Composite fluorescent powder and preparation method thereof

Abstract

The invention discloses composite fluorescent powder and a preparation method thereof, and belongs to the technical field of inorganic luminescent materials. The composite fluorescent powder contains A wt% of KPbBr and (100-A) wt% of KBr, and A is equal to 5-95. In the KPbBr / KBr composite system, KPbBr is a luminous component and emits orange yellow light under the irradiation of ultraviolet light. The composite fluorescent powder can be prepared only through simple dissolution and crystallization processes. An expensive cesium source is replaced by a cheap potassium source, the process is simple and environment-friendly, the cost is low, and the product has excellent stability and can be applied to the fields of solid-state illumination, photoelectric detection, anti-counterfeiting marks and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of inorganic luminescent materials, and particularly relates to a composite fluorescent powder and a preparation method thereof. BACKGROUND

[0002] As the core component of solid-state lighting and display devices, the luminescent performance of the fluorescent powder directly determines the color rendering index and color gamut range of the terminal product. Compared with traditional rare earth fluorescent powder or organic luminescent material, metal halide perovskite material is considered to be a new generation of display and lighting key material after quantum dots due to its excellent characteristics such as large extinction coefficient, high fluorescent quantum yield, narrow half-peak width of emission spectrum and adjustable band gap, and has attracted widespread attention in the fields of light-emitting diodes, photodetectors and anti-counterfeiting encryption.

[0003] Among various metal halides, all-inorganic cesium lead halide (CsPbX3, X = Cl, Br, I) has become a research hotspot due to its excellent thermal stability and environmental stability. However, although CsPbX3 has excellent photoelectric performance, it still faces the severe challenge of high cost of raw materials in large-scale commercial application. Cesium, as a rare alkali metal element, has extremely low abundance in the earth's crust, and the mining and purification process is complex, resulting in its high market price. This greatly increases the production cost of the material and limits its widespread application in low-cost industrial lighting fields. In order to break this cost barrier, it has become an industry consensus to find a substitute element with abundant reserves, low price and similar performance. Potassium and cesium belong to the same alkali metal group and have similar chemical properties, but potassium has extremely high reserves in the earth's crust and is low in price. Therefore, using potassium ions to replace expensive cesium ions to prepare potassium-based lead halide luminescent materials can greatly reduce the cost of raw materials and has great economic value.

[0004] Although potassium-based materials have broad prospects, the mainstream process for preparing such metal halide luminescent materials still has significant defects. The mainstream process usually adopts high-temperature hot injection method, for example, the method disclosed in patent CN105950151A requires heating under the protection of inert gas to remove water and oxygen, and the reaction system is severely dependent on long-chain ligands such as oleic acid and oleylamine, which requires high equipment and is difficult to produce continuously. The solvents used in most processes are toxic organic solvents such as DMF, DMSO or toluene, for example, a composite green fluorescent powder preparation method disclosed in patent CN114605997A uses DMSO as a solvent. These organic solvents not only have biological toxicity, but also pose potential harm to human health and the environment, and increase the cost of waste liquid treatment, which does not meet the development trend of green chemistry.

[0005] To solve the above problems, the development of green and environmentally friendly preparation process has become a research hotspot. For example, attempts are made to use low-toxicity alcohol solvents such as ethanol to replace high-toxicity solvents, or to directly explore water-phase synthesis paths. However, there are great challenges in synthesizing lead halide perovskites with water as the solvent. The difficulty lies in the extremely low solubility of lead halide precursors in water and the easy hydrolysis of lead halide coordination ions in water environment. Current solutions usually require the addition of high-concentration hydrobromic acid to control the pH in the strong acid range to inhibit hydrolysis, which not only causes serious corrosion to the equipment, but also increases the operation risk; or hydrothermal synthesis method is used, but this usually needs to be carried out in a high-temperature and high-pressure reactor, which has high energy consumption and is difficult to realize continuous production. Therefore, the development of a green preparation method that abandons organic solvents and strong acids, is simple to operate, has low cost, and can obtain high-quality K2PbBr4-based composite fluorescent powder, is of great significance for promoting the industrial application of this type of material. SUMMARY

[0006] The present application aims to provide a new orange-yellow composite fluorescent powder and a preparation method thereof, and aims to solve the problems of harsh preparation conditions and organic solvent pollution in the prior art. The method takes advantage of the significant difference in solubility of each raw material at different temperatures, and realizes the water-phase preparation of metal halide fluorescent materials by accurately controlling the feeding sequence and reaction kinetics. To achieve the above-mentioned purpose, the present application proposes a composite fluorescent powder containing K2PbBr4 luminescent unit, specifically, the composite fluorescent powder contains A wt% of K2PbBr4 and (100-A) wt% of KBr, wherein A=5~95, and the preparation steps of the composite fluorescent powder are as follows: (1) Dissolve KBr in 80~98 ℃ deionized water to obtain a clear KBr solution; (2) Add PbBr2 to the above KBr solution and stir for 12~24 h to obtain a mixed aqueous solution; (3) The product is separated, washed and dried to obtain K2PbBr4 / KBr composite fluorescent powder.

[0007] The molar concentration of the KBr solution in step (1) is 7~16.3 mol / L.

[0008] The molar ratio of KBr to PbBr2 in step (2) is 2:1~100:1.

[0009] The prepared K2PbBr4 in the fluorescent powder is a light-emitting component, which emits bright orange-yellow fluorescence with a peak wavelength of 595 nm under excitation of 300-390 nm ultraviolet light. In the aqueous crystallization process, due to the similar crystallization habit and solubility change rule of K2PbBr4 and KBr, both tend to co-precipitate during the cooling process. This characteristic makes it difficult to completely separate and purify K2PbBr4 from KBr in the conventional crystallization operation, thereby naturally forming a closely symbiotic K2PbBr4 / KBr composite system.

[0010] The present application strictly limits the feeding order of potassium first and then lead, because the solubility of PbBr2 in water is extremely low, it is difficult to dissolve directly in water and easy to hydrolyze. Dissolving KBr first is to pre-build a high concentration of Br - coordination field. When the subsequent addition of PbBr2 is difficult to dissolve, the high concentration of Br - coordination effect, to promote the formation of Pb 2+ and Br - to form a soluble [PbBr x ] 2-x complex ion. This coordination solubilization strategy is the key prerequisite to realize the high concentration of PbBr2 in aqueous solution and further reaction to generate K2PbBr4. The temperature range is set to 80-98 ℃, which can first break the solubility barrier, and the solubility of K2PbBr4 and PbBr2 increases significantly with the increase of temperature. Below 80 ℃, the solubility of the precursor (especially PbBr2) in KBr aqueous solution is insufficient, which cannot form a high concentration of supersaturated precursor solution, resulting in insufficient crystallization driving force during subsequent cooling, and the yield is extremely low. When the temperature is higher than 98 ℃, the water as solvent will evaporate violently, it is difficult to accurately control the solution concentration, and it is difficult to maintain the stability of the reaction system under normal pressure. Therefore, 80-980 ℃ is the best temperature range to build a high concentration of hot saturated solution.

[0011] The concentration range of KBr solution is the core parameter for adjusting the "matrix-luminescent" ratio. If the concentration is lower than 7 mol / L, the Br - concentration in the solution is insufficient, which cannot provide enough coordination ability to dissolve the subsequent added PbBr2, resulting in the reaction cannot be carried out. If the concentration is higher than 16.3 mol / l, the solution viscosity is too large, the ion diffusion is blocked, and KBr will precipitate too fast during the cooling process, which is easy to wrap the unreacted impurities or cause the increase of crystal defects, affecting the luminous brightness of the fluorescent powder.

[0012] The brightness of the prepared composite phosphor is related to the molar ratio of KBr to PbBr2, which ranges from 2:1 to 100:1. Above 100:1, the K2PbBr4 content is low and the KBr content is high, resulting in a significant decrease in luminescence brightness; below 2:1, PbBr2 cannot be completely dissolved, which introduces PbBr2 into the system, and the luminescence brightness also decreases sharply.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Excellent stability: The phosphor described in this invention is composed of a unique K2PbBr4 / KBr composite phase. This specific microstructure significantly improves the stability of the material. Experiments show that after the composite phosphor is exposed to air for 50 days, its crystal structure remains intact, no impurity peaks appear, and the luminescence performance is stable. (2) Low cost: In terms of raw material selection, the use of inexpensive potassium element significantly reduces the cost of raw materials. The orange-yellow light excited by ultraviolet light is achieved without the need for rare earth ion doping. In terms of synthesis medium, this invention completely replaces the expensive anhydrous organic solvent in the traditional process with deionized water, and does not require the consumption of a large amount of inert protective gas. This combination of "cheap raw materials + cheap solvent" significantly reduces the production cost. (3) Simple process: This invention proposes a new green aqueous phase synthesis process that completely eliminates organic solvents, strong acids, and inert gas protection. The entire preparation process can be carried out at normal pressure and low temperature, without the need for high-temperature and high-pressure reactors or complex vacuum glove boxes. Composite phosphors can be prepared through simple dissolution, stirring, and cooling crystallization steps. This process is simple to operate, has low energy consumption, and mild reaction conditions. Attached Figure Description

[0014] Appendix Figure 1 XRD pattern of the composite phosphor prepared in Example 1; Appendix Figure 2 XRD comparison of fresh and 50-day-old composite phosphor samples prepared in Example 1; Appendix Figure 3 Excitation and emission spectra of the composite phosphor prepared in Example 1. Detailed Implementation Example

[0016] Take 8.5 g potassium bromide and 11.5 g lead bromide, dissolve them successively in 10 mL of deionized water at 83 °C, heat and stir at 500 rpm for 12 h to form a hot saturated supernatant and an undissolved solid precipitate. Separate the supernatant while it is hot, and after cooling and crystallization, dry it in an oven at 70 °C for 12 h to obtain K2PbBr4 / KBr composite phosphor.

[0017] Example 2 Take 10.3 g potassium bromide and 9.7 g lead bromide, dissolve them in 10 mL of deionized water at 85 °C, heat and stir at 600 rpm for 15 h to form a hot saturated supernatant and an undissolved solid precipitate. Separate the supernatant while it is hot, and after cooling and crystallization, dry it in an oven at 75 °C for 12 h to obtain K2PbBr4 / KBr composite phosphor.

[0018] Example 3 Take 14 g of potassium bromide and 6.1 g of lead bromide, dissolve them in 10 mL of deionized water at 90 °C, heat and stir at 700 rpm for 18 h to form a hot saturated supernatant and an undissolved solid precipitate. Separate the supernatant while it is hot, and after cooling and crystallization, dry it in an oven at 80 °C for 12 h to obtain K2PbBr4 / KBr composite phosphor.

[0019] Example 4 Take 16.4 g of potassium bromide and 3.6 g of lead bromide, dissolve them in 10 mL of deionized water at 95 °C, heat and stir at 800 rpm for 20 h to form a hot saturated supernatant and an undissolved solid precipitate. Separate the supernatant while it is hot, and after cooling and crystallization, dry it in an oven at 85 °C for 12 h to obtain K2PbBr4 / KBr composite phosphor.

[0020] Example 5 Take 19.4 g of potassium bromide and 0.6 g of lead bromide, dissolve them in 10 mL of deionized water at 98 °C, heat and stir at 500 rpm for 24 h to form a hot saturated supernatant and an undissolved solid precipitate. Separate the supernatant while it is hot, and after cooling and crystallization, dry it in an oven at 90 °C for 12 h to obtain K2PbBr4 / KBr composite phosphor.

[0021] Results and Analysis: X-ray diffraction analysis was performed on the sample prepared in Example 1 (e.g. Figure 1 As shown in the figure), the results show that the product spectrum matches the standard card, clearly distinguishing the K2PbBr4 phase and the KBr phase. Stability test results ( Figure 2 This indicates that the composite phosphor retains its crystal structure intact after being exposed to air for 50 days. Figure 3 The excitation spectrum (black curve) and emission spectrum (red curve) of this composite phosphor are shown. The excitation spectrum reveals a broad and strong absorption band in the ultraviolet region, enabling effective excitation by common ultraviolet LED chips. Under 365 nm ultraviolet light excitation, the material exhibits bright, broadband emission with a peak centered at approximately 595 nm, displaying a vibrant orange-yellow fluorescence. Combined with its excellent stability and low-cost aqueous preparation process, this composite phosphor possesses significant application value in solid-state lighting, anti-counterfeiting labeling, and photoelectric detection.

Claims

1. A composite phosphor and its preparation method, characterized in that, The composite phosphor contains A wt% K2PbBr4 and (100-A) wt% KBr, wherein A = 5-95, and its preparation method includes the following steps: (1) Dissolve KBr in deionized water at 80–98 °C to obtain a clear KBr solution; (2) Add PbBr2 to the above KBr solution and stir for 12-24 h to obtain a mixed aqueous solution; (3) The product is separated, washed and dried to obtain K2PbBr4 / KBr composite phosphor.

2. The composite phosphor and its preparation method according to claim 1, characterized in that, The molar concentration of the KBr solution in step (1) is 7–16.3 mol / L.

3. The composite mineral phosphor and its preparation method according to claim 1, characterized in that, In step (2), the molar ratio of KBr to PbBr2 is 2:1 to 100:1.

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