A purple fluorescent material based on MOF-derived composite material and a preparation method thereof

Abstract

This invention discloses a purple fluorescent material based on MOF-derived composite materials and its preparation method, belonging to the field of functional materials. The material is a composite material (CuI@C) composed of cuprous iodide nanoparticles and a porous carbon matrix. The preparation method includes: firstly, pyrolyzing a copper-containing MOF to obtain a copper-carbon precursor (Cu@C), and then reacting Cu@C with iodine vapor via a gas-phase iodination method to generate CuI@C. This invention utilizes the spatial confinement and stabilizing effect of the MOF-derived carbon matrix to effectively control the size and defects of CuI, enabling the material to emit only high-purity, single-color purple fluorescence with a center wavelength of approximately 418 nm under ultraviolet light excitation, completely suppressing the red emission commonly found in traditional CuI materials and significantly improving luminescence efficiency. This method is simple, reproducible, and the obtained material has application value in fields such as solid-state lighting and anti-counterfeiting.

Description

Technical Field

[0001] This invention belongs to the field of functional materials technology, specifically relating to a luminescent material, and more particularly to a novel composite material that emits high-purity purple fluorescence under short-wavelength ultraviolet light excitation and its preparation method. This material can be used in solid-state lighting, fluorescent anti-counterfeiting, optical sensing and optical communication devices. Background Technology

[0002] Purple fluorescent materials, especially those emitting wavelengths in the 400-440 nm band, can produce high-purity purple light under ultraviolet light excitation at specific wavelengths. They are key materials for constructing high-color-rendering white LEDs, achieving high-level fluorescent anti-counterfeiting, and short-wavelength optical communication. Cuprous iodide (CuI), as a direct bandgap semiconductor material, has attracted much attention due to its potential optoelectronic properties. Theoretically, CuI can emit blue-violet light under appropriate excitation. However, it is well known to those skilled in the art that bulk or micron-sized CuI crystals prepared by conventional methods (such as hydrothermal methods and precipitation methods) typically have the following inherent defects in their luminescence performance: Impure emission color, accompanied by red emission: Due to the abundance of intrinsic defects (such as copper vacancies, iodine interstitials, etc.) or impurity energy levels within the crystal, its photoluminescence spectrum often exhibits one or more broadened, non-negligible red or deep red emission bands (typically located at 600-750 nm) near the desired blue-violet main peak (~418 nm) or in the longer wavelength direction. This multi-band emission severely reduces the color purity of the violet fluorescence (leading to a higher CIE coordinate y-value), limiting its application in fields requiring high monochromaticity light sources.

[0003] Low luminescence efficiency (quantum yield): The severe nonradiative recombination centers (such as defects and grain boundaries) in bulk CuI cause the excited state energy to be dissipated in the form of heat, resulting in a generally low photoluminescence quantum yield, which is difficult to meet the brightness requirements of practical devices.

[0004] Performance stability is greatly affected by the preparation process: the morphology, grain size and defect concentration of CuI are extremely sensitive to its luminescence performance, while traditional preparation methods require high precision in controlling reaction conditions, have poor reproducibility and large batch-to-batch performance fluctuations.

[0005] To improve the luminescence properties of CuI, existing technologies have made some attempts, such as modulating its optical properties through elemental doping, surface coating, or nano-sizing. However, these methods are often complex in process, or can only partially suppress red emission, making it difficult to fundamentally achieve high-purity, high-efficiency single violet emission, and their improvement on material stability is limited.

[0006] Metal-organic frameworks (MOFs), as porous crystalline materials, offer highly tunable structures, channels, and metal nodes. Using MOFs as precursors, structurally inherited porous carbon-based composites can be obtained through pyrolysis, where metal species are highly dispersed in nanoparticle form and confined within a carbon matrix. This structure provides a unique platform for controlling the size, dispersion, and surrounding chemical environment of functional nanomaterials. However, the application of MOF-derived strategies to prepare high-performance CuI-based purple fluorescent materials, and the utilization of the spatial confinement of the carbon matrix to obtain high-purity single-violet emission, has not yet been publicly reported.

[0007] Therefore, there is a need in the field for a novel method to prepare a purple fluorescent material with high color purity that can effectively overcome the above-mentioned defects of traditional CuI materials. Summary of the Invention

[0008] This invention aims to solve the technical problems of impure luminescence color (accompanied by red emission) and the significant influence of preparation process on the performance of existing cuprous iodide-based fluorescent materials. It provides a novel composite material with simple process, good reproducibility, and high purity purple luminescence, as well as its preparation method.

[0009] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: This invention provides a purple fluorescent material based on MOF-derived composite materials, which is a composite material composed of CuI nanoparticles and a porous carbon matrix, denoted as CuI@C.

[0010] The CuI nanoparticles are highly dispersed in the channels or surface of the porous carbon matrix, with an average particle size of 1-50 nm, preferably 2-20 nm.

[0011] The porous carbon matrix is ​​derived from the pyrolysis derivative of copper-containing metal-organic framework (Cu-MOF) compounds and has a hierarchical porous structure inherited from the precursor MOF.

[0012] Under ultraviolet light excitation at wavelengths of 250-380 nm, the CuI@C composite material emits only a single fluorescence peak located in the range of 410-430 nm with a full width at half maximum (FWHM) of less than 70 nm. Its y-value in the CIE 1931 chromaticity coordinates is less than 0.10, preferably less than 0.08, and there is no obvious fluorescence emission in the wavelength range of 600-800 nm.

[0013] In a second aspect, the present invention provides a method for preparing the purple fluorescent material as described in the first aspect, comprising the following steps: S1. Preparation of copper-carbon precursor (Cu@C): Under an inert atmosphere, copper-containing metal-organic framework (Cu-MOF) compounds were subjected to programmed temperature pyrolysis to obtain a precursor Cu@C in which copper nanoparticles are embedded in porous carbon; S2. Solid-phase iodination reaction: The Cu@C obtained in step S1 and elemental iodine are physically isolated in a sealed container and subjected to a gas-phase iodination reaction at 30-80℃ for 2-24 hours, so that the iodine vapor reacts with the copper nanoparticles in Cu@C to generate CuI@C composite material. S3. Post-processing: After the reaction is complete, the product is removed, and the residual iodine adsorbed by physical adsorption is removed to obtain the target purple fluorescent material CuI@C.

[0014] Preferably, in step S1, the copper-containing metal-organic framework compound is HKUST-1 (also known as Cu3(BTC)2, BTC = 1,3,5-benzenetricarboxylic acid). The pyrolysis procedure is as follows: under an inert atmosphere, the temperature is increased to 200-300°C at a rate of 5-15°C / min, then increased slowly to 350-500°C at a rate of 1-5°C / min, and held at this temperature for 60-180 minutes, followed by natural cooling to room temperature.

[0015] Preferably, in step S2, the mass ratio of Cu@C to elemental iodine is 1:(2-10). The sealed container is a sealable glass or quartz container. The iodination reaction temperature is preferably 35-45℃, and the reaction time is preferably 6-12 hours.

[0016] Compared with the prior art, the present invention has the following significant advantages: Achieving ultra-high color purity single-color purple emission: Through the spatial confinement effect of the MOF-derived carbon matrix, the size and growth of CuI nanoparticles were effectively controlled, suppressing the formation of large grains and specific defects in the bulk material that easily lead to red emission. Simultaneously, the surface passivation effect of the carbon matrix on the CuI nanoparticles further reduced surface defect states. The synergistic effect of these two factors completely suppressed the red-band emission commonly found in traditional CuI materials, resulting in pure purple emission (center wavelength ~418 nm) with a narrow half-maximum width at half-maximum (HWHM) and extremely low CIE-y value.

[0017] The process is simple, reproducible, and highly stable: This invention employs a two-step method (pyrolysis + gas-phase iodization), with readily available raw materials, simple operation, and no need for complex equipment. The structural uniformity of the MOF precursor ensures batch-to-batch consistency of product performance.

[0018] This invention provides a new approach to materials design: It successfully applies the MOF derivatization strategy to the controllable preparation of copper halide-based fluorescent materials, providing a new paradigm for the precise control of the composition, structure and properties of functional nanocomposites through precursor engineering. Attached Figure Description

[0019] Figure 1 The image shows the photoluminescence (PL) spectrum of the CuI@C composite material prepared in Example 1 of this invention under 325 nm ultraviolet light excitation. The inset is a magnified view (400-500 nm), showing no red emission.

[0020] Figure 2 This is a digital photograph of the CuI@C composite material prepared in Example 1 of the present invention under 325 nm ultraviolet light irradiation, showing bright purple fluorescence. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. The following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods not specifically described in the embodiments are generally performed under conventional conditions or as recommended by the manufacturer.

[0022] Example 1: Preparation of CuI@C composite material 1. Preparation of Cu@C precursor: a. Raw materials: Purchase commercially available HKUST-1 powder.

[0023] b. Pyrolysis: Weigh 0.090 g of HKUST-1 powder and spread it evenly in a quartz boat. Place the quartz boat in the isothermal zone of a tube furnace. Purge the furnace tube with high-purity argon gas (flow rate 50 sccm) for 30 minutes to purge air. Then, under argon atmosphere protection, raise the temperature from room temperature to 250°C at a rate of 10°C / min, then raise it slowly to 400°C at a rate of 2°C / min, and hold at 400°C for 120 minutes.

[0024] c. Cooling: After the reaction is complete, stop heating and maintain the argon flow to allow the sample to cool naturally to room temperature (<50℃) in the tube furnace. Remove the sample to obtain a black powder, which is the Cu@C precursor.

[0025] Preparation of CuI@C by gas-phase iodination: a. Apparatus: A 50 mL glass weighing bottle with a ground glass stopper is used as the reaction vessel.

[0026] b. Sample loading: Spread approximately 0.090 g of the prepared Cu@C powder (actual mass may be slightly reduced) in a quartz boat. Separately weigh 0.40 g of iodine particles and place them at the bottom of the same glass container, ensuring that the iodine particles do not have direct physical contact with the quartz boat containing Cu@C.

[0027] c. Reaction: Quickly tighten the container lid and place it in a preheated drying oven at 40°C. Maintain the reaction at 40°C for 8 hours. During this process, iodine sublimates into purple vapor, filling the container and reacting with the copper nanoparticles in Cu@C in a solid-gas reaction.

[0028] d. Post-processing: After the reaction is complete, remove the container and open it in a fume hood. Transfer the product (now a pale yellow powder) along with the quartz boat to a petri dish and place it in a vacuum drying oven at 40°C for 2 hours to remove physically adsorbed residual iodine. The final product is obtained and denoted as CuI@C-1.

[0029] Optical performance: The PL spectrum was measured using a fluorescence spectrometer under 325 nm laser excitation. The results are as follows: Figure 1 As shown, the sample exhibits only a single symmetrical strong emission peak (centered at 418 nm). In the long-wavelength region of 600-800 nm, the signal intensity is comparable to the baseline noise, and no distinguishable emission peaks were detected, demonstrating the singularity of the emission. Under UV illumination, the sample emits bright, uniform purple fluorescence. Figure 2 ).

[0030] Example 2: Effect of different pyrolysis temperatures The final pyrolysis temperature in step 1 of Example 1 was changed to 350℃ and 450℃, while other conditions remained unchanged, and samples CuI@C-350 and CuI@C-450 were prepared respectively.

[0031] Results: CuI@C-350 exhibited slightly weaker CuI crystallinity and smaller particles (3-8 nm), with a slight blue shift of the emission peak to 415 nm. CuI@C-450 showed better CuI crystallinity and slightly larger particles (8-20 nm), with the emission peak located at 420 nm, but a slightly increased full width at half maximum (FWHM). No red emission was observed in any of the samples. This indicates that the pyrolysis temperature can adjust the particle size and luminescence properties of the products within a certain range.

[0032] Example 3: Effect of different iodization times The iodination reaction time in step 2 of Example 1 was changed to 4 hours and 12 hours.

[0033] Results: XRD analysis of the sample reacting for 4 hours showed a small amount of residual copper and low PL intensity. Samples reacting for 8 and 12 hours showed complete copper conversion to CuI, with similar PL properties. This indicates that 8 hours was sufficient to complete the reaction.

[0034] Comparative Example 1: Control experiment without carbon matrix confinement Without going through the MOF pyrolysis step, copper nanoparticles with an average particle size of about 50 nm, which have a similar copper content to those in HKUST-1, were directly reacted with iodine vapor under the same conditions (40℃, 8h).

[0035] Results: Micron-sized CuI aggregates were obtained. A strong emission band was observed at 680 nm, but the purity of the purple luminescence was poor; this demonstrates that the spatial confinement effect of the MOF-derived carbon matrix is ​​crucial for obtaining high-purity purple luminescence.

[0036] In summary, this invention successfully prepared a high-performance CuI@C purple fluorescent composite material through a clever MOF derivatization and gas-phase iodization strategy, effectively solving the problem of impure luminescence in traditional CuI materials, and has broad application prospects in the field of advanced lighting and display.

Claims

1. A purple fluorescent material based on MOF-derived composite materials, characterized in that, The material is a composite material CuI@C composed of cuprous iodide nanoparticles and a porous carbon matrix; wherein the cuprous iodide nanoparticles are dispersed in the porous carbon matrix; the material emits a single fluorescence peak with a center wavelength of 410-430 nm and a full width at half maximum (FWHM) of less than 70 nm when excited by ultraviolet light with a wavelength of 250-380 nm, and there is no obvious fluorescence emission in the wavelength range of 600-800 nm.

2. The purple fluorescent material according to claim 1, characterized in that, The average particle size of the cuprous iodide nanoparticles is 1-100 nm.

3. The purple fluorescent material according to claim 1, characterized in that, The porous carbon matrix is ​​derived from the pyrolysis derivatives of copper-containing metal-organic framework compounds.

4. The purple fluorescent material according to claim 3, characterized in that, The copper-containing metal-organic framework compound is HKUST-1.

5. A method for preparing a purple fluorescent material as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Under an inert atmosphere, copper-containing metal-organic framework compounds were subjected to programmed temperature pyrolysis to obtain the copper-carbon precursor Cu@C; S2. Place the Cu@C obtained in step S1 and elemental iodine in a sealed container and carry out a gas-phase iodization reaction at 30-80°C for 2-24 hours to allow the copper in the Cu@C to react with the iodine vapor and generate the CuI@C composite material.

6. The method according to claim 5, characterized in that, In step S1, the pyrolysis procedure is as follows: under an inert atmosphere, the temperature is increased to 200-300℃ at a rate of 5-15℃ / min, and then increased to 350-500℃ at a rate of 1-5℃ / min and held for 60-180 minutes.

7. The method according to claim 5, characterized in that, In step S2, the mass ratio of Cu@C to elemental iodine is 1:(2-10).

8. The method according to claim 5, characterized in that, In step S2, the Cu@C and elemental iodine are physically isolated in the sealed container.

9. The method according to claim 5, characterized in that, In step S2, the temperature of the gas-phase iodination reaction is 35-45℃, and the reaction time is 6-12 hours.

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