinium nitrate, europium nitrate and ammonium tungstate respectively _; Gd(NO ₃ ) ₃ ·6H ₂ O, europium nitrate Eu(NO ₃ ) ₃ ·6H ₂ O and ammonium tungstate (NH ₄ ) ₅ H ₅ [H ₂ (WO ₄ ) ₆ ]·H ₂ O were dissolved in In deionized water, respectively form sodium nitrate solution, 1mol/L magnesium nitrate solution, 1mol/L gadolinium nitrate solution, 1mol/L europium nitrate solution, 1mol/L ammonium tungstate solution with molar volume ratio concentration of 1mol/L ; Mix sodium nitrate solution, magnesium nitrate solution, gadolinium nitrate solution, europium nitrate solution and ammonium tungstate solution together, after stirring, prepare a mixed solution;

Weigh citric acid, the mol ratio of citric acid and metal ion is n _{citric acid} :n _{metal ion} =2:1; Add citric acid to mixed solution, adopt the mode of stirring to make citric acid and mixed solution mix evenly, form transparent sol; Place the obtained sol in a constant temperature water bath at 85°C, heat and stir the sol with a magnetic stirrer for 15 hours to form a wet gel; place the prepared wet gel in an oven at 120°C, Carry out aging and drying treatment, and after 12 hours, a light yellow xerogel with loose texture is obtained;

Put the dry gel in the crucible, put the crucible containing the dry gel into the muffle furnace, and start calcining under the air atmosphere, firstly, the temperature is raised to 450°C at a rate of 3°C/min, and the temperature is kept for 3h; then The temperature was raised to 1000°C at a rate of 3°C/min; the final temperature was kept for 5 hours and then the furnace was cooled to room temperature; NaGd _0.8 Eu _0.2 MgWO ₆ red phosphor was prepared.

Example 3

Molar ratio is n _NaNO3 : n _{Mg(NO3)2·6H2O} : n _{Gd(NO3)3·6H2O} : n _{Eu(NO3)3·6H2O} : n _{(NH4)5H5[H2(WO4)6]·H2O} =1 : ₁ : 0.9: 0.1: 0.18 Weigh _sodium nitrate, magnesium nitrate, gadolinium nitrate, _europium nitrate and ammonium tungstate respectively _; Gd(NO ₃ ) ₃ ·6H ₂ O, europium nitrate Eu(NO ₃ ) ₃ ·6H ₂ O and ammonium tungstate (NH ₄ ) ₅ H ₅ [H ₂ (WO ₄ ) ₆ ]·H ₂ O were dissolved in In deionized water, respectively form sodium nitrate solution, 1mol/L magnesium nitrate solution, 1mol/L gadolinium nitrate solution, 1mol/L europium nitrate solution, 1mol/L ammonium tungstate solution with molar volume ratio concentration of 1mol/L ; Mix sodium nitrate solution, magnesium nitrate solution, gadolinium nitrate solution, europium nitrate solution and ammonium tungstate solution together, after stirring, prepare a mixed solution;

Weigh citric acid, the molar ratio of citric acid and metal ions is n _{citric acid} :n _{metal ions} =1.2:1; add citric acid to the mixed solution, and mix the citric acid and the mixed solution evenly by stirring to form a transparent sol; Place the obtained sol in a constant temperature water bath at 90°C, heat and stir the sol with a magnetic stirrer for 15 hours to form a wet gel; place the obtained wet gel in an oven at 110°C, Carry out aging and drying treatment, and after 16 hours, a light yellow xerogel with a loose texture is obtained;

Put the dry gel in the crucible, put the crucible containing the dry gel into the muffle furnace, and start calcination under the air atmosphere, firstly raise the temperature to 400°C at a rate of 4°C/min, and keep it for 1h; then The temperature was raised to 950°C at a rate of 4°C/min; the final temperature was kept for 4.5h and then cooled to room temperature with the furnace; the NaGd _0.9 Eu _0.1 MgWO ₆ red phosphor was prepared.

Example 4

Molar ratio is n _NaNO3 : n _{Mg(NO3)2 6H2O} : n _{Gd(NO3)3 6H2O} : n _{Eu(NO3)3 6H2O} : n _{(NH4)5H5[H2(WO4)6] H2O} = 1.2 : ₁ : 0.95: 0.05: 0.17 Weigh _sodium nitrate, magnesium nitrate, gadolinium nitrate, _europium nitrate and ammonium tungstate respectively _; Gd(NO ₃ ) ₃ ·6H ₂ O, europium nitrate Eu(NO ₃ ) ₃ ·6H ₂ O and ammonium tungstate (NH ₄ ) ₅ H ₅ [H ₂ (WO ₄ ) ₆ ]·H ₂ O were dissolved in In deionized water, respectively form sodium nitrate solution, 1mol/L magnesium nitrate solution, 1mol/L gadolinium nitrate solution, 1mol/L europium nitrate solution, 1mol/L ammonium tungstate solution with molar volume ratio concentration of 1mol/L ; Mix sodium nitrate solution, magnesium nitrate solution, gadolinium nitrate solution, europium nitrate solution and ammonium tungstate solution together, after stirring, prepare a mixed solution;

Weigh citric acid, the molar ratio of citric acid and metal ions is n _{citric acid} : n _{metal ions} = 1.5: 1; add citric acid to the mixed solution, and mix the citric acid and the mixed solution evenly by stirring to form a transparent sol; The obtained sol was placed in a constant temperature water bath at 100°C, and the sol was heated and stirred with a magnetic stirrer for 16 hours to form a wet gel; the prepared wet gel was placed in an oven at 130°C, Carry out aging and drying treatment, and after 18 hours, a light yellow xerogel with loose texture is obtained;

Put the dry gel in the crucible, put the crucible containing the dry gel into the muffle furnace, and start calcining under the air atmosphere, firstly raise the temperature to 500°C at a rate of 5°C/min, and keep it for 2h; then The temperature was raised to 900°C at a rate of 5°C/min; the final temperature was kept for 5 hours and then cooled to room temperature with the furnace; the NaGd _0.95 Eu _0.05 MgWO ₆ red phosphor was prepared.

The method for preparing tungstate red fluorescent powder based on a sol-gel combustion method in the present invention can prepare a tungstate red fluorescent material with good stability, high color purity and high luminous efficiency, which is very suitable for white LEDs.

Claims (7)

1. prepare the method for tungstate red fluorescent powder based on sol-gel combustion method, it is characterized in that, specifically implement according to following steps:

Step 1, first take SODIUMNITRATE NaNO respectively ₃, magnesium nitrate Mg (NO ₃) ₂6H ₂o, Gadolinium trinitrate Gd (NO ₃) ₃6H ₂o, europium nitrate Eu (NO ₃) ₃6H ₂o and ammonium tungstate (NH ₄) ₅h ₅[H ₂(WO ₄) ₆] H ₂o; Then take five kinds of salt are dissolved in deionized water respectively and are made into five kinds of salts solutions, finally five kinds of salts solutions are mixed formation mixing solutions;

Step 2, first taking citric acid and add in the mixing solutions that step 1 obtains, forming colloidal sol through stirring; Then colloidal sol is placed in thermostat water bath and adds thermosetting wet gel; Xerogel is obtained finally by oven dry;

Step 3, the xerogel obtained is put into retort furnace calcine through step 2, prepare tungstate NaGd _1-xeu _xmgWO ₆red fluorescence powder.

2. the method preparing tungstate red fluorescent powder based on sol-gel combustion method according to claim 1, is characterized in that, described step 1 is specifically implemented according to following steps:

Step 1.1, be n in molar ratio _naNO3: n _{mg (NO3) 26H2O}: n _{gd (NO3) 36H2O}: n _{eu (NO3) 36H2O}: n _{(NH4) 5H5 [H2 (WO4) 6] H2O}=1 ~ 1.2:1 ~ 1.2:0.95 ~ 0.8:0.05 ~ 0.2:0.17 ~ 0.2 takes SODIUMNITRATE NaNO respectively ₃, magnesium nitrate Mg (NO ₃) ₂6H ₂o, Gadolinium trinitrate Gd (NO ₃) ₃6H ₂o, europium nitrate Eu (NO ₃) ₃6H ₂o and ammonium tungstate (NH ₄) ₅h ₅[H ₂(WO ₄) ₆] H ₂o;

Step 1.2, the SODIUMNITRATE NaNO will taken in step 1.1 ₃, magnesium nitrate Mg (NO ₃) ₂6H ₂o, Gadolinium trinitrate Gd (NO ₃) ₃6H ₂o, europium nitrate Eu (NO ₃) ₃6H ₂o and ammonium tungstate (NH ₄) ₅h ₅[H ₂(WO ₄) ₆] H ₂o is dissolved in deionized water respectively, forms sodium nitrate solution, the magnesium nitrate solution of 1mol/L, the Gadolinium trinitrate solution of 1mol/L, the europium nitrate solution of 1mol/L, 1mol/L ammonium tungstate solution that molecular volume specific concentration is 1mol/L respectively;

Step 1.3, the sodium nitrate solution formed in step 1.2, magnesium nitrate solution, Gadolinium trinitrate solution, europium nitrate solution and ammonium tungstate solution to be mixed, after stirring, be mixed with mixing solutions.

3. the method preparing tungstate red fluorescent powder based on sol-gel combustion method according to claim 2, is characterized in that, SODIUMNITRATE NaNO in described step 1.1 ₃, magnesium nitrate Mg (NO ₃) ₂6H ₂o, Gadolinium trinitrate Gd (NO ₃) ₃6H ₂o, europium nitrate Eu (NO ₃) ₃6H ₂o and ammonium tungstate (NH ₄) ₅h ₅[H ₂(WO ₄) ₆] H ₂the mol ratio of O is preferably n _naNO3: n _{mg (NO3) 26H2O}: n _{gd (NO3) 36H2O}: n _{eu (NO3) 36H2O}: n _{(NH4) 5H5 [H2 (WO4) 6] H2O}=1.1:1:0.85:0.15:0.17.

4. the method preparing tungstate red fluorescent powder based on sol-gel combustion method according to claim 1, is characterized in that, described step 2 is specifically implemented according to following steps:

Step 2.1, take citric acid, the mol ratio of citric acid and metal ion is n _{citric acid}: n _{metal ion}=1 ~ 2:1;

Step 2.2, the citric acid taken in step 2.1 added the mixing solutions that step 1 prepares, adopt the mode stirred that citric acid is mixed with mixing solutions, the colloidal sol of formation transparence;

Step 2.3, be positioned in the thermostat water bath of 80 DEG C ~ 100 DEG C by the colloidal sol obtained through step 2.2, utilize magnetic stirring apparatus heat colloidal sol and stir, the time is 10h ~ 20h, forms wet gel;

Step 2.4, the wet gel obtained through step 2.3 to be placed in baking oven, under 100 DEG C ~ 130 DEG C conditions, carry out aging, drying and processing, after 10h ~ 18h, obtain xerogel.

5. the method preparing tungstate red fluorescent powder based on sol-gel combustion method according to claim 1, is characterized in that, described step 3 is specifically implemented according to following steps:

Step 3.1, the xerogel obtained through step 2 is positioned in crucible;

Step 3.2, the crucible that xerogel is housed in step 3.1 is put into retort furnace, in 800 DEG C ~ 1000 DEG C temperature ranges, carry out calcination processing, prepare tungstate NaGd _1-xeu _xmgWO ₆red fluorescence powder.

6. the method preparing tungstate red fluorescent powder based on sol-gel combustion method according to claim 5, is characterized in that, the tungstate NaGd obtained of preparation in described step 3.2 _1-xeu _xmgWO ₆red fluorescence powder, its x=0.05,0.10,0.15,0.20;

The preferred value of x is 0.15.

7. the method preparing tungstate red fluorescent powder based on sol-gel combustion method according to claim 5, is characterized in that, the calcination process in described step 3.2 is implemented in accordance with the following methods:

First with the ramp to 400 of 2 DEG C/min ~ 5 DEG C/min DEG C ~ 500 DEG C, insulation 1h ~ 3h;

Again with the ramp to 800 of 2 DEG C/min ~ 5 DEG C/min DEG C ~ 1000 DEG C;

Room temperature is cooled to the furnace after being finally incubated 4h ~ 6h.