White phosphor perovskite-type green fluorescent powder with high quantum efficiency and anti-thermal quenching of luminescence and preparation method thereof

Abstract

The present application discloses a white phosphorescent perovskite green fluorescent powder with high quantum efficiency and anti-thermal quenching of luminescence and a preparation method thereof. The chemical general formula is: M9Tb(PO4)7, where M is any one of Ca, Sr, Ba, and Mg; the fluorescent powder is synthesized by a high-temperature solid-phase method. The M9Tb(PO4)7 fluorescent powder exhibits the characteristics of anti-thermal quenching and high luminescence efficiency. At 200 °C, it can still maintain 125% of the emission intensity at room temperature (25 °C), effectively solving the problem of poor thermal stability existing in the prior art, and at the same time solving the problem of low luminescence efficiency caused by low doping concentration of Tb 3+ ​

Description

Technical Field

[0001] The present application relates to the technical field of inorganic functional material synthesis, in particular to a white phosphorite-type green phosphor with high quantum efficiency and anti-thermal quenching of luminescence and a preparation method thereof. Specifically, it relates to a preparation method of a white phosphorite-type green phosphor Sr9Tb(PO4)7 with high quantum efficiency and anti-thermal quenching of luminescence. Background Art

[0002] Rare earth elements have become important raw materials for the research and development of rare earth fluorescent materials due to their unique electronic structure and optical properties. my country has successively developed Y(P,V)O4:Eu for high-pressure mercury lamps. 3+ Red powder, Y2O3:Eu for color TV 3+ and Y2O3S:Eu 3+ Red powder, rare earth tri-color phosphors, X-ray intensifying screens, up-conversion materials, rare earth scintillators, rare earth long afterglow materials, rare earth phosphors for PDP, and development of rare earth phosphors for WLED.

[0003] In recent years, rare earth fluorescent materials have become the mainstream of luminescent materials, and have played a leading role in many fields such as WLED phosphors, PDP, long afterglow materials, quantum tailoring and upconversion, showing incomparable advantages. However, the rare earth fluorescent materials currently developed generally have problems such as low quantum efficiency and poor thermal stability. At the same time, the overall research level of green fluorescent materials in my country still lags behind that of foreign countries, lacking original results and patents.

[0004] Rare earth ion Tb 3+ It has been widely studied because of its lower 5d energy level and simple energy level spectrum. n-1 The energy of 5d is low, which can realize the transition from 4f to 5d and has a wide spectrum structure with simple splitting. 3+ Due to the different symmetry of the position of the ions in the matrix, 2 to 5 broadband peaks can be obtained. 3+ The position of the 4f-5d transition and excitation spectrum of the ion changes with the change of the matrix lattice environment. The different symmetries result in different splitting of the absorption spectrum and the excitation spectrum. In addition, Tb 3+ The luminescence of ions is mainly caused by 5 D4→ 7 F J (J=6,5,4,3,2) transitions, and the 5 D4→ 7 F5 transition can show green emission, so Tb 3+ It is an effective activator ion for preparing green phosphor materials. Based on the above properties, Tb 3+Doped rare earth fluorescent materials have a wide range of applications in fields such as PDP, WLED, fingerprint recognition, anti-counterfeiting, etc. However, most of the reported Tb 3+ -doped luminescent materials have problems such as low doping concentration and poor thermal stability, which limit the absorption efficiency and luminescence intensity of Tb 3+ -doped fluorescent powder materials.

[0005] For luminescent materials, the luminescence properties of activators are different in different matrices, mainly affected by factors such as the intensity of the crystal field, electronegativity, covalency, and symmetry of the crystal environment in the matrix lattice.

[0006] Phosphates are a type of common inorganic functional material with unique mineral structures and physical and chemical properties. They have relatively low synthesis temperatures and good stability and are widely used in various fields. In the phosphate system, the M9Ln(PO4)7 (M = any one of Ba, Sr, Ca, Mg; Ln = any one of Sc, Y, Lu, La) crystals with a whitlockite-type structure have rich replaceable cation sites, providing greater possibilities for the doping of activator ions. Therefore, they have the potential to be candidate matrix materials for phosphors.

[0007] For example, CN201810559802.4 discloses a red strontium magnesium phosphate fluorescent material, its preparation method and application. The fluorescent material has a whitlockite-type crystal structure, and an Eu 2+ -ion-doped red fluorescent material Sr 19 Mg2(PO4) 14 :Eu 2+ is synthesized by adjusting the preparation conditions and raw material ratios. The absolute quantum yield of the obtained phosphor can reach 79%; however, the obtained material cannot achieve the effect of emitting green light, and the application of the whitlockite crystal structure in green phosphors is not realized. The absolute quantum yield of the obtained phosphor is only 79%.

[0008] The information disclosed in the background art section is only intended to increase the understanding of the overall background of the present invention and should not be regarded as an admission or an indication in any form that this information constitutes the prior art known to those of ordinary skill in the art. Summary of the Invention

[0009] The present application provides a whitlockite-type green fluorescent powder with high quantum efficiency and anti-thermal quenching of luminescence and its preparation method for the above technical problems. The M9Tb(PO4)7 green phosphor is successfully prepared by the high-temperature solid-phase method. The prepared M9Tb(PO4)7 luminescent material exhibits high quantum efficiency and anti-thermal quenching.

[0010] The present application provides a white phosphosilicate green fluorescent powder with high quantum efficiency and anti-thermal quenching luminescence, and its chemical general formula is: M9Tb(PO4)7, where M is any one of Ba, Sr, Ca, and Mg; this fluorescent powder is synthesized by a high-temperature solid-phase method.

[0011] Preferably, the chemical general formula is: Sr9Tb(PO4)7. The various properties of this fluorescent powder are optimal.

[0012] Preferably, the optimal excitation wavelength of this fluorescent powder is 233 nm; the optimal emission wavelength of this fluorescent powder is 550 nm.

[0013] Preferably, at 200 °C, the emission intensity of this fluorescent powder is 1.25 times that at room temperature (25 °C). The emission intensity of this fluorescent powder can gradually increase with the increase of temperature and other properties remain unchanged, indicating that this fluorescent powder has good thermal stability.

[0014] Preferably, under the excitation of a wavelength of 254 nm, Sr9Tb(PO4)7 exhibits quantum cutting performance, with an internal quantum efficiency of 164% and an absorption efficiency of 19.6%.

[0015] Preferably, the color coordinates of Sr9Tb(PO4)7 are located in the green light region, and the color coordinate values are (0.3361, 0.5818).

[0016] The synthesized fluorescent powder has the above properties. This fluorescent powder realizes the substitution doping of Tb for the Ln site in the white phosphosilicate structure, effectively utilizes the characteristics of the rich replaceable cation sites in the white phosphosilicate crystal, and obtains a fluorescent powder that excites green light with high quantum efficiency and anti-thermal quenching luminescence.

[0017] On the other hand, the present application also provides a preparation method of the above fluorescent powder, including the following steps: after pre-sintering the ground mixed raw materials, performing a solid-phase reaction to obtain this fluorescent powder;

[0018] During the solid-phase reaction, the reactants are heated from room temperature to 1200 - 1400 °C at a heating rate of 3 - 5 °C / min, kept at 1200 - 1400 °C for 8 h, and then cooled to room temperature at a cooling rate of 3 - 5 °C / min.

[0019] Preferably, the raw materials include: M source compound, P source compound, Tb source compound; where the M source compound is any one of Ca source compound, Sr source compound, Ba source compound, and Mg source compound; the purity of the raw materials is 99.9%. The raw materials used in the reaction can be any compound containing the above required elements.

[0020] Preferably, the Sr source compound is SrCO3; the P source compound is NH4H2PO4; the Tb source compound is Tb2O3; the Ca source compound is CaCO3; the Ba source compound is BaCO3; the Mg source compound is MgCO3.

[0021] Preferably, the grinding is carried out in an agate mortar for 15 minutes of sufficient grinding.

[0022] Preferably, the heating program for pre-sintering: the material is heated from room temperature to 500 - 700 °C at a heating rate of 1 - 3 °C / min, after holding for 2 hours at 500 - 700 °C, it is cooled to room temperature with the furnace.

[0023] Preferably, it further includes: re-grinding the pre-sintered material for 30 minutes.

[0024] Preferably, the molar ratio of each reactant is SrCO3:Tb2O3:NH4H2PO4 = 17 - 19:0.5 - 1.5:13 - 15. More preferably, the molar ratio of each reactant is SrCO3:Tb2O3:NH4H2PO4 = 18:1:14.

[0025] The preparation method of the phosphor includes the following steps:

[0026] (1) Weighing: Accurately weigh 1.7205 g of SrCO3 (99.9%), 1.0427 g of NH4H2PO4 (99.9%), and 0.2369 g of Tb2O3 (99.99%) according to the stoichiometric ratio.

[0027] (2) Grinding: Mix all the raw materials and carry out sufficient grinding in an agate mortar for 15 minutes. After grinding, put the reactants into a corundum crucible.

[0028] (3) Pre-sintering stage: Put the corundum crucible containing the reactants into a muffle furnace, set the heating program: heat from room temperature to 600 °C at a heating rate of 2 °C / min, hold at this temperature for 2 hours, finally, cool to room temperature with the furnace, take out the pre-sintered product, and re-grind for 30 minutes.

[0029] (4) Solid-phase reaction stage: Heat the re-ground sample from room temperature to 1300 °C at a heating rate of 4 °C / min, hold at this temperature for 8 hours, then cool to room temperature at a cooling rate of 4 °C / min, and finally obtain the phosphor.

[0030] The beneficial effects that this application can produce include:

[0031] 1) The white phosphor of perovskite type with high quantum efficiency and anti-thermal quenching provided by this application, the M9Tb(PO4)7 phosphor exhibits the property of anti-thermal quenching. At 200 °C, it can still maintain 125% of the emission intensity at room temperature (25 °C), effectively solving the problem of poor thermal stability in the existing technology. At the same time, this phosphor also has the property of high quantum efficiency, and the internal quantum efficiency reaches 164% under the excitation of 254 nm. This result indicates that the luminescent materials with poor thermal stability have application potential in the fields of PDP, WLED, fingerprint recognition, anti-counterfeiting, etc. This phosphor effectively solves the problems of poor thermal stability and low luminescence efficiency due to low doping concentration of Tb 3+ in the existing technology.

[0032] 2) The white phosphor of perovskite type with high quantum efficiency and anti-thermal quenching provided by this application can be prepared only by solid-phase reaction. The reaction is easy to perform, the equipment is simple,

[0033] energy-saving and environmentally friendly, and suitable for large-scale industrial production. Description of the Drawings

[0034] Figure 1 It is the XRD pattern of Sr9Tb(PO4)7 in Example 1 of this application;

[0035] Figure 2 It is the excitation spectrum and emission spectrum of Sr9Tb(PO4)7 in Example 1 of this application;

[0036] Figure 3 It is the variable-temperature spectrum of Sr9Tb(PO4)7 in Example 1 of this application, and the inset is the change trend of the integrated intensity of the variable-temperature spectrum;

[0037] Figure 4 It is the quantum efficiency diagram of Sr9Tb(PO4)7 in Example 1 of this application;

[0038] Figure 5 It is the chromaticity coordinate diagram of Sr9Tb(PO4)7 in Example 1 of this application. Detailed Embodiments

[0039] The present invention will be further described in detail below in conjunction with the drawings and embodiments, but the present invention is not limited in any way. Any transformation or improvement based on the teachings of the present invention falls within the protection scope of the present invention.

[0040] Embodiments

[0041] In the following embodiments, the materials and instruments used are obtained from commercial channels without special instructions; the detection methods used are existing methods without special instructions.

[0042] Example 1 Preparation of Sr9Tb(PO4)7 Fluorescent Material

[0043] (1) Weighing: Accurately weigh 1.7205 g of SrCO3 (99.9%), 1.0427 g of NH4H2PO4 (99.9%), and 0.2369 g of Tb2O3 (99.99%) according to the stoichiometric ratio.

[0044] (2) Grinding: Mix all the raw materials and grind them thoroughly in an agate mortar for 15 min. After grinding, put the reactants into a corundum crucible.

[0045] (3) Pre-sintering stage: Put the corundum crucible containing the reactants into a muffle furnace and set the heating program: Heat from room temperature to 600 °C at a heating rate of 2 °C / min, hold at this temperature for 2 h, and finally, cool to room temperature with the furnace. Take out the pre-sintered product and grind it again for 30 min.

[0046] (4) Solid-state reaction stage: Heat the sample after re-grinding from room temperature to 1300 °C at a heating rate of 4 °C / min, hold at this temperature for 8 h, then cool to room temperature at a cooling rate of 4 °C / min. Finally, take out the sample, grind it to obtain the final sample for subsequent characterization tests.

[0047] Example 2

[0048] The difference from Example 1 is that the raw material SrCO3 is replaced by CaCO3; the molar ratio of the raw materials for the solid-state reaction is CaCO3:Tb2O3:NH4H2PO4 = 17:0.5:13

[0049] During the solid-state reaction, heat the reactants from room temperature to 1200 °C at a heating rate of 3 °C / min, hold at 1400 °C for 8 h, and then cool to room temperature at a cooling rate of 3 °C / min.

[0050] Pre-sintering heating program: Heat the material from room temperature to 500 °C at a heating rate of 1 °C / min, hold at 500 °C for 2 h, and then cool to room temperature with the furnace. Obtain Ca9Tb(PO4)7.

[0051] Example 3

[0052] The difference from Example 1 is that the raw material SrCO3 is replaced by BaCO3; the molar ratio of the raw materials for the solid-state reaction is BaCO3:Tb2O3:NH4H2PO4 = 19:1.5:15.

[0053] During the solid-state reaction, heat the reactants from room temperature to 1400 °C at a heating rate of 5 °C / min, hold at 1200 °C for 8 h, and then cool to room temperature at a cooling rate of 5 °C / min.

[0054] Pre-sintering heating program: The material is heated from room temperature to 700 °C at a heating rate of 3 °C / min, held at 700 °C for 2 h, and then cooled to room temperature with the furnace. Ba9Tb(PO4)7 is obtained.

[0055] Example 4

[0056] The difference from Example 1 is that the raw material SrCO3 is replaced by MgCO3; the molar ratio of raw materials for solid-phase reaction is MgCO3:Tb2O3:NH4H2PO4 = 18:1:14. Mg9Tb(PO4)7 is obtained.

[0057] The samples obtained in Example 1 are respectively subjected to XRD detection according to the existing common methods, and the excitation spectrum diagram, emission spectrum diagram, variable-temperature spectrum diagram, quantum efficiency diagram, and chromaticity coordinate diagram of the phosphor are measured. The results obtained in the other examples are similar to those in Example 1 and will not be elaborated here.

[0058] Result analysis:

[0059] Figure 1 This is the XRD pattern of Sr9Tb(PO4)7 and Sr9Fe(PO4)7 (PDF#51-0427) in Example 1 of the present invention. It can be seen from the figure that they correspond one by one, indicating that the sample is successfully synthesized.

[0060] Figure 2 This is the excitation spectrum diagram and emission spectrum diagram of Sr9Tb(PO4)7 in Example 1 of the present invention; the optimal excitation wavelength of Sr9Tb(PO4)7 is 233 nm, and the optimal emission wavelength is 550 nm. In Figure 2 the left half, using a wavelength of 550 nm as the monitoring wavelength, the excitation spectrum of Sr9Tb(PO4)7 is obtained. A total of 4 diffraction peaks appear. The diffraction peak at 233 nm corresponds to 4f 8 →4f 7 5d 1 energy level transition. The diffraction peak at 267 nm corresponds to 7 F6→ 9 D J transition. The diffraction peak at 354 nm corresponds to 7 F6→ 5 D2 energy level transition. The diffraction peak at 378 nm corresponds to 7 F6→ 5 D3 energy level transition. In Figure 2 the right half, using 233 nm as the excitation wavelength, the emission spectrum of Sr9Tb(PO4)7 is obtained. A total of 4 diffraction peaks appear, located at 490 nm, 550 nm, 586 nm, and 626 nm respectively, corresponding to 5 D4→ 7 F J(J = 6, 5, 4, 3) energy level transitions.

[0061] Figure 3 This is the variable-temperature spectrogram of Sr9Tb(PO4)7 in Example 1 of the present invention. The inset is the integrated intensity diagram of the variable-temperature spectrum. As the temperature changes, except for the intensity, the emission spectrum of Sr9Tb(PO4)7 does not change otherwise and exhibits the property of anti-thermal quenching, and can still maintain 1.25 times the emission intensity at room temperature (25 °C) at 200 °C.

[0062] Figure 4 This is the quantum efficiency diagram of Sr9Tb(PO4)7 in Example 1 of the present invention. Sr9Tb(PO4)7 exhibits the property of quantum cutting under 254 nm excitation, with an internal quantum efficiency of 164%, an external quantum efficiency of 35.2%, and an absorption efficiency of 19.6%.

[0063] Figure 5 This is the chromaticity coordinate diagram of Sr9Tb(PO4)7 in Example 1 of the present invention. Its chromaticity coordinates are located in the green light region, and the chromaticity coordinate values are (0.3361, 0.5818).

[0064] For the phosphor samples obtained in the remaining examples, the obtained results are the same as above and will not be repeated here.

[0065] It can be seen from Figures 1 to 5 that the phosphor provided by this application has good internal quantum efficiency, external quantum efficiency, and absorption efficiency. Among them, the internal quantum efficiency reaches 164%, the external quantum efficiency reaches 35.2%, and the absorption efficiency is 19.6%. The internal quantum efficiency of this phosphor is much higher than that of existing green phosphors. At the same time, this phosphor has good thermal stability and can still maintain 1.25 times the emission intensity at room temperature (25 °C) at 200 °C. And it can be excited by light with an optimal excitation wavelength of 233 nm to generate green light. The phosphor can be used to prepare LED devices according to existing methods.

[0066] Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A white phosphosilicate-type green fluorescent powder with anti-thermal quenching luminescence, characterized in that, The chemical general formula is: Sr9Tb(PO4)7; this phosphor is synthesized by the high-temperature solid-state method; The chromaticity coordinates of Sr9Tb(PO4)7 are located in the green light region, and the chromaticity coordinate values are (0.3361, 0.5818); The optimal excitation wavelength of this phosphor is 233 nm; the optimal emission wavelength of this phosphor is 550 nm.

2. The green fluorescent powder according to claim 1, characterized in that Under the excitation of light with a wavelength of 254 nm, Sr9Tb(PO4)7 exhibits quantum cutting performance, with an internal quantum efficiency of 164% and an external quantum efficiency of 35.2%, and the absorption efficiency is 19.6%.

3. The green fluorescent powder according to claim 2, wherein, At 200 °C, the emission intensity of this phosphor is 1.25 times that at 25 °C.

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