A g-C3N4-doped mixed lanthanide metal-organic framework white luminescent material and preparation method thereof

Abstract

The present invention discloses a g-C3N4-doped mixed lanthanide metal-organic framework white luminescent material and a preparation method thereof. 3+ Metal salts and Eu 3+ The metal salt is dissolved in an appropriate amount of deionized water to form a solution, which is then stirred and mixed with the ligand. The mixed solution is then transferred to a hydrothermal reactor for a hydrothermal reaction. The resulting product is centrifugally cleaned with deionized water and anhydrous ethanol and dried to obtain the yellow-emitting Ln-MOFs luminescent material, TbEu(cpioa). The clean, dry TbEu(cpioa) and g-C3N4 are dissolved in deionized water and stirred, then transferred to a hydrothermal reactor and placed in a constant-temperature forced-air drying oven for another hydrothermal reaction, ultimately yielding a white luminescent material. The prepared white luminescent material is then packaged with a UV LED chip to form a light-emitting device, which can emit white light with a high color rendering index, with a luminous flux and luminous intensity more than ten times higher than those of Ln-MOFs.

Description

Technical Field

[0001] The present invention belongs to the field of new material technology inventions, and specifically relates to a preparation method for improving the luminous intensity of a mixed lanthanide metal MOFs luminescent material and a luminescent device thereof by doping g-C3N4. Background Art

[0002] Lanthanide metal-organic framework materials (Ln-MOFs) are a special type of luminescent MOF, which is prepared by doping rare earth elements into metal-organic frameworks (MOFs). They have the luminescent properties of both MOFs and rare earth materials. In order to achieve white light emission, Ln is usually introduced into the matrix material. 3+ As the luminescence center, by adjusting the Ln 3+ The ratio of nitrate can adjust the intensity of different colors of light, and finally the three colors of red, green and blue are combined to emit white light. Therefore, Ln 3+ Ion doping into metal-organic frameworks (Ln-MOFs) is considered one of the most promising materials for white light-emitting diode (WLED) applications.

[0003] Currently, the fabrication of LED devices is primarily based on phosphors and light-emitting chips. There are three common approaches to producing white light LEDs: (i) a blue LED chip stimulating a single-phase yellow or mixed green and red phosphor; (ii) a near-ultraviolet LED chip stimulating red, green, and blue phosphors; and (iii) a combination of three monochromatic LEDs (red, green, and blue). WLEDs composed of a blue chip and yellow phosphor offer advantages such as high luminous intensity, high efficiency, low cost, and ease of fabrication. However, due to the lack of red light from the combined yellow and blue light, they suffer from unstable and high color temperature, as well as a low color rendering index. Devices fabricated from a near-ultraviolet chip and three-color red, green, and blue phosphors do significantly improve color rendering index due to the addition of red light, while retaining the advantage of high efficiency. However, due to the three-phase nature of the phosphors, they suffer from color temperature instability and high cost. The third approach, producing white light by mixing red, green, and blue LEDs, suffers from poor stability and is prone to color deviation due to variations in the fluorescence of a particular LED color. Therefore, in comparison, WLEDs made of single-phase white light-emitting Ln-MOFs phosphors have greater potential and have shown broad application prospects in the near-ultraviolet LED field in recent years.

[0004] However, due to the interaction between the ligand and Ln 3+ The antenna effect between them makes the white light emission weak. Therefore, Ln-MOF materials are compounded with other functional materials to achieve fluorescence synergy between different materials. While taking advantage of the diverse luminescence structure of MOF, the optical performance of the luminescent material is significantly improved. Summary of the Invention

[0005] The present invention proposes a preparation method for improving the luminous intensity of mixed lanthanide metal MOFs luminescent materials and their luminescent devices by doping with g-C3N4. The yellow-light-emitting TbEu(cpioa) luminescent material is doped with g-C3N4 with blue light emission, and stronger white light emission is ultimately obtained by changing the ratio of g-C3N4 to TbEu(cpioa).

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

[0007] 1. A single-phase g-C3N4@TbEu(cpioa) white light emitting material:

[0008] The g-C3N4@TbEu(cpioa) white light emitting material is firstly doped with red and green luminescent centers Eu in the ligand H3cpioa by in-situ encapsulation method. 3+ and Tb 3+ TbEu(cpioa) was prepared, and then TbEu(cpioa) and g-C3N4 were synthesized into g-C3N4@TbEu(cpioa) white light emitting material by a hydrothermal method.

[0009] The hydrothermal synthesis process is completed in a polytetrafluoroethylene-lined hydrothermal reactor, and the final product is a white powder with good crystallinity and uniform particles.

[0010] The role of H3cpioa is to transfer energy to Tb through the antenna effect. 3+ Eu 3+ Green and red luminescent centers are obtained, while g-C3N4 provides strong blue emission. This luminescent material can emit bright white light under ultraviolet light with a wavelength of 365nm, and the luminescence spectrum covers the entire visible light range from blue to red. When packaged with a commercially available LED chip into a light-emitting device, it can achieve bright white illumination at a voltage of 3.0 to 3.4V.

[0011] The introduction of g-C3N4 provides strong blue light, so there is no need to introduce La 3+ , thus more Tb can be introduced into the ligand 3+ Eu 3+ , which also enhances the emission of green and red light, making it possible to regulate white light.

[0012] 2. A method for preparing a mixed lanthanide MOFs white light emitting material, the steps of the method are as follows:

[0013] 1) Place 5-(4-carboxyl-phenoxy)-isophthalic acid (H3cpioa), terbium salt, and europium salt in a beaker and add deionized water to dissolve;

[0014] 2) Stirring the mixed solution at room temperature for 30 minutes and adding dilute nitric acid solution dropwise to adjust the pH of the solution to 5-6;

[0015] 3) The above solution was transferred to a stainless steel reactor lined with polytetrafluoroethylene and placed in a constant temperature forced air drying oven for hydrothermal reaction. The reaction temperature was controlled at 120°C and the reaction time was controlled at 72 hours.

[0016] 4) The reacted powder was centrifugally washed with deionized water and anhydrous ethanol, and dried at 60° C. for 24 hours to obtain TbEu(cpioa) yellow light emitting material;

[0017] 5) TbEu(cpioa) and g-C3N4 were mixed and dissolved in deionized water in a beaker and stirred for 30 minutes;

[0018] 6) The above solution was transferred to a stainless steel reactor lined with polytetrafluoroethylene and placed in a constant temperature forced air drying oven for hydrothermal reaction. The reaction temperature was controlled at 80°C and the reaction time was controlled at 24 hours.

[0019] 7) The reacted powder was centrifugally washed with deionized water and anhydrous ethanol, and dried at 60°C for 24 hours to obtain g-C3N4@TbEu(cpioa) white light emitting material;

[0020] The lining of the hydrothermal reactor is made of polytetrafluoroethylene or PPL material, and the outer shell is made of stainless steel. The pressure in the reactor is controlled by the amount of solution added, and the reaction is carried out under high temperature and high pressure environment.

[0021] The white powder has fine and uniform particles, good dispersibility, and high crystallinity. It has a broad blue emission peak, a narrow green emission peak, and a sharp red light emission spectrum within the range of 350 to 650 nm.

[0022] 3. Application of g-C3N4@TbEu(cpioa) white light emitting material in WLED

[0023] 1) Add appropriate amount of organic silica gel to the beaker;

[0024] 2) Evenly mix the g-C3N4@TbEu(cpioa) white light emitting material, organic silica gel A and organic silica gel B glue weighed on weighing paper in a ratio of (1.5:4:1);

[0025] 3) coating the uniform mixture on a 365nm UV LED chip;

[0026] 4) Place the packaged WLED in an oven and bake at 100°C for 6 hours to cure.

[0027] The present invention has the following beneficial effects:

[0028] 1) The present invention obtains a g-C3N4@TbEu(cpioa) white light emitting material with stronger white light emission after doping with g-C3N4 through a simple hydrothermal synthesis method.

[0029] 2) The WLED encapsulated by g-C3N4@TbEu(cpioa) white light emitting material emits bright white light at a voltage of 3.0V~3.4V, with a color rendering index of 89.5, a color temperature of 4534K, and a luminous flux and luminous efficacy of 1.59lm and 2.25lm / W.

[0030] 3) Compared with LaTbEu(cpioa) without g-C3N4, the luminous flux and luminous efficiency of the light-emitting device of the present invention are improved by more than ten times, proving its potential application in the field of luminescence. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a schematic diagram of the hydrothermal reactor structure: 1-fixing screws, 2-upper end cover, 3-reactor body, 4-sealing gasket, 5-lower end cover, 6-liner cover, 7-liner;

[0032] Figure 2 This is the X-ray diffraction pattern obtained in Example 1;

[0033] Figure 3 is the TEM spectrum of the product obtained in Example 1;

[0034] Figure 4 is the X-ray photoelectron spectrum of the product g-C3N4@TbEu(cpioa) obtained in Example 1;

[0035] Figure 5 is the thermogravimetric spectrum of the product obtained in Example 1;

[0036] Figure 6 is the emission spectrum of the product obtained in Example 1;

[0037] Figure 7 is the CIE chromaticity diagram of the product obtained in Example 1;

[0038] Figure 8 This is the energy transfer mode present in the product obtained in Example 1;

[0039] Figure 9 An LED device formed by packaging the product obtained in Example 1 with an LED chip;

[0040] Figure 10 is the photoluminescence spectrum of an LED device formed by packaging the product obtained in Example 1 with LaTbEu(cpioa);

[0041] Figure 11This is a photo of an LED device formed by encapsulating the product obtained in Example 3;

[0042] Figure 12 This is the electroluminescence spectrum of the LED device formed by encapsulating the product obtained in Example 3. DETAILED DESCRIPTION

[0043] like Figure 1 The figure shows a stainless steel reactor for performing a hydrothermal reaction according to the present invention. The inner lining 7 of the reactor body 3 is made of polytetrafluoroethylene or PPL material. The upper end surface of the inner lining 7 is provided with an inner lining cover 6. Above the inner lining cover 6 are provided a lower end cover 5 and an upper end cover 2 installed by fixing screws 1. The lower end cover 5 and the reactor body 3 are sealed by a sealing gasket 4. The present invention places the prepared reaction solution into the hydrothermal reactor. Under high temperature and high pressure, the solute molecules react to ultimately generate TbEu(cpioa) and g-C3N4@TbEu(cpioa) powder. The g-C3N4@TbEu(cpioa) white light emitting material emits bright white light under 365nm ultraviolet light excitation. It is packaged with a commercially available LED chip into a light-emitting device, which achieves bright white illumination at a voltage of 3.0 to 3.4V.

[0044] Example 1:

[0045] g-C3N4 doped with TbEu(cpioa)

[0046] 8.6602 g of lanthanum nitrate hexahydrate, 9.0586 g of terbium nitrate hexahydrate, and 8.9212 g of europium nitrate hexahydrate were respectively dissolved in 100 mL of deionized water and stirred for a period of time to obtain lanthanum nitrate, terbium nitrate, and europium nitrate solutions with a molar concentration of 0.2 mol / L.

[0047] In reactor 1, 3.6 mL, 0.372 mL, and 0.028 mL of lanthanum nitrate, terbium nitrate, and europium nitrate solutions were weighed in a molar ratio of 0.9:0.093:0.007, respectively. In reactor 2, 3.96 mL and 0.04 mL of terbium nitrate and europium nitrate solutions were weighed in a molar ratio of 0.99075:0.00925, respectively. 0.8 mmol of 5-(4-carboxy-phenoxy)-isophthalic acid (0.26085 g) was dissolved in deionized water and added to reactors 1 and 2. The mixture was stirred at room temperature for 30 minutes, during which dilute nitric acid was added dropwise to adjust the pH of the solution to 5-6. After stirring, the solution was transferred to a 100 mL polytetrafluoroethylene-lined container with a filling level of approximately 50%. The three reactors were placed in a constant-temperature forced-air drying oven for a hydrothermal reaction at 120°C for 72 hours. After the reaction was completed, the powders obtained from the four reactors were washed three times with deionized water and three times with anhydrous ethanol by centrifugation, and then placed in a constant temperature drying oven at 60°C for 24 hours.

[0048] The TbEu(cpioa) obtained in reaction vessel 2 was weighed, and 50 mg of TbEu(cpioa) was weighed and placed in reaction vessel 3. 0.075 mg of g-C3N4 was added to the reaction vessel and mixed with TbEu(cpioa), deionized water was added to dissolve, and stirred at room temperature. After stirring, the solution was transferred to a 100 mL polytetrafluoroethylene liner. The reactor was placed in a constant temperature forced air drying oven for hydrothermal reaction at 80°C for 24 hours. After the reaction was completed, the powder obtained in the reactor was washed with deionized water and anhydrous ethanol by centrifugation three times each, and then dried in a constant temperature drying oven at 60°C for 24 hours. Finally, a white g-C3N4@TbEu(cpioa) powder with fine and uniform particle size was obtained.

[0049] Figure 2 The XRD spectra of LaTbEu(cpioa), TbEu(cpioa), and g-C3N4@Ln(cpioa) are shown. The synthesized products in this spectrum fully match the standard spectra. Comparison of the g-C3N4@Ln(cpioa) formed after the addition of g-C3N4 with the standard spectra reveals a slight shift in the diffraction peaks, but the overall framework remains unchanged, confirming that the addition of g-C3N4 to La(cpioa) does not alter its crystal structure.

[0050] Figure 3 Transmission electron micrographs of LaTbEu(cpioa), TbEu(cpioa), and g-C3N4@Ln(cpioa) obtained in Example 1 are shown. The g-C3N4@Ln(cpioa) exhibits similar morphologies, all appearing fragmented.

[0051] Figure 4 The figure below shows the X-ray photoelectron spectroscopy of g-C3N4@Ln(cpioa) powder. From the XPS results, it can be concluded that g-C3N4 binds to Ln(cpioa) through weak interactions.

[0052] Figure 5 The thermogravimetric curves of the three products obtained show that the frameworks of LaTbEu(cpioa), TbEu(cpioa) and g-C3N4@Ln(cpioa) can maintain good thermal stability before 300℃, among which g-C3N4@TbEu(cpioa) loses weight at 300℃, which may be due to the shedding of g-C3N4.

[0053] Figure 6 Figure 2 is the fluorescence emission spectrum of LaTbEu(cpioa) and g-C3N4@Ln(cpioa) at room temperature. It can be seen that g-C3N4@TbEu(cpioa) has a higher emission intensity.

[0054] Figure 7 Are the CIE chromaticity coordinates corresponding to the emission spectra, which are LaTbEu(cpioa):(0.36,0.36), g-C3N4@TbEu(cpioa):(0.34,0.37).

[0055] Figure 8 The energy transfer simulation diagram in g-C3N4@TbEu(cpioa) shows that there may be two forms of energy transfer in the system: one is the energy transfer from organic ligand to metal ion (LMCT); the other is the energy transfer from metal ion Tb 3+ to Eu 3+ Energy transfer of ions (MMCT).

[0056] Since g-C3N4 does not match the energy levels of metal ions and H3cpioa, it is not conducive to energy transfer, so g-C3N4 can always show strong blue light emission. In addition, in terms of white light modulation, it is not necessary to add La after adding g-C3N4. 3 + , more Tb can be added to the matrix 3+ and Eu 3+ , thus obtaining a stronger emission.

[0057] Figure 9 The light-emitting device is a packaged LaTbEu(cpioa) and g-C3N4@Ln(cpioa) LED chip, and the light-emitting picture is at a voltage of 3.2V.

[0058] Example 2:

[0059] Reactors 1, 2, and 3 were filled with 2.9715 mL and 0.03 mL of terbium nitrate and europium nitrate solutions, respectively, at a molar ratio of 0.99075:0.00925. 0.1956 g of 5-(4-carboxy-phenoxy)-isophthalic acid (0.6 mmol) was dissolved in deionized water and added to the three reactors 1, 2, and 3. The mixture was stirred at room temperature for 30 minutes. During this time, dilute nitric acid solution was added dropwise to reactor 1 to adjust the pH to 5-6. An equal volume of deionized water was added dropwise to reactor 2. Sodium hydroxide solution was added dropwise to reactor 3 to adjust the pH to 7-8. After stirring, the solution was transferred to a 100 mL polytetrafluoroethylene-lined container with a filling level of approximately 50%. The three reactors were placed in a constant-temperature forced-air drying oven for a hydrothermal reaction at 120°C for 72 hours. After the reaction was completed, the powders obtained from the three reactors were washed three times with deionized water and three times with anhydrous ethanol by centrifugation, and then placed in a constant temperature drying oven at 60°C for 24 hours.

[0060] The TbEu(cpioa) obtained in reaction vessels 1, 2, and 3 were weighed, and the yields of reaction vessels 1, 2, and 3 were calculated to be 77.4%, 54.2%, and 51.2%, respectively.

[0061] The experimental results show that a higher yield of TbEu(cpioa) can be obtained by adding dilute nitric acid under acidic conditions.

[0062] Example 3:

[0063] Add 0.4 g of silicone rubber A and 0.1 g of silicone rubber B to reactors 1, 2, and 3 respectively, and mix them evenly. Then, add 0.1 g, 0.15 g, and 0.2 g of g-C3N4@TbEu(cpioa) to reactors 1, 2, and 3 respectively, and stir and mix evenly. Coat the uniform mixture on a 365 nm ultraviolet LED chip. Place the packaged LED in an oven and bake at 100 ° C for 6 hours to solidify to obtain the final LED device.

[0064] like Figure 11 and Figure 12 As shown, the actual picture and electroluminescence spectrum prove that organic silica gel A: organic silica gel B glue: g-C3N4@TbEu(cpioa)=4:1:1.5 can obtain the best luminescence.

Claims

1. A g-C3N4-doped mixed lanthanide metal-organic framework white luminescent material, characterized in that: TbEu(cpioa) which emits yellow light under ultraviolet light and g-C3N4 which emits blue light are doped to obtain g-C3N4@TbEu(cpioa) luminescent material with white light emission.

2. The g-C3N4-doped mixed lanthanide metal-organic framework white luminescent material according to claim 1, characterized in that: By changing the Tb 3+ and Eu 3+ The molar ratio of metal ions and the mass ratio of g-C3N4 to TbEu(cpioa) regulate the luminescent color of the luminescent material; Tb in white light emitting materials 3+ , Eu 3+ The optimal molar ratio is 0.99075:0.00925, and the optimal mass ratio of g-C3N4 to TbEu(cpioa) is 100:0.

15.

3. A light-emitting device prepared using the white light-emitting material according to claim 1, characterized in that: The light emitting device is prepared by the following method: 1) Add appropriate amount of silicone rubber to the beaker; 2) Evenly mix g-C3N4@TbEu(cpioa) white light emitting material, organic silica gel A and organic silica gel B in a ratio of 1.5:4:1; 3) coating the uniform mixture on a 365nm UV LED chip for packaging; 4) Place the packaged WLED in an oven and bake at 100 °C for 6 hours to cure.

4. The light emitting device according to claim 3, wherein: The light-emitting device emits white light at a voltage of 3.0 to 3.4 V, with a color rendering index of 89.5, a color temperature of 4534 K, and a luminous flux and luminous efficacy of 1.59 lm and 2.25 lm / W.

5. The method for preparing the white luminescent material according to claim 1, wherein: The following steps are involved: Step 1) Place Tb 3+ and Eu 3+ The nitrate solutions were dissolved in deionized water, stirred, and prepared into ion solutions; Step 2) Transfer the Tb configured in step 1) to 3+ Solution, Eu 3+ The solution and the organic ligand H3cpioa were dissolved in deionized water and stirred at room temperature, and during the stirring process, dilute nitric acid was added dropwise to adjust the pH of the solution to acidic; Step 3) The solution from step 2) was transferred to a stainless steel reactor lined with polytetrafluoroethylene and placed in a constant temperature forced air drying oven for hydrothermal reaction to obtain TbEu(cpioa); Step 4) The powder after the hydrothermal reaction in step 3) was washed with deionized water and anhydrous ethanol, and dried at 60° C. for 24 hours; Step 5) Dissolve the TbEu(cpioa) and g-C3N4 obtained in step 4) in deionized water and stir at room temperature for 30 minutes; Step 6) The solution from step 5) is transferred to a hot reactor and placed in a constant temperature forced air drying oven for hydrothermal reaction; Step 7) The powder after the hydrothermal reaction in step 6) was washed with deionized water and anhydrous ethanol, and dried at 60° C. for 24 hours.

6. The preparation method according to claim 5, characterized in that: In the step 2): Tb 3+ and Eu 3+ The molar ratio is 0.99075:0.00925; The organic ligand is 5-(4-carboxy-phenoxy)-isophthalic acid.

7. The preparation method according to claim 5, characterized in that: In the step 2), The stirring time is 30 minutes; The concentration of dilute nitric acid is 0.1 M / L, and the pH of the solution is adjusted to 5-6 using dilute nitric acid.

8. The preparation method according to claim 5, characterized in that: In step 3), the reaction temperature of the hydrothermal reaction is controlled at 120°C and the reaction time is controlled at 72 h; In step 6), the reaction temperature of the hydrothermal reaction is controlled at 80° C. and the reaction time is controlled at 24 h.

9. The preparation method according to claim 5, characterized in that: In the step 3), the lining of the thermal reactor is made of polytetrafluoroethylene or PPL material, the outer shell is made of stainless steel material, and the filling degree of the solution in the thermal reactor is 45% to 50%.

Images