White light-emitting upconversion rare earth doped nanomaterial and preparation method thereof

Abstract

The present invention discloses a white-light-emitting upconversion rare-earth-doped nanomaterial and a preparation method thereof. The core-shell structured LiYF4:xHo@LiYbF4@LiYF4 upconversion nanoparticles (0 < x ≤ 0.02) with a particle size of 28-38 nm are synthesized by the high-temperature co-precipitation method. They have good dispersibility and obvious upconversion luminescence. Under 980 nm laser excitation, they exhibit upconversion fluorescence at 480 nm, 540 nm and 650 nm, making their overall color show white light, and having good application prospects in the fields of biomedicine, solar cells, temperature sensors and photocatalytic degradation, etc.

Description

Technical Field

[0001] This invention belongs to the field of fluorescent nanomaterial preparation technology, specifically relating to a white luminescent upconversion rare earth-doped nanomaterial and its preparation method. Background Technology

[0002] Lanthanide-doped upconversion materials have attracted widespread attention due to their narrow-band emission, low background signal, excellent photostability, and abundant step-level energy, enabling them to emit colors of different wavelengths. These superior properties make them highly promising for multicolor emission. Currently, there are two main methods to achieve multicolor emission. One method involves controlling the intensity of different red, green, and blue light by doping rare-earth ions at different interlayers in the upconversion process, such as doping with Tm under 798 nm laser excitation. 3+ Ho 3+ and Yb 3+ Tellurate, doped with Er under 980 nm laser excitation 3+ Tm 3+ and Yb 3+ NaYF4, doped with Tm under 980 nm laser excitation 3+ Ho 3+ and Yb 3+ YF3 is an important technology for achieving multicolor emission in a single material. Another technology is to control multiple excitation sources to achieve multicolor emission, but such multi-source white light materials have stable optical aberrations and low luminous efficiency. In recent decades, many effective strategies have been tried to achieve white light emission, such as: rational selection of host lattice, crystal field effect, dopant ion type and concentration, core-shell structure control, particle size adjustment, and construction of sublattice clusters. Among these, controlling the energy absorption process through core-shell structure is a simple and feasible method.

[0003] Rare earth fluoride matrix materials have attracted much attention due to their low phonon energy. Among them, the hexagonal ring sublattice structure in the tetragonal phase LiYF4 may effectively suppress the energy cross-relaxation between sensitized ions and improve the sensitization efficiency, making it a matrix material comparable to NaYF4. Summary of the Invention

[0004] The purpose of this invention is to provide a white luminescent upconversion rare earth-doped nanomaterial and its preparation method.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] One objective of this invention is to provide a white luminescent upconversion rare-earth-doped nanomaterial with a core-shell structure, comprising, from the inside out, LiY. (1-x)F4: xHo nanocrystalline core, LiYbF4 sensitizer layer and LiYF4 inert shell, where 0 < x ≤ 0.02. By changing the structure of the material to cause changes in the energy transfer process, white light emission can be achieved.

[0007] Furthermore, the particle size of the nanomaterial is 28 - 38 nm.

[0008] Furthermore, the nanomaterial exhibits upconversion fluorescence at 480 nm, 540 nm, and 650 nm under a 980 nm laser.

[0009] The second object of the present invention is to provide a method for preparing the above-mentioned upconversion rare earth doped nanomaterial with white light emission, which includes the following steps;

[0010] (1) Preparation of Ho 3+ doped LiY (1-x) F4 nanocrystalline core

[0011] a) Mix (1 - x) mmol of YCl3·6H2O, x mmol of HoCl3·6H2O, 8 ml of oleic acid and 12 ml of octadecene, stir at a speed of 500 r / min and evacuate to a vacuum degree of 0.08 MPa, then slowly heat up to 150 °C, keep warm for half an hour, and then naturally cool to room temperature to obtain a rare earth oleic acid complex;

[0012] b) Mix the methanol solution containing 4 mmol of NH4F and the methanol solution containing 1.5 mmol of LiOH, oscillate for 10 - 30 s, and then slowly inject it into the rare earth oleic acid complex obtained in step a), and keep warm for 30 - 60 min;

[0013] c) Evacuate to a vacuum degree of 0.08 MPa and raise the temperature to 80 °C, keep warm for 15 - 30 min to remove water and methanol;

[0014] d) Introduce nitrogen, continue to heat up to 300 °C and keep warm for 60 - 90 min, and then naturally cool to room temperature;

[0015] e) Add absolute ethanol for precipitation, then centrifuge once at 7000 rpm, and then centrifuge and wash twice with a mixed solution of cyclohexane and ethanol (1:4, v / v). The obtained product is dissolved in cyclohexane to obtain an ion - doped LiY (1-x) F4: xHo nanocrystalline core;

[0016] (2) Formation of the LiYbF4 sensitizer layer

[0017] f) Mix 1 mmol YbCl3·6H2O, 8 ml oleic acid and 12 ml octadecene, stir at 500 r / min and evacuate to a vacuum of 0.08 MPa, then slowly heat to 150 °C, keep warm for half an hour, and then cool naturally to room temperature.

[0018] g) First add the LiY prepared in step (1) to the reaction solution in step f). (1-x) F4:xHo nanocrystal nuclei were added, followed by the addition of a methanol solution containing 4 mmol NH4F and a methanol solution containing 1.5 mmol LiOH, and the mixture was kept at this temperature for 30-60 min.

[0019] h) Evacuate to a vacuum level of 0.08 MPa and raise the temperature to 80°C, hold for 15-30 minutes to remove water and methanol;

[0020] i) Introduce nitrogen gas, continue heating to 300℃ and hold for 60-90 minutes, then allow to cool naturally to room temperature;

[0021] j) Anhydrous ethanol was added to precipitate the product, followed by centrifugation at 7000 rpm once, and then washing twice with a mixture of cyclohexane and ethanol (1:4, v / v). The resulting product dissolved in cyclohexane to obtain LiY. (1-x) F4:xHo@LiYbF4 nanocrystal nuclei;

[0022] (3) Preparation of LiYF4 inert shell

[0023] k) Mix 1 mmol YCl3·6H2O, 8 ml oleic acid and 12 ml octadecene, stir at 500 r / min and evacuate to a vacuum of 0.08 MPa, then slowly heat to 150 °C, keep warm for half an hour, and then cool naturally to room temperature.

[0024] l) First add the LiY prepared in step (2) to the reaction solution in step j). (1-x) F4: xHo@LiYbF4 nanocrystal cores were added, followed by the addition of a methanol solution containing 4 mmol NH4F and a methanol solution containing 1.5 mmol LiOH, and the mixture was kept at this temperature for 30-60 min.

[0025] m) Evacuate to a vacuum level of 0.08 MPa and raise the temperature to 80℃, hold for 15-30 minutes to remove water and methanol;

[0026] n) Introduce nitrogen gas, continue heating to 300℃ and hold for 60-90 minutes, then allow to cool naturally to room temperature;

[0027] o) Anhydrous ethanol was added to precipitate the product, followed by centrifugation at 7000 rpm once, and then washing twice with a mixture of cyclohexane and ethanol (1:4, v / v). The resulting product dissolved in cyclohexane to obtain LiY. (1-x) F4:xHo@LiYbF4@LiYF4.

[0028] The beneficial effects of this invention are as follows:

[0029] (1) The present invention uses tetragonal LiYF4 with low phonon energy as a substrate, doping it with Ho and coating it with an active shell of LiYbF4 to absorb 980nm infrared photons, and then coating the surface with an inert shell of LiYF4 to reduce the transfer of energy to surface defects and improve fluorescence intensity.

[0030] (2) The upconversion nanoparticles prepared by this invention have good dispersion and obvious upconversion luminescence. Under 980nm laser excitation, they exhibit upconversion fluorescence of 480nm, 540nm and 650nm, making their overall color white. They have good application prospects in biomedicine, solar cells, temperature sensors and photocatalytic degradation.

[0031] (3) This invention is the first to synthesize LiY by high-temperature coprecipitation method. (1-x) F4:xHo@LiYbF4@LiYF4 has low preparation cost, simple process operation, short time consumption, and is easy to prepare. Attached Figure Description

[0032] Figure 1 The images show X-ray diffraction patterns of the nanomaterials prepared in the examples and comparative examples.

[0033] Figure 2 LiY prepared for the example 0.995 F4:Ho 0.005 Transmission electron microscopy image (a) and particle size distribution diagram (b) of @LiYbF4;

[0034] Figure 3 Upconversion emission patterns (a) and LiY nanomaterials prepared for the examples and comparative examples under 980 nm excitation. 0.995 F4:Ho 0.005 The color coordinates (b) corresponding to @LiYbF4@LiYF4. Detailed Implementation

[0035] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto.

[0036] The example demonstrates the preparation of LiY via a high-temperature co-precipitation method. (1-x)F4:xHo@LiYbF4@LiYF4 nanoparticles

[0037] Step 1: Preparation of Ho 3+ Doped LiYF4 nanocrystal nuclei:

[0038] (a) Mix (1-x)mmol YCl3·6H2O, xmmol HoCl3·H2O, 8ml oleic acid and 12ml octadecene in a 250mL three-necked flask, place it in a polytetrafluoroethylene rotor, set the rotation speed to 500r / min, turn on the vacuum pump to evacuate to a vacuum degree of 0.08 MPa, then slowly raise the temperature to 150℃, keep it at that temperature for half an hour, and then cool it naturally to room temperature to obtain rare earth oleic acid complex.

[0039] (b) Mix a methanol solution containing 4 mmol NH4F and a methanol solution containing 1.5 mmol LiOH and shake for 10-30 s. Then slowly inject the mixture into the obtained rare earth oleic acid complex and keep it warm for 30-60 min. At this time, rare earth nanoparticles begin to nucleate and grow.

[0040] (c) Turn on the vacuum pump, evacuate to a vacuum level of 0.08 MPa, and raise the temperature to 80°C. Keep it at this temperature for 15-30 minutes to remove water and methanol.

[0041] (d) Introduce nitrogen gas, continue heating to 300℃ and hold for 60-90 minutes. After the reaction is complete, allow it to cool naturally to room temperature.

[0042] (e) Add anhydrous ethanol to precipitate and centrifuge once at 7000 rpm, then wash twice with a mixed solution of cyclohexane and ethanol (1:4, v / v), and finally dissolve the product in cyclohexane to obtain LiY. (1-x) F4:xHo (x=0.005, 0.01, 0.02).

[0043] Step 2: In the prepared Ho 3+ LiYF4 nanocrystal cores are coated with a LiYbF4 active shell:

[0044] (f) Mix 1 mmol YbCl3·6H2O, 8 ml oleic acid and 12 ml octadecene in a 250 mL three-necked flask, place it in a polytetrafluoroethylene rotor, set the rotation speed to 500 r / min, turn on the vacuum pump to evacuate to a vacuum degree of 0.08 MPa, then slowly raise the temperature to 150℃, keep it at that temperature for half an hour, and then let it cool naturally to room temperature.

[0045] (g) The prepared LiY is first added to the reactants obtained in step (f). （1-x）F4:xHo nanocrystals were added, followed by the addition of a methanol solution containing 4 mmol NH4F and a methanol solution containing 1.5 mmol LiOH, and the mixture was kept at this temperature for 30-60 min.

[0046] (h) Turn on the vacuum pump, evacuate to a vacuum level of 0.08 MPa, and raise the temperature to 80°C. Keep it at this temperature for 15-30 minutes to remove water and methanol.

[0047] (i) Introduce nitrogen gas, continue heating to 300℃ and hold for 60-90 min, and allow to cool naturally to room temperature after the reaction is complete.

[0048] (j) Add anhydrous ethanol to precipitate and centrifuge once at 7000 rpm, then wash twice with a mixed solution of cyclohexane and ethanol (1:4, v / v), and finally dissolve the product in cyclohexane to obtain LiY. (1-x) F4:xHo@LiYbF4 (x=0.005, 0.01, 0.02).

[0049] Step 3: In the prepared LiY (1-x) F4:xHo@LiYbF4 nanocrystalline cores are coated with an inert LiYF4 shell:

[0050] (k) Mix 1 mmol YCl3·6H2O, 8 ml oleic acid and 12 ml octadecene in a 250 mL three-necked flask, place a polytetrafluoroethylene rotor in it, set the rotation speed to 500 r / min, turn on the vacuum pump to evacuate to a vacuum degree of 0.08 MPa, slowly raise the temperature to 150 °C, keep it at that temperature for half an hour, and then let it cool naturally to room temperature.

[0051] (l) First, add the prepared LiY to the reactants obtained in step (k). (1-x) F4:xHo@LiYbF4 nanocrystal cores were added, followed by the addition of a methanol solution containing 4 mmol NH4F and a methanol solution containing 1.5 mmol LiOH, and the mixture was kept at this temperature for 30-60 min.

[0052] (m) Turn on the vacuum pump, evacuate to a vacuum level of 0.08 MPa, and raise the temperature to 80℃. Keep it at this temperature for 15-30 minutes to remove water and methanol.

[0053] (n) Introduce nitrogen gas, continue heating to 300℃ and hold for 60-90 minutes. After the reaction is complete, allow it to cool naturally to room temperature.

[0054] (o) Add anhydrous ethanol to precipitate and centrifuge once at 7000 rpm, then wash twice with a mixed solution of cyclohexane and ethanol (1:4, v / v), and finally dissolve the product in cyclohexane to obtain LiY. (1-x)F4:xHo@LiYbF4@LiYF4 (x=0.005, 0.01, 0.02).

[0055] Comparative example: LiYb prepared by high-temperature co-precipitation method 0.995 F4:Ho 0.005 @LiYF4 nanoparticles

[0056] 0.995 mmol YbCl3·6H2O, 0.005 mmol HoCl3·6H2O, 8 ml oleic acid, and 12 ml octadecene were mixed in a 250 mL three-necked flask. The mixture was then placed in a polytetrafluoroethylene rotor, and the rotation speed was set to 500 r / min. A vacuum pump was turned on to evacuate the mixture to a vacuum level of 0.08 MPa. The mixture was then slowly heated to 150 °C and held at that temperature for half an hour. After that, it was allowed to cool naturally to room temperature to obtain a rare earth oleic acid complex.

[0057] (b) Mix a methanol solution containing 4 mmol NH4F and a methanol solution containing 1.5 mmol LiOH and shake for 10-30 s. Then slowly inject the mixture into the obtained rare earth oleic acid complex and keep it warm for 30-60 min. At this time, rare earth nanoparticles begin to nucleate and grow.

[0058] (c) Turn on the vacuum pump, evacuate to a vacuum level of 0.08 MPa, and raise the temperature to 80°C. Keep it at this temperature for 15-30 minutes to remove water and methanol.

[0059] (d) Introduce nitrogen gas, continue heating to 300℃ and hold for 60-90 minutes. After the reaction is complete, allow it to cool naturally to room temperature.

[0060] (e) Add anhydrous ethanol to precipitate and centrifuge once at 7000 rpm, then wash twice with a mixed solution of cyclohexane and ethanol (1:4, v / v), and finally dissolve the product in cyclohexane to obtain LiYb. 0.995 F4:Ho 0.005 Nanocrystalline nuclei.

[0061] Step 2: In the prepared Ho 3+ The surface of the doped LibYF4 nanocrystal core is coated with an inert LiYF4 shell:

[0062] (f) Mix 1 mmol YCl3·6H2O, 8 ml oleic acid and 12 ml octadecene in a 250 mL three-necked flask, place it in a polytetrafluoroethylene rotor, set the rotation speed to 500 r / min, turn on the vacuum pump to evacuate to a vacuum degree of 0.08 MPa, then slowly raise the temperature to 150℃, keep it at that temperature for half an hour, and then let it cool naturally to room temperature.

[0063] (g) The prepared LiYb is first added to the reactants obtained in step (f). 0.995F4:Ho 0.005 Nanocrystalline nuclei were then added, followed by the addition of a methanol solution containing 4 mmol NH4F and a methanol solution containing 1.5 mmol LiOH, and incubated for 30-60 minutes.

[0064] (h) Turn on the vacuum pump, evacuate to a vacuum level of 0.08 MPa, and raise the temperature to 80°C. Keep it at this temperature for 15-30 minutes to remove water and methanol.

[0065] (i) Introduce nitrogen gas, continue heating to 300℃ and hold for 60-90 min, and allow to cool naturally to room temperature after the reaction is complete.

[0066] (j) Add anhydrous ethanol to precipitate and centrifuge once at 7000 rpm, then wash twice with a mixed solution of cyclohexane and ethanol (1:4, v / v), and finally dissolve the product in cyclohexane to obtain LiYb. 0.995 F4:Ho 0.005 @LiYF4 nanoparticles.

[0067] Performance testing:

[0068] 1. Crystal form characterization

[0069] The samples synthesized in the examples and comparative examples were dried, ground into powder, and characterized by X-ray diffraction. The results are as follows: Figure 1 As shown. By Figure 1 It can be proven that the synthesized nanomaterials are all tetragonal LiYF4, and the Ho... 3+ The molar concentration of doping can cause lattice expansion or contraction.

[0070] 2. Morphological characteristics:

[0071] The LiY synthesized in Example 1 0.995 F4:Ho 0.005 @LiYbF4 was dispersed in cyclohexane, dropped onto a silicon wafer, and after drying, its morphology and size were measured by transmission electron microscopy. The results are as follows: Figure 2 As shown. By Figure 2 The prepared sample has a uniform morphology and a size of approximately 35 nm.

[0072] 3. Upconversion spectroscopy test:

[0073] The samples synthesized in Examples 1 and Comparative Example 1 were placed in four-way cuvettes, respectively, with an external 980nm laser as the light source and a laser power of 1500-2000mW / cm². 2 Fluorescence spectroscopy was performed, and the results are as follows: Figure 3 As shown. By Figure 3 It can be observed that the sample exhibits upconversion fluorescence at 480nm, 540nm, and 655nm, and Ho3+ The upconversion blue fluorescence emission intensity is highest at a doping concentration of 0.5% mmol. This can be illustrated by using color coordinates to demonstrate the optimal doping concentration of 0.5% mmol. 3+ The sample emitted white light, and this doping concentration was the preferred concentration.

[0074] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A white luminescent upconversion rare-earth-doped nanomaterial, characterized in that: This nanomaterial has a core-shell structure, which consists of LiY from the inside out. (1-x) F4:xHo nanocrystal core, LiYbF4 sensitization layer and LiYF4 inert shell, wherein 0 <x≤0.02; The nanomaterial exhibits upconversion fluorescence at 480 nm, 540 nm, and 650 nm under a 980 nm laser wavelength. The preparation of this nanomaterial includes the following steps; (1) YCl3·6H2O, HoCl3·6H2O, LiOH, NH4F were mixed with oleic acid and octadecene according to the stoichiometric ratio. After high-temperature treatment in an inert gas atmosphere, the mixture was cooled to room temperature and then centrifuged and washed to obtain ion-doped LiY. (1-x) F4:xHo nanocrystal nuclei; (2) After mixing YbCl3·6H2O, LiOH, NH4F with oleic acid and octadecene according to the stoichiometric ratio, add the LiY prepared in step (1). (1-x) F4:xHo nanocrystal nuclei were used, followed by high-temperature treatment with an inert gas atmosphere. After the reaction, the mixture was allowed to cool naturally to room temperature, allowing the epitaxially grown active shell to coat the nanocrystal nuclei and form a LiYbF4 sensitized layer. The resulting LiY was then obtained by centrifugation and washing. (1-x) F4:xHo@LiYbF4 nanocrystal nuclei; (3) After mixing YCl3·6H2O, LiOH, NH4F with oleic acid and octadecene according to the stoichiometric ratio, add the LiY prepared in step (2). (1-x) F4:xHo@LiYbF4 nanocrystal nuclei were prepared, and then inert gas was introduced for high-temperature treatment. After the reaction was completed, the material was naturally cooled to room temperature, so that the epitaxially grown LiYF4 inert shell was coated on the nanocrystal nuclei. The material was then obtained by centrifugation and washing.

2. The white luminescent upconversion rare-earth-doped nanomaterial according to claim 1, characterized in that: The particle size of this nanomaterial is 28-38 nm.

3. The white luminescent upconversion rare-earth-doped nanomaterial according to claim 1, characterized in that: The volume ratio of oleic acid to octadecene used in each step is 8:

12.

4. The white luminescent upconversion rare-earth-doped nanomaterial according to claim 1, characterized in that: The high-temperature treatment mentioned in each step involves holding the temperature at 300℃ for 60-90 minutes.

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