CN111019655B - Up-conversion luminescent silica aerogel and preparation method thereof - Google Patents

Up-conversion luminescent silica aerogel and preparation method thereof Download PDF

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CN111019655B
CN111019655B CN201911234656.9A CN201911234656A CN111019655B CN 111019655 B CN111019655 B CN 111019655B CN 201911234656 A CN201911234656 A CN 201911234656A CN 111019655 B CN111019655 B CN 111019655B
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nayf
silicon dioxide
conversion luminescent
silica aerogel
aerogel
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CN111019655A (en
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温红丽
李翠婷
谢胜杰
苏少珊
郝志峰
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Guangdong University of Technology
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    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
    • C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
    • C09K11/7766—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing two or more rare earth metals
    • C09K11/7772—Halogenides
    • C09K11/7773—Halogenides with alkali or alkaline earth metal
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
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Abstract

The invention belongs to the technical field of up-conversion luminescent anti-counterfeiting materials, and particularly relates to up-conversion luminescent silicon dioxide aerogel and a preparation method thereof. The invention provides an up-conversion luminescent silicon dioxide aerogel, which is formed by compounding a rare earth-doped up-conversion luminescent material and silicon dioxide aerogel; the rare earth doping up-conversion luminescent material is NaYF4 Yb/Er micron tube and/or NaYF4 Yb/Er micron rod. The invention adopts nano porous material silicon dioxide aerogel as display matrix material, the silicon dioxide aerogel is transparent, NaYF 4 Yb/Er is present in the form of microtubes and/or microrods, NaYF 4 The Yb/Er and the silicon dioxide aerogel are uniformly compounded, have good up-conversion luminescence performance under 980nm laser irradiation, emit green light visible to naked eyes, have a light waveguide effect and can be used in the field of up-conversion luminescence anti-counterfeiting excited by near-infrared laser.

Description

Up-conversion luminescent silica aerogel and preparation method thereof
Technical Field
The invention belongs to the technical field of up-conversion luminescent anti-counterfeiting materials, and particularly relates to up-conversion luminescent silicon dioxide aerogel and a preparation method thereof.
Background
With the rapid development of science and technology, the counterfeit products are endlessly and difficultly identified, which causes great economic loss to people's life, and the anti-counterfeiting work is very important. The rare earth ion doped up-conversion luminescent material is a novel fluorescent material with good prospect and wide application, and can convert low-energy invisible near-infrared light exciting light into high-energy visible short-wave emission. The one-dimensional up-conversion micron rod and the micron tube are in an air medium, and up-conversion luminescence can be axially transmitted along the micron rod/tube, so that the up-conversion luminescence has an optical waveguide effect. NaYF 4 The matrix up-conversion luminescent material has low biological toxicity and high chemical stability, and can be used for display, anti-counterfeiting and the likeThe field has potential applications.
Currently, NaYF 4 The host system up-conversion luminescent material is mostly compounded with Polydimethylsiloxane (PDMS) to be used as a display and anti-counterfeiting material. However, NaYF is used in display and anti-counterfeiting materials 4 Is present in the form of nanoparticles, NaYF 4 The micron tube and/or micron rod is difficult to be evenly compounded with PDMS due to the large size, NaYF 4 The microtubes and/or the microrods may deposit or build up locally in the PDMS, making it locally opaque.
Disclosure of Invention
In view of the above, the present invention provides an upconversion luminescent silica aerogel and a preparation method thereof, wherein the upconversion luminescent silica aerogel comprises NaYF 4 Yb/Er is present in the form of microtubes and/or microrods, NaYF 4 Yb/Er and silica aerogel are uniformly compounded to have optical waveguide effect.
The specific technical scheme of the invention is as follows:
the up-conversion luminescent silica aerogel is formed by compounding a rare earth-doped up-conversion luminescent material and silica aerogel;
the rare earth doped up-conversion luminescent material is NaYF 4 Yb/Er micron tube and/or NaYF 4 Yb/Er micron rod.
The silica aerogel is a solid material consisting of ultrafine particles, the interior of the silica aerogel consists of more than 95% of air and less than 5% of silica skeleton, and the silica aerogel has excellent performances of high specific surface area, high porosity, low density, low thermal conductivity and the like.
In the invention, a nano-porous material silicon dioxide aerogel is adopted as a display matrix material, the silicon dioxide aerogel is transparent, and the silicon dioxide aerogel and a rare earth doped up-conversion luminescent material NaYF are mixed 4 Yb/Er composite, NaYF 4 Yb/Er is present in the form of microtubes and/or microrods, NaYF 4 The Yb/Er micron tube and/or micron rod is uniformly compounded with the silicon dioxide aerogel, the up-conversion luminescent silicon dioxide aerogel is integrally transparent, no obvious opaque accumulation or deposition is seen, and the silicon dioxide aerogel has uniform light transmissionThe anti-counterfeiting liquid has good performance and display performance, has good up-conversion luminescence performance under 980nm laser irradiation, emits green light visible to naked eyes, has a light waveguide effect, and can be used in the field of up-conversion luminescence anti-counterfeiting excited by near-infrared laser. And, NaYF 4 Yb/Er micron tube and/or NaYF 4 The Yb/Er micron rod has toughening effect on the silicon dioxide aerogel, and solves the problems that the silicon dioxide aerogel is easy to crack after being dried, has poor mechanical property and is difficult to completely form and process.
In the invention, NaYF 4 The Yb/Er micron tube has a hollow structure, NaYF 4 The Yb/Er micron rod has a solid structure.
Preferably, the NaYF 4 Yb/Er micron tube and/or NaYF 4 The length of the Yb/Er micron rod is 7-25 μm;
the NaYF 4 Yb/Er micron tube or NaYF 4 The diameter of the Yb/Er micron rod and/or the diameter of the rod is 2-5 μm.
In the invention, NaYF 4 Yb/Er micron tube and/or NaYF 4 The Yb/Er micron rod has even pipe diameter and/or rod diameter distribution, so that the upconversion luminescent silica aerogel has better toughness and is not easy to chap. The rare earth doped up-conversion luminescent material is preferably NaYF 4 The up-conversion luminescent silica aerogel has better optical waveguide effect under the condition of Yb/Er micron tubes.
Preferably, NaYF 4 In Yb/Er, the content of Yb is 0 to 100 mol%, the content of Er is 0 to 10 mol%, more preferably, the content of Yb is 20 mol%, and the content of Er is 2 mol%;
the mass ratio of the rare earth doped up-conversion luminescent material to the silicon dioxide aerogel is (2000-20000): 1, preferably (5000 to 10000): 1.
the invention also provides a preparation method of the up-conversion luminescent silicon dioxide aerogel, which comprises the following steps:
a) mixing sodium hydroxide, a surfactant, soluble yttrium salt, soluble ytterbium salt, soluble erbium salt and deionized water to obtain a first reaction solution;
b) adding ammonium fluoride and hydrochloric acid into the first reaction solution to obtain a second reaction solution, and heating the second reaction solution for reaction to obtain a crystal material;
c) and adding the crystal material into the silicon dioxide aerogel precursor, adjusting the pH value, and standing to obtain the up-conversion luminescent silicon dioxide aerogel.
The upconversion luminescent silicon dioxide aerogel is prepared by compounding NaYF4 Yb/Er micron tubes and/or micron rods in the high-porosity and transparent silicon dioxide aerogel matrix material through a sol-gel method, and the upconversion luminescent silicon dioxide aerogel is simple, convenient, efficient, safe, reliable and easy to industrialize.
Preferably, the silica aerogel precursor in the step c) is prepared by condensing and refluxing tetraethyl silicate, absolute ethyl alcohol, N-dimethylformamide, hydrochloric acid and deionized water.
In the invention, when the silicon dioxide aerogel precursor is prepared, the volume ratio of absolute ethyl alcohol, N-dimethylformamide to deionized water is 4.348:0.195:0.45, and the volume ratio of tetraethyl silicate to 0.1M hydrochloric acid is (6-9): 1.
preferably, the surfactant of step a) is selected from sodium citrate or EDTA;
the soluble yttrium salt is selected from yttrium acetate or yttrium trifluoroacetate;
the soluble ytterbium salt is selected from ytterbium acetate or ytterbium trifluoroacetate;
the soluble erbium salt is selected from erbium acetate or erbium trifluoroacetate.
Preferably, the molar ratio of the surfactant to the sodium hydroxide in the step a) is (0.12-0.36): 2.1, more preferably (0.24 to 0.32): 2.1;
the mol ratio of the ammonium fluoride to the hydrochloric acid in the step b) is (6-7): (2-5), more preferably (1.4-1.8): 1, more preferably 1.6: 1.
In the invention, the molar ratio of the surfactant to the sodium hydroxide can be adjusted to ensure that the NaYF is prepared 4 Yb/Er micron tube and/or NaYF 4 The Yb/Er micron rod has homogeneous diameter and/or diameter distribution, and the up-converting luminescent silica aerogel has high toughness and less chapping.
Preferably, the temperature of the heating reaction in the step b) is 180-220 ℃, the time of the heating reaction is 16-24 h, more preferably, the temperature of the heating reaction is 200-220 ℃, and the time of the heating reaction is 18-22 h;
the temperature of the condensation reflux in the step c) is 50-80 ℃, the time of the condensation reflux is 60-100 min, and more preferably, the temperature of the condensation reflux is 60-70 ℃, and the time of the condensation reflux is 70-90 min.
Preferably, after the standing in step c) and before the obtaining of the upconversion luminescent silica aerogel, the method further comprises:
and (3) soaking the product after standing in absolute ethyl alcohol and n-hexane in sequence, removing the soaking solution, and drying. The drying is preferably natural drying by volatilization at normal temperature.
In the invention, after the mixing in the step a), stirring is preferably carried out for 15 min at normal temperature to obtain a first reaction solution;
preferably stirring for 60 min in the step b) to obtain a second reaction solution, wherein the heating reaction specifically comprises the following steps: and transferring the second reaction solution to a polytetrafluoroethylene lining, putting the polytetrafluoroethylene lining into a high-pressure reaction kettle, and putting the reaction kettle into an oven for heating reaction.
And c), preferably adopting ammonia water to adjust the pH value to 7, and sealing and standing.
The invention also provides an anti-counterfeiting material, which comprises the upconversion luminescent silica aerogel prepared by the preparation method in the technical scheme and/or the upconversion luminescent silica aerogel prepared by the preparation method in the technical scheme.
In summary, the present invention provides an upconversion luminescent silica aerogel, which is formed by compounding a rare earth doped upconversion luminescent material and a silica aerogel; the rare earth doped up-conversion luminescent material is NaYF 4 Yb/Er micron tube and/or NaYF 4 Yb/Er micron rod. In the invention, a nano-porous material silicon dioxide aerogel is adopted as a display matrix material, the silicon dioxide aerogel is transparent, and the silicon dioxide aerogel and a rare earth doped up-conversion luminescent material NaYF are mixed 4 Yb/Er composite, NaYF 4 Yb/Er exists in the form of microtubes and/or micronsRod, NaYF 4 Yb/Er micron tube and/or NaYF 4 The Yb/Er micron rod and the silicon dioxide aerogel are uniformly compounded, the upconversion luminescent silicon dioxide aerogel is transparent as a whole, obvious opaque accumulation or deposition is not seen, the uniform light transmittance and display performance are achieved, the upconversion luminescent material has good upconversion luminescent performance under 980nm laser irradiation, visible green light is emitted, the optical waveguide effect is achieved, and the upconversion luminescent material can be used in the field of upconversion luminescent anti-counterfeiting excited by near-infrared laser. And, NaYF 4 Yb/Er micron tube and/or NaYF 4 The Yb/Er micron rod has toughening effect on the silicon dioxide aerogel, and overcomes the problems that the silicon dioxide aerogel is easy to crack after being dried, has poor mechanical property and is difficult to completely form and process.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below.
FIG. 1 is a Scanning Electron Microscope (SEM) of Sample 1 in example 1, wherein (a) is 30 μm, (b) is 10 μm, and (c) is a particle size distribution diagram;
FIG. 2 is a Scanning Electron Micrograph (SEM) of Sample 2 of example 2, wherein (a) is scale 30 μm, (b) is scale 10 μm, and (c) is a particle size distribution diagram;
FIG. 3 is a Scanning Electron Microscope (SEM) of Sample 3 in example 3, wherein (a) is 30 μm, (b) is 10 μm, and (c) is a particle size distribution diagram;
FIG. 4 is a Transmission Electron Micrograph (TEM) and a particle size distribution chart of Sample 4 in comparative example 1;
FIG. 5 is a schematic structural view of a Nikon Ni-U microscope;
FIG. 6 is a fluorescence micrograph of Sample 1 in bright field (top panel) and dark field (bottom panel) of example 1;
FIG. 7 is a fluorescence micrograph of Sample 2 in bright field (top panel) and dark field (bottom panel) of example 2;
FIG. 8 is a fluorescence micrograph of Sample 3 of example 3 in bright field (top panel) and dark field (bottom panel);
FIG. 9 is a graph of upconversion fluorescence spectra of Sample 1, Sample 2 and Sample 3 of examples 1-3 under 980nm laser excitation, with laser power of 2W;
FIG. 10 is the converted emission spectrum of Sample 4 of comparative example 1 at 980nm laser excitation, laser power 2W;
FIG. 11 shows Yb 3+ Ion and Er 3+ An ion energy transfer up-conversion luminescence mechanism diagram;
FIG. 12 is a physical diagram of the upconversion luminescent silica aerogel 1 in example 1, wherein (a) the physical diagram is in a bright field, (b) the physical diagram is in a fluorescent state under 980nm laser irradiation in a dark field, and the laser power is 0.5W;
FIG. 13 is a physical diagram of the upconversion luminescent silica aerogel 2 in example 2, wherein (a) the physical diagram is in a bright field, (b) the physical diagram is in a fluorescent state under 980nm laser irradiation in a dark field, and the laser power is 0.5W;
FIG. 14 is a diagram of example 3, namely a real object of upconversion luminescent silica aerogel 3, (a) a real object under a bright field, (b) a real object of fluorescence under 980nm laser irradiation under a dark field, and the laser power is 0.5W;
FIG. 15 is a diagram of a sample of the upconversion luminescent silica aerogel 4 in comparative example 1, wherein (a) the sample is a diagram under a bright field, (b) the sample is a diagram of a fluorescent sample under 980nm laser irradiation under a dark field, and the laser power is 0.5W;
fig. 16 is a physical diagram of a silica aerogel of comparative example 2.
Detailed Description
In view of the above, the present invention provides an upconversion luminescent silica aerogel and a preparation method thereof, wherein the upconversion luminescent silica aerogel comprises NaYF 4 The Yb/Er exists in the form of micron tube and/or micron rod, NaYF 4 Yb/Er and silica aerogel are uniformly compounded to have optical waveguide effect.
The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the raw materials used in the specific examples, hydrated yttrium acetate (Y (CH) 3 CO 2 ) 3 .xH 2 0, 99.9%), ytterbium acetate hydrate (Yb (CH) 3 CO 2 ) 3 .xH 2 0, 99.9%), erbium acetate hydrate (Er (CH) 3 CO 2 ) 3 .xH 2 0, 99.9%), acetic acid (CH) 3 COOH, >99.7%), ammonium fluoride (NH) 4 F, >98%), sodium hydroxide (NaOH,>98%) and hydrochloric acid (HCl,>37 wt%) were purchased from Sigma-Aldrich; cyclohexane (AR, 99.5%), absolute ethanol (pharmaceutical grade, 99.5%), sodium citrate dihydrate (AR, 99.0%), N-dimethylformamide (DMF, 98%) and tetraethyl silicate (TEOS, 98%) were purchased from michelin corporation; aqueous ammonia (25 wt%) was purchased from Tianjin Daimao; deionized water was self-made in the laboratory and the purchased laboratory reagents were used directly without any treatment.
Preparing a solution: mixing yttrium acetate (Y (CH) 3 CO 2 ) 3 .xH 2 0, 99.9%), ytterbium acetate hydrate (Yb (CH) 3 CO 2 ) 3 .xH 2 0, 99.9%), erbium acetate hydrate (Er (CH) 3 CO 2 ) 3 .xH 2 0, 99.9%), ammonium fluoride (NH) 4 F, >98%), sodium hydroxide (NaOH,>98%), hydrochloric acid (HCl,>37%), sodium citrate dihydrate (AR, 99.0%), hydrochloric acid (HCl,>37 wt%) of the above-mentioned components are dissolved in water, and the above-mentioned solutions are respectively made into 0.2M, 2M, 5M, 1M, 0.4M and 0.1M solutions, and then refrigerated in refrigerator at 8 deg.C for stand-by.
Example 1
The preparation method of the up-conversion luminescent silica aerogel comprises the following steps:
(1) deionized water (5 mL), NaOH aqueous solution (0.42 mL, 5M), sodium citrate (0.3 mL, 0.4M), yttrium acetate (1.56 mL, 0.2M), ytterbium acetate (0.4 mL, 0.2M) and erbium acetate (0.04 mL, 0.2M) are sequentially added into a polytetrafluoroethylene lining with the volume of 20 mL, and stirred for 15 min at normal temperature to obtain a first reaction solution;
(2) and adding an ammonium fluoride aqueous solution (3.2 mL, 2M) and a hydrochloric acid solution (4 mL, 1M) into the first reaction liquid, continuously stirring for 60 min to obtain a second reaction liquid, placing the tetrafluoroethylene liner into a high-pressure reaction kettle, placing the high-pressure reaction kettle into an oven for heating reaction (crystal growth) at 200 ℃ for 20 h to obtain a crystal material NaYF4: Yb/Er (20/2%).
(3) After the heating reaction is finished, cooling the reaction liquid in the high-pressure reaction kettle to room temperature, transferring the reaction liquid into a centrifuge tube, shaking uniformly, centrifuging at 6000 rpm for 3min, and pouring out the upper layer liquid. Continuously adding deionized water (12 mL), shaking uniformly, centrifuging at 6000 rpm for 3min, and repeating for 3 times; finally, the resulting crystalline material was dispersed in deionized water (12 mL) and stored under sealed refrigeration, with Sample labeled Sample 1.
(4) Sequentially adding tetraethyl silicate (5.643 mL), absolute ethyl alcohol (4.348 mL), N-dimethylformamide (0.195 mL), hydrochloric acid (0.7 mL, 0.1M) and deionized water (0.45 mL) into a brown two-neck flask, and condensing and refluxing for 80 min at the temperature of 65 ℃ to obtain a silicon dioxide aerogel precursor;
(5) and (3) after the silicon dioxide aerogel precursor is cooled to room temperature, adding a crystal material Sample 1 (0.5 mL), adjusting the pH value to 7 by using ammonia water (0.1M), sealing and standing the gel, soaking the gel in absolute ethyl alcohol and normal hexane in sequence after the gel is formed, changing the solution every 12 h, removing the soaking solution, volatilizing at normal temperature and naturally drying to obtain the up-conversion luminescent silicon dioxide aerogel 1, and sealing and storing by using a transparent sealing bag.
Example 2
This example was carried out to prepare an upconversion luminescent silica aerogel, the procedure was the same as in example 1, except that:
in the step (1), the dosage of the sodium citrate is 0.5 mL, namely the molar ratio of the sodium citrate to NaOH is 0.2: 2.1, and the obtained crystal material Sample is marked as Sample 2;
in the step (5), the added crystal material is Sample 2, and the up-conversion luminescent silica aerogel 2 is obtained.
Example 3
This example was carried out to prepare an upconversion luminescent silica aerogel, the procedure was the same as in example 1, except that:
in the step (1), the amount of the sodium citrate is 0.7 mL, namely the molar ratio of the sodium citrate to NaOH is 0.28: 2.1, and the obtained crystal material Sample is marked as Sample 3.
In the step (5), the added crystal material is Sample 3, and the up-conversion luminescent silica aerogel 3 is obtained.
Comparative example 1
This comparative example carried out the preparation of an upconversion luminescent silica aerogel, having NaYF4: Yb/Er (20/2%) present in the form of particles, comprising the following steps:
(1) sequentially adding yttrium acetate (1.56 mL, 0.2M), ytterbium acetate (0.4 mL, 0.2M), erbium acetate (0.04 mL, 0.2M), oleic acid (3 mL, 90%) and 1-octadecylene (7 mL, 90%) into a two-neck flask, and heating to 150 ℃ in a heating jacket and keeping for 1 h to remove water in the solution to obtain a first reaction solution containing a rare earth-oleic acid complex precursor;
(2) the first reaction was cooled to room temperature and NaOH in methanol (1 mL, 1M) and NH were added 4 F methanol solution (4 mL, 0.4M), raise the temperature to 45 ℃, keep stirring for 1 h; then, the temperature was raised to 110 ℃ to remove methanol from the solution; the temperature is raised to 280 ℃ under the argon atmosphere, and the reaction is finished after the crystal grows for 1 hour.
(3) After the reaction is finished, the reaction solution in the two-neck flask is cooled to room temperature, the reaction solution is transferred to a centrifuge tube, absolute ethyl alcohol (4 mL, 99.5%) is added, shaking and shaking are carried out, the mixture is centrifuged at 6000 rpm for 3min, and the upper layer liquid is poured out. Continuously adding cyclohexane (4 mL, 99.5%) and absolute ethyl alcohol (8 mL, 99.5%), shaking up, and centrifuging at 6000 rpm for 3 min; continuously pouring out the upper liquid, adding cyclohexane (4 mL, 99.5%), absolute ethyl alcohol (4 mL, 99.5%) and methanol (4 mL, 99.9%), shaking up, centrifuging at 6000 rpm for 3min, and pouring out the upper liquid; finally, the resulting particles were dispersed in cyclohexane (12 mL, 99.5%) and stored under sealed refrigeration, the solution was light yellow and the Sample was labeled as Sample 4.
(4) Sequentially adding tetraethyl silicate (5.643 mL), absolute ethyl alcohol (4.348 mL), nitrogen-nitrogen dimethylformamide (0.195 mL), hydrochloric acid (0.7 mL, 0.1M) and deionized water (0.45 mL) into a brown two-neck flask, and condensing and refluxing for 80 min at 65 ℃ to obtain a silicon dioxide aerogel precursor;
(5) cooling the silicon dioxide aerogel precursor to room temperature, adding a crystal material Sample 4 (0.5 mL), adjusting the pH value to 7 by using ammonia water (0.1M), sealing and standing for gelation, sequentially soaking the gel in absolute ethyl alcohol and n-hexane after the gel is formed, changing the solution every 12 h, removing the soaking solution, volatilizing at room temperature and naturally drying to obtain the up-conversion luminescent silicon dioxide aerogel 4, and sealing and storing by using a transparent sealing bag.
Comparative example 2
This comparative example carried out the preparation of silica aerogel, comprising the following steps:
(1) sequentially adding tetraethyl silicate (5.643 mL), absolute ethyl alcohol (4.348 mL), nitrogen-nitrogen dimethylformamide (0.195 mL), hydrochloric acid (0.7 mL, 0.1M) and deionized water (0.45 mL) into a brown two-neck flask, and condensing and refluxing for 80 min at 65 ℃ to obtain a silicon dioxide aerogel precursor;
(2) cooling the silicon dioxide aerogel precursor to room temperature, adjusting pH to 7 with ammonia water (0.1M), sealing and standing for gelation, soaking with anhydrous ethanol and n-hexane in sequence after gelation is formed, changing the solution every 12 h, removing the soaking solution, volatilizing at normal temperature, naturally drying to obtain silicon dioxide aerogel, and sealing and storing with a transparent sealing bag.
Example 6
1. Structural characterization
Sample 1, Sample 2 and Sample 3 obtained in examples 1 to 3 were characterized by a scanning electron microscope using a Hitachi S-4800 type scanning electron microscope at an operating voltage of 20 KV, and the detection results are shown in fig. 1 to 3.
Transmission electron microscopy characterization was performed on Sample 4 obtained in comparative example 1 using a Japanese Electron (JEOL) JEM-2100HR electron microscope at an operating voltage of 200 KV, with the results shown in FIG. 4.
Referring to FIG. 1, a Scanning Electron Microscope (SEM) of Sample 1 in example 1 is shown, and scale 3 in FIG. 1 (a)0 μm, scale of 10 μm in FIG. 1 (b), NaYF 4 Yb/Er appeared as rods with the particle size distribution of FIG. 1 (c) having a statistical mean size of 3.05 x 9.23 μm;
referring to FIG. 2, the Scanning Electron Micrograph (SEM) of Sample 2 in example 2 is shown, wherein the scale in FIG. 2 (a) is 30 μm, the scale in FIG. 2 (b) is 10 μm, and NaYF 4 Yb/Er appeared tubular, and the statistical mean size of the particle size distribution plot of FIG. 2 (c) was around 2.07 x 8.25 μm;
referring to FIG. 3, the Scanning Electron Micrograph (SEM) of Sample 3 in example 3 is shown, wherein the scale in FIG. 3 (a) is 30 μm, the scale in FIG. 3 (b) is 10 μm, and NaYF 4 Yb/Er appeared tubular and the particle size distribution of FIG. 3 (c) had a statistical mean size of around 2.518 x 17.05. mu.m.
As can be seen from comparison of FIGS. 1 to 3, sodium citrate is used as a surfactant to assist in growing NaYF 4 Yb/Er (20/2%) crystal, the crystal being oriented in the axial direction, i.e. [001 ]]And (4) directionally growing. When the amount of sodium citrate is less (0.12 mmol), NaYF 4 Yb/Er is rod-shaped. Sodium citrate inhibited the crystals to some extent with increasing sodium citrate dosage [001 ]]The crystal is changed from a micron rod into a micron tube by the growth of the periphery of the axis in the direction, the size is reduced and then increased, and the tube hole is gradually increased. When the using amount of the sodium citrate is 0.20 mmol, the crystal is in a stage of converting a micron rod into a micron tube, the shape and the size are uneven, and the average size is relatively small.
FIG. 4 shows a Transmission Electron Microscope (TEM) and particle size distribution of Sample 4 in comparative example 1, with a ruler of 100 nm, NaYF 4 The Yb/Er particles appeared to be spheroidal and relatively uniform in size, with a statistical mean size of 32.95 x 22.20 nm in the particle size distribution plot.
2. Fluorescent microscopy analysis
And performing fluorescence microscopic characterization on Sample 1, Sample 2 and Sample 3 obtained in the embodiments 1 to 3 by using a Nikon ECLPSENi-U type fluorescence microscope, wherein the used light source is 980nm near-infrared laser, and the exposure time is 200 ms.
Please refer to fig. 5, which is a schematic structural diagram of a nikon Ni-U microscope, the 980nm laser is input from an input port, after the 980nm laser is converged by a focusing lens, the direction of the exciting light is changed by beam splitters DM 1 and DM 2, and finally the exciting light enters an objective lens to irradiate a sample, and the detection result is shown in fig. 6 to 8.
FIG. 6 is a fluorescent micrograph of Sample 1 of example 1 in bright (top) and dark (bottom) fields, with a 20 μm scale, relatively uniform size, and NaYF in dark field 4 Yb/Er (20/2%) micrometer rods up-convert to emit green light under the irradiation of 980nm excitation light, and show yellow light in bright field due to the presence of white light. When laser irradiates the A area, the micron rod presents an optical waveguide phenomenon, and is more obvious in a dark field. With the increase of laser power, the luminous intensity is enhanced, and the optical waveguide phenomenon is more obvious. When laser irradiates the B area with more dense microrods, light can be coupled with the surrounding microrods, the optical waveguide phenomenon is more remarkable, and the luminous intensity is also remarkably enhanced.
FIG. 7 is a fluorescence micrograph of Sample 2 of example 2 in bright field (top view) and dark field (bottom view), with a scale of 20 μm and less uniform size, and the fluorescence microscopy phenomenon is substantially identical to that of FIG. 6.
FIG. 8 is a fluorescence micrograph of Sample 3 of example 3 in bright field (top) and dark field (bottom) at 20 μm, relatively uniform size, fluorescence microscopy substantially identical to that of FIG. 6,
3. detection of luminescent Properties
The upconversion luminescence performance test was performed on Sample 1, Sample 2, Sample 3 in examples 1 to 3 and Sample 4 in comparative example 1 using a HORIBA FluoroMax-4 fluorescence spectrometer with external laser wavelength of 980nm and power of 2W, and the test results are shown in fig. 9 and 10.
FIG. 9 shows the upconversion fluorescence spectra of Sample 1, Sample 2 and Sample 3 of examples 1-3 under 980nm laser excitation, with laser power of 2W. FIG. 9 shows that the emission peak is Er under the excitation of 980nm near-infrared laser 3+ At 415 nm, 525 nm, 542 nm and 655 nm, respectively, the upconversion luminescence process can be explained with reference to fig. 11, Yb when excited with a 980nm laser 3+ The ions are excited as sensitized ions by first capturing photons of the light source, and then are excited from the ground state 2 F 7/2 Transition to 2 F 5/2 Energy level, then part of Yb therein 3+ The ion radiation transitions back to the ground state and transfers energy to the adjacent Yb 3+ Ion, another part of Yb 3+ The ions continuously transfer energy to the adjacent Er 3+ Ions. Er 3+ The energy level of the ions is in a step section, and the energy difference among a plurality of energy levels is equivalent to the energy of 980nm exciting light, so the Er 3+ The ions can continuously absorb the energy of a plurality of 980nm photons and gradually jump to a higher energy level, and then the radiation jump emits the photons with high energy, so that the up-conversion emission is realized; wherein, Er 3+ Weak purple luminescence from 2 G 9/2 → 4 I 15/2 The transition of (1) is an up-conversion transition emission process of three photons, and corresponds to an emission peak at 415 nm; and its strong green luminescence comes from 2 H 11/2 → 4 I 15/2 And 4 S 3/2 → 4 I 15/2 the transition of (2) is an up-conversion transition emission process of two photons, and respectively corresponds to emission peaks at 525 nm and 542 nm; furthermore, Er 3+ Part of red light is emitted, but is relatively weak, is covered by green light and can not be distinguished by naked eyes, and is also an up-conversion transition emission process of two photons, and an emission peak corresponding to 655 nm comes from 4 F 9/2 → 4 I 15/2 Is detected. Comparing Sample 1, Sample 3 and Sample 5, the luminous intensity is increased along with the increase of the amount of sodium citrate, which shows that the luminous intensity is increased when NaYF4 Yb/Er (20/2%) is converted from a micron rod into a micron tube; and as the size increases, the luminous intensity also increases.
FIG. 10 shows the upconversion fluorescence spectrum of Sample 4 of comparative example 1 under 980nm laser excitation, with laser power of 2W. FIG. 10 shows that the emission peak is Er under the excitation of 980nm near-infrared laser 3+ The characteristic emission peaks of (A) are at 415 nm, 525 nm, 542 nm and 655 nm, and can be seen from FIG. 11, which are respectively originated from 2 G 9/2 → 4 I 15/2 、 2 H 11/2 → 4 I 15/2 And 4 S 3/2 → 4 I 15/2 and 4 F 9/2 → 4 I 15/2 is detected.
4. Visual observation of material object
Please refer to fig. 12, which is a diagram of an example 1 upconversion luminescent silica aerogel 1. FIG. 12 (a) is a pictorial representation in the bright field, which shows that the upconversion luminescent silica aerogel 1 of example 1 is transparent, has no significant cracks, and shows a uniform-sized NaYF 4 The Yb/Er (20/2%) micron rod has toughening effect on silica aerogel. FIG. 12 (b) is a physical diagram of 980nm laser irradiation in dark field with laser power of 0.5W, the upconversion luminescent silica aerogel 1 of example 1 emits macroscopic green upconversion light, and NaYF 4 The photoluminescence of the Yb/Er (20/2%) micrometer rods is consistent.
Fig. 13 is a schematic diagram of the upconversion luminescent silica aerogel 2 in example 2. FIG. 13 (a) is a diagram of a sample in bright field, which shows that the upconversion luminescent silica aerogel 2 of example 2 is transparent, has obvious cracks, and shows that the NaYF has a non-uniform size 4 The Yb/Er (20/2%) micron rod has no obvious toughening effect on the silicon dioxide aerogel. FIG. 13 (b) is a diagram of a 980nm laser irradiation in dark field with a laser power of 0.5W, the upconversion luminescent silica aerogel 2 of example 2 emits macroscopic green upconversion light, and NaYF 4 Yb/Er (20/2%) micron tube photoluminescence is consistent, and meanwhile, weak optical waveguide phenomenon can be found.
Fig. 14 is a schematic diagram of luminescent silica aerogel 3 converted in example 3. FIG. 14 (a) is a pictorial representation in bright field, which shows that the upconversion luminescent silica aerogel 3 of example 3 is transparent and has no significant cracks, illustrating the uniform size of the NaYF 4 The Yb/Er (20/2%) micron tube has toughening effect on the silicon dioxide aerogel. FIG. 14 (b) is a pictorial representation of 980nm laser irradiation in dark field with laser power of 0.5W, with example 2 upconverting luminescent silica aerogel 2 emitting macroscopic upconverting green light, and NaYF 4 The photoluminescence of Yb/Er (20/2%) micron tubes is consistent. Due to NaYF in the silica aerogel 3 converted to luminescence in example 3 4 The Yb/Er (20/2%) micron tube has longer length and larger tube hole, the optical waveguide effect is more obvious,significant optical waveguide phenomena can be observed.
Fig. 15 is a schematic diagram of the luminescent silica aerogel 4 converted in comparative example 1. FIG. 15 (a) is a pictorial representation in the bright field, which shows that the luminescent silica aerogel 4 converted in comparative example 1 is light yellow transparent and has a partial crack, illustrating that NaYF 4 The Yb/Er (20/2%) nano-particles have toughening effect on the silicon dioxide aerogel, but are not obvious. FIG. 15 (b) is a pictorial representation of 980nm laser irradiation in dark field with a laser power of 0.5W, with comparative example 1 upconversion luminescent silica aerogel 4 emitting a macroscopic green upconversion consistent with NaYF4: Yb/Er (20/2%) nanoparticle photoluminescence. No optical waveguide phenomenon is found because the NaYF4 Yb/Er (20/2%) nano particles are granular and have no optical waveguide effect.
FIG. 16 is a schematic representation of a silica aerogel of comparative example 2. Comparative example 2 silica aerogel is transparent as a whole, is a good display material, can be used as a display matrix material instead of Polydimethylsiloxane (PDMS), but is prone to crack after being dried, which indicates that the mechanical property is poor and complete forming and processing are difficult.
In summary, the invention adopts the nano-porous material silicon dioxide aerogel as the display matrix material, the silicon dioxide aerogel is transparent, and the silicon dioxide aerogel and the rare earth doped up-conversion luminescent material NaYF are mixed 4 Yb/Er composite, NaYF 4 Yb/Er is present in the form of microtubes and/or microrods, NaYF 4 The Yb/Er micro-tube and/or the micro-rod is uniformly compounded with the silicon dioxide aerogel, has good up-conversion luminescence property under the irradiation of 980nm laser, emits green light visible to naked eyes, has a light waveguide effect, and can be used in the field of up-conversion luminescence anti-counterfeiting excited by near-infrared laser. And, NaYF 4 The Yb/Er micron tube and/or micron rod has toughening effect on the silicon dioxide aerogel, and solves the problems that the silicon dioxide aerogel is easy to crack after being dried, has poor mechanical property and is difficult to completely form and process.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and amendments can be made without departing from the principle of the present invention, and these modifications and amendments should also be considered as the protection scope of the present invention.

Claims (9)

1. The up-conversion luminescent silica aerogel is characterized in that the up-conversion luminescent silica aerogel is formed by compounding a rare earth doped up-conversion luminescent material and silica aerogel;
the rare earth doped up-conversion luminescent material is NaYF 4 Yb/Er micron tube or NaYF 4 Yb/Er micron rods;
NaYF 4 in the Yb/Er, the content of Yb is 20-98 mol% and the content of Er is 2-10 mol%;
the up-conversion luminescent silicon dioxide aerogel is formed by compounding a rare earth doped up-conversion luminescent material and silicon dioxide aerogel and comprises the following steps:
a) mixing sodium hydroxide, sodium citrate, soluble yttrium salt, soluble ytterbium salt, soluble erbium salt and deionized water to obtain a first reaction solution, wherein the molar ratio of the sodium citrate to the sodium hydroxide is (0.12-0.36): 2.1;
b) adding ammonium fluoride and hydrochloric acid into the first reaction liquid to obtain a second reaction liquid, and then heating the second reaction liquid to react to obtain a crystal material, wherein the molar ratio of the ammonium fluoride to the hydrochloric acid is (6-7): (2-5), wherein the temperature of the heating reaction is 180-220 ℃, and the time of the heating reaction is 16-24 h;
c) and adding the crystal material into the silicon dioxide aerogel precursor, adjusting the pH value, and standing to obtain the up-conversion luminescent silicon dioxide aerogel.
2. The upconversion luminescent silica aerogel according to claim 1, wherein the NaYF is selected from the group consisting of NaYF, and NaYF, or NaYF, wherein NaYF is selected from the NaYF, or a combination of NaYF, or a combination of a 4 Yb/Er micron tube or NaYF 4 The length of the Yb/Er micron rod is 7-25 μm;
the NaYF 4 Yb/Er micron tube or NaYF 4 The diameter of the Yb/Er micron rod is 2 μm to 5 μm.
3. The upconversion luminescent silica aerogel according to claim 1,
the mass ratio of the rare earth doped up-conversion luminescent material to the silicon dioxide aerogel is (2000-20000): 1.
4. the preparation method of the up-conversion luminescent silica aerogel is characterized by comprising the following steps of:
a) mixing sodium hydroxide, sodium citrate, soluble yttrium salt, soluble ytterbium salt, soluble erbium salt and deionized water to obtain a first reaction solution, wherein the molar ratio of the sodium citrate to the sodium hydroxide is (0.12-0.36): 2.1;
b) adding ammonium fluoride and hydrochloric acid into the first reaction liquid to obtain a second reaction liquid, and then heating the second reaction liquid to react to obtain a crystal material, wherein the molar ratio of the ammonium fluoride to the hydrochloric acid is (6-7): (2-5), wherein the temperature of the heating reaction is 180-220 ℃, and the time of the heating reaction is 16-24 h;
c) and adding the crystal material into the silicon dioxide aerogel precursor, adjusting the pH value, and standing to obtain the up-conversion luminescent silicon dioxide aerogel.
5. The preparation method according to claim 4, wherein the silica aerogel precursor in step c) is prepared by condensing and refluxing tetraethyl silicate, absolute ethanol, N-dimethylformamide, hydrochloric acid and deionized water.
6. The method of claim 4 wherein the soluble yttrium salt of step a) is selected from yttrium acetate or yttrium trifluoroacetate;
the soluble ytterbium salt is selected from ytterbium acetate or ytterbium trifluoroacetate;
the soluble erbium salt is selected from erbium acetate or erbium trifluoroacetate.
7. The preparation method of claim 5, wherein the temperature of the condensation reflux in step c) is 50 ℃ to 80 ℃, and the time of the condensation reflux is 60 min to 100 min.
8. The preparation method according to claim 4, wherein after the standing in step c) and before the obtaining of the upconversion luminescent silica aerogel, the method further comprises:
and (3) soaking the product after standing in absolute ethyl alcohol and n-hexane in sequence, removing the soaking solution, and drying.
9. An anti-counterfeiting material, which is characterized by comprising the up-conversion luminescent silica aerogel according to any one of claims 1 to 3 and/or the up-conversion luminescent silica aerogel prepared by the preparation method according to any one of claims 4 to 8.
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