Red luminescent fluorescent powder of lithium-ion-doped double tungstate and preparation method of red luminescent fluorescent powder

Abstract

The invention discloses lithium ion doped double tungstate red luminescent fluorescent powder and a preparation method thereof, and particularly relates to the technical field of fluorescent materials. The general chemical formula of the fluorescent powder is K < 1-x > LixEu (WO4) 2, wherein x is a molar fraction which is more than or equal to 0 and less than or equal to 0.5. The double-tungstate red-light fluorescent powder can emit red light with high intensity, good color purity and strong thermal stability under the excitation of blue light with the wavelength of 393 nm, the raw materials are easy to obtain, the preparation is simple (a sol-gel method), the calcination temperature is low (900 DEG C), the thermal stability is excellent, and the double-tungstate red-light fluorescent powder is an ideal fluorescent powder material of the red-light fluorescent powder in a trichromatic fluorescent powder type white-light LED.

Description

Technical Field

[0001] The invention relates to the technical field of fluorescent materials, and in particular to a red luminescent fluorescent powder of a lithium ion-doped bitungstate and a preparation method thereof. Background Art

[0002] As we all know, by Eu 3+ Ion-activated red phosphors play an important role in WLEDs because they can improve the color rendering index, color temperature in the red spectral region, and excellent light quality. The commercial red phosphors currently used in WLEDs are Y2O2S:Eu 3+ , this kind of fluorescent powder has high color temperature, low color rendering index, low luminous efficiency, and poor chemical stability (Journal of Alloys and Compounds, Volume 720, 5 October 2017, Pages 29-38). To this end, researchers have successively developed red phosphors with high luminous efficiency and good chemical stability, such as CaSrAl2SiO7:Eu 3+ , Li 0.04 Ca 0.93 SiO3:Eu 3+ 、Bi 3+ 、CaTiO3:Eu 3+ 、M2Si5N 8 :Eu 2+ (M=Ca,Sr,Ba),(Y,Gd)BO3:Eu 3+ Phosphor. In addition, there are tungstate or molybdate phosphors, such as Li3Ba2Y3(WO4)8:Eu 3+ (CeramicsInternational, Volume 42, Issue 12, September 2016, Pages 13648-13653), SrWO4:Eu 3+ (Optical Materials, Volume 33, Issue 6, April 2011, Pages 909-913), (Ca 1-x-y ,Ln y )MoO4:xEu 3+ (Ln=Y,Gd)(Journal of Alloys and Compounds, Volume 505, Issue 1, 27August 2010, Pages 239-242), Y2WO6:Eu 3+(Journal of Solid State Chemistry, Volume 184, Issue 4, April 2011, Pages 843-847) and Y6W2O 15 :Eu 3+ (Journal of Luminescence, Volume 126, Issue 2, October 2007, Pages 881-885). 3+ Among the doped red phosphors, the phosphors with tungstate or molybdate (CaMoO4) crystal structures have a broad and strong charge transfer band (CTB), and in the ultraviolet region Eu 3+ The excitation intensity of the ions is very high. At wavelengths of about 393nm and 464nm, Eu 3+ The excitation intensity of ions is very high. Therefore, tungsten / molybdate red phosphors have attracted widespread attention from researchers (Physica B: Condensed Matter, Volume 582, 1 April 2020, 411999).

[0003] In addition, recently, double molybdate or tungstate ALn(MO4)2 (A=Li + ,Na + ,K + ; Ln = trivalent rare earth ion; M = Mo 6+ , W 6+) has good chemical and thermal stability and shows high luminescence intensity (Journal of Materials Science: Materials in Electronics, volume 26, pages 6659-6666 (2015)). JP Huang et al. (Inorg. Chem. 2011, 50, 22, 11487-11492) systematically studied the structure and luminescence properties of trivalent rare earth ion double tungstate phosphor AEu (WO4) 2. And reported that the luminescence intensity and color purity of LiEu (WO4) 2 and NaEu (WO4) 2 are higher than those of KEu (WO4) 2. Ying Liu prepared LiLn(MO4)2 (Ln = La, Eu, Gd, Y; M = W, Mo) phosphors and reported that LiEu(MoO4)2 and LiEu(WO4)2 phosphors showed higher red emission intensity under 395nm excitation, and the red emission intensity was higher than that of Ln = La, Gd and Y phosphors (RSC Adv., 2014, 4, 4754-4762). Guo et al. proposed that AEu(MoO4)2 (A = Li, Na and K) showed a wider CT band at 616nm and emitted bright red emission at 616nm (Appl. Phys. A 94, 365–371 (2009)). Liu.Y. et al. (Inorganic Chemistry 201453 (21), 11457-11466) found that Tm 3+ -Dy 3+ -Eu 3+ The energy migration occurs in NaGd(WO4)2 phosphor. 3+ When the ion content is low, it can sensitize Eu 3+ ions and compensate for the red component. Studies have shown that Li, Na and K ions dope Eu 3+ However, different alkali metal ions have a great influence on the luminescence properties of Eu doped 3+ The chemical bonding and luminescence properties of the double molybdate and tungstate phosphors have different effects on the tungstate or molybdate phosphors. Recently, some studies have reported that LiEu(MoO4)2 and LiEu(WO4)2 phosphors have better luminescence properties than K and Na-based phosphors (Journal of Luminescence, Volume 201, September 2018, Pages 364-371), which may be due to the fact that the lithium ions in the double tungstate or molybdate phosphors increase the covalency of the bond.

[0004] Doping with multiple rare earth ions to enhance the luminescence performance of double tungstate red phosphors is a common method in scientific research and industry, and has been widely used. Its advantage is that it can achieve more ideal luminescence performance with less excitation energy, and the energy-saving effect is better than the commercial red phosphors that have been launched on the market. However, the disadvantages of multiple rare earth ion doping are also obvious. However, with the development of science and technology, the industry's demand for rare earth elements is increasing, resulting in rising prices. Therefore, its large amount of rare earth elements has led to the high cost of multiple rare earth ion doping to enhance luminescence performance, which limits its further commercial application. Based on the above reasons, many researchers have turned their research to improving the matrix structure of double tungstate phosphors to improve their luminescence performance. However, this method often fails to achieve ideal red light luminescence performance, so further improvements are needed to improve its commercial application potential. Summary of the invention

[0005] To this end, the present invention provides a red luminescent phosphor of a lithium ion-doped bitungstate and a preparation method thereof to solve the above-mentioned problems.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] According to one aspect of the present invention, a red luminescent phosphor of a lithium-doped bitungstate is provided, the chemical formula of which is K 1-x Li x Eu(WO4)2, where x is the mole fraction 0≤x≤0.5.

[0008] Furthermore, the chemical formula is K 1-x Li x Eu(WO4)2, x=0.3.

[0009] Furthermore, the raw materials of the red luminescent phosphor include: ammonium tungstate, europium nitrate hexahydrate, polyethylene glycol, citric acid and nitrate, wherein the nitrate is potassium nitrate and / or lithium nitrate.

[0010] According to another aspect of the present invention, a method for preparing a red luminescent phosphor of a lithium ion-doped bitungstate is provided, comprising:

[0011] Step 1, dissolving nitrate and europium nitrate hexahydrate in ethanol water, stirring to fully dissolve, adding citric acid, and then immediately adding ammonium tungstate, stirring vigorously until dissolved, clear and transparent, to obtain a mixed solution;

[0012] Step 2, adding PEG to the mixed solution, heating and stirring until a white sol is formed;

[0013] Step three, stirring the white sol in a water bath until it becomes a transparent sol; heating and drying the obtained sol to form a brown dry gel; grinding the dry gel, annealing it, calcining it, and cooling it to obtain a red luminescent phosphor of a lithium-doped bitungstate.

[0014] Further, it is characterized in that, in the step one, different substance amount ratios of potassium nitrate: lithium nitrate are added to the nitrate = 10:0; 8:2; 7:3; 6:4; 5:5.

[0015] Furthermore, in the step 1, the amount of citric acid added is 2.5:1 to the metal ion ratio.

[0016] Furthermore, in the step 1, the amount of ammonium tungstate added is ammonium tungstate: europium nitrate hexahydrate = 2:1.

[0017] Furthermore, in the step 2, the amount of PEG added is PEG: citric acid = 1:1.

[0018] Furthermore, in step 2, the heating and stirring conditions are stirring at 80° C. for 4 hours.

[0019] Furthermore, in step three, the water bath condition is stirring in a water bath at 80°C for 3 hours; the heating and drying condition is heating at a temperature of 150°C for 12 hours; the annealing condition is annealing at 300°C for 3 hours; and the calcination condition is calcining at 900°C for 3 hours.

[0020] The present invention has the following advantages:

[0021] The improved method for the double tungstate red light phosphor matrix of the present invention reduces the cost compared with the traditional method and has greater commercial application potential.

[0022] The double tungstate red phosphor of the present invention can emit red light with high intensity, good color purity and strong thermal stability under the excitation of blue light with a wavelength of 393nm, and the raw materials are easily available, the preparation is simple (sol-gel method), the calcination temperature is low (900°C), and the thermal stability is excellent. It is an ideal phosphor material for the red phosphor in the three-primary color phosphor type white light LED. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. Obviously, the drawings in the following description are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0024] The structures, proportions, sizes, etc. illustrated in this specification are only used to match the contents disclosed in the specification so as to facilitate understanding and reading by persons familiar with the technology. They are not used to limit the conditions under which the present invention can be implemented, and therefore have no substantial technical significance. Any structural modification, change in proportion or adjustment of size shall still fall within the scope of the technical contents disclosed in the present invention without affecting the effects and purposes that can be achieved by the present invention.

[0025] Figure 1 A flow chart for preparing a red luminescent phosphor of a lithium ion-doped bitungstate provided in Example 1 of the present invention;

[0026] Figure 2 A structural diagram of the red luminescent phosphor of the lithium ion-doped bitungstate provided in Example 1 of the present invention;

[0027] Figure 3 The red luminescent phosphor composition diagram of the lithium ion doped bitungstate provided in Experimental Example 1 of the present invention; wherein a-phosphor K 1-x Li x Eu(WO4)2(x=0) structure refinement; b-Phosphor K 1-x Li x Eu(WO4)2(x=0.3) structure refinement; c-phosphor K 1-x Li x Eu(WO4)2(x=0.5) structure refinement map;

[0028] Figure 4 The appearance of the phosphor of Example 1 provided in Experimental Example 1 of the present invention; wherein the a-phosphor K 0.7 Li 0.3 Powder morphology of Eu(WO4)2; b-Phosphor K 0.7 Li 0.3 Energy spectrum of Eu(WO4)2;

[0029] Figure 5 The ultraviolet absorption spectra of Example 1 and Example 2 provided in Experimental Example 1 of the present invention and the Eg value calculated according to the Kubelka-Munk formula are shown in FIG. 1 ; wherein the a-phosphor K 0.7 Li 0.3 UV-visible absorption spectra of Eu(WO4)2 and KEu(WO4)2; b- K converted by Kubelka-Munk formula 0.7 Li 0.3 Eu(WO4)2 and KEu(WO4)2 absorption spectra;

[0030] Figure 6The amount of Li of different substances in Examples 1-5 provided in Experimental Example 1 of the present invention + Excitation and emission spectra of doped double tungstate phosphors; a-phosphor K 1-x Li x Excitation spectra of Eu(WO4)2 (x = 0, 0.2, 0.3, 0.4 and 0.5); b-Emission spectra of phosphors, the inset shows the emission intensity as Li + Concentration change trend graph;

[0031] Figure 7 K provided in Experimental Example 1 of the present invention 0.7 Li 0.3 Color coordinate diagram of Eu(WO4)2;

[0032] Figure 8 The relationship between the emission spectrum and relative emission intensity of the phosphor of Example 1 under excitation at a wavelength of 393 nm and the temperature is shown in Figure 1; wherein the a-phosphor K 0.7 Li 0.3 Emission spectrum of Eu(WO4)2 changing with temperature; b- K in thermal quenching process 0.7 Li 0.3 Activation energy diagram of Eu(WO4)2 and KEu(WO4)2 phosphors; c-phosphor K 0.7 Li 0.3 The emission intensity of Eu(WO4)2 and KEu(WO4)2 varies with temperature; dK 0.7 Li 0.3 The position coordinate diagram of Eu(WO4)2 and KEu(WO4)2 phosphors during thermal quenching;

[0033] Fig. 9 The luminescence lifetime decay of the phosphor of Example 1 provided in Experimental Example 1 of the present invention; wherein, the a-phosphor K 1-x Li x The fluorescence lifetime spectrum of Eu(WO4)2 (x = 0, 0.3 and 0.5); b- The emission spectrum under a certain excitation energy was measured using a BaSO4 integrating sphere, and the phosphor K was excited with the same energy. 0.7 Li 0.3 Efficiency diagram of Eu(WO4)2. The inset shows the emission spectrum in the range of 550-700nm. DETAILED DESCRIPTION

[0034] The following is a description of the implementation of the present invention by specific embodiments. People familiar with the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] The red luminescent phosphor of the lithium ion-doped double tungstate of the present invention has a chemical formula of K 1-x Li x Eu(WO4)2, where x is the mole fraction 0≤x≤0.5.

[0036] Example 1

[0037] This embodiment provides a red luminescent phosphor of a lithium ion-doped bitungstate with a chemical formula of K 0.7 Li 0.3 Eu(WO4)2.

[0038] Raw materials: KNO3 is 17.5%, LiNO3 is 7.5%, Eu(NO3)3·6H2O is 25%, H 40 N 10 O 41 W 12 ·xH2O is 50%.

[0039] Preparation process diagram Figure 1 As shown, the preparation method is as follows:

[0040] Step 1: Use a balance to weigh KNO3, LiNO3 and Eu(NO3)3·6H2O and dissolve them in a beaker filled with a mixed solution of deionized water and ethanol, and stir for 10 minutes to fully dissolve them; then add citric acid in the beaker according to the molar ratio of metal ions to citric acid of 1:2.5, and immediately add H 40 N 10 O 41 W 12 ·xH2O (added at a ratio of 2:1 to Eu(NO3)3·6H2O), stir vigorously for 35 min until the solution becomes clear;

[0041] Step 2, adding a certain amount of PEG (the ratio of the amount of PEG to the amount of citric acid is 1:1) to the stirred solution, and stirring at 80° C. for 4 h until a white sol is formed;

[0042] Step 3: Place the mixed solution in an 80°C water bath and stir for 3 hours until a transparent sol is formed. The obtained sol is heated at 150°C for 12 hours to generate a brown dry gel as a precursor. Subsequently, the dry gel is fully ground in an agate mortar, annealed at 300°C for 3 hours, and then calcined at 900°C for 3 hours. After cooling to room temperature, the Li + Doped double tungstate red phosphor composition.

[0043] Example 2

[0044] This embodiment provides a red luminescent phosphor of a lithium ion-doped bitungstate with a chemical formula of K 1- x Li x Eu(WO4)2, x=0;

[0045] Raw materials: KNO3 is 25%, Eu(NO3)3·6H2O is 25%, H 40 N 10 O 41 W 12 ·xH2O is 50%.

[0046] Preparation method: Same as Example 1.

[0047] Example 3

[0048] This embodiment provides a red luminescent phosphor of a lithium ion-doped bitungstate with a chemical formula of K 1- x Li x Eu(WO4)2, x = 0.5;

[0049] Raw materials: KNO3 is 12.5%, LiNO3 is 12.5%, Eu(NO3)3·6H2O is 25%, H 40 N 10 O 41 W 12 ·xH2O is 50%.

[0050] Preparation method: Same as Example 1.

[0051] Example 4

[0052] This embodiment provides a red luminescent phosphor of a lithium ion-doped bitungstate with a chemical formula of K 1- x Li x Eu(WO4)2, x = 0.2;

[0053] Raw materials: KNO3 is 25%, LiNO3 is 5%, Eu(NO3)3·6H2O is 25%, H 40 N10 O 41 W 12 ·xH2O is 50%.

[0054] Preparation method: Same as Example 1.

[0055] Example 5

[0056] This embodiment provides a red luminescent phosphor of a lithium ion-doped bitungstate with a chemical formula of K 1- x Li x Eu(WO4)2, x = 0.4;

[0057] Raw materials: KNO3 is 15%, LiNO3 is 10%, Eu(NO3)3·6H2O is 25%, H 40 N 10 O 41 W 12 ·xH2O is 50%.

[0058] Preparation method: Same as Example 1.

[0059] Experimental example

[0060] The red luminescent phosphors of the lithium ion-doped bitungstates of Examples 1-5 were analyzed:

[0061] Figure 2-Figure 4 The phosphors of Examples 1-5 were tested. Figure 2 It shows that the structure of the prepared phosphor has not changed significantly, and Figure 3 a, b and c show K 1-x Li x The structural refinement results of the components of the Eu(WO4)2 phosphor prepared when x=0 (Example 2), x=0.3 (Example 1) and x=0.5 (Example 3). Figure 4 a shows the prepared phosphor K 0.7 Li 0.3 The morphology of Eu(WO4)2 shows that the morphology is relatively uniform. Figure 4 b shows the phosphor K 0.7 Li 0.3 The energy spectrum results of Eu(WO4)2 morphology show the presence of Li + and K + It can be seen that the target product was successfully prepared.

[0062] Figure 5 a The KEu(WO4)2 phosphor of Example 2 and the KEu(WO4)2 phosphor of Example 1 were tested. 0.7 Li 0.3The ultraviolet absorption spectrum of Eu(WO4)2, according to the absorption spectrum, Figure 5 b According to the Kubelka-Munk formula, the Eg values ​​were calculated to be 2.85 and 3.23 eV respectively. The results show that Li + Doping effectively increases the Eg value of the phosphor.

[0063] In order to fully evaluate the prepared cation Li + The luminescence properties of doped double tungstate phosphors are evaluated by excitation and emission spectra at room temperature and high temperature. + The luminescence performance changes after Figure 6 The different Li shown in a and b + The amount of substance doped with ditungstate K 1-x Li x The excitation and emission spectra of Eu(WO4)2 (x=0, 0.2, 0.3, 0.4 and 0.5) phosphors are analyzed. It is shown that as Li + The change of doping amount, when excited at 393nm, the red light intensity of the emission spectrum first increases and then decreases. When x=0.3, the typical red light phosphor has the strongest luminescence intensity at the excitation peak of 393nm and the emission peak of 615nm. Therefore, the present invention determines that Li + The optimal doping amount is x = 0.3. Figure 7 As shown, K 0.7 Li 0.3 The International Commission on Illumination (CIE) coordinates of Eu(WO4)2 phosphor were determined. + The effect of substitution on the luminescence color. Experiments have found that different Li + Ion concentration K 1-x Li x The CIE coordinates of Eu(WO4)2 phosphors are all located in the red light region, and the coordinates (x, y) have almost no difference.

[0064] Figure 8 a shows that under the excitation of 393 nm wavelength, K 0.7 Li 0.3 The emission spectrum and relative emission intensity of Eu(WO4)2 are related to temperature. Figure 8 It can be clearly seen in a that K 0.7 Li 0.3 The emission intensity of Eu(WO4)2 phosphor decreases with increasing temperature. This phenomenon is attributed to the thermal quenching effect of the phosphor. Figure 8 c shows K 0.7 Li 0.3 The emission intensity of Eu(WO4)2 and KEu(WO4)2 phosphors changes with temperature. It can be seen that in the test temperature range, K0.7 Li 0.3 The emission intensity of Eu(WO4)2 is always higher than that of KEu(WO4)2. 0.7 Li 0.3 The emission intensity of Eu(WO4)2 is always higher than that of KEu(WO4)2. In the temperature range of 25-100℃, the emission intensity does not decrease, and then decreases with increasing temperature. The higher the temperature, the lower the emission intensity. However, the emission intensity of KEu(WO4)2 phosphor decreases significantly with increasing temperature. This result shows that Li-doped + K 0.7 Li 0.3 The thermal stability of Eu(WO4)2 is better than that of KE(WO4)2 phosphor. It can be seen that when the temperature exceeds 200℃, K 0.7 Li 0.3 The luminescence intensity of Eu(WO4)2 and KEu(WO4)2 will decrease faster with increasing temperature. As the temperature increases, the emission intensity decreases faster. Generally speaking, the thermal quenching temperature (T50) refers to the temperature equivalent to 50% of its original emission intensity. The temperature is equivalent to 50% of its original emission intensity value. Figure 8 As shown in c, the T50 values ​​of the two phosphors are greater than 300℃, so it can be considered that although both phosphors have good thermal stability, K 0.7 Li 0.3 The thermal stability of Eu(WO4)2 phosphor is better than that of KEu(WO4)2 phosphor.

[0065] According to the Arrhenius equation, Figure 8 As shown in b, the activation energy ΔE can be calculated by KEu(WO4)2 and K 0.7 Li 0.3 The ΔE of Eu(WO4)2 phosphors are 0.218eV (ΔE1) and 0.279eV (ΔE2). The thermal quenching mechanism of luminescence intensity can be explained by the crossover mechanism, such as Figure 8 d. According to the crossover mechanism, the thermal conductivity of the phosphor is 3+ The thermal quenching behavior of ion-activated phosphors at high temperatures can be attributed to the non-radiative transformation of excited electrons. 5 The excited electrons in the D0 state can overcome the energy barrier (activation energy, ΔE) by absorbing thermal energy, migrate to the CT band, and then relax to 7 F J , which leads to the non-radiative transformation effect. 3+ The thermal quenching pathway of activated phosphors may be 5 D0→CT band→ 7 FJ Therefore, the low energy CT band will be located at a lower position and have a lower ΔE. 3+ The probability of non-radiative transformation of activated phosphors increases, and the luminescence intensity will be greatly reduced. As the temperature increases, excited electrons can easily overcome energy barriers, resulting in a significant decrease in luminescence intensity. In this study, the calculated K 0.7 Li 0.3 Eu in Eu(WO4)2 3+ (0.279eV) is higher than KEu(WO4)2(0.218eV). This means that K 0.7 Li 0.3 Eu(WO4)2 phosphor has better thermal stability.

[0066] Fig. 9 a shows K 1-x Li x The luminescence lifetime decay of Eu(WO4)2 phosphor (x=0, 0.3 and 0.5). The luminescence lifetime decay curve under 393nm excitation and 615nm emission conditions. According to the formula, the average decay time when x=0.3 and 0.5 is calculated to be 0.426 and 0.419ms respectively. The results show that Li doped KEu(WO4)2 phosphor + Ions can increase K 1-x Li x The life of Eu(WO4)2 phosphor. The results show that Li doped in KEu(WO4)2 phosphor + Ions can increase K 1-x Li x The maximum lifetime of Eu(WO4)2 phosphor is 0.426ms. 0.7 Li 0.3 The maximum lifetime of Eu(WO4)2 phosphor reaches 0.426ms. These decay times can be regarded as Eu 3+ from 5 D0→ 7 F2 transformed Eu 3+ Luminescence attenuation. Fig. 9 b shows the K after BaSO4 powder was excited at a wavelength of 393 nm. 0.7 Li 0.3 Reflection line, emission spectrum and spectrum of Eu(WO4)2 phosphor. 1-x Li x The internal quantum efficiency (IQE) values ​​of Eu(WO4)2 phosphors (x = 0, 0.3 and 0.5) are 14.42%, 22.48% and 8.04% respectively. It can be seen from the calculation results that K 0.7 Li 0.3The IQE of Eu(WO4)2 phosphor is higher than that of KE(WO4)2 and K 0.5 Li 0.5 Eu(WO4)2 phosphor has high IQE.

[0067] The Li of the present invention + The introduction of ions changes the K 1-x Li x The lattice parameters of Eu(WO4)2 phase, Eu-O and WO bond distances. After calculation, K 0.7 Li 0.3 The band gap energy (Eg) of Eu(WO4)2 solid solution and KEu(WO4)2 phosphor are 2.85 and 3.23 eV respectively. 1- x Li x Eu(WO4)2 phosphor has a wavelength of 393 nanometers ( 7 F0→ 5 L6) excitation, it emits bright red light at a wavelength of 615 nanometers. + The addition of ions can significantly increase K 1-x Li x The luminescence intensity of Eu(WO4)2 phosphor is + The luminescence intensity is strongest when the ion concentration is 0.3. Compared with KEu(WO4)2 phosphor (0.218eV), K 0.7 Li 0.3 Eu(WO4)2 phosphor has higher thermal activation energy (0.279eV) and better thermal stability. 0.7 Li 0.3 The maximum lifetime of Eu(WO4)2 phosphor is 0.426 milliseconds and the internal quantum efficiency is 22.48%.

[0068] In short, K 0.7 Li 0.3 Eu(WO4)2 phosphor can emit red light with high intensity, good color purity and strong thermal stability under the excitation of 393nm wavelength blue light. Moreover, the raw materials are easily available, the preparation is simple (sol-gel method), the calcination temperature is low (900℃), and the thermal stability is excellent. It is an ideal phosphor material for red phosphor in tri-color phosphor type white light LED.

[0069] Although the present invention has been described in detail above by general description and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements can be made to the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all belong to the scope of protection claimed by the present invention.

Claims

1. A red luminescent phosphor of a lithium-ion-doped double tungstate, characterized in that: The chemical formula is K 1-x Li x Eu(WO4)2, where x is the mole fraction 0≤x≤0.

5.

2. The red luminescent phosphor of a lithium ion-doped bitungstate according to claim 1, characterized in that: The chemical formula is K 1-x Li x Eu(WO4)2, x=0.

3.

3. The red luminescent phosphor of a lithium ion-doped bitungstate according to claim 1, characterized in that: The raw materials of the red luminescent phosphor include: ammonium tungstate, europium nitrate hexahydrate, polyethylene glycol, citric acid and nitrate, wherein the nitrate is potassium nitrate and / or lithium nitrate.

4. A method for preparing a red luminescent phosphor of a lithium ion-doped bitungstate, characterized in that: include: Step 1, dissolving nitrate and europium nitrate hexahydrate in ethanol water, stirring to fully dissolve, adding citric acid, and then immediately adding ammonium tungstate, stirring vigorously until dissolved, clear and transparent, to obtain a mixed solution; Step 2, adding PEG to the mixed solution, heating and stirring until a white sol is formed; Step 3, stirring the white sol in a water bath until it becomes a transparent sol; heating and drying the obtained sol into a brown dry gel; The dried gel is ground, annealed, calcined, and cooled to obtain a red luminescent phosphor of a lithium-ion-doped bitungstate.

5. The method for preparing a red luminescent phosphor of a lithium ion-doped bitungstate according to claim 4, characterized in that: In the step 1, different molar ratios of potassium nitrate: lithium nitrate are added to the nitrate = 10:0; 8:2; 7:3; 6:4; 5:

5.

6. The method for preparing a red luminescent phosphor of a lithium ion-doped bitungstate according to claim 4, characterized in that: In the step 1, the added amount of citric acid is 2.5:1 to the metal ion ratio.

7. The method for preparing a red luminescent phosphor of a lithium ion-doped bitungstate according to claim 4, characterized in that: In the step 1, the amount of ammonium tungstate added is ammonium tungstate: europium nitrate hexahydrate = 2:

1.

8. The method for preparing a red luminescent phosphor of a lithium ion-doped bitungstate according to claim 4, characterized in that: In the step 2, the amount of PEG added is PEG: citric acid = 1:

1.

9. The method for preparing a red luminescent phosphor of a lithium ion-doped bitungstate according to claim 4, characterized in that: In the step 2, the heating and stirring condition is stirring at 80° C. for 4 hours.

10. The method for preparing a red luminescent phosphor of a lithium ion-doped bitungstate according to claim 4, characterized in that: In the step three, the water bath condition is stirring in a water bath at 80° C. for 3 hours; the heating and drying condition is heating at a temperature of 150° C. for 12 hours; the annealing condition is annealing at 300° C. for 3 hours; and the calcination condition is calcining at 900° C. for 3 hours.

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