High-efficiency and high-yield white light carbon dot fluorescent powder as well as synthesis method and application thereof

Abstract

The invention belongs to the field of fluorescent materials, and particularly relates to efficient and high-yield white light carbon dot fluorescent powder, a synthesis method and application. The synthesis method comprises the following steps: step 1, dissolving melamine in DMF (Dimethyl Formamide), transferring into a high-temperature reaction kettle for reaction after the melamine is fully dissolved by ultrasonic dispersion, and cooling to room temperature after the reaction is finished; and 2, filtering the reacted mixed solution, drying a solid product obtained by filtering, and cooling to room temperature to obtain the white light carbon dot fluorescent powder. The white light carbon dot fluorescent powder is synthesized in one step through a melamine solvothermal method, and the obtained solid white light carbon dots have good light stability and thermal stability and long preservation time. The yield of the carbon dots reaches up to 75%, the quantum yield is 37%, the synthesis method is simple, and industrial production is easy. Meanwhile, the fluorescent material has a wider fluorescence emission range, is applied to the field of lighting devices such as white light LEDs and has a higher color rendering index.

Description

Technical Field

[0001] The invention belongs to the field of fluorescent materials, and in particular relates to a high-efficiency and high-yield white light carbon dot fluorescent powder, a synthesis method and an application in a white light LED luminescent layer. Background Art

[0002] As the fourth generation of lighting sources, white light emitting diodes (WLEDs) have been widely used in the fields of lighting and display due to their advantages of energy saving, environmental protection, high efficiency, safety, long life and small size. They have become the most promising high-tech direction in this century. At present, there are three main strategies to achieve photoluminescent LED white light emission: using blue LED chips to excite yellow phosphors, ultraviolet LED chips to excite blue, green and red primary colors to synthesize white light, and 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. Although the second strategy will obtain WLEDs with higher CRI values, it is difficult to achieve large-scale production and application due to the complex manufacturing and high cost. The third strategy, the use of white phosphors can solve the above problems. Therefore, the preparation of white light emitting materials has become a research hotspot.

[0003] Carbon dots (CDs) as a new type of luminescent material have attracted extensive attention from researchers. Compared with perovskite quantum dots, rare earth nanoparticles and other luminescent materials, they have good biocompatibility, stability and low cost. CDs-based phosphors are considered to be the next generation of good photoelectric conversion materials.

[0004] A method for preparing white light graphene quantum dot phosphor is disclosed in the document with patent number "CN2020111295609", including: mixing melamine, p-phenylenediamine and a solvent evenly to form a reaction solution; heating the reaction solution for hydrothermal reaction, cooling to room temperature, and finally filtering and drying to obtain white light graphene quantum dot phosphor. This scheme uses p-phenylenediamine and melamine as precursors and anhydrous ethanol as a reaction solvent. It is a dual precursor reaction, which has high raw material costs, complex synthesis process, and low yield of CDs products, about 10%, which greatly limits the application of CDs-based phosphors. In order to solve the above-mentioned problems of CDs in the synthesis process and improve the application prospects of CDs-based phosphors, we propose a new method for synthesizing white light CDs from a single precursor in a one-step method that is efficient and convenient. Summary of the invention

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

[0006] In order to achieve the above object, the present invention adopts the following technical scheme: a method for synthesizing white light carbon dot phosphor with high efficiency and high yield, comprising the following steps:

[0007] Step 1, dissolving melamine in DMF, dispersing it by ultrasonication until it is fully dissolved, transferring it to a high temperature reactor for reaction, and cooling it to room temperature after the reaction is completed;

[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 light carbon dot phosphor.

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

[0010] Furthermore, the reaction conditions of the high temperature reactor in the above step 1 are: temperature of 180-240° C., and time of 8-14 hours.

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

[0012] Furthermore, the above-mentioned white light carbon dot phosphor is used in the application of white light LED light-emitting layer.

[0013] Furthermore, the application of the above-mentioned high-efficiency and high-yield white light carbon dot phosphor for the white light LED light-emitting layer comprises the following steps:

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

[0015] Step 2: Take AB-silica gel and mix them evenly, stir and mix the white light carbon dot phosphor and the adhesive in a mass ratio of 1:1-2, and deposit the mixture on the LED excitation substrate;

[0016] Step 3: Curing in an oven and encapsulating to obtain a white light LED device.

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

[0018] Furthermore, the curing is specifically performed by continuously heating in an oven at 80-100° C. for 0.5-1 hour.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The present invention uses only melamine as a single precursor and DMF as a reaction solvent to synthesize solid white light carbon dots in one step. The raw material cost is low, the product yield is high, the synthesis method is simple and efficient, and it has the characteristics of large-scale production;

[0021] 2. The present invention synthesizes solid white light carbon dots by a one-step solvothermal method, which does not require auxiliary luminescence through other matrices and can be directly applied to the LED light-emitting layer. The material has good thermal stability, stable optical properties and long shelf life;

[0022] 3. The solid white light carbon dots obtained by the present invention have a yield of up to 75%, and the product obtained by the present invention has a high quantum yield (37%). The fluorescence spectrum covers almost the entire visible light region, and has the characteristics of a high color rendering index (CRI>80) when applied to LED lighting devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 and Figure 2 This is a structural characterization diagram of the white light carbon dots of 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 XRD pattern of carbon dots;

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

[0026] Figure 3 The high-resolution XPS spectrum and fluorescence performance diagram of the white light carbon dots of Example 1 of the present invention;

[0027] in Figure 3 a is a high-resolution C1s image; Figure 3 b is a high-resolution N1s image; Figure 3 c is a high-resolution O1s image; 3d is a spectrum of CDs under different excitations; Figure 3 e is the fluorescence lifetime diagram of CDs; Figure 3 f is the PLQY diagram of CDs;

[0028] Figure 4 It is the CI E coordinate diagram of white light LED;

[0029] Figure 5 This is the spectrum of white light LED. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific implementation methods.

[0031] Embodiment 1, a method for synthesizing white light carbon dot phosphor with high efficiency and high yield, comprising the following steps:

[0032] Step 1: weigh 0.2g of melamine into a beaker, add 10ml of N,N-dimethylformamide (DMF), and ultrasonicate for 15min until it is fully dissolved; transfer the above solution to a high temperature and high pressure reactor and react at 200° for 10h; after the reaction is completed and the temperature is 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° for 2 h, and cool it to room temperature to obtain solid white light carbon dots.

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

[0035] Figure 1 a TEM image of 20 nm shows that white light carbon dots have an obvious aggregation effect. It can be clearly seen that carbon dots of different sizes aggregate together to form a large-scale highly carbonized planar structure. Figure 1 b 10nm TEM more clearly shows that the carbon dots of different particle sizes are distributed on the surface of the large carbonized structure, and the graphite spacing is clearly 0.21, corresponding to the lattice spacing in the (100) plane of the graphite structure. The TEM image shows that the white light emission of the carbon dots as a composite light comes from the superposition of the emission wavelengths of the carbon dots of different particle sizes. At the same time, the obvious aggregation effect and the large-scale planar carbonization structure inhibit the energy transfer between the different particle sizes and the luminescence band gap of CDs, and at the same time inhibit the spin-vibration effect of the carbon dots, thereby preventing the generation of non-radiative transitions, achieving the effect of suppressing the ACQ effect, and realizing solid white light emission. Figure 2 From the XRD graph of a, we can see that a broad diffraction peak appears at 26°, which corresponds to the graphite structure of the carbon dot graphite carbon (002) interlayer spacing. At the same time, there is an obvious strong diffraction peak at 29°, proving that the carbon dot is in a highly crystallized graphitized space. Figure 2 The Raman spectrum characterization of b shows that the D band and G band of the graphite structure at 1390cm-1 and 1563cm-1 are very close in intensity. G / I D The ratio is 1.04, indicating that CDs have a highly graphitized structure.

[0036] pass Figure 2c FT-IR images were used to study the structure and functional groups of white light CDs. At 3132cm-1 and 3358cm-1, there are obvious NH double peak stretching vibrations belonging to primary amines, and at 1657cm-1, there is the stretching vibration of the carbonyl C=O double bond. At 1525cm-1, there is the stretching vibration of C=N, and at 801cm-1, there is an obvious absorption peak unique to the triazine ring. The full XPS spectrum of W-CDs clearly shows three typical peaks: carbon (285eV), oxygen (531eV), nitrogen (400eV) ( Figure 2 d). This indicates that CDs are composed of the same elements and have a very high nitrogen content. High-resolution XPS shows ( Figure 3 ac), the C1S of the carbon dots can be deconvoluted into three peaks, namely C=C (284.5eV) corresponding to sp2 carbon, CO / CN (285.0eV) corresponding to sp3 carbon, and carbon-based carbon C=O (288.1eV). The N1S deconvoluted into two peaks, namely pyridine nitrogen (C=N) (399.0eV) and amide nitrogen (399.6eV). The O1S spectrum deconvoluted can be divided into C=O (532.9eV) and CO (532.3eV). These results show that the carbon dots have rich functional groups, the higher nitrogen content comes from the precursor melamine, and the lower O content indicates that DMF is also involved in the reaction as a solvent. Figure 3 From the white light carbon dots fluorescence spectrum of (d), it can be seen that the white light carbon dots have a large half-peak width, almost covering 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 the PLQY was 37%.

[0037] Embodiment 2, a method for synthesizing white light carbon dot phosphor with high efficiency and high yield, comprising the following steps:

[0038] The operation steps of this example are the same as those of Example 1. The difference is that 0.1 g of melamine is weighed, 15 ml of DMF is added, and after being fully dissolved, it is transferred to a high-pressure reactor and reacted at 180° for 6 hours. The CIE coordinates of the obtained white light carbon dots are (0.25, 0.26).

[0039] Embodiment 3, a method for synthesizing white light carbon dot phosphor with high efficiency and high yield, comprising the following steps:

[0040] The operation steps of this example are the same as those of Example 1. The difference is that 0.15 g of melamine is weighed, 20 ml of DMF is added, and after being fully dissolved, it is transferred to a high-pressure reactor for reaction at 240° for 6 hours. The CIE coordinates of the obtained white light carbon dots are (0.24, 0.27).

[0041] Embodiment 4, a method for synthesizing white light carbon dot phosphor with high efficiency and high yield, comprising the following steps:

[0042] The operation steps of this example are the same as those of Example 1. The difference is that 0.25 g of melamine is weighed, 25 ml of DMF is added, and after being fully dissolved, it is transferred to a high-pressure reactor for reaction at 240° for 12 hours. The CIE coordinates of the obtained white light carbon dots are (0.24, 0.28).

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

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

[0045] Step 2: Mix AB-silica gel in a mass ratio of 1:4, mix the phosphor and adhesive in a mass ratio of 1:2, and deposit the mixture on the InGaN chip of the LED;

[0046] Step 3: Heat continuously in an oven at 80° C. for 1 hour to finally cure and package to obtain a white light LED device.

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

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

[0049] Step 2: Mix AB-silica gel in a mass ratio of 1:3, mix the phosphor and the adhesive in a mass ratio of 1:1, and deposit the mixture on the InGaN chip of the LED;

[0050] Step 3: Continuously heat in an oven at 90° C. for 0.5 hours to finally cure and package to obtain a white light LED device.

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

[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 principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for synthesizing white light carbon dot phosphor with high efficiency and high yield, characterized by: The following steps are included Step 1, dissolving melamine in DMF, dispersing it by ultrasonication until it is fully dissolved, transferring it to a high temperature reactor for reaction, and cooling it to room temperature after the reaction is completed; 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 light carbon dot phosphor.

2. The method for synthesizing a highly efficient and high-yield white light carbon dot phosphor according to claim 1, characterized in that: The amount of melamine used is 0.1-0.25 g, and the amount of DMF used is 10-25 ml.

3. The method for synthesizing a highly efficient and high-yield white light carbon dot phosphor according to claim 2, characterized in that: The reaction conditions of the high temperature reactor in step 1 are: temperature of 180-240° C. and time of 8-14 hours.

4. A high-efficiency and high-yield white light carbon dot phosphor according to claim 1.

5. Application of the white light carbon dot phosphor according to claim 1 in a white light LED light emitting layer.

6. The use of a high-efficiency and high-yield white light carbon dot phosphor for a white light LED light emitting layer according to claim 5, characterized in that: The following steps are included Step 1: Use a commercial InGaN chip with an emission wavelength of 380-420nm as an LED excitation substrate; Step 2: Take AB-silica gel and mix them evenly, stir and mix the white light carbon dot phosphor and the adhesive in a mass ratio of 1:1-2, and deposit the mixture on the LED excitation substrate; Step 3: Curing in an oven and encapsulating to obtain a white light LED device (the white light phosphor is used as an LED color conversion layer).

7. The use of a high-efficiency and high-yield white light carbon dot phosphor for a white light LED light emitting layer according to claim 6, characterized in that: The mass ratio of the AB-silica gel is 1:

4.

8. The use of a high-efficiency and high-yield white light carbon dot phosphor according to claim 6 or 7 for a white light LED light emitting layer, characterized in that: The curing step is to heat the mixture in an oven at 80-100°C for 0.5-1 hour.

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