Composite film capable of generating white fluorescence under excitation of near ultraviolet light as well as preparation method and application of composite film

Abstract

The invention discloses a composite film capable of being excited by near ultraviolet light to generate white fluorescence and a preparation method of the composite film. The preparation method comprises the following steps: (1) preparing a blue light carbon dot solution by taking a natural plant jasmine flower as a carbon source and utilizing a hydrothermal synthesis method; (2) adding the blue light carbon dot solution and natural vegetable dye berberine into a polyvinyl alcohol aqueous solution, adding glycerol as a cross-linking agent, and uniformly mixing to prepare a precursor solution; and (3) vertically immersing a substrate into the prepared precursor solution at a constant speed, standing, vertically pulling the substrate, then putting the substrate into a drying box for drying, and repeatedly immersing, pulling and drying to obtain the composite fluorescent film with a certain thickness. The method is simple, and raw materials are wide in source, green and non-toxic; the prepared film emits white fluorescence under excitation of near ultraviolet light, and white light emission with different properties can be obtained by changing parameters of raw materials. As a near ultraviolet excited fluorescent material for a white light LED, the fluorescent material can be applied to the fields of display, illumination, sensing and the like.

Description

Technical Field

[0001] The invention relates to the field of composite films, in particular to a natural plant-based composite film which can be excited by near-ultraviolet light to produce white fluorescence and a preparation method thereof. Background Art

[0002] At present, fluorescent materials for white light LEDs are all made through chemical synthesis, which has diversity and color adjustability, but the disadvantages of complex synthesis, high cost and environmental damage limit their practical application. Natural plant dyes refer to dyes extracted from the roots, stems, leaves and fruits of plants without chemical processing. They are non-toxic, low-cost and have strong fluorescence, which gives them significant advantages in the field of white light LEDs.

[0003] In 2021, the inventors publicly reported the luminescence properties of Coptis chinensis extract (berberine) powder, and found that it can emit bright yellow light under the excitation of blue light or near-ultraviolet light (Applied Optics, 2021, 60: 4716-4722). In 2023, the inventors studied a film that can produce white fluorescence when excited by blue light, and applied for a patent (patent number ZL 2023 10620819.7). This film is a composite luminescent film of berberine and red light carbon dots. The prepared film can produce white fluorescence under the excitation of 430nm blue light, and can be used as a fluorescent material for blue light-excited white light LEDs. However, white light LED devices excited by blue light have problems such as low color reproduction and poor color stability.

[0004] White light LED devices excited by near ultraviolet light, due to the insensitivity of vision to near ultraviolet light, the color of this type of white light LED is determined by the fluorescent material, so the color is stable and the color reproduction is high. To this end, the present invention uses natural plant jasmine as a carbon source to prepare carbon dots, and the prepared carbon dots emit blue light under the excitation of near ultraviolet light. Since berberine can be excited by blue light and near ultraviolet light to produce yellow light, it is compounded with berberine to prepare a composite film, and the composite film can be excited by near ultraviolet light to produce white fluorescence. Since the emission peak of the prepared carbon dots almost coincides with the absorption peak of berberine, energy transfer can occur between the two, so the luminescence spectrum of the composite film can be adjusted by changing relevant parameters. Summary of the invention

[0005] The purpose of the present invention is to synthesize a composite film that can be excited by near-ultraviolet light to produce white fluorescence. The film prepared by the present invention is a composite film of blue light carbon dots prepared using natural plant jasmine as a carbon source and natural plant dye berberine. The present invention has the characteristics of low cost, green environmental protection, simple method, etc., and can be used as a fluorescent material for white light LED excited by near-ultraviolet light, and is applied to the fields of display, lighting and sensing.

[0006] The object of the present invention is achieved by the following technical measures:

[0007] A method for preparing a composite film that generates white fluorescence under near-ultraviolet light excitation comprises the following steps:

[0008] (1) Synthesis of blue light carbon dot solution: Take a certain amount of fresh jasmine flowers, use anhydrous ethanol as an extraction solvent, and soak at room temperature; then take an appropriate amount of the extract for hydrothermal carbonization, centrifuge, and filter the supernatant to obtain a blue light carbon dot solution;

[0009] (2) Preparation of precursor solution: polyvinyl alcohol was dissolved in deionized water, and a certain amount of glycerol, blue light carbon dot solution and berberine were added in sequence, and magnetic stirring was performed at room temperature to obtain a uniform and stable precursor solution;

[0010] (3) Preparation of composite thin film: The substrate is vertically immersed in the prepared precursor solution at a uniform speed. After standing, the substrate is vertically pulled up at a certain rate. The substrate is then placed in a drying oven for drying. A composite thin film of a certain thickness can be obtained by repeated immersion, pulling up and drying.

[0011] The preferred embodiment is that in step (1), the usage ratio of the fresh jasmine to anhydrous ethanol is 1:25 (g:ml), the hydrothermal carbonization reaction temperature is 160-200°C, and the reaction time is 3-5h.

[0012] The preferred solution comprises the following raw material components in the following weight ratio (ml:ml:g): 1-10ml of glycerol, 10-20ml of blue light carbon dot solution, and 0.01-0.05g of berberine.

[0013] The composite film obtained by the above preparation method is applied in the fields of display, lighting and sensing.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: the present method is based on natural plants, especially specifically selecting fresh jasmine as a carbon source, and synthesizing carbon dots that produce blue light when excited by near-ultraviolet light through a simple hydrothermal method, and mixing them with polyvinyl alcohol, berberine and glycerol, and preparing a composite film that can be excited by near-ultraviolet light to produce white fluorescence by a pulling method, and its luminescence spectrum can be regulated by changing relevant parameters.

[0015] Compared with white light excited by blue light, the present application is excited by near-ultraviolet light to produce white fluorescence with stable color and high color reproduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a transmission electron microscope image of blue light carbon dots synthesized by hydrothermal method using natural plant jasmine as carbon source;

[0017] Figure 2The emission spectra of fluorescent carbon dots synthesized by the hydrothermal method under different excitation wavelengths are shown in the present invention, using natural plant jasmine (a), green radish leaves (b), lemon juice (c), pomegranate leaves (d), persimmon leaves (e), pitaya juice (f), mulberry stems (g), mulberry leaves (h) and tea leaves (i) as carbon sources;

[0018] Figure 3 The absorption spectrum (a) of the berberine aqueous solution used in the present invention and the emission spectrum (b) at different excitation wavelengths (300-380nm);

[0019] Figure 4 These are the luminescence photos and luminescence spectrum diagrams of the white light LED device prepared with the composite film described in Example 1.

[0020] Figure 5 This is an emission spectrum of the composite film described in Example 2 under 365nm near-ultraviolet light excitation; DETAILED DESCRIPTION

[0021] The present invention is described in detail below by way of examples. It is necessary to point out that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Those skilled in the art in this field can make some non-essential improvements and adjustments to the present invention based on the above content of the present invention.

[0022] Embodiment 1:

[0023] (1) Take 4 g of fresh jasmine, use 100 mL of anhydrous ethanol as an extraction solvent, soak at room temperature, and collect the extract after 18 hours; take 16 mL of the extract and mix it with 4 mL of deionized water, then transfer the mixed solution to a reactor for hydrothermal carbonization, set the reaction temperature to 160°C, the reaction time to 3 hours, and naturally cool to room temperature after the reaction is completed; then centrifuge at 3000 rpm for 10 minutes, take the supernatant and filter it to obtain the fluorescent carbon dot solution of this embodiment.

[0024] The transmission electron microscope image of the fluorescent carbon dots is as follows Figure 1 As shown in FIG. 1 , the carbon dots are quasi-spherical nanoparticles with good monodispersity and an average size of about 2.5 nm. The emission spectra of the fluorescent carbon dots described in this embodiment at different excitation wavelengths are shown in FIG. Figure 2 As shown in a, it emits bright blue light under the excitation of near-ultraviolet light.

[0025] (2) Dissolve 0.4 g of polyvinyl alcohol in 10 ml of deionized water, add 1 ml of glycerol, 10 ml of fluorescent carbon dot solution, and 0.02 mg of berberine in sequence, and stir magnetically at room temperature to obtain a uniform and stable precursor solution.

[0026] (3) The cleaned substrate is vertically immersed in the prepared precursor solution at a uniform speed. After standing for 60 seconds, the substrate is vertically pulled up at a rate of 3 cm / min. The substrate is then placed in a drying oven and dried at 100° C. for 1 hour. The composite film of this embodiment can be obtained by repeating the immersion, pulling and drying for 9 times.

[0027] The composite film of this embodiment is combined with a near-ultraviolet LED chip (365nm) to obtain a white light LED. The luminous photos and luminous spectrum are shown in FIG. Figure 4 As shown, the color coordinates of the device are (0.244, 0.313).

[0028] Embodiment 2:

[0029] The preparation method of the composite film of this embodiment is the same as that of embodiment 1, except that different amounts of berberine (0.01 mg, 0.02 mg, 0.03 mg, 0.05 mg) are added in step (2). The composite film of this embodiment is obtained by dipping, pulling and drying once in step (3).

[0030] The emission spectrum of the composite film under 365nm near-ultraviolet light excitation is as follows: Figure 5 As shown, the emission spectrum presents a blue light emission band attributed to the carbon dots and a yellow-green light emission band attributed to berberine, and the intensity ratio of the two emission bands changes with the change of the amount of berberine added.

[0031] Comparative Example 1

[0032] The preparation method of the fluorescent carbon dot solution described in this embodiment is the same as that in Example 1, except that different carbon sources are used respectively: green radish leaves, lemon juice, pomegranate leaves, persimmon leaves, pitaya juice, dried mulberries, mulberry leaves and tea leaves to obtain the fluorescent carbon dot solution.

[0033] The emission spectra of the above fluorescent carbon dot solution at different excitation wavelengths are as follows: Figure 2 bi. Compare Figure 2 a and Figure 2 bi, it can be seen that the fluorescent carbon dots prepared with jasmine as the carbon source emit bright blue light under the excitation of near-ultraviolet light, and the mixture of blue light and yellow light can produce white light; and with the change of excitation wavelength, the emission wavelength does not change significantly, which is beneficial to improve the performance and stability of white light devices. However, the fluorescent carbon dots prepared with green radish leaves as the carbon source ( Figure 2 bg), can emit blue light under the excitation of near-ultraviolet light, but with the change of excitation wavelength, the emission wavelength has a significant red shift, which is not conducive to the improvement of the performance and stability of white light devices. Figure 2(h, i), under the excitation of near-ultraviolet light, red light is emitted, and the mixture of red light and yellow light cannot produce white light. Therefore, the present invention selects jasmine as the carbon source to prepare fluorescent carbon dots.

[0034] The above embodiments are provided for the purpose of a clearer explanation and are not intended to limit the implementation methods. Other changes or modifications in different forms may be made on this basis, and the changes or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A method for preparing a composite film that generates white fluorescence under near-ultraviolet light excitation, characterized in that: The steps include: (1) Synthesis of blue light carbon dot solution: Take a certain amount of fresh jasmine flowers, use anhydrous ethanol as an extraction solvent, and soak at room temperature; then take an appropriate amount of the extract for hydrothermal carbonization, centrifuge, and filter the supernatant to obtain a blue light carbon dot solution; (2) Preparation of precursor solution: polyvinyl alcohol was dissolved in deionized water, and a certain amount of glycerol, blue light carbon dot solution and berberine were added in sequence, and magnetic stirring was performed at room temperature to obtain a uniform and stable precursor solution; (3) Preparation of composite thin film: The substrate is vertically immersed in the prepared precursor solution at a uniform speed. After standing, the substrate is vertically pulled up at a certain rate. The substrate is then placed in a drying oven for drying. A composite fluorescent film of a certain thickness can be obtained by repeated immersion, pulling up and drying.

2. The preparation method according to claim 1, characterized in that In step (1), the usage ratio of the fresh jasmine to anhydrous ethanol is 1:25 (g:ml), the hydrothermal carbonization reaction temperature is 160-200°C, and the reaction time is 3-5h.

3. The preparation method according to claim 1, characterized in that: The invention comprises the following raw material components in the following weight ratio (ml:ml:g): 1-10ml of glycerol, 10-20ml of blue light carbon dot solution and 0.01-0.05g of berberine.

4. Application of the composite fluorescent film obtained by the preparation method according to any one of claims 1 to 3 in the fields of display, lighting and sensing.

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