A fluoride upconversion luminescence film, a preparation method and application thereof

Abstract

This invention provides a fluoride upconversion luminescent thin film, its preparation method, and its application. The preparation method includes: (1) mixing a Na source, an F source, and a first solvent to obtain a first solution; (2) mixing at least three rare earth metal sources and a second solvent to obtain a second solution; (3) sequentially coating the first solution and the second solution onto a substrate, and obtaining the fluoride luminescent thin film after reaction. The first solvent and the second solvent each independently include methanol, and the at least three rare earth metal sources include rare earth nitrates. This invention directly prepares a fluoride upconversion luminescent thin film by in-situ integral growth on a substrate. The resulting film is uniform, dense, and has strong luminescence intensity. The operation is simple, the preparation time is short, and it is suitable for widespread application.

Description

Technical Field

[0001] This invention belongs to the field of light-emitting thin film technology, and relates to a fluoride upconversion light-emitting thin film, its preparation method and application. Background Technology

[0002] Wavelength-conversion luminescent materials are broadly classified into two categories: upconversion (UC) and downconversion (DC). Upconversion materials can absorb two or more low-energy photons (such as near-infrared light) and emit higher-energy photons (such as visible light), exhibiting anti-Stokes luminescence properties. Fluorides, especially sodium rare-earth fluorides (such as NaYF4-based luminescent materials), are widely recognized as ideal upconversion matrix materials due to their low phonon energy, high chemical stability, wide transmittance range, and excellent luminous efficiency, showing significant application prospects in multilayer optical storage disks, photoluminescent screens, anti-counterfeiting encryption, and photovoltaic cells.

[0003] To date, the most common methods for preparing fluoride luminescent thin films involve physical vapor deposition (PVD) and chemical solution methods. PVD includes molecular beam epitaxy, electron beam deposition, pulsed laser deposition, and magnetron sputtering; however, these methods require expensive film-forming equipment and demanding substrate requirements, resulting in extremely high preparation costs. Chemical solution methods include sol-gel preparation, electrodeposition, and embedding nanocrystals into polymer matrices; these methods are complex and require careful preparation of nanoparticles.

[0004] For example, CN109929203A discloses a method for preparing a wavelength-conversion luminescent thin film, which mainly includes: synthesizing NaYF4-based upconversion or downconversion luminescent nanoparticles with oleic acid functional groups on the surface using a solvothermal method; dissolving PMMA in anisole to form a carrier solution; dispersing the nanoparticles therein and forming a film on a clean substrate using a spin-coating method; and finally obtaining a PMMA-coated luminescent thin film by low-temperature drying. However, this method is essentially still an indirect preparation route of "first synthesizing nanoparticles, then dispersing them into a film." Its film formation process depends on polymer coating and spin-coating processes. The thickness uniformity, crystallinity, and long-term stability of the film may be limited by the polymer matrix and process parameters. Furthermore, it cannot achieve in-situ directional growth of nanocrystals on the substrate and interface optimization. Therefore, it has limitations in some optoelectronic applications that require high film crystallinity, purity, and interface characteristics.

[0005] Therefore, developing an integrated preparation method that can directly grow high-quality, highly adhesive, and structurally controllable fluoride luminescent thin films in situ on substrates is of great research significance and application value. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a fluoride upconversion luminescent thin film, its preparation method, and its applications. This invention directly prepares a fluoride upconversion luminescent thin film through in-situ integral growth on a substrate. The resulting film is uniform, dense, and exhibits strong luminescence intensity. The process is simple, the preparation time is short, and it is suitable for widespread application.

[0007] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a fluoride upconversion luminescent thin film, the method comprising: (1) Mix the Na source, F source and the first solvent to obtain the first solution; (2) Mix at least three rare earth metal sources and a second solvent to obtain a second solution; (3) The first solution and the second solution are sequentially coated onto the substrate, and the fluoride luminescent film is obtained after reaction; The first solvent and the second solvent each independently comprise methanol, and the at least three rare earth metal sources comprise rare earth nitrates.

[0008] In this invention, a fluoride film is grown by directly coating a precursor solution onto a substrate. Its core advantages are that it achieves chemical bonding growth of the film layer, resulting in strong adhesion; it avoids the introduction of organic binders, making the film purer and denser, with better optical performance; the process steps are simplified, and the chemical composition, thickness, and microstructure of the film can be precisely controlled, making it more suitable for the integration of high-performance optoelectronic devices.

[0009] Furthermore, it should be noted that this invention requires a two-step coating process. Mixing all raw materials together at the beginning will lead to precipitation, preventing uniform coating on the substrate surface and significantly reducing the uniformity and density of the prepared film. Additionally, methanol is used as both the first and second solvents, offering better solubility compared to other alcohols such as ethanol. This results in a more uniform and dense film with higher luminous intensity. Moreover, the luminescent film prepared with rare earth nitrates exhibits high luminous efficiency, more uniform surface morphology, and higher purity. In contrast, rare earth chlorides contain Cl... - , and Cl - Will be with Na + The formation of NaCl can negatively impact the luminescence of the thin film; rare earth oleates need to be synthesized in-house, which is a relatively complicated process and results in low luminescence intensity.

[0010] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0011] Preferably, the Na source in step (1) includes sodium hydroxide.

[0012] Preferably, the F source in step (1) includes ammonium fluoride.

[0013] In this invention, NaOH, in addition to serving as a Na source, can also provide an alkaline environment for the system; while NH4 in NH4F + It reacts with NaOH to produce ammonia water, and the final NaYF4 has a high purity and does not contain other impurity elements.

[0014] Preferably, the ratio of Na source, F source and first solvent in step (1) is (0.05~0.12)g:(0.074~0.176)g:(5~6)mL, for example 0.05g:0.074g:5mL, 0.07g:0.09g:5.2mL, 0.08g:0.1g:5.5mL, 0.09g:0.13g:5.7mL, 0.1g:0.15g:5.9mL or 0.12g:0.176g:6mL, etc.

[0015] Preferably, the mixing method in step (1) includes ultrasound.

[0016] Preferably, the at least three rare earth metal sources in step (2) include at least three of the following: Y source, La source, Ce source, Nd source, Eu source, Gd source, Tb source, Dy source, Ho source, Yb source, Er source, Tm source, or Gd source.

[0017] Preferably, the ratio of the total molar amount of the at least three rare earth metal sources in step (2) to the molar amount of the F source in step (1) is 1:(4~6), for example, 1:4, 1:4.5, 1:5, 1:5.5 or 1:6, etc.

[0018] Preferably, the at least three rare earth metal sources in step (2) are Y source, Yb source and Er source, such as Y(NO3)3·6H2O, Yb(NO3)3·6H2O and Er(NO3)3·6H2O.

[0019] In this invention, when using Y, Yb, and Er sources, NaYF4:Yb:Er luminescent films can be prepared. This type of luminescent film combines the excellent crystal and chemical properties of NaYF4 with the efficient energy transfer and upconversion luminescence mechanism of the Yb / Er system, exhibiting high brightness, tunable color, low background, good stability, and good device integration, giving it significant advantages in fields such as bioimaging, anti-counterfeiting, security marking, and optoelectronic device gain.

[0020] Preferably, the molar ratio of the Y source, Yb source and Er source is (150~180):(30~50):1, for example 150:30:1, 155:33:1, 160:35:1, 165:38:1, 170:40:1, 175:45:1 or 180:50:1, etc.

[0021] In this invention, controlling the molar ratio of Y source, Yb source and Er source within the above range is more conducive to improving the energy absorption and transfer efficiency of the sensitizer, suppressing the concentration quenching between activators, and thus significantly enhancing the upconversion luminescence intensity and fluorescence lifetime of the film.

[0022] Preferably, in the coating process described in step (3), the volume ratio of the first solution and the second solution is 1:(0.8~1.2), for example, 1:0.8, 1:0.9, 1:1, 1:1.1 or 1:1.2, etc.

[0023] Preferably, the substrate in step (3) includes any one of glass, silicon, FTO (fluorine-doped tin oxide), or ITO (tin-doped indium oxide).

[0024] Preferably, the coating method in step (3) includes spin coating.

[0025] Preferably, the reaction in step (3) is carried out in a vacuum environment.

[0026] Preferably, the vacuum level of the vacuum environment is ≤1×10⁻⁶. -4 Pa, for example 1×10 -5 Pa, 3×10 -5 Pa, 5×10 - 5 Pa, 8×10 -5 Pa or 1×10 -4 Pa, etc.

[0027] Preferably, the reaction temperature in step (3) is 295℃~300℃, such as 295℃, 296℃, 297℃, 298℃, 299℃ or 300℃, and the time is 0.25h~1.5h, such as 0.25h, 0.5h, 1h, 1.2h or 1.5h.

[0028] In this invention, by controlling the reaction temperature and time within the above-mentioned preferred range, it is more conducive to inducing the transformation of the crystal from the cubic phase to the highly efficient hexagonal phase and controlling the morphology of the film, thereby improving the upconversion luminescence efficiency of the film while ensuring that it has good light transmittance and surface flatness and uniformity.

[0029] In a second aspect, the present invention provides a fluoride upconversion luminescent film prepared by the preparation method described in the first aspect, wherein the fluoride upconversion luminescent film comprises NaAF4:B:C, and A, B and C in NaAF4:B:C are selected from three different rare earth elements.

[0030] Preferably, the fluoride upconversion luminescent film is NaYF4:Yb:Er.

[0031] Preferably, the thickness of the fluoride upconversion luminescent film is 100nm~150nm, such as 100nm, 110nm, 120nm, 130nm, 140nm or 150nm.

[0032] Thirdly, the present invention provides an application of the fluoride upconversion luminescent film as described in the second aspect, the application including applications in the fields of multilayer optical storage disks, photoluminescent screens, anti-counterfeiting encryption, or photovoltaic cells.

[0033] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0034] Compared with the prior art, the present invention has the following beneficial effects: The preparation method provided by this invention is simple, convenient, and easy to operate. The prepared upconversion luminescent film is uniform and dense and has stronger fluorescence than the luminescent film prepared by spin coating of nanoparticles. Attached Figure Description

[0035] Figure 1 These are X-ray diffraction (XRD) patterns of the NaYF4:Yb:Er thin films prepared in Examples 1-3, Example 8, and Comparative Example 3.

[0036] Figure 2 This is the XRD pattern of the NaGdF4:Yb:Er thin film prepared in Example 5.

[0037] Figure 3 These are upconversion fluorescence spectra of the NaYF4:Yb:Er films prepared in Examples 1-2, Examples 6-7, and Comparative Example 1.

[0038] Figure 4 These are upconversion fluorescence spectra of the NaYF4:Yb:Er films prepared in Examples 3 and Comparative Examples 2-4.

[0039] Figure 5 These are the upconversion fluorescence spectra of the films prepared in Examples 4-5 and Example 8.

[0040] Figure 6This is a scanning electron microscope image of the NaYF4:Yb:Er thin film prepared in Example 1.

[0041] Figure 7 This is a scanning electron microscope image of the NaYF4:Yb:Er thin film prepared in Example 2.

[0042] Figure 8 This is a scanning electron microscope image of the NaYF4:Yb:Er thin film prepared in Example 3.

[0043] Figure 9 This is a scanning electron microscope image of the NaYF4:Yb:Er thin film prepared in Example 4.

[0044] Figure 10 This is a scanning electron microscope image of the NaGdF4:Yb:Er thin film prepared in Example 5.

[0045] Figure 11 This is a scanning electron microscope image of the NaYF4:Yb:Er thin film prepared in Example 6.

[0046] Figure 12 This is a scanning electron microscope image of the NaYF4:Yb:Er thin film prepared in Example 7.

[0047] Figure 13 This is a scanning electron microscope image of the NaYF4:Yb:Er thin film prepared in Example 8.

[0048] Figure 14 This is a scanning electron microscope image of the NaYF4:Yb:Er thin film prepared in Comparative Example 1.

[0049] Figure 15 This is a scanning electron microscope image of the NaYF4:Yb:Er thin film prepared in Comparative Example 2.

[0050] Figure 16 This is a scanning electron microscope image of the NaYF4:Yb:Er thin film prepared in Comparative Example 3.

[0051] Figure 17 This is a scanning electron microscope image of the NaYF4:Yb:Er thin film prepared in Comparative Example 4. Detailed Implementation

[0052] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0053] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this application; the terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion.

[0054] Example 1 This embodiment provides a method for preparing NaYF4:Yb:Er luminescent thin films: Preparation of Y(NO3)3 solution: Weigh 3.83 g of Y(NO3)3·6H2O (10 mmol) and 10 mL of methanol into a 20 mL glass bottle, sonicate until dissolved, and store in a sealed container at room temperature; Preparation of Yb(NO3)3 solution: Weigh 4.67 g of Yb(NO3)3·6H2O (10 mmol) and 10 mL of methanol into a 20 mL glass bottle, sonicate until dissolved, and store in a sealed container at room temperature; Preparation of Er(NO3)3 solution: Weigh 0.46 g of Er(NO3)3·6H2O (1 mmol) and 5 mL of methanol into a 20 mL glass bottle, sonicate until dissolved, and store in a sealed container at room temperature; Weigh 0.12 g of NaOH, 0.17 g of NH4F, and 5 mL of methanol, mix and sonicate to dissolve. Take 50 μL and spin-coat it onto a glass slide. In a 20 mL glass bottle, measure 1.2 mL of Y(NO3)3 solution (1 mmol / mL), 0.30 mL of Yb(NO3)3 solution (1 mmol / mL), and 37.5 μL of Er(NO3)3 solution (0.2 mmol / mL). Add 10 mL of methanol, mix thoroughly, and take 50 μL of this solution to spin-coat it onto the glass slide. In a vacuum chamber (1... 10 -4 Heat to 300 Pa) A NaYF4:Yb:Er upconversion luminescent film was obtained by reacting at C for 30 min.

[0055] Example 2 This embodiment provides a method for preparing NaYF4:Yb:Er luminescent thin films: Preparation of Y(NO3)3 solution: Weigh 3.83 g of Y(NO3)3·6H2O (10 mmol) and 10 mL of methanol into a 20 mL glass bottle, sonicate until dissolved, and store in a sealed container at room temperature; Preparation of Yb(NO3)3 solution: Weigh 4.67 g of Yb(NO3)3·6H2O (10 mmol) and 10 mL of methanol into a 20 mL glass bottle, sonicate until dissolved, and store in a sealed container at room temperature; Preparation of Er(NO3)3 solution: Weigh 0.46 g of Er(NO3)3·6H2O (1 mmol) and 5 mL of methanol into a 20 mL glass bottle, sonicate until dissolved, and store in a sealed container at room temperature; Weigh 0.05 g of NaOH, 0.074 g of NH4F, and 5 mL of methanol, mix and sonicate to dissolve. Take 50 μL and spin-coat it onto a glass slide. In a 20 mL glass bottle, measure 0.4 mL of Y(NO3)3 solution (1 mmol / mL), 0.1 mL of Yb(NO3)3 solution (1 mmol / mL), and 12.5 μL of Er(NO3)3 solution (0.2 mmol / mL). Add 10 mL of methanol, mix thoroughly, and take 50 μL of this solution to spin-coat it onto the glass slide. In a vacuum chamber (1... 10 -4 Heat to 300 Pa) The NaYF4:Yb:Er upconversion luminescent film was obtained by reacting at C for 1 h.

[0056] Example 3 The difference between this embodiment and Example 1 is that 0.05g of NaOH, 0.074g of NH4F, and 5mL of methanol were weighed, mixed, and dissolved by ultrasonication, and 50μL was spin-coated onto a glass slide. 3.83g of Y(NO3)3·6H2O (10mmol), 4.67g of Yb(NO3)3·6H2O (10mmol), and 0.46g of Er(NO3)3·6H2O were replaced with 3.03g of YCl3·6H2O, 3.87g of YbCl3·6H2O, and 0.82g of ErCl3·6H2O, respectively. The remaining preparation methods and parameters are consistent with those in Example 1.

[0057] Example 4 The difference between this embodiment and Embodiment 1 is that 0.12g of NaOH is replaced with 0.36g of NaOH; The remaining preparation methods and parameters are consistent with those in Example 1.

[0058] Example 5 The difference between this embodiment and Example 1 is that 0.05 g of NaOH, 0.074 g of NH4F, and 5 mL of methanol were weighed, mixed, and ultrasonically dissolved. 50 μL of this solution was then spin-coated onto a glass slide. 3.83 g of Y(NO3)3·6H2O (10 mmol) was replaced with 10 mmol of Gd(NO3)3·6H2O. 0.4 mL of Gd(NO3)3 solution (1 mmol / mL), 0.1 mL of Yb(NO3)3 solution (1 mmol / mL), and 12.5 μL of Er(NO3)3 solution (0.2 mmol / mL) were measured, and 10 mL of methanol was added. After thorough mixing, 50 μL of this solution was spin-coated onto the aforementioned glass slide.

[0059] The remaining preparation methods and parameters are consistent with those in Example 1.

[0060] Example 6 The difference between this embodiment and Embodiment 1 is that in the vacuum cavity (1 10 -4 Heat to 150 Pa) C reaction for 1 hour; the rest of the preparation methods and parameters are consistent with those in Example 1.

[0061] Example 7 The difference between this embodiment and Embodiment 1 is that in the vacuum cavity (1 10 -4 Heat to 300 Pa) C reacts for 2 hours; The remaining preparation methods and parameters are consistent with those in Example 1.

[0062] Example 8 The difference between this embodiment and Embodiment 1 is that the vacuum level is changed, and the preparation is carried out in an air environment. The remaining preparation methods and parameters are consistent with those in Example 1.

[0063] Comparative Example 1 The difference between this comparative example and Example 1 is that 0.12 g of NaOH, 0.17 g of NH4F and 5 mL of methanol were mixed and dissolved by ultrasonication, and then 1.2 mL of Y(NO3)3 solution (concentration 1 mmol / mL), 0.3 mL of Yb(NO3)3 solution (concentration 1 mmol / mL) and 37.5 μL of Er(NO3)3 solution (concentration 0.2 mmol / mL) were added. After thorough mixing, 100 μL of the solution was spin-coated onto the glass slide. The remaining preparation methods and parameters are consistent with those in Example 1.

[0064] Comparative Example 2 The difference between this comparative example and Example 1 is that the NaYF4:Yb:Er luminescent film was prepared by the sol-gel method: 0.4 mL of YCl3 solution (concentration 1 mmol / mL), 0.1 mL of YbCl3 solution (concentration 1 mmol / mL) and 12.5 μL of ErCl3 solution (concentration 0.2 mmol / mL) were measured, and 10 mL of methanol was added. After thorough mixing, oleic acid and octadecene were added and stirred. Then, 0.05 g of NaOH and 0.074 g of NH4F solution dissolved in 5 mL of methanol were added and stirred continuously for 1 h. The methanol solvent was removed by heating at 80 °C for 40 min. Then, vacuuming and N2 filling were performed three times, with the temperature increased by 20 °C each time to form a precursor sol. Then, 100 μL of this solution was spin-coated onto the glass slide. The remaining preparation methods and parameters are consistent with those in Example 1.

[0065] Comparative Example 3 This comparative example provides a method for preparing NaYF4:Yb:Er luminescent thin films using rare earth oleates: Preparation of Y(OA)3 solution: Weigh 3.03 g of YCl3·6H2O (20 mmol), 9.13 g of sodium oleate, then add 15 mL of water, 20 mL of ethanol and 35 mL of n-hexane, stir magnetically and simmer for 70 minutes. The reaction was carried out under reflux at C for 4 hours. After the reaction was completed, a water / ethanol mixture (5 / 1, volume ratio) was added and the mixture was washed several times until the lower layer was clear. 1 mL of the upper layer was taken and evaporated to determine the molar concentration of the product. The supernatant Y(OA)3 was collected and stored in a sealed container at room temperature.

[0066] Preparation of Yb(OA)3 solution: Weigh 3.87 g of YbCl3·6H2O (20 mmol), 9.13 g of sodium oleate, then add 15 mL of water, 20 mL of ethanol and 35 mL of n-hexane, stir magnetically and simmer at 70°C. The reaction was carried out under reflux at C for 4 hours. After the reaction was completed, a water / ethanol mixture (volume ratio 5 / 1) was added and the mixture was washed several times until the lower layer was clear. 1 mL of the upper layer was taken and evaporated to determine the molar concentration of the product. The supernatant Yb(OA)3 was collected and stored in a sealed container at room temperature.

[0067] Preparation of Er(OA)3 solution: Weigh 3.82 g of ErCl3·6H2O (10 mmol), 9.13 g of sodium oleate, then add 15 mL of water, 20 mL of ethanol and 35 mL of n-hexane, stir magnetically and simmer at 70°C. The reaction was carried out under reflux at C for 4 hours. After the reaction was completed, a water / ethanol mixture (5 / 1, volume ratio) was added and the mixture was washed several times until the lower layer was clear. 1 mL of the upper layer was taken and evaporated to determine the molar concentration of the product. The supernatant Er(OA)3 was collected and stored in a sealed container at room temperature.

[0068] Weigh 0.05 g of NaOH, 0.074 g of NH4F, and 5 mL of methanol, mix and sonicate to dissolve. Take 50 μL and spin-coat it onto a glass slide. In a 20 mL glass bottle, measure 3.33 mL of Y(OA)3 solution (concentration 0.12 mmol / mL), 0.91 mL of Yb(OA)3 solution (concentration 0.11 mmol / mL), and 17.9 μL of Er(OA)3 solution (concentration 0.14 mmol / mL). Add 10 mL of n-hexane, mix thoroughly, and take 50 μL of this solution to spin-coat it onto the aforementioned glass slide. In a vacuum chamber (1... 10 -4 The temperature was raised to 298 Pa. After reacting at C for 1 hour, a NaYF4:Yb:Er upconversion luminescent film was obtained.

[0069] Comparative Example 4 The difference between this comparative example and Example 1 is that methanol is replaced with ethanol; The remaining preparation methods and parameters are consistent with those in Example 1.

[0070] Performance testing The luminescent thin films prepared in Examples 1-8 and Comparative Examples 1-4 were subjected to XRD and optical tests (980nm laser). The test results are as follows: Figures 1-17 And as shown in Table 1. The PL intensity in Table 1 refers to the intensity at a wavelength of 540 nm. (It can be understood that for the same sample, the higher the test power, the higher the PL intensity.) Table 1 Figure 1 The figures show the XRD patterns of NaYF4:Yb:Er films prepared using the methods of Examples 1-3, Example 8, and Comparative Example 3, respectively. As can be seen from the figures, the films obtained in Examples 1-3 are relatively pure hexagonal phases (β phases), and the films are uniform and dense. Figures 6-8 The luminescence efficiency of NaYF4 is greatly affected by crystal symmetry. Compared to the more symmetrical cubic phase (α phase), the β phase, due to its lower lattice symmetry, can effectively enhance the electronic coupling between rare earth ion energy levels, thus exhibiting stronger upconversion fluorescence. A comparison of XRD patterns in Examples 1 and 8 shows that the film prepared in a vacuum environment is β phase, while the film prepared in air contains α phase. Table 1 shows that the fluorescence of the α phase is relatively lower, and the film uniformity is also worse. Figure 13 ). Figure 2 The image shows the XRD pattern of the NaGdF4:Yb:Er film prepared using Example 5, illustrating that this method can also prepare upconversion luminescent films on other matrices, but the film uniformity will be worse. Figure 10 ).

[0071] Figure 3 The upconversion fluorescence spectra of the NaYF4:Yb:Er thin films prepared using the methods of Examples 1, 2, 6, 7, and Comparative Example 1 were obtained using a 980nm laser with a power of 0.5W. As shown in Table 1, although the fluorescence in Comparative Example 1 was strong, a white precipitate formed on the spin-coated turbid solution substrate before annealing, indicating that a uniform and dense thin film could not be formed. Figure 14 SEM images also show the formation of linear solids, making them unsuitable for practical applications; the results of Examples 6 and 7 demonstrate that excessively low temperatures and annealing times lead to decreased fluorescence intensity, and that the surface uniformity of the film decreases at low temperatures. Figure 11 The time is too long and has little effect on surface uniformity. Figure 12 ).

[0072] Figure 4 The upconversion fluorescence spectra of the NaYF4:Yb:Er thin films prepared using the methods of Example 3 and Comparative Examples 2-4 were obtained using a 980nm laser with a power of 1.63W. The figures show that uniform and dense thin films can be prepared using chloride and oleate salts. Figure 15 , Figure 16 However, its fluorescence is weaker than that of nitrate. In Comparative Example 4, replacing methanol with ethanol resulted in NH4F becoming insoluble, thus exhibiting larger grains adhering to its SEM surface. Figure 17 According to EDS, the aggregation of Y and F elements is evident, and the corresponding fluorescence decreases sharply. Comparative Example 2 shows a film prepared by the sol-gel method; although the film is uniform ( Figure 15 However, due to the presence of more solvent oleic acid and octadecene during spin coating, and a correspondingly lower amount of rare earth ions, the fluorescence is weaker.

[0073] Figure 5 The upconversion fluorescence spectra of NaYF4:Yb:Er thin films prepared using the methods of Examples 4-5 and Example 8, respectively, were obtained using a 980nm laser with a power of 0.7W. (See Table 1 and...) Figure 9 , Figure 10 and Figure 13 It is known that when too much NaOH is added, Gd is used instead of Y, or annealing is carried out in an air atmosphere, not only will the fluorescence of the film weaken, but the uniformity and density of the film surface will also decrease.

[0074] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a fluoride upconversion luminescent thin film, characterized in that, The preparation method includes: (1) Mix the Na source, F source and the first solvent to obtain the first solution; (2) Mix at least three rare earth metal sources and a second solvent to obtain a second solution; (3) The first solution and the second solution are sequentially coated onto the substrate, and the fluoride upconversion luminescent film is obtained after reaction; The first solvent and the second solvent each independently comprise methanol, and the at least three rare earth metal sources comprise rare earth nitrates.

2. The preparation method according to claim 1, characterized in that, The Na source in step (1) includes sodium hydroxide; Preferably, the F source in step (1) includes ammonium fluoride.

3. The preparation method according to claim 1 or 2, characterized in that, The ratio of Na source, F source and first solvent in step (1) is (0.05~0.12)g:(0.074~0.176)g:(5~6)mL; Preferably, the mixing method in step (1) includes ultrasound.

4. The preparation method according to any one of claims 1-3, characterized in that, The at least three rare earth metal sources mentioned in step (2) include at least three of the following: Y source, La source, Ce source, Nd source, Eu source, Gd source, Tb source, Dy source, Ho source, Yb source, Er source, Tm source, or Gd source.

5. The preparation method according to any one of claims 1-4, characterized in that, The ratio of the total molar amount of the at least three rare earth metal sources in step (2) to the molar amount of the F source in step (1) is 1:(4~6); Preferably, the at least three rare earth metal sources in step (2) are Y source, Yb source and Er source; Preferably, the molar ratio of the Y source, Yb source and Er source is (150~180):(30~50):

1.

6. The preparation method according to any one of claims 1-5, characterized in that, The substrate in step (3) includes any one of glass, silicon, FTO, or ITO; Preferably, in the coating process described in step (3), the volume ratio of the first solution to the second solution is 1:(0.8~1.2); Preferably, the coating method in step (3) includes spin coating.

7. The preparation method according to any one of claims 1-6, characterized in that, The reaction described in step (3) is carried out in a vacuum environment; Preferably, the vacuum level of the vacuum environment is ≤1×10⁻⁶. -4 Pa; Preferably, the reaction temperature in step (3) is 295℃~300℃ and the time is 0.25h~1.5h.

8. A fluoride upconversion luminescent thin film prepared by the preparation method according to any one of claims 1-7, characterized in that, The fluoride upconversion luminescent film comprises NaAF4:B:C, wherein A, B, and C in NaAF4:B:C are selected from three different rare earth elements.

9. The fluoride upconversion luminescent thin film according to claim 8, characterized in that, The fluoride upconversion luminescent film is NaYF4:Yb:Er; Preferably, the thickness of the fluoride upconversion luminescent film is 100nm~150nm.

10. An application of the fluoride upconversion luminescent thin film as described in claim 8 or 9, characterized in that, The applications include multi-layer optical storage disks, photoluminescent screens, anti-counterfeiting encryption, and photovoltaic cells.

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