Blue light excitable cu-based fluorescent material and preparation method thereof

Abstract

The application belongs to the field of photoelectric functional materials, and discloses a blue light excitable Cu-based fluorescent material and a preparation method thereof. The material is obtained by room temperature reaction of 4-pytrz and halogenated cuprous CuX (X=Br, I), wherein 4-pytrz is 4-(4H-1,2,4-triazole-4-yl)pyridine. Two highly stable coordination polymers, complex 1 [CuBr(4-pytrz)2] n and complex 2 [Cu2I2(4-pytrz)] n are designed and synthesized, which have good thermal stability, exhibit a wide excitation band covering from deep ultraviolet light to blue light region, and have a quantum efficiency of 19.36% under blue light excitation. The complexes exhibit effective solid-state emission and enhanced light stability, and have wide application prospects.

Description

Technical Field

[0001] The present invention belongs to the field of optoelectronic functional materials, and in particular relates to a blue light-excitable Cu-based fluorescent material and a preparation method thereof. Background Art

[0002] Light-emitting diodes (LEDs) are attractive candidates for next-generation lighting and display applications due to their high efficiency, long operating lifetime, and high reliability. A white correlated color temperature (CCT) with a high color rendering index (CRI) can be achieved by using a blue LED chip to excite a yellow phosphor. Advanced commercial yellow LEDs are made from direct-bandgap III-V semiconductors, such as InGaN and AlGaInP, via expensive high-vacuum and high-temperature thin-film growth processes such as molecular beam epitaxy and metal-organic chemical vapor deposition. In an era of scarce natural resources, high manufacturing costs limit their use in large-scale lighting and displays. Considering the sustainability and environmental friendliness of LED technology, the development of inexpensive metal complexes as efficient yellow phosphors to replace rare-earth-based wLEDs is highly desirable.

[0003] In recent years, metal halide complexes have been widely studied as promising phosphors due to their broad excitation bands, tunable emission bands, and high brightness in the ultraviolet region. Cubic copper halide clusters with the structural formula [Cu4X4L4] (X = Cl, Br, I; L = N or p-terminal ligand) exhibit excellent photoluminescence (PL) with high quantum yields. However, a major drawback of these complexes is their low photochemical stability under UV irradiation. Furthermore, such complexes typically exhibit poor absorption bands in the visible region, making them unsuitable for blue gallium nitride (GaN) LED chips. Broad-excitation LEDs offer several advantages, including high energy efficiency, long lifetime, fast start-up, durability, small size, environmental friendliness, dimming capability, color selection, low heat generation, controllability, cost-effectiveness, and ease of integration. Therefore, developing high-performance Cu(I)-based white LEDs with a broadband excitation band and superior thermal stability to meet the requirements of commercial applications remains a challenge. Summary of the Invention

[0004] The present invention aims to provide a blue-light-excitable Cu-based fluorescent material and a preparation method thereof. The raw materials of the fluorescent material are readily available, the preparation method is simple, the yield is high, and the material has good thermal stability. The material exhibits a wide excitation band covering the deep ultraviolet to blue light regions, and its quantum efficiency under blue light excitation can reach 19.36%. The material is a highly efficient LED photoluminescent material with broad application prospects.

[0005] The above technical objectives of the present invention are achieved through the following technical solutions:

[0006] The first aspect of the present invention provides a blue light-excitable inexpensive Cu-based fluorescent material, the structural formula of which is: Complex 1 [CuBr(4-pytrz)2] n and complex 2 [Cu2I2(4-pytrz)] n ; Wherein 4-pytrz is 4-(4H-1,2,4-triazol-4-yl)pyridine.

[0007] Complex 1 crystallized in the orthorhombic 'I ba m' space group with the crystal parameters a = 22.2556(2)Å, b = 12.92070(10)Å, c = 13.3239(2)Å, α = 90°, β = 90°, γ = 90°, Z = 4, V = 3831.39(7)Å 3 The asymmetric unit of complex 1 consists of a crystallographically unique Cu(I) and two ligands 4-pytrz. The connections of 4-pytrz are disordered and have two connection modes, forming a two-dimensional (2D) MOF assembled by connecting CuBr and organic ligands 4-pytrz.

[0008] Complex 2 crystallized in the orthorhombic 'P 21 21 2' space group with crystal parameters of a = 11.5513(12) Å, b = 14.4556(15) Å, c = 6.3291(7) Å, α = 90°, β = 90°, γ = 90°, Z = 4, V = 1056.84(19) Å 3 Complex 2 is characterized by Cu2I2 interconnected to form a single-chain ladder ribbon extending along the crystallographic a-axis, with 4-pytrz segments connecting [CuI] n The ribbons are stacked along both sides of the copper iodide skeleton and extend along the crystallographic b-axis to form a two-dimensional (2D) MOF assembled by connecting Cu2I2 and 4-pytrz.

[0009] A second aspect of the present invention provides a method for preparing the above-mentioned blue light excitable inexpensive metal Cu-based fluorescent material, the method comprising:

[0010] S1. Preparation of the organic ligand 4-pytrz: Under inert gas, 4-aminopyridine and N,N'-bis(dimethylaminomethylene)hydrazine were placed in a flask, p-toluenesulfonic acid monohydrate and xylene were added, and the mixture was stirred and heated under reflux for 23-24 hours. After the reaction, the xylene was poured out, and the residue was washed with petroleum ether to remove the N,N-bis(dimethylaminomethylene)hydrazine. The remaining solid was added with dichloromethane until just dissolved, and then the same volume of petroleum ether was added and recrystallized at low temperature to obtain a pure needle-shaped solid, which is the organic ligand 4-pytrz.

[0011] S2. Preparation of the complex: 4-pytrz and CuX (X = Br, I) were added separately to acetonitrile solvent, stirred thoroughly, and filtered to remove the precipitate. The resulting filtrate was placed in a beaker, sealed with plastic wrap and punctured, and allowed to evaporate at room temperature for 1.5-3.5 days. Colorless, transparent crystals were filtered to obtain the complex. The crystals were washed with solvent and distilled water, and dried to obtain pure yellow crystals. This preparation method utilizes readily available raw materials, is simple, and has a high yield.

[0012] Furthermore, in step S1, the molar ratio of 4-aminopyridine, N,N'-bis(dimethylaminomethylene)hydrazine, and p-toluenesulfonic acid monohydrate is (74.4 ~ 75.1): (163.6 ~ 164.1): (7.0 ~ 7.21);.

[0013] Furthermore, in step S1, the stirring and heating reflux treatment is carried out for 23 h to 24 h, and the heating reflux temperature is 160° C. to 162° C.

[0014] Furthermore, in step S2, the molar ratio of 4-pytrz to CuX is (0.09 ~ 0.11): (0.04 ~ 0.06); the volume of the acetonitrile solvent is 20 ml ~ 22 ml.

[0015] Furthermore, in the step S2, the standing volatilization is performed at a volatilization temperature of 15° C. to 25° C.

[0016] A third aspect of the present invention provides the use of the above-mentioned blue light-excitable inexpensive metal Cu-based fluorescent material in a light emitting diode (LED).

[0017] The new, inexpensive, blue-light-excitable Cu-based fluorescent materials synthesized in this study exhibit efficient solid-state emission and enhanced photostability under blue light irradiation. The blue light excitation wavelength range is 400 nm to 470 nm, and the quantum efficiency under blue light excitation is 19.36%. Cu-based fluorescent materials are promising blue-light-excitable phosphors with great potential for application in full-spectrum white LEDs.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) The present invention provides broad-excitation Cu(I)-based fluorescent materials. Complexes 1 and 2 both exhibit broad excitation bands covering the deep ultraviolet to blue region. The photoluminescence quantum yields (PLQYs) of complexes 1 and 2 in the solid state are 5.76% and 19.36%, respectively.

[0020] (2) The organic ligand 4-pytrz provided by the present invention has a simple preparation method and can be connected and assembled with inexpensive CuX to obtain a two-dimensional (2D) Cu-based complex. The preparation method is simple and the yield is high.

[0021] (3) The quantum efficiency can reach 19.36% under blue light excitation. The complex exhibits effective solid-state emission and enhanced photostability, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings in the embodiments are briefly introduced below.

[0023] Figure 1 The X-ray crystal structures of complexes 1 and 2 are shown; hydrogen atoms are omitted.

[0024] Figure 2 is the infrared spectrum of the complex and the organic ligand 4-pytrz;

[0025] Figure 3 is the powder X-ray diffraction pattern of complexes 1 and 2;

[0026] Figure 4 Thermogravimetric diagrams of complexes 1 and 2;

[0027] Figure 5 are the fluorescence excitation and emission spectra of complexes 1 and 2;

[0028] Figure 6 is the photoluminescence quantum efficiency of complexes 1 and 2 measured at 298K;

[0029] Figure 7 is the PL lifetime decay curve of complexes 1 and 2;

[0030] Figure 8 Temperature-dependent photoluminescence spectra of complexes 1 and 2;

[0031] Figure 9 The temperature-dependent CIE diagrams of complexes 1 and 2. DETAILED DESCRIPTION

[0032] The following further describes a method for preparing a blue light-excitable inexpensive Cu-based fluorescent material and its technical effects. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0033] In the following specific embodiments of the present invention, a method for preparing a blue light-excitable inexpensive Cu-based fluorescent material comprises the following steps:

[0034] S1. Preparation of organic ligand 4-pytrz: Under inert gas protection, 4-aminopyridine (74.4 ~ 75.1 mmol) and N,N'-bis(dimethylaminomethylene)hydrazine (163.6 ~ 164.1 mmol) were placed in a flask, p-toluenesulfonic acid monohydrate (7.0 ~ 7.21 mmol) and xylene (80 ~ 85 mL) were added, and the mixture was heated to reflux at 160°C ~ 162°C for 23~24 h. After the reaction, the xylene was poured out, and the residue was washed with petroleum ether to remove the N,N-bis(dimethylaminomethylene)hydrazine. The remaining solid was added with dichloromethane until just dissolved, and then the same volume of petroleum ether was added and recrystallized at a low temperature of 14~15°C to obtain a pure needle-shaped solid, which is the organic ligand 4-pytrz.

[0035] S2. Preparation of the complex: 4-pytrz (0.09-0.11 mmol) and CuX (X = Br, I) (0.04-0.06 mmol) were separately added to acetonitrile solvent (20-22 mL), stirred and filtered to remove the precipitate, the mixed solution was sealed with plastic wrap in a beaker and pierced with holes, evaporated at room temperature for 3 days, filtered to obtain colorless transparent crystals, washed with solvent and distilled water, and dried to obtain pure yellow crystals.

[0036] The details of the reagents involved in the experiment are shown in Table 1; the reagents involved were used directly without further purification. The equipment and instruments used in the experiment are shown in Table 2.

[0037] Table 1 Reagents

[0038]

[0039] Table 2 Main instruments

[0040]

[0041] The present invention is described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention. Example 1

[0042] The present invention proposes a method for preparing a blue light-excitable inexpensive Cu-based fluorescent material. The method comprises a single crystal structure, and the molecular formula of the single crystal structure of the complex material is: the structural formula of the complex 1 is [CuBr(4-pytrz)2] n The structural formula of complex 2 is [Cu2I2(4-pytrz)] n ; Wherein, 4-pytrz is 4-(4H-1,2,4-triazol-4-yl)pyridine.

[0043] The specific preparation method is as follows:

[0044] S1. Preparation of the organic ligand 4-pytrz: Under inert gas, 4-aminopyridine (7.06 g, 74.4 mmol) and N,N'-bis(dimethylaminomethylene)hydrazine (23.23 g, 163.6 mmol) were placed in a flask. p-Toluenesulfonic acid monohydrate (1.33 g, 7.0 mmol) and 80.0 mL of xylene were added, and the mixture was heated to reflux at 160°C for 24 h. After the reaction, the xylene was decanted, and the residue was washed with petroleum ether to remove the N,N'-bis(dimethylaminomethylene)hydrazine. The remaining solid was added to dichloromethane until dissolved, and then the same volume of petroleum ether was added and recrystallized at low temperature to obtain pure needle-shaped solid 4-(4H-1,2,4-triazol-4-yl)pyridine in a yield of 64.72%.

[0045] S2. Preparation of complex 1: 4-pytrz (14.6 mg, 0.1 mmol) and CuBr (7.2 mg, 0.05 mmol) were separately added to 20 mL of acetonitrile solvent, stirred and filtered to remove the precipitate, the mixed solution was sealed with plastic wrap in a beaker and punctured, and evaporated at room temperature for 3 days. Colorless transparent crystals were obtained by filtration, washed with solvent and distilled water, and dried to obtain pure yellow crystals with a yield of 48.96%.

[0046] S3. Preparation of complex 2: 4-pytrz (14.6 mg, 0.1 mmol) and CuI (9.5 mg, 0.05 mmol) were separately added to 20 mL of acetonitrile solvent, stirred and filtered to remove the precipitate, the mixed solution was sealed with plastic wrap in a beaker and punctured, and evaporated at room temperature for 3 days. Colorless transparent crystals were obtained by filtration, washed with solvent and distilled water, and dried to obtain pure yellow crystals with a yield of 56.72%. Example 2

[0047] Crystals prepared by solvothermal method were collected under microscope, and crystallographic data of the complex were obtained on a Bruker APEX-II CCD instrument equipped with graphite monochromator Mo Kα (λ = 0.71073 Å), collected at the corresponding temperature. Data collection, data reduction, and unit optimization were performed using the Bruker Instrument Service v4.2.2 and SAINT V8.34A packages. The structure of the complex was solved using the SHELXS package, and the crystal data were optimized using the full matrix least squares method using the SHELXL package. Absorption correction was performed using the multi-scan package SADABS. The hydrogen atoms of the organic ligands were detected using the riding mode of the SHELXTL package in F 2Anisotropic optimization was performed on the 3D-Hydroxy-2-[4-[4-(4-oxo-3-nitrogen)]-1-[ ...

[0048] Table 3 Crystallographic parameters of the complexes

[0049] .

[0050] Table 4 Important bond lengths (Å) and bond angles (°) in the complex crystal structures

[0051] Example 3

[0052] Infrared absorption spectroscopy analysis: Figure 2 As shown in the figure, the black line is the infrared absorption spectrum of the ligand 4-pytrz, and the red line is the infrared absorption spectrum of the complex. From this figure, it can be seen that the absorption spectrum of the complex and the absorption spectrum of the ligand are very consistent, indicating that the organic ligand is indeed present in the complex. Example 4

[0053] Powder X-ray diffraction analysis: Figure 3 As shown, the black spectrum is the XRD pattern of the complex powder, and the red spectrum is the result obtained from the single crystal X-ray diffraction (SC-XRD) data. It can be seen from the figure that the experimental value and the simulation value of the complex are in very good agreement, indicating that the complex is a pure phase. Example 5

[0054] Thermogravimetric analysis: Figure 4 The thermal stability of the complexes was investigated using thermogravimetric analysis (TGA), as shown in Figure 2. The TGA curves reveal high thermal stability and a two-step decomposition of both complexes. Complex 1 exhibits an initial weight loss of approximately 21% to 24% between 280°C and 500°C, due to the removal of halogens and some ligands. Complex 2 exhibits an initial weight loss of approximately 31% to 34% between 500°C and 800°C, while the second weight loss between 500°C and 800°C can be attributed to the complete removal of the remaining ligands. Example 6

[0055] Fluorescence test: Figure 5 As shown, complexes 1 and 2 exhibit wide excitation band coverage from deep ultraviolet light to blue light. Under excitation at 470 nm, complex 1 exhibits a strong emission band centered at 615 nm, which is orange light emission with a full width at half maximum (FWHM) of approximately 122 nm. Under excitation at 400 nm, complex 2 exhibits a strong emission band centered at 555 nm, which is yellow light emission with a full width at half maximum (FWHM) of approximately 136 nm. Figure 6As shown in Figure 2, the photoluminescence quantum yields (PLQY) of complexes 1 and 2 in the solid state are 5.76% and 19.36%, respectively. Figure 7 The photoluminescence (PL) decay curve is shown as a double exponential decay. The PL lifetimes of complexes 1 and 2 are 1.26 μs and 2.47 μs, respectively. The solid-state photophysical data of the complexes at room temperature are shown in Table 5. The fluorescence decay rate of the complexes ( k r ) ( k r = Φ PL τ −1 ) are 4.57 × 10 4 s −1 and 7.48 × 10 4 s −1 Considering Φ PL = k r / ( k r + k nr ),in k nr is the rate of the non-radiative process including non-radiative singlet decay and ISC, k nr The estimated values ​​were 7.48 × 10 5 s −1 and 3.26 × 10 5 s −1 .

[0056] Table 5 Solid-state photophysical data of the complexes at room temperature

[0057]

[0058] a Radiative rate constant calculated K r = Φ / τ. b Nonradiative rateconstant calculated K nr = (1-Φ) / τ. Example 7

[0059] Temperature-dependent photoluminescence spectroscopy analysis: Figure 8As shown in the temperature-dependent (TD) emission spectra, complexes 1 and 2 have similar luminescence temperature dependence, both exhibiting a thermal quenching effect, and the temperature-related emission changes of complexes 1 and 2 are slightly different. As the temperature gradually increases from 80 K to 500 K, the emission center of complex 1 exhibits a small blue shift of approximately 10 nm, while the emission center of complex 2 exhibits a 10 nm red shift when the temperature gradually increases from 80 K to 320 K, and then a 25 nm blue shift when the temperature increases to 500 K.

[0060] The change of CIE coordinates is consistent with the change of maximum emission wavelength with temperature. Figure 9 The corresponding CIE coordinates of complex 1 change from (0.6133, 0.3857) at 80 K to (0.5503, 0.4446) at 500 K. The corresponding CIE coordinates of complex 2 change from (0.4355, 0.535) at 80 K to (0.4407, 0.5201) at 320 K and finally to (0.3753, 0.5393) at 500 K.

[0061] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A blue light-excitable Cu-based fluorescent material, characterized in that: The blue light-excitable Cu-based fluorescent material is complex 1 or complex 2, and the structural formula of complex 1 is: [CuBr(4-pytrz)2] n The structural formula of the complex 2 is: [Cu2I2(4-pytrz)] n , wherein 4-pytrz is 4-(4H-1,2,4-triazol-4-yl)pyridine, and n is an integer greater than or equal to 1.

2. The blue light excitable Cu-based fluorescent material according to claim 1, characterized in that: The unit cell parameters of the complex 1 are a = 22.2556(2) Å, b = 12.92070(10) Å, c = 13.3239(2) Å, α = 90°, β = 90°, γ = 90°, Z = 4, V = 3831.39(7) Å 3 ; The unit cell parameters of the complex 2 are a = 11.5513(12) Å, b =14.4556(15) Å, c = 6.3291(7) Å, α = 90°, β = 90°, γ = 90°, Z = 4, V = 1056.84(19)Å 3 .

3. The method for preparing a blue light excitable Cu-based fluorescent material according to claim 1 or 2, characterized in that: The steps include: S1. Preparation of organic ligand 4-pytrz: Under inert gas protection, 4-aminopyridine and N,N'-bis(dimethylaminomethylene)hydrazine were added to a reactor, p-toluenesulfonic acid monohydrate and xylene were added, and the mixture was stirred, heated and refluxed. After the reaction was completed, the reaction product was collected, washed with petroleum ether, dissolved in dichloromethane, and recrystallized by adding an equal volume of petroleum ether to obtain 4-(4H-1,2,4-triazol-4-yl)pyridine, abbreviated as 4-pytrz; S2. Preparation of complex: 4-pytrz, CuX, X = Br or I were added to acetonitrile solvent, stirred thoroughly, and filtered. The filtrate was sealed in a beaker with plastic wrap and pierced with holes. The beaker was allowed to stand for evaporation. The product was precipitated, filtered, washed, and dried to obtain the complex, wherein X = Br was used to synthesize complex 1, and X = I was used to synthesize complex 2.

4. The method for preparing a blue light excitable Cu-based fluorescent material according to claim 3, wherein: In step S1, the molar ratio of 4-aminopyridine, N,N'-bis(dimethylaminomethylene)hydrazine, and p-toluenesulfonic acid monohydrate is 74.4-75.1: 163.6-164.1: 7.0-7.

2.

5. The method for preparing a blue light excitable Cu-based fluorescent material according to claim 3, wherein: In step S2, the molar ratio of 4-pytrz to CuX is 0.09-0.11: 0.04-0.

06.

6. The method for preparing a blue light excitable Cu-based fluorescent material according to claim 3, wherein: In the step S1, the stirring and heating reflux treatment time is 23 h to 24 h, and the reflux heating temperature is 160° C. to 162° C.

7. The method for preparing a blue light excitable Cu-based fluorescent material according to claim 3, wherein: In the step S2, the temperature for standing and volatilizing is 15° C. to 25° C., and the time for standing and volatilizing is 1.5 to 3.5 days.

8. Application of the blue light excitable Cu-based fluorescent material according to claim 1 or 2 in the field of light emitting diodes.

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