Method for preparing green fluorescent carbon nitride powder by non-doping means and application of green fluorescent carbon nitride powder in white light LED
Technical Field
The invention belongs to the technical field of fluorescent carbon nitride powder preparation, and particularly relates to a method for preparing green fluorescent carbon nitride powder by a non-doping method and application of the green fluorescent carbon nitride powder in a white light LED.
Background
Graphite phase carbon nitride (g-C)3N4) Is formed by two elements of C and N in sp2The conjugated aromatic system formed by hybridization has excellent luminescence property, so that the conjugated aromatic system is expected to be used for preparing LEDs. The ultraviolet excitation type tricolor fluorescent powder used by the current commercial LED is mainly rare earth fluorescent powder. Graphite phase carbon nitride powders have found less use in LEDs, primarily because the fluorescence wavelength of the original graphite phase carbon nitride is concentrated in the blue band and the quantum yield is relatively low. In recent years, the preparation method by doping benzene molecules has been reportedThe preparation of the green fluorescent carbon nitride material (CN 106833609A) has complicated and complicated preparation steps. And a patent (CN 106928996A) reports that a white light LED device is prepared by packaging a blue light fluorescent powder ACN, a green fluorescent powder PhCN and a red organic fluorescent powder 2DPAFO by using an ultraviolet LED chip. Because the excitation light wavelength of the existing graphite phase carbon nitride powder is in an ultraviolet region, blue fluorescent powder is required to be packaged together when a white light LED is prepared. Therefore, it is necessary to develop a graphite-phase carbon nitride powder which has simple preparation method, high fluorescence quantum yield and can be directly excited by blue light and can be used for preparing white light LEDs.
Disclosure of Invention
The invention aims to provide a method for preparing green fluorescent graphite-phase carbon nitride powder by a non-doping means and application of the green fluorescent graphite-phase carbon nitride powder in a white light LED. The method prepares graphite-phase carbon nitride powder capable of emitting green fluorescence under the excitation of blue light by a non-doping method, and prepares a white light LED device by using a 450 nm LED chip and combining red fluorescent powder.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method for preparing green fluorescent graphite-phase carbon nitride powder by a non-doping means comprises the following steps:
(1) placing a crucible containing graphite-phase carbon nitride powder in the center of a furnace chamber of a vacuum tube furnace, and reserving an air inlet and an air outlet at two ends of a quartz tube;
(2) introducing inert protective gas into the quartz tube, starting the tube furnace to raise the temperature to 800 ℃ for a period of time, and naturally cooling to room temperature to obtain reddish brown powder;
(3) dispersing the reddish brown powder in NaOH solution, slowly stirring at 60-80 ℃, reacting for a period of time, centrifuging, removing precipitate, and retaining supernatant;
(4) gradually dripping acid into the supernatant to gradually adjust the pH of the solution to be neutral;
(5) and centrifugally washing to retain the precipitate, and drying to obtain the graphite-phase carbon nitride powder capable of emitting green fluorescence under the excitation of blue light.
The application of the graphite-phase carbon nitride powder in the white light LED is as follows: mixing the prepared graphite-phase carbon nitride powder with a small amount of red fluorescent material, and encapsulating the mixture on a 450 nm LED chip by using high-transmittance resin adhesive to prepare the white LED.
Further, the amount of the graphite phase carbon nitride powder added is 1 to 50 g. The inert protective gas is nitrogen or argon. The flow rate of the inert protective gas is 50-100 mL/min. The temperature rise speed of the tubular furnace is 1-15 ℃/min. The maintaining time after the temperature rise is 1-6 h. The concentration of the NaOH solution is 1-10 mol/L; the acid used for adjusting the pH is HCl and HNO3Or H2SO4。
Untreated graphite phase carbon nitride powder prepared by conventional methods has a band gap of about 2.7 eV, and thus graphite phase carbon nitride powder generally produces blue fluorescence under ultraviolet excitation. In the field of catalysis, g-C with a large number of defects can be prepared by a heat treatment process3N4And the absorbed light is obviously red-shifted, the band gap is reduced, but the quantum yield is further reduced, and even the fluorescence characteristic is lost (figure 1). The invention firstly obtains reddish brown powder with larger red shift of excitation light and emission light through heat treatment, then obtains graphite-phase carbon nitride powder with defects through NaOH chemical shearing, can effectively improve fluorescence quantum yield, and the fluorescence emission of the sheared nano-sheets or quantum dots can generate blue shift due to quantum confinement effect, thereby obtaining nano-belt-shaped structures with defects, the excitation and emission of the nano-belts are blue shift relative to the reddish brown powder, but aiming at the graphite-phase carbon nitride powder before treatment, the excitation and emission of the nano-belts have large red shift, the maximum excitation wavelength is shifted from an ultraviolet region (about 350 nm) to a blue region (about 450 nm), the emission wavelength is shifted from the blue region (about 450 nm) to a green region (about 500 nm) (figure 1), and the absolute quantum yield is doubled, from 3.8 ± 0.3% to 23.6% (fig. 3). If the reddish brown powder is not treated with alkali, the fluorescence intensity is very low, and the acid is added to remove the negative charges on the surface of the material, so that the material is settled and can be washed and dried to obtain powder (figure 2)。
The invention has the advantages that:
(1) the method for preparing the green fluorescent graphite-phase carbon nitride powder by a non-doping method and the application of the green fluorescent graphite-phase carbon nitride powder in the white light LED have the advantages of simple preparation method, low equipment requirement, easiness in obtaining, no toxicity and environmental friendliness.
(2) The graphite-phase carbon nitride solid powder prepared by the method has the advantages of high fluorescence quantum yield and no photobleaching characteristic.
(3) The green fluorescent graphite-phase carbon nitride prepared by the method can be directly excited by blue light of 450 nm to emit green fluorescence. The white light LED device can be prepared by combining the red fluorescent material and packaging on a 45 nm LED chip, and has good color rendering index and color temperature.
Drawings
FIG. 1 is an emission spectrum of ordinary graphite-phase carbon nitride, graphite-phase carbon nitride powder treated at 750 ℃ and green fluorescent graphite-phase carbon nitride powder obtained in example 5 at the maximum excitation wavelength;
FIG. 2 is a photograph of a green fluorescent graphite-phase carbon nitride dispersion in example 5, taken with acid to obtain a precipitate, and a photograph of the green fluorescent graphite-phase carbon nitride powder obtained after drying under a fluorescent lamp and a 365 nm ultraviolet lamp, taken with an excitation emission spectrum;
FIG. 3 is a graph showing an absolute quantum yield test chart of green fluorescent graphite-phase carbon nitride powder obtained in example 5;
FIG. 4 is a schematic diagram, a schematic diagram and an effect diagram of white LED prepared from the green fluorescent graphite-phase carbon nitride powder obtained in example 5;
FIG. 5 is a color coordinate diagram of a white LED prepared from the green fluorescent graphite-phase carbon nitride powder obtained in example 5.
Detailed Description
Example 1
Weighing 1 g of graphite-phase carbon nitride powder, placing the graphite-phase carbon nitride powder in a crucible, placing the crucible in the center of a quartz tube of a tube furnace, introducing nitrogen at the flow rate of 50 mL/min, heating the crucible to 600 ℃ at the speed of 1 ℃/min, keeping the temperature for 1 h, naturally cooling the crucible to obtain reddish brown powder, dispersing the reddish brown powder in a NaOH solution, slowly stirring the mixture at the temperature of 60 ℃, reacting for a period of time, centrifuging the mixture, removing the precipitate, and keeping the supernatant. HCl was gradually added dropwise to the supernatant and the pH of the solution was gradually adjusted to neutral. And centrifuging, washing, retaining the precipitate, drying to obtain graphite-phase carbon nitride powder capable of emitting green fluorescence under the excitation of blue light, mixing the prepared graphite-phase carbon nitride powder with a small amount of red fluorescent material, and encapsulating the mixture on a 450 nm LED chip by using high-transmittance resin adhesive to prepare the white light LED.
As shown in FIG. 1, CN derived from ordinary graphite-phase carbon nitride and graphite-phase carbon nitride heat-treated at 750 ℃ is shownheat-750Red shift in fluorescence wavelength but reduced intensity, CNheat-750The fluorescence intensity is obviously enhanced after the NaOH treatment, and the peak position is relatively common C3N4Resulting in a red-shifted fluorescence spectrum.
Example 2
Weighing 10 g of graphite-phase carbon nitride powder, placing the graphite-phase carbon nitride powder in a crucible, placing the crucible in the center of a quartz tube of a tube furnace, introducing argon at the flow rate of 50 mL/min, heating the crucible to 650 ℃ at the speed of 3 ℃/min, keeping the temperature for 2 h, naturally cooling the crucible to obtain reddish brown powder, dispersing the reddish brown powder in 1 mol/LNaOH solution, slowly stirring the mixture at the temperature of 60 ℃, reacting for a period of time, centrifuging the mixture, removing the precipitate, and keeping the supernatant. Gradually adding HNO dropwise into the supernatant3The solution pH was gradually adjusted to neutral. And centrifuging, washing, retaining the precipitate, drying to obtain graphite-phase carbon nitride powder emitting green under the excitation of blue light, mixing the prepared graphite-phase carbon nitride powder with a small amount of red fluorescent material, and encapsulating the mixture on a 450 nm LED chip by using high-transmittance resin adhesive to prepare the white LED.
Example 3
Weighing 20 g of graphite-phase carbon nitride powder, placing the graphite-phase carbon nitride powder in a crucible, placing the crucible in the center of a quartz tube of a tube furnace, introducing argon at a flow rate of 75 mL/min, heating the graphite-phase carbon nitride powder to 700 ℃ at a speed of 5 ℃/min, keeping the temperature for 4 h, naturally cooling the graphite-phase carbon nitride powder to obtain reddish brown powder in the crucible, dispersing the reddish brown powder in a NaOH solution, slowly stirring the mixture at 80 ℃, reacting for a period of time, centrifuging the mixture to remove precipitates, and keeping a supernatantAnd (4) liquid. Gradually adding HNO dropwise into the supernatant3The solution pH was gradually adjusted to neutral. And centrifuging, washing, retaining the precipitate, drying to obtain graphite-phase carbon nitride powder emitting green fluorescence under the excitation of blue light, mixing the prepared graphite-phase carbon nitride powder with a small amount of red fluorescent material, and encapsulating the mixture on a 450 nm LED chip by using high-transmittance resin adhesive to prepare the white light LED.
Example 4
Weighing 30 g of graphite-phase carbon nitride powder, placing the graphite-phase carbon nitride powder in a crucible, placing the crucible in the center of a quartz tube of a tube furnace, introducing nitrogen at the flow rate of 100 mL/min, heating the mixture to 750 ℃ at the speed of 7.5 ℃/min, keeping the temperature for 6 h, naturally cooling the mixture to obtain reddish brown powder in the crucible, dispersing the reddish brown powder in NaOH solution, slowly stirring the mixture at the temperature of 70 ℃, reacting for a period of time, centrifuging and discarding the precipitate, and keeping the supernatant. Gradually adding H dropwise into the supernatant2SO4The solution pH was gradually adjusted to neutral. And centrifuging, washing, retaining the precipitate, drying to obtain graphite-phase carbon nitride powder emitting green fluorescence under the excitation of blue light, mixing the prepared graphite-phase carbon nitride powder with a small amount of red fluorescent material, and encapsulating the mixture on a 450 nm LED chip by using high-transmittance resin adhesive to prepare the white light LED.
Example 5
Weighing 40 g of graphite phase carbon nitride powder, placing the graphite phase carbon nitride powder in a crucible, placing the crucible in the center of a quartz tube of a tube furnace, introducing nitrogen at the flow rate of 100 mL/min, heating the crucible to 750 ℃ at the speed of 7.5 ℃/min, keeping the temperature for 1 h for natural cooling to obtain reddish brown powder in the crucible, dispersing the reddish brown powder in 4 mol/LNAOH solution, slowly stirring the mixture at the temperature of 60 ℃, reacting for a period of time, centrifuging and removing precipitates, and keeping a supernatant. HCl was gradually added dropwise to the supernatant and the pH of the solution was gradually adjusted to neutral. And centrifuging, washing, retaining the precipitate, drying to obtain prepared graphite-phase carbon nitride powder emitting green fluorescence under the excitation of blue light, mixing the prepared graphite-phase carbon nitride powder with a small amount of red fluorescent material, and encapsulating the mixture on a 450 nm LED chip by using high-transmittance resin adhesive to prepare the white light LED.
Example 6
Weighing 50 g of graphite-phase carbon nitride powderPlacing the powder in a crucible, placing the crucible in the center of a quartz tube of a tube furnace, introducing nitrogen at the flow rate of 100 mL/min, heating the crucible to 800 ℃ at the speed of 15 ℃/min, then keeping the temperature for 1 h for natural cooling to obtain reddish brown powder in the crucible, dispersing the reddish brown powder in 10 mol/LNaOH solution, slowly stirring the mixture at the temperature of 80 ℃, reacting for a period of time, centrifuging and discarding the precipitate, and keeping the supernatant. Gradually adding H dropwise into the supernatant2SO4The solution pH was gradually adjusted to neutral. And centrifuging, washing, retaining the precipitate, drying to obtain graphite-phase carbon nitride powder emitting green fluorescent light under the excitation of blue light, mixing the prepared graphite-phase carbon nitride powder with a small amount of red fluorescent material, and encapsulating the mixture on a 450 nm LED chip by using high-transmittance resin adhesive to prepare the white light LED.
The above description is only a preferred embodiment of the present invention, and all equivalent changes and modifications made in accordance with the claims of the present invention should be covered by the present invention.