CN115466614B - White luminescent soft material based on lanthanide deep eutectic solvent and carbon dots and preparation method thereof - Google Patents

Abstract

The invention discloses a white luminescent soft material based on a lanthanide low eutectic solvent and carbon dots and a preparation method thereof, comprising the following steps: mixing an amide substance with a europium salt and heating it to obtain a first low eutectic solvent; mixing an amide substance with a terbium salt and heating it to obtain a second low eutectic solvent; heating and drying a mixed solution of a carbon source and a surface passivator, and then stirring and pyrolyzing it to prepare blue-light carbon dots; and mixing the first low eutectic solvent, the second low eutectic solvent, the blue-light carbon dots and a diluent in proportion to obtain a white luminescent soft material.

Description

White luminescent soft material based on lanthanide deep eutectic solvent and carbon dots and preparation method thereof

Technical Field

The present invention belongs to the technical field of white light materials, and in particular relates to a white light-emitting soft material based on a lanthanide low eutectic solvent and carbon dots and a preparation method thereof.

Background technique

The statements herein merely provide background information related to the present invention and do not necessarily constitute prior art.

White light materials have attracted the attention of researchers due to their applications in lighting, display, smart materials and other fields. White light materials are generally composed of three primary color luminescent bodies (i.e. red, green and blue) or two complementary color luminescent bodies (such as blue and yellow). At present, the best solution to achieve artificial white light is light-emitting diodes, that is, white light LEDs. From the perspective of the process of achieving white light, it can be divided into two categories: one is to combine semiconductor chips with multiple luminous colors to achieve white light. This method is expensive and difficult to popularize. The second is to first excite a monochromatic semiconductor chip to emit a monochromatic light, which can excite the phosphor to emit fluorescence, and the monochromatic light and fluorescence are mixed to form white light. This method of combining semiconductor chips with fluorescent substances to achieve white light is the mainstream choice in the current white light lighting field, such as coating yellow phosphor on blue LED chips and coating red, green and blue primary color phosphors on ultraviolet LED chips.

The white light LED obtained by the above method has the defects that the solid phosphor is easy to settle and difficult to disperse, and the uneven distribution will seriously affect the luminous effect; in addition, the bonding strength between the phosphor and the substrate is insufficient, resulting in limited ductility of the substrate, making it difficult to use in flexible display devices.

Summary of the invention

In view of the shortcomings of the prior art, the object of the present invention is to provide a white luminescent soft material based on a lanthanide low eutectic solvent and carbon dots and a preparation method thereof.

In order to achieve the above object, the present invention is implemented through the following technical solutions:

In a first aspect, the present invention provides a method for preparing a white luminescent soft material based on a lanthanide deep eutectic solvent and carbon dots, comprising the following steps:

Mixing the amide substance and the europium salt and heating them to obtain a first deep eutectic solvent;

Mixing the amide substance and the terbium salt and heating them to obtain a second deep eutectic solvent;

The mixed solution of the carbon source and the surface passivator is heated and dried, and then stirred and pyrolyzed to prepare blue light carbon dots;

The first low eutectic solvent, the second low eutectic solvent, the blue light carbon dots and the diluent are mixed in proportion to prepare the white light emitting soft material.

In a second aspect, the present invention provides a white luminescent soft material based on a lanthanide low eutectic solvent and carbon dots, which is prepared by the preparation method.

In a third aspect, the present invention provides a white light LED, comprising an LED chip and a white light-emitting soft material layer loaded on the LED chip.

The beneficial effects achieved by one or more embodiments of the present invention are as follows:

Directly utilizing lanthanide metal ions with luminescent ability to synthesize type IV low eutectic solvents to obtain lanthanide luminescent fluids can overcome the problems of uneven doping and concentration quenching faced by powder samples, and does not require the introduction of conventional solvents, thus avoiding the dilemma of lanthanide luminescent compounds being restricted by solvents, and obtaining white luminescent soft materials more efficiently and conveniently.

The reason for introducing PDES as a diluent is that if CD is directly dissolved in the luminescent DES, the latter will have too strong fluorescence to obtain white light, and the luminescent DES needs to be diluted to control its luminescence intensity within a range close to that of CD. PDES will not have a negative impact on the luminescence ability of the three components and can give the mixed liquid the ability to polymerize.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

FIG1 is a flow chart of the preparation process of the white luminescent material in the present invention;

FIG2 is a flow chart of the preparation process of red-light-emitting EuDES in an embodiment of the present invention (a) and a photograph of EuDES emitting red light (b);

FIG3 is a flow chart of the preparation process of TbDES emitting green light in an embodiment of the present invention (a) and a photograph of TbDES emitting green light (b);

FIG4 is a flow chart of the preparation process of carbon dots in an embodiment of the present invention;

In Figure 5, (a) is the emission spectrum of CETP-4, λex = 365nm, the inset shows the corresponding optical photograph of the white luminescent fluid, (b) is the CIE chromaticity coordinates of each luminescent component and the white luminescent fluid, (c) is a photograph of the LED device under natural light and ultraviolet light, and (d) is the luminescence image of the luminescent elastomer under excitation of 365nm ultraviolet lamp.

In FIG6 , a is the infrared spectrum of EuDES, and b is the infrared spectrum of TbDES.

In FIG. 7 , a is a DSC graph of EuDES, b is a DSC graph of TbDES, and c is a TGA graph of EuDES and TbDES.

In Figure 8, a is the viscosity law diagram of EuDES and TbDES obtained under different raw material ratios, b is the viscosity change law diagram of EuDES-8 and TbDES-8 at different temperatures, c is the conductivity diagram of EuDES and TbDES obtained under different raw material ratios, and d is the cyclic voltammogram of EuDES-8 and TbDES-8.

In FIG9 , a is a fluorescence excitation and emission spectrum of EuDES-8, b is a fluorescence excitation and emission spectrum of TbDES-8, and c is a quantum yield diagram of EuDES and TbDES with different ligand contents.

In Figure 10, a is the infrared spectra of CDs and raw materials TEPA and EDTA, b is the UV-visible absorption and fluorescence spectra of 0.2 mg/mL CDs aqueous solution, and c is the fluorescence emission spectra of 0.2 mg/mL CDs aqueous solution at different excitation wavelengths.

Detailed ways

It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

The inventors found that lanthanide compounds show strong luminescence ability in visible light (such as Eu ³⁺ , Tb ³⁺ ) and near-infrared regions (such as Nd ³⁺ , Er ³⁺ , Yb ³⁺ ), and have the advantages of narrow emission, high color purity, long excited state lifetime, and excellent photostability. However, lanthanide elements, which are luminescent centers, are prone to coordination and fluorescence quenching when encountering polar protic solvents. To address this problem, the inventors tried to use solvophobic ligands to reduce the contact between lanthanide metal ions and solvents, but this did not fundamentally solve the problem and would affect the selection of ligands in lanthanide luminescent complexes, restricting the development of lanthanide luminescent materials.

The inventors have found through experiments that by using new solvents instead of conventional solvents, such as ionic liquids and low eutectic solvents, the luminescence intensity of lanthanide salts in low eutectic solvents is significantly increased compared with water, methanol or ethanol, and the luminescence is stable and is not affected by external temperature and water content.

In a first aspect, the present invention provides a method for preparing a white luminescent soft material based on a lanthanide deep eutectic solvent and carbon dots, comprising the following steps:

Mixing and heating the amide substance and the europium salt to obtain the first deep eutectic solvent EuDES;

Mixing the amide substance and the terbium salt and heating them to obtain the second deep eutectic solvent TbDES;

The mixed solution of the carbon source and the surface passivator is heated and dried, and then stirred and pyrolyzed to prepare blue light carbon dots;

The first low eutectic solvent, the second low eutectic solvent, the blue light carbon dots and the diluent are mixed in proportion to prepare the white light emitting soft material.

In some embodiments, the amide substance is urea.

In some embodiments, the europium salt is europium nitrate.

In some embodiments, the terbium salt is terbium nitrate.

In some embodiments, the molar ratio of the europium salt to the amide substance is 1:2 to 1:8;

The molar ratio of the terbium salt to the amide substance is 1:2 to 1:8.

When the ratio of europium salt or terbium salt to amide substances is 1:1, neither can form a uniform and stable liquid. When the ratio is 1:10 or above, a liquid can be formed during the heating process, but after standing at 25°C for 3 hours, urea-like crystals precipitate.

The low eutectic solvent obtained using europium nitrate is light pink under sunlight, and the low eutectic solvent obtained using terbium nitrate is colorless. The two exhibit orange-red and green fluorescence respectively under ultraviolet light.

In some embodiments, the temperature of the blending heating is 50-60° C., and the time of the blending heating is 0.5-1.5 h.

In some embodiments, the carbon source is ethylenediaminetetraacetic acid disodium salt.

In some embodiments, the surface passivating agent is tetraethylenepentamine.

Preferably, the pyrolysis temperature is 200-250° C. and the pyrolysis time is 1-3 h.

In some embodiments, in the white luminescent soft material, the mass ratio of EuDES to TbDES is 2:1 to 3:1, and the mass of the blue light emitting carbon dots is adjusted so that its concentration in the mixture reaches 0.1-0.5 mg/mL.

In some embodiments, the diluent is PDES.

In a second aspect, the present invention provides a white luminescent soft material based on a lanthanide low eutectic solvent and carbon dots, which is prepared by the preparation method.

In a third aspect, the present invention provides a white light LED, comprising an LED chip and a white light-emitting soft material layer loaded on the LED chip.

The design of white light LED is divided into two steps. The first step is to use amide substances such as urea to mix and heat with europium salts or terbium salts to obtain two low eutectic solvents with red or green luminescence ability. Then, a solvent-free pyrolysis method is used to synthesize hydrophilic blue light carbon dots in one step. Then, the two lanthanide-based low eutectic solvents and carbon dots are mixed in appropriate proportions to obtain a white luminescent fluid.

The second step is to use this white luminescent fluid and solidify it on the ultraviolet LED chip by glue dripping to obtain a light-emitting device.

The present invention will be further described below in conjunction with the embodiments.

Example 1

(1) Preparation of lanthanide deep eutectic solvent (LnDES)

The synthesis method of the low eutectic solvent is to mix europium nitrate and terbium nitrate with urea respectively, and heat at 55°C for one hour to obtain a clear and transparent liquid.

The mass ratio of europium nitrate and urea was adjusted to 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, and 1:10, respectively. When the mass ratio was 1:1 and 1:10, no stable target product could be formed. When the mass ratio was 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, and 1:10, the products prepared were recorded as EuDES-1, EuDES-2, EuDES-3, EuDES-4, EuDES-5, EuDES-6, EuDES-7, and EuDES-8, respectively, as shown in Table 1.

The mass ratio of terbium nitrate and urea was adjusted to be 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, and 1:10, respectively. When the mass ratios were 1:1 and 1:10, stable target products could not be formed. When the mass ratios were 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, and 1:10, the products prepared were respectively recorded as TbDES-1, TbDES-2, TbDES-3, TbDES-4, TbDES-5, TbDES-6, TbDES-7, and TbDES-8, as shown in Table 1.

Table 1

As shown in Figures 2 and 3, the ratio of lanthanide salts and urea that can form a low eutectic solvent is 1:2 to 1:8. When the ratio is 1:1, both cannot form a uniform and stable liquid. When the ratio is 1:10 or above, a liquid can be formed during the heating process, but after standing at 25°C for 3 hours, urea-like crystals precipitate.

In addition, the low eutectic solvent obtained using europium nitrate is light pink under sunlight, and the low eutectic solvent obtained using terbium nitrate is colorless. The two exhibit orange-red and green fluorescence respectively under ultraviolet light.

(2) Preparation of blue light carbon dots

For the synthesis of carbon dots, the selected carbon source was disodium ethylenediaminetetraacetic acid, the surface passivating agent was tetraethylenepentamine, and the solvent-free thermal decomposition method was adopted.

The experimental procedure is to dissolve 1.27g of ethylenediaminetetraacetic acid disodium salt in 15ml of water, place it in a three-necked flask, and then add 5ml of tetraethylenepentamine. First, heat at 150℃, stir vigorously for 1h to remove water; then heat at 220℃, stir vigorously and react for 2h.

(3) Tuning white light liquid and obtaining white light devices

In the experiment of tuning white light liquid, the blue light component was selected as undialyzed carbon dots, the green light component was TbDES-8 (1:9), the red light component was EuDES-8 (1:9), and polymerizable DES (PDES) was used as a diluent.

The general idea and method of adjusting white light is to obtain the relationship between the optimal concentration of CD, the ratio between EuDES and TbDES and the luminescence through experiments, and then fix the concentration of CD to 0.2 mg/mL and the ratio between EuDES and TbDES to 2:1 to 3:1. Then adjust the dosage of PDES, EuDES and TbDES to control the fluorescence intensity of the luminescent DES to make it compatible with the luminescence intensity of the carbon dots, thereby obtaining a white light liquid (CTEP).

The reason for introducing PDES as a diluent is that if CD is directly dissolved in the luminescent DES, the latter will have too strong fluorescence to obtain white light, and the luminescent DES needs to be diluted to control its luminescence intensity within a range close to that of CD. PDES will not have a negative impact on the luminescence ability of the three components and can give the mixed liquid the ability to polymerize.

As shown in FIG5 , the prepared white light liquid is a light yellow transparent liquid under sunlight, and the light yellow color is caused by the dispersion of carbon dots; it exhibits white fluorescence under ultraviolet light, and the CIE coordinates are (0.31, 0.33).

After obtaining the white light liquid, the white light liquid is solidified onto the ultraviolet LED chip by using a glue dripping method. After the circuit is connected, the LED can be seen to emit bright white light without short circuit.

In addition, the white light liquid is polymerized into an elastomer. Although the fluorescence intensity is reduced due to the cross-linked structure, a fluorescent elastomer with a variety of fluorescent colors is still obtained.

Results and Discussion

First, according to the infrared images of EuDES and TbDES, as shown in Figure 6, it can be seen that in LnDES, the wide band of 3070-3590 cm ^-1 corresponds to NH or OH stretching vibration, which may come from urea and crystal water. The peaks around 1650 and 1580 cm ^-1 correspond to the stretching vibration of C=O, and the peak of 1470 cm ^-1 corresponds to the stretching vibration of CN, proving the presence of Urea in LnDES. And compared with the raw material Urea, the stretching vibration peak of the carbonyl group in DES is red-shifted, and the stretching vibration peak of the amino group is blue-shifted. The reason should be that the carbonyl group in Urea participates in the formation of coordination bonds, which causes the change of electron density. Therefore, it is inferred that urea is coordinated with europium ions or terbium ions through carbonyl oxygen, thereby forming a lanthanide low eutectic solvent.

Through DSC test, we know that as the amount of ligand increases, the melting point of LnDES decreases, and the lowest melting point of EuDES can reach -61°C, and the lowest melting point of TbDES can reach -66°C. This is also an indirect evidence that the coordination structure of LnDES with different ligand contents is different.

In addition, the thermal decomposition temperature of europium-based DES is 265°C, and the thermal decomposition temperature of terbium-based DES is 259°C, both of which have good thermal stability.

According to rheological tests, unlike the common type III DES which has a higher viscosity, the viscosity of LnDES is lower and can be reduced to below 100 cP as the ligand ratio increases.

The viscosity of LnDES changes, which in turn affects the conductivity. The conductivity of LnDES-8 with lower viscosity is doubled compared to LnDES-1 with higher viscosity. In addition, LnDES has a wide electrochemical window of nearly 2V.

Through fluorescence spectrum test, it can be seen that the maximum emission peak of europium-based low eutectic solvent is 613nm under 365nm ultraviolet light excitation, and the maximum emission peak of terbium-based DES is 543nm under 365nm ultraviolet light excitation. Comprehensive analysis of other secondary peaks shows that their emission is consistent with the characteristic emission of europium and terbium elements. No emission peak from the ligand is found, and it is proved that different ligand dosages have no effect on the emission wavelength of LnDES. However, according to the quantum yield results, it can be seen that a larger ligand dosage can increase the quantum yield of LnDES, which can be increased by up to about 30%.

The synthesis process of carbon dots should involve the decomposition of disodium ethylenediaminetetraacetic acid salt and the in situ surface grafting reaction between the amine groups of tetraethylenepentamine and the carboxyl groups in the pyrolyzed material. This can be confirmed by the IR results. In the IR spectrum, it can be seen that the two peaks at 1669cm ^-1 and 1593cm ^-1 in the carbon dots correspond to the stretching vibration of the C=O bond of the amide group, and the broad peak at 3390cm ^-1 corresponds to the stretching vibration of the NH in the amide group.

According to the fluorescence spectrum, the emission peak of the carbon dots after dialysis shifts from 435nm before dialysis to about 455nm, and from the CIE chromaticity diagram, the luminescent color is also close to cyan, so it is not suitable for use as a blue light component. Therefore, in the experiment of tuning white light, undialyzed carbon dots are selected as the blue light component.

In summary, red-light-emitting EuDES and TbDES were obtained using urea, europium nitrate and terbium nitrate respectively, and carbon dots with blue light emission ability were synthesized. The three were dissolved in PDES in appropriate proportions to obtain a liquid with white light emission ability. The liquid was solidified onto a UV LED chip by glue dripping to obtain a white light LED.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims (7)

1. A method for preparing a white luminescent soft material based on a lanthanide deep eutectic solvent and carbon dots, characterized in that it comprises the following steps: Mixing and heating the amide substance and the europium salt to obtain the first deep eutectic solvent EuDES; Mixing the amide substance and the terbium salt and heating them to obtain the second deep eutectic solvent TbDES; The mixed solution of the carbon source and the surface passivator is heated and dried, and then stirred and pyrolyzed to prepare blue light carbon dots; The first low eutectic solvent, the second low eutectic solvent, the blue light carbon dots and the diluent are mixed in proportion to prepare a white light-emitting soft material; The amide substance is urea; The europium salt is europium nitrate; The terbium salt is terbium nitrate; The molar ratio of europium salt to amide substance is 1:2~1:8; The molar ratio of terbium salt to amide substance is 1:2~1:8; The carbon source is disodium ethylenediaminetetraacetic acid; The surface passivating agent is tetraethylenepentamine. 2. The method for preparing a white luminescent soft material based on a lanthanide low eutectic solvent and carbon dots according to claim 1 is characterized in that the temperature of the co-mixing heating is 50-60°C and the time of the co-mixing heating is 0.5-1.5h. 3. The method for preparing a white luminescent soft material based on a lanthanide low eutectic solvent and carbon dots according to claim 1, characterized in that the pyrolysis temperature is 200-250°C and the pyrolysis time is 1-3h. 4. The method for preparing a white light-emitting soft material based on a lanthanide low eutectic solvent and carbon dots according to claim 1, characterized in that in the white light-emitting soft material, the mass ratio of EuDES to TbDES is 2:1~3:1, and the mass of the blue light carbon dots is adjusted so that its concentration in the mixture reaches 0.1-0.5 mg/mL. 5 . The method for preparing a white luminescent soft material based on a lanthanide low eutectic solvent and carbon dots according to claim 1 , wherein the diluent is PDES. 6. A white luminescent soft material based on a lanthanide low eutectic solvent and carbon dots, characterized in that it is prepared by the preparation method described in any one of claims 1 to 5. 7. A white light LED, characterized by comprising an LED chip and the white light-emitting soft material layer according to claim 6 loaded on the LED chip.