A high-efficiency, high-yield white carbon dot phosphor, its synthesis method and application

Abstract

This invention belongs to the field of fluorescent materials, specifically relating to a high-efficiency, high-yield white carbon dot phosphor, its synthesis method, and its applications. The synthesis method includes the following steps: Step 1: Melamine is dissolved in DMF, ultrasonically dispersed until fully dissolved, and then transferred to a high-temperature reactor for reaction. After the reaction is complete, the mixture is cooled to room temperature. Step 2: The mixed solution after the reaction is filtered, the resulting solid product is dried, and cooled to room temperature to obtain the white carbon dot phosphor. The white carbon dot phosphor is synthesized in one step via a melamine solvothermal method. The solid white carbon dots obtained by this invention exhibit good photostability and thermal stability, and have a long shelf life. The carbon dot yield is as high as 75%, and the quantum yield (37%). The synthesis method is simple and easy for industrial production. It also has a wider fluorescence emission range, making it suitable for applications in white LEDs and other lighting devices, and has a higher color rendering index.

Description

Technical Field

[0001] This invention belongs to the field of fluorescent materials, and particularly relates to a high-efficiency, high-yield white light carbon dot phosphor, its synthesis method, and its application in the light-emitting layer of white LEDs. Background Technology

[0002] White light-emitting diodes (WLEDs), as the fourth generation of lighting sources, have been widely used in lighting and display fields due to their advantages of energy saving, environmental friendliness, high efficiency, safety, long lifespan, and small size, becoming one of the most promising high-tech directions of this century. Currently, there are three main strategies for achieving white light emission from photoluminescent LEDs: using blue LED chips to excite yellow phosphors, using ultraviolet LED chips to excite blue, green, and red primary colors to synthesize white light, and using ultraviolet LED chips to excite white phosphors. For the first strategy, due to the lack of long-wavelength emission, the color rendering index (CRI) of WLEDs is relatively low. While the second strategy yields WLEDs with higher CRI values, its complex manufacturing process and high cost make large-scale production difficult. The third strategy, using white phosphors, can solve the above problems. Therefore, the preparation of white light-emitting materials has become a research hotspot.

[0003] Carbon dots (CDs) have attracted widespread attention from researchers as a novel luminescent material. Compared to perovskite quantum dots and rare-earth nanoparticles, they possess excellent biocompatibility, stability, and low cost. CD-based phosphors are considered to be a promising next-generation photoelectric conversion material.

[0004] A method for preparing white-light graphene quantum dot phosphors is disclosed in patent document CN2020111295609, comprising: mixing melamine, p-phenylenediamine, and a solvent to form a reaction solution; heating the reaction solution to carry out a hydrothermal reaction; cooling to room temperature; and finally filtering and drying to obtain white-light graphene quantum dot phosphors. This method uses both p-phenylenediamine and melamine as precursors and anhydrous ethanol as the reaction solvent, which is a dual-precursor reaction. This results in high raw material costs, a complex synthesis process, and a low yield of CDs (quantum dot phosphors), around 10%, which greatly limits the application of CDs-based phosphors. To solve the above-mentioned problems in the synthesis process of CDs and improve the application prospects of CDs-based phosphors, we propose a new, efficient, and convenient one-step method for synthesizing white-light CDs using a single precursor. Summary of the Invention

[0005] The purpose of this invention is to provide a one-step method for efficiently preparing white carbon dot phosphors from a single precursor and its application, in order to solve the problems of high cost, complex synthesis process, low yield, and difficulty in large-scale synthesis of white carbon dot materials in the prior art.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a method for synthesizing high-efficiency and high-yield white light carbon dot phosphor, comprising the following steps:

[0007] Step 1: Dissolve melamine in DMF, disperse it thoroughly by ultrasonication, then transfer it to a high-temperature reactor for reaction. After the reaction is complete, cool it to room temperature.

[0008] Step 2: Filter the mixed solution after the reaction, dry the solid product obtained by filtration, and cool it to room temperature to obtain white carbon dot phosphor.

[0009] Furthermore, the dosage of melamine is 0.1-0.25g, and the dosage of DMF is 10-25ml.

[0010] Furthermore, the reaction conditions in the high-temperature reactor in step one above are: temperature 180-240℃, time 8-14 hours.

[0011] Furthermore, the above-mentioned high-efficiency, high-yield white carbon dot phosphor.

[0012] Furthermore, the aforementioned white carbon dot phosphor is used in the light-emitting layer of white LEDs.

[0013] Furthermore, the application of the aforementioned high-efficiency, high-yield white carbon dot phosphor in the light-emitting layer of white LEDs includes the following steps:

[0014] Step 1: Use a commercially available InGaN chip with an emission wavelength of 380-420nm as the LED excitation substrate;

[0015] Step 2: Mix AB-silicone evenly, and thoroughly mix the white carbon dot phosphor and binder at a mass ratio of 1:1-2. Deposit the mixture onto the LED excitation substrate.

[0016] Step 3: Curing in an oven and encapsulation to obtain white LED devices.

[0017] Furthermore, the mass ratio of the AB-silicone mentioned above is 1:4.

[0018] Furthermore, the above-mentioned curing process specifically involves continuous heating in an oven at 80-100°C for 0.5-1 hour.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] 1. This invention uses only melamine as a single precursor and DMF as a reaction solvent to synthesize solid white light carbon dots in a one-step process. It features low raw material costs, high product yield, a simple and efficient synthesis method, and the potential for large-scale production.

[0021] 2. This invention synthesizes solid white light carbon dots via a one-step solvothermal method, eliminating the need for additional matrix-assisted luminescence and allowing direct application to LED light-emitting layers. The material exhibits good thermal stability, stable optical properties, and long shelf life.

[0022] 3. The solid white carbon dots obtained by this invention have a yield of up to 75%, and the product obtained by this invention also has a high quantum yield (37%). The fluorescence spectrum covers almost the entire visible light region, and it has the characteristic of high color rendering index (CRI > 80) when applied to LED lighting devices. Attached Figure Description

[0023] Figure 1 and Figure 2 This is a structural characterization diagram of the white carbon dots in Example 1 of the present invention;

[0024] in Figure 1 ab are TEM images of CDs at 20nm and 5nm, respectively. Figure 2 a is the carbon dot XRD pattern;

[0025] Figure 2 Raman spectrum of b carbon point; Figure 2 c is the FT-IR plot of carbon dots; Figure 2 d represents the XPS total spectrum of the CDs;

[0026] Figure 3 This is a high-resolution XPS spectrum and fluorescence performance diagram of the white carbon dot in Example 1 of the present invention;

[0027] in Figure 3 a is a high-resolution C1s plot; Figure 3 b is a high-resolution N1s plot; Figure 3 c is the high-resolution O1s plot; 3d are the spectra of CDs under different excitations. Figure 3 e represents the fluorescence lifetime of CDs; Figure 3 f is the PLQY plot of CDs;

[0028] Figure 4 This is a CIE coordinate diagram of a white LED.

[0029] Figure 5 This is the spectrum of a white LED. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] Example 1: A method for synthesizing high-efficiency, high-yield white light carbon dot phosphor, comprising the following steps:

[0032] Step 1: Weigh 0.2g of melamine into a beaker, add 10ml of N,N-dimethylformamide (DMF), and sonicate for 15min until fully dissolved; transfer the solution to a high-temperature, high-pressure reactor and react at 200°C for 10h; after the reaction is complete and the temperature has cooled to room temperature,

[0033] Step 2: Filter the reaction product through filter paper to obtain a white, flaky crystalline solid product. Collect the solid product and transfer it to a vacuum drying oven, dry it at 140°C for 2 hours, and cool it to room temperature to obtain solid white carbon dots.

[0034] The CIE coordinates (0.27, 0.30) are close to pure white light, with a carbon dot yield of 75% and a quantum yield of 37%.

[0035] Figure 1 A 20nm TEM image shows that the white carbon dots exhibit a significant aggregation effect. It can be clearly seen that carbon dots of different sizes aggregate together to form a planar structure with large size and high carbonization. Figure 1 A 10nm TEM image more clearly shows carbon dots of different sizes distributed on the surface of the large carbonized structure, with a clear graphite spacing of 0.21, corresponding to the lattice spacing within the (100) plane of the graphite structure. The TEM image reveals that the white light emission from the carbon dots, as composite light, originates from the superposition of wavelengths emitted by carbon dots of different sizes. Simultaneously, the significant aggregation effect and the large-size planar carbonized structure suppress energy transfer between different particle sizes and luminescence band gaps of the carbon dots, while also suppressing the spin-vibration effect within the carbon dot molecules, thereby preventing non-radiative transitions and achieving the suppression of the ACQ effect, thus realizing solid-state white light emission. Figure 2 The XRD pattern of a shows a broad diffraction peak at 26°, corresponding to the graphitic structure of the carbon dots in the carbon (002) interlayer spacing. Simultaneously, a distinct strong diffraction peak appears at 29°, proving that the carbon dots are located in a highly crystalline graphitized space. Furthermore, through… Figure 2 Raman spectral characterization of b shows that the D and G bands at 1390 cm⁻¹ and 1563 cm⁻¹ are graphite structures, and their intensities are very close. G / I D The ratio of 1.04 indicates that CDs have a highly graphitized structure.

[0036] pass Figure 2The structure and functional groups of white light CDs were investigated using FT-IR spectra. Obvious double stretching vibrations of NH4+, belonging to primary amines, were observed at 3132 cm⁻¹ and 3358 cm⁻¹, while stretching vibrations of the carbonyl C=O double bond were observed at 1657 cm⁻¹. C=N stretching vibrations were present at 1525 cm⁻¹, and a distinct absorption peak characteristic of the triazine ring appeared at 801 cm⁻¹. The XPS full spectrum of the W-CDs clearly showed three typical peaks: carbon (285 eV), oxygen (531 eV), and nitrogen (400 eV). Figure 2 d). This indicates that CDs are all composed of the same elements and have a very high nitrogen content. High-resolution XPS display ( Figure 3 The C1S spectra of carbon dots deconvolve into three peaks: C=C (284.5 eV) corresponding to sp2 carbon, CO / CN (285.0 eV) corresponding to sp3 carbon, and carbon-based carbon C=O (288.1 eV). The N1S spectra deconvolve into two peaks: pyridine nitrogen (C=N) (399.0 eV) and amide nitrogen (399.6 eV). The O1S spectra deconvolve into C=O (532.9 eV) and CO (532.3 eV). These results indicate that carbon dots possess abundant functional groups, the high nitrogen content originates from the precursor melamine, and the low O content suggests that DMF, acting as a solvent, also participates in the reaction. Figure 3 The fluorescence spectrum of the white carbon dots in d shows that the white carbon dots have a large half-width, covering almost the entire visible light region. At the same time, obvious emission peaks appear at 400nm, 490nm, and 580nm, further proving that the white light emission comes from the superposition of light of different emission wavelengths. Figure 3 e and Figure 3 f shows that at the optimal excitation wavelength, its fluorescence lifetime was measured to be 1.16 ns and its PLQY to be 37%.

[0037] Example 2: A method for synthesizing high-efficiency, high-yield white light carbon dot phosphor, comprising the following steps:

[0038] The operating steps in this embodiment are the same as in Example 1. The difference is that 0.1g of melamine was weighed, 15ml of DMF was added, and after complete dissolution, it was transferred to a high-pressure reactor and reacted at 180°C for 6 hours. The C1E coordinates of the white light carbon dots obtained were (0.25, 0.26).

[0039] Example 3: A method for synthesizing high-efficiency, high-yield white light carbon dot phosphor, comprising the following steps:

[0040] The operating steps in this embodiment are the same as in Example 1. The difference is that 0.15g of melamine was weighed, 20ml of DMF was added, and after complete dissolution, it was transferred to a high-pressure reactor and reacted at 240°C for 6 hours. The C1E coordinates of the white light carbon dots obtained were (0.24, 0.27).

[0041] Example 4: A method for synthesizing high-efficiency, high-yield white light carbon dot phosphor, comprising the following steps:

[0042] The operating steps in this embodiment are the same as in Example 1. The difference is that 0.25g of melamine was weighed, 25ml of DMF was added, and after complete dissolution, it was transferred to a high-pressure reactor and reacted at 240°C for 12 hours. The C1E coordinates of the white light carbon dots obtained were (0.24, 0.28).

[0043] Example 5: An application of a high-efficiency, high-yield white carbon dot phosphor in the light-emitting layer of a white LED, comprising the following steps:

[0044] Step 1: Use a commercially available InGaN chip with an emission wavelength of 380nm as the LED excitation substrate, and use the white carbon dot phosphor from Example 1 above as the LED color conversion layer.

[0045] Step 2: Mix AB-silicone at a mass ratio of 1:4 until homogeneous, and mix phosphor and binder at a mass ratio of 1:2 until fully stirred. Deposit the mixture onto the InGaN chip of the LED.

[0046] Step 3: After heating continuously in an oven at 80°C for 1 hour, the white LED device is finally cured and encapsulated.

[0047] Example 6: An application of a high-efficiency, high-yield white carbon dot phosphor in the light-emitting layer of a white LED, comprising the following steps:

[0048] Step 1: Use a commercially available InGaN chip with an emission wavelength of 400nm as the LED excitation substrate, and use the white carbon dot phosphor from Example 1 above as the LED color conversion layer.

[0049] Step 2: Mix AB-silicone at a mass ratio of 1:3 until homogeneous, and mix phosphor and binder at a mass ratio of 1:1 thoroughly. Deposit the mixture onto the InGaN chip of the LED.

[0050] Step 3: After continuous heating in an oven at 90℃ for 0.5 hours, the white LED device is finally cured and packaged.

[0051] like Figure 4 and Figure 5As shown, WLEDs emit high-quality pure white light when driven by a 30mA current, with CIE coordinates of (0.33, 0.33), CCT of 5405K, and a color rendering index (CRI) of 80.9, which meets a very high standard for commercial white light use and can be applied in a variety of applications.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for synthesizing white light carbon dot fluorescent powder, characterized in that: The method comprises the following steps Step one, dissolve melamine in DMF, ultrasonic dispersion, after fully dissolving, transfer to high temperature reaction kettle for reaction, cool to room temperature after reaction; Step two, filter the mixed solution after reaction, dry the solid product obtained by filtration, cool to room temperature, obtain white light carbon dot fluorescent powder; The amount of melamine is 0.1-0.25g, and the amount of DMF is 10-25ml; The reaction conditions of the high temperature reaction kettle in step one are: temperature is 180-240℃, time is 8-14 hours.

2. A white light carbon dot fluorescent powder prepared by the method of claim 1.

3. The application of a white light carbon dot fluorescent powder prepared by the method of claim 1 to a white light LED light emitting layer. 4.The application of white light carbon dot fluorescent powder for white light LED light emitting layer according to claim 3, characterized in that: The method comprises the following steps Step one, use a commercial InGaN chip with an emission wavelength of 380-420nm as an LED excitation substrate; Step two, take AB-silica gel and mix uniformly, mix the white light carbon dot fluorescent powder and the adhesive with a mass ratio of 1:1-2, deposit the mixture on the LED excitation substrate; Step three, solidify in an oven, package to obtain a white light LED device, and the white light carbon dot fluorescent powder serves as an LED color conversion layer. 5.The application of white light carbon dot fluorescent powder for white light LED light emitting layer according to claim 4, characterized in that: The mass ratio of AB-silica gel is 1:

4. 6.The application of white light carbon dot fluorescent powder for white light LED light emitting layer according to claim 4 or 5, characterized in that: Solidification specifically refers to continuous heating in an oven at 80-100°C for 0.5-1 hour.

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