A cheap metal-organic fluorescent material for high-power LED lighting

Abstract

The present invention discloses the preparation and application of a cheap metal-organic fluorescent material for high-power LED lighting. The chemical formula of the complex is: [Cu₄I₄(bbimb)₂]ₙ, where the ligand bbimb is 1,2-bis((1H-benzoimidazol-1-yl)methyl)benzene, and its chemical formula is: C₂₂H₁₈N₄; the complex crystal belongs to the monoclinic system, the space group of the complex is P21 / c, and the crystal parameters of the complex are a = 11.3850(3) Å, b = 16.1962(3) Å, c = 26.8795(6) Å, α = 90°, β = 98.879(2)°, γ = 90°, Z = 4, V = 4897.02(19) ų. The present invention also provides a preparation method of the complex, which is simple, has good stability and high yield. The obtained complex shows orange fluorescence emission under the irradiation of a 365 nm ultraviolet lamp. And a large temperature range of zero thermal quenching occurs in the temperature range from 80 K to 500 K, and its fluorescence intensity hardly quenches with the increase of temperature, having broad application prospects in the field of ZTQ materials. Moreover, the optical properties of the LED assembled with the complex as the material are studied, and the LED shows good white light emission performance under high-throughput current.

Description

Technical Field

[0001] The present invention relates to the field of crystalline functional materials, and particularly to the preparation and application of a cheap metal-organic fluorescent material for high-power LED lighting. Background Art

[0002] Light-emitting diodes (LEDs) have been widely used as a new generation of light sources due to their high efficiency, long operating life, high reliability, etc. White LEDs (w-LEDs) with a high color rendering index (CRI) and a low correlated color temperature (CCT) in indoor lighting are usually obtained by using a blue light-emitting LED chip to excite a yellow phosphor. For example, a blue InGaN LED chip (440 - 480 nm) and a yellow Y3Al5O 12 :Ce 3+ (YAG:Ce 3+ ) phosphor is commonly used in the manufacture of commercial w-LEDs. Considering sustainable development and environmentally friendly LED technologies, it is highly necessary to develop cheap metal complexes as efficient yellow phosphors to replace rare-earth w-LEDs.

[0003] In recent years, copper halide complexes have been widely studied as promising fluorescent agents due to their wide excitation bands, tunable emission bands, and high quantum yields in the ultraviolet region. Among them, metal halide cubic clusters with the molecular formula [M4X4L4] (M = Cu(I), X = Cl, Br, I; L = N- or P-terminal ligand) are excellent molecular fluorophores with high quantum yields. However, a major drawback of such complexes is their low photochemical stability under ultraviolet irradiation conditions. For example, such complexes usually exhibit poor absorption bands in the visible region and are not suitable for blue light-emitting gallium nitride LED chips.

[0004] Therefore, the development of high-performance copper-containing white LEDs that meet the requirements of commercial applications and have high quantum efficiency and excellent thermal stability remains a challenge. Summary of the Invention

[0005] To solve the problem of poor photochemical stability of existing fluorescent agents, the present invention provides the preparation and application of a cheap metal-organic fluorescent material for high-power LED lighting.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A cheap metal-organic fluorescent material for high-power LED lighting, wherein the organic fluorescent material is a complex with the chemical formula: [Cu4I4(bbimb)2] n , where the ligand bbimb is 1,2-bis((1H-benzoimidazol-1-yl)methyl)benzene, and its chemical formula is: C 22 H18 N4, where n ≥ 1 in the above chemical formula; the complex crystal belongs to the monoclinic system, the space group of the complex is P21 / c, and the crystal parameters of the complex are α = 90°, β = 98.879(2)°, γ = 90°, Z = 4,

[0008] Furthermore, Cu in the complex + is four-coordinated and forms a tetrahedral configuration of Cu4I4 by connecting with four I atoms in different spatial environments; the halogen atoms in the complex come from CuI in the raw materials, and the N atoms come from two bbimb ligands; in the complex, the bbimb ligand is connected to Cu4I4 to form a one-dimensional chain structure.

[0009] The present invention provides a method for preparing the above complex, including the following reaction steps:

[0010] Add a mixed solvent of cuprous iodide, ligand 1,2-bis((1H-benzoimidazol-1-yl)methyl)benzene, acetonitrile and methanol into a reaction kettle, carry out a heating reaction, then naturally cool to room temperature, filter to obtain crystals, wash the above crystals repeatedly with distilled water and acetonitrile, and dry in air to obtain the complex.

[0011] Furthermore, the molar ratio of ligand 1,2-bis((1H-benzoimidazol-1-yl)methyl)benzene to cuprous iodide is 0.09 - 0.11:0.09 - 0.11.

[0012] Furthermore, the volume ratio of acetonitrile to methanol is 5.9 - 6.1:1.9 - 2.1.

[0013] Furthermore, the temperature of the heating reaction is 115°C - 125°C, and the reaction time is 70 - 74 hours.

[0014] Furthermore, the method for preparing the above ligand 1,2-bis((1H-benzoimidazol-1-yl)methyl)benzene includes the following reaction steps:

[0015] Add DMF solvent to benzimidazole and stir for 10 minutes, then add an aqueous KOH solution, stir for 15 - 25 minutes, slowly add o-dichlorobenzyl, stir for 4 - 6 hours, then add water to the reaction mixture, continue to stir for 1 hour, and finally filter and dry the mixture to obtain ligand 1,2-bis((1H-benzoimidazol-1-yl)methyl)benzene.

[0016] Furthermore, the molar ratio of o-dichlorobenzyl, benzimidazole, and KOH required for the synthesis of ligand 1,2-bis((1H-benzoimidazol-1-yl)methyl)benzene is 12.4 - 12.6:24.9 - 25.1:24.9 - 25.1; the volume of the DMF:water is 25 - 35 ml:15 - 25 ml.

[0017] Further, the temperature required for the synthesis of 1,2-bis((1H-benzimidazol-1-yl)methyl)benzene is 20 °C - 30 °C. After adding the aqueous KOH solution, the stirring reaction time is 20 minutes, and after adding o-dichlorobenzyl, the stirring reaction time is 4 hours.

[0018] Further, the application of the complex in full-spectrum white LEDs.

[0019] Advantages of the present invention:

[0020] The present invention has developed a new complex [Cu4I4(bbimb)2] n , which has a high quantum efficiency and exhibits a relatively stable fluorescence color with increasing temperature, and has good thermal stability and color stability; the present invention also provides a method for preparing the above complex, which has easily available synthetic materials, a simple synthesis method, and a high yield; the pc-wLED made by mixing the above complex with a commercial green powder and assembling it with a light-emitting diode shows significant optical properties at a working current of 300 mA: CCT = 4483 K, Ra = 95, CIE coordinates (0.3599, 0.3556), and has great application potential in full-spectrum white LEDs. Description of the drawings

[0021] Figure 1 It is the structural diagram of the X-ray crystal of the complex [Cu4I4(bbimb)2] n (hydrogen atoms are omitted in this figure for clarity);

[0022] Figure 2 It is the powder X-ray diffraction pattern of the complex [Cu4I4(bbimb)2] n ;

[0023] Figure 3 It is the infrared spectra of the complex [Cu4I4(bbimb)2] n and the organic ligand bbimb;

[0024] Figure 4 It is the thermogravimetric diagram of the complex [Cu4I4(bbimb)2] n ;

[0025] Figure 5 It is the fluorescence excitation and emission spectra of the complex [Cu4I4(bbimb)2] n at 298 K;

[0026] Figure 6 It is the fluorescence lifetime decay curve of the complex [Cu4I4(bbimb)2] n at room temperature;

[0027] Figure 7 is the complex [Cu4I4(bbimb)2] n of the variable-temperature fluorescence spectrum;

[0028] Figure 8 is the complex [Cu4I4(bbimb)2] n of the ultraviolet excitation diagrams at different temperatures;

[0029] Figure 9 is the complex [Cu4I4(bbimb)2] n of the temperature-dependent fluorescence emission intensity integral diagram;

[0030] Figure 10 is the complex [Cu4I4(bbimb)2] n of the variable-temperature CIE diagram;

[0031] Figure 11 (a) is the EL spectrum of the LED chip (λmax = 365 nm) based on the complex [Cu4I4(bbimb)2] n under the operating current of 10 - 300 mA flux; Figure 11 (b) is the EL spectrum of the LED chip (λmax = 365 nm) based on the complex [Cu4I4(bbimb)2] n under the operating current of 10 - 300 mA flux; Figure 11 (c) is the CIE coordinates of the LED chip (λmax = 365 nm) based on the complex [Cu4I4(bbimb)2] n under the operating current of 10 - 300 mA flux; Figure 11 (d) is the operating diagram of the LED chip (λmax = 365 nm) based on the complex [Cu4I4(bbimb)2] n ;

[0032] Figure 12 is the complex [Cu4I4(bbimb)2] n of the photoluminescence quantum efficiency diagram measured at 298K. Specific Embodiments

[0033] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and a preferred embodiment.

[0034] The first aspect of the present invention provides a cheap metal-organic fluorescent material for high-power LED lighting:

[0035] It is a complex with the chemical formula: [Cu4I4(bbimb)2] n , where the ligand bbimb is 1,2-bis((1H-benzoimidazol-1-yl)methyl)benzene, and its chemical formula is: C 22 H 18 N4, where n≥1 in the above chemical formula, and the crystal structure is as shown in Figure 1 . The complex crystal belongs to the monoclinic system, the space group of the complex is P21 / c, and the crystal parameters of the complex are α = 90°, β = 98.879(2)°, γ = 90°, Z = 4,

[0036] In the complex, Cu + is four-coordinated and is connected to four I atoms in different spatial environments to form a tetrahedral configuration of Cu4I4; the halogen atoms in the complex come from CuI in the raw materials, and the N atoms come from two bbimb ligands; in the complex, the bbimb ligand is connected to Cu4I4 to form a one-dimensional chain structure.

[0037] The second aspect of the present invention provides a preparation method of a cheap metal-organic fluorescent material for high-power LED lighting, including the following reaction steps:

[0038] S1. Preparation of the ligand 1,2-bis((1H-benzoimidazol-1-yl)methyl)benzene:

[0039] Add DMF solvent to benzimidazole and stir for 10 minutes, then add an aqueous KOH solution, stir for 15 - 25 minutes, slowly add o-dichlorobenzyl, stir for 4 - 6 hours, then add water to the reaction mixture, continue to stir for 1 hour, and finally filter the mixture and dry it to obtain a white solid; among them, KOH is used as a catalyst and does not participate in the reaction, which can improve the reaction efficiency. Under an alkaline dry environment, o-dichlorobenzyl reacts with benzimidazole to generate the ligand 1,2-bis((1H-benzoimidazol-1-yl)methyl)benzene.

[0040] S2. Preparation of the complex [Cu4I4(bbimb)2] n :

[0041] Seal the mixture of cuprous iodide, the ligand 1,2-bis((1H-benzoimidazol-1-yl)methyl)benzene, acetonitrile and methanol in a polytetrafluoroethylene high-pressure reaction kettle, carry out a heating reaction, then naturally cool to room temperature, filter to obtain bright yellow crystals suitable for X-ray diffraction analysis, wash the above crystals repeatedly with distilled water and acetonitrile, and dry them in the air to obtain pure yellow crystals, namely the complex [Cu4I4(bbimb)2] n .

[0042] The third aspect of the present invention provides the application of a cheap metal-organic fluorescent material for high-power LED lighting as an excitable phosphor in a full-spectrum white LED, as described above.

[0043] The sources of the reagents involved in the following experimental procedures are shown in Table 1; the reagents involved were used directly without further purification.

[0044] Table 1 Reagent Table

[0045]

[0046]

[0047] The equipment and instruments used in the following experimental procedures are shown in Table 2:

[0048] Table 2 Main Instruments

[0049]

[0050] Example 1:

[0051] DMF solvent (30 ml) was added to benzimidazole (2.95 g, 25 mmol) and stirred for 10 minutes. Then, KOH solution (1.4 g, 25 mmol) dissolved in water (10 ml) was added, and after stirring for 20 minutes, o-dichlorobenzyl (2.19 g, 12.5 mmol) was slowly added. After stirring for 4 hours, water (20 ml) was added to the reaction mixture, and stirring was continued for 1 hour. Finally, the mixture was filtered and dried to obtain a white solid; among them, KOH was used as a catalyst and did not participate in the reaction, which could improve the reaction efficiency. Under an alkaline dry environment, o-dichlorobenzyl and benzimidazole underwent a substitution reaction to form the ligand 1,2-bis((1H-benzimidazol-1-yl)methyl)benzene, with a yield of 80%.

[0052] A mixture of copper(I) iodide (19.0 mg, 0.1 mmol), ligand 1,2-bis((1H-benzimidazol-1-yl)methyl)benzene (33.4 mg, 0.1 mmol), acetonitrile (6 mL), and methanol (2 mL) was sealed in a 15 mL polytetrafluoroethylene autoclave and reacted at 120 °C for 3 days. Then, after natural cooling to room temperature, the mixture was filtered to obtain bright yellow crystals suitable for X-ray diffraction analysis. The above crystals were repeatedly washed with distilled water and acetonitrile and dried in air to obtain pure yellow crystals, namely the complex [Cu4I4(bbimb)2] n , with a yield of 72%.

[0053] The above crystals were collected under a microscope, and their crystallographic data were obtained on a Bruker APEX-II CCD instrument with graphite monochromatic radiation Collected at room temperature of 25 °C. The crystallographic data collection, data reduction and unit cell refinement were carried out using two software packages, Bruker Instrument Service v4.2.2 and SAINT V8.34A. The structure of the complex was solved using the SHELXS software package, and the crystal data were refined by full-matrix least-squares method using the SHELXL software package. The absorption correction was performed using the multi-scan software package SADABS. The hydrogen atoms of the organic ligands were optimized anisotropically on F 2 by the riding mode in the SHELXTL software package. The final crystallographic data of the complex are shown in Table 3, and the selected bond lengths and bond angles (°) of the complex are shown in Table 4.

[0054] Table 3 Crystallographic parameters of the complex

[0055]

[0056] a R1 = Σ(||F0| - |F c ||) / Σ|F0|; b wR2 = [Σw(|F0 2 | - |F c 2 |) 2 / Σw|F0 2 | 2 ) 1 / 2 ; c GOF = [∑[w(F0 2 - F c 2 ) 2 / (N obs - N params )] 1 / 2 ,

[0057] based on the data I > 2σ(I).

[0058] Table 4 Selected bond lengths and bond angles (°) in the crystal structure of the complex

[0059]

[0060]

[0061]

[0062] Powder X-ray diffraction analysis: As Figure 2 shown, the black line (bottom) is plotted from the experimental data, and the red line (top) is simulated by computer according to the crystal structure. FromFigure 2 It can be seen that the experimental values and simulated values of the complex can fit very well, indicating that the complex is a pure phase.

[0063] Infrared absorption spectroscopy analysis: As Figure 3 shown, the black spectrum (upper) is the infrared absorption spectrum of the ligand bbimb, and the red spectrum (lower) is the infrared absorption spectrum of the complex. From Figure 3 it can be seen that the absorption spectrum of the complex can fit very well with that of the ligand, indicating that there is indeed an organic ligand in the complex.

[0064] Thermogravimetric analysis: As Figure 4 shown, the thermal stability of the complex from room temperature to 850 °C was studied. It can be seen from the TGA curve that the complex exhibits good thermal stability, and its mass loss is divided into two steps. Due to the removal of halogens and some ligands, the first weight loss of the complex was observed to be about 35 - 39% between 200 - 400 °C. The second weight loss between 400 - 650 °C can be attributed to the complete removal of the remaining ligands.

[0065] Fluorescence test: As Figure 5 shown, the complex exhibits a strong emission band centered at 620 nm, and the full width at half maximum (FWHM) is about 130 nm. As Figure 6 shown, the PL lifetime is 9.73 μs. At 25 °C, the complex emits orange light, and the emission center is 620 nm. As shown in Table 5, the photoluminescence quantum yield (PLQY) of the complex in the solid state is 82.39%, and the fluorescence decay rate (k r )(k r = Φ PL τ -1 ) is 6.32×10 4 s -1 . Considering that Φ PL = k r / (k r + k nr ), where k nr is the rate of non - radiative processes including non - radiative singlet decay and ISC, the k nr value of the complex is estimated to be 1.35×10 4 s -1 .

[0066] Table 5 Solid - state photophysical data of the complex at room temperature

[0067]

[0068] a Radiative rate constant calculatedK r= Φ / τ. b Nonradiative rateconstant calculated K nr = (1 - Φ) / τ.

[0069] Study on fluorescence quenching properties: The present invention studied the temperature dependence of fluorescence, and the complex showed that the fluorescence intensity did not change significantly with the increase in temperature. As Figure 7 and Figure 9 shown, as the temperature gradually increased from 80 K to 500 K, there was a slight blue shift of about 12 nm in the emission center of the complex, and its fluorescence intensity did not change significantly with the increase in temperature. The results showed that the complex exhibited relatively stable fluorescence color with the change of temperature. As Figure 8 and Figure 10 shown, as the temperature increased, the luminescence of the complex changed from orange at low temperature (80 K) to yellow at high temperature (500 K). Correspondingly, the CIE coordinates changed from (0.52, 0.47) at 80 K to (0.48, 0.49) at 500 K. The change in CIE coordinates was consistent with the fluorescence emission shift with the increase in temperature.

[0070] Study on the properties of LED devices of the complex: Considering the high photoluminescence quantum efficiency and thermal stability of fluorescence, the present invention studied the LED performance of the complex using an LED chip (λmax = 365 nm). The results of single pc - wLEDs are as Figure 11 (a) shown. As Figure 11 (a) and Table 6 shown, below 300 mA, the electroluminescence (EL) intensity of the yellow - emitting complex increased with the increase in current. For the white - light LED based on the complex (commercial blue powder BAM (BaMgAl 10 O 17 :Eu 2+ ) and commercial green powder (Ba,Sr)2SiO4:Eu 2+ ), the electroluminescence spectrum covered the entire visible light region of 400 - 800 nm (i.e., white - light emission), as Figure 11 (b) shown, and the electroluminescence intensity gradually increased in the range of 10 - 300 mA.

[0071] To demonstrate the practical application potential as a pc - wLEDs device, the present invention recorded the color stability at different currents. As Figure 11As shown in (c), within the range of flux current (10 - 300 mA), CIE x (about 0.359) and CIE y (about 0.356) remain basically unchanged. As shown in Table 6, when the flux current is 300 mA, the CRI value of the complex-based wLED is as high as 95 and the CCT is 4483 K. The low CCT and high CRI values show the good optical performance of the pc-wLED at high flux currents. As Figure 11 shown in (d), on the left is a photo of the LED device when it is not powered on, and on the right is a photo of the LED device after it is powered on. The bright white light emission also demonstrates its good optical performance.

[0072] As Figure 12 shown, the photoluminescence quantum efficiency of its complex is as high as 82.39%, with a relatively high luminescence intensity, which confirms its good optical performance.

[0073] Table 6 EL parameters of complex-based white LEDs at different currents

[0074]

[0075] The above is only the preferred embodiment of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements are also within the protection scope of the present invention.

Claims

1. A metal-organic fluorescent material for LED lighting, characterized in that, The organic fluorescent material is a complex with the chemical formula: [Cu4I4(bbimb)2]n, where the ligand bbimb is 1,2-bis((1H-benzoimidazol-1-yl)methyl)benzene with the chemical formula: C22H18N4, and n≥1 in the above chemical formula; the complex crystal belongs to the monoclinic system, the space group of the complex is P21 / c, and the crystal parameters of the complex are a = 11.3850(3) Å, b = 16.1962(3) Å, c = 26.8795(6) Å, α = 90°, β = 98.879(2)°, γ = 90°, Z = 4, V = 4897.02(19) Å3; In the complex, Cu+ is four-coordinated and forms a tetrahedral configuration of Cu4I4 by connecting with four I atoms in different spatial environments; the halogen atoms in the complex come from CuI in the raw materials, and the N atoms come from two bbimb ligands; in the complex, the bbimb ligand is connected with Cu4I4 to form a one-dimensional chain structure.

2. The preparation method of the organic fluorescent material according to claim 1, characterized in that: It includes the following reaction steps: Add a mixed solvent of cuprous iodide, ligand 1,2-bis((1H-benzoimidazol-1-yl)methyl)benzene, acetonitrile and methanol into a reaction kettle, carry out a heating reaction, then naturally cool to room temperature, filter to obtain crystals, wash the above crystals repeatedly with distilled water and acetonitrile, and dry in air to obtain the complex.

3. The preparation method of the organic fluorescent material according to claim 2, characterized in that: The molar ratio of the ligand 1,2-bis((1H-benzoimidazol-1-yl)methyl)benzene to cuprous iodide is 0.09 - 0.11:0.09 - 0.

11.

4. The preparation method of the organic fluorescent material according to claim 2, characterized in that: The volume ratio of acetonitrile to methanol is 5.9 - 6.1:1.9 - 2.

1.

5. The preparation method of the organic fluorescent material according to claim 2, characterized in that: The temperature of the heating reaction is 115°C - 125°C, and the reaction time is 70 - 74 hours.

6. The preparation method of the organic fluorescent material according to claim 2, wherein: The preparation method of the ligand 1,2-bis((1H-benzoimidazol-1-yl)methyl)benzene includes the following reaction steps: Add DMF solvent to benzimidazole, stir for 10 minutes, then add KOH aqueous solution, stir for 15 - 25 minutes, slowly add o-dichlorobenzyl, stir for 4 - 6 hours, then add water to the reaction mixture, continue to stir for 1 hour, and finally filter and dry the mixture to obtain the ligand 1,2-bis((1H-benzoimidazol-1-yl)methyl)benzene.

7. The preparation method of the organic fluorescent material according to claim 6, characterized in that: The molar ratio of o-dichlorobenzyl, benzimidazole, and KOH required for the synthesis of the ligand 1,2-bis((1H-benzoimidazol-1-yl)methyl)benzene is 12.4 - 12.6:24.9 - 25.1:24.9 - 25.1; the volume of DMF: water is 25~35 ml: 15~25 ml.

8. The preparation method of the organic fluorescent material according to claim 6, characterized in that: The temperature required for the synthesis of 1,2-bis((1H-benzoimidazol-1-yl)methyl)benzene is 20°C - 30°C, the stirring reaction time after adding KOH aqueous solution is 20 minutes, and the stirring reaction time after adding o-dichlorobenzyl is 4 hours.

9. Use of the organic fluorescent material according to claim 1, characterized in that, The application of the complex in full-spectrum white light LEDs.

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