A preparation method for applying large-sized upconversion nanoparticles to near-infrared narrow-band photodetectors

Abstract

The present invention discloses a preparation method for applying large-sized upconversion nanoparticles to a near-infrared narrow-band photodetector. The photodetector is prepared based on UCNPs / MAPbI3, Au@AgNRs / UCNPs / MAPbI3, or Au@AgNRs / UCNPs / Au@Ag NRs / UCNPs / MAPbI3. The diameter of UCNPs is positively correlated with the dark current, and the competitive relationship between the size of upconversion nanoparticles and the performance of the near-infrared photodetector is verified by changing the size of UCNPs. When the performance of the Au@Ag NRs / UCNPs / MAPbI3 photodetector prepared using 150-nm upconversion nanoparticles reaches an extreme value, the photo-response ability, detection ability, and external quantum efficiency are 0.51 A / W, 6.9×109 Jones, and 64.9%, respectively.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of near-infrared narrow-band photodetectors, and particularly relates to a method for applying large-size upconversion nanoparticles to the preparation of near-infrared narrow-band photodetectors. Background Art

[0002] Near-infrared light is invisible light. Its strong penetration ability and low attenuation in the propagation medium make it widely used in imaging, monitoring systems, and optical communication. Because near-infrared narrow-band photodetectors have a strong ability to resist background radiation interference and meet the requirements of fields such as imaging and monitoring, biosensing, and security systems, they have attracted extensive attention from scientific researchers. Generally speaking, traditional near-infrared narrow-band photodetectors can be realized through the following strategies, such as combining broadband photodetectors with external optical microcavities or optical band-pass filters; manipulating the quantum efficiency through the charge collection narrowing mechanism; using the proton effect to enhance the absorption of objective wavelengths. However, these methods inevitably increase the complexity and cost of the device structure.

[0003] Using a photosensitive material with narrow-band absorption as the light-sensing layer is one of the most effective methods to achieve narrow-band light detection. Moreover, the outstanding features of this strategy are its flexibility, simplicity of manufacturing, adjustable spectral response, adjustable optical properties, and low cost. Upconversion nanoparticles doped with lanthanide elements can absorb photons of multiple near-infrared frequencies and convert them into photons of visible frequencies that are easy to detect. Previous studies have shown that upconversion nanoparticles have narrow-band near-infrared wavelength selective absorption, and the full width at half maximum of fluorescence is below 30 nm. However, the low upconversion luminescence efficiency and high pump threshold properties of upconversion nanoparticles are the main limitations for their further development in the field of light detection. Generally, the photoluminescence intensity of upconversion nanoparticles is related to the diameter of the nanoparticles. Under the excitation of a 980 nm laser, for hexagonal NaYF 4 :Yb 3+ ,Er 3+ with a size less than 100 nm, the photoluminescence efficiency is still lower than that of large-size nanomaterials. Theoretically, under the condition of the same number of incident photons per unit time, the higher the luminescence intensity of upconversion nanoparticles, the higher the concentration of photo carriers in the photosensitive layer, and the better the performance of the photodetector. Therefore, an attempt is made to use large-size upconversion nanoparticles combined with the local surface plasmon resonance effect of metal nanostructures to effectively enhance the upconversion luminescence intensity, thereby further obtaining a high photocurrent density. Unfortunately, due to the low charge carrier mobility of organic semiconductors (MAPbI 3 )(at 10 -5 -10 -3 cm 2 V -1 S -1Within a certain range, increasing the film thickness will prolong the time of charge transport and collection, inevitably having a negative impact on the response speed and performance of the photodetector. Summary of the Invention

[0004] To solve the above problems, the present invention first prepared a near-infrared narrow-band photodetector with plasma composite large-size upconversion nanoparticles (>50 nm) by the alternating self-assembly method. The performance of the photodetector reaches the optimum when the size of the upconversion nanoparticles is 150 nm.

[0005] Using doped lanthanide upconversion nanoparticles (UCNPs) as absorptive photoactive materials for light detection is a feasible strategy to obtain near-infrared narrow-band photodetectors. The concentration of photo carriers is one of the main factors affecting the performance of photodetectors, which depends to a large extent on the photoluminescence intensity of UCNPs. Generally speaking, excellent performance of photodetectors requires high photocurrent and low dark current. The present invention adopted a three-phase self-assembly method to fabricate large-area flat and dense monolayers of gold-silver core-shell nanorods (Au@AgNRs) and UCNPs of different sizes. Au@AgNRs / UCNPs and Au@AgNRs / UCNPs / Au@AgNRs / UCNPs composite films were prepared by the same method. It was demonstrated experimentally and theoretically that the local surface plasmon resonance effect has little effect on the upconversion luminescence of large-size UCNPs, especially those larger than 150 nm. More local surface plasmon resonance layers do not result in more obvious upconversion fluorescence enhancement, especially in large-size UCNPs. Then, for the first time, the present invention applied UCNPs with a size larger than 50 nm to near-infrared narrow-band photodetectors by the three-phase self-assembly method. The diameter of UCNPs is positively correlated with the dark current. By changing the size of UCNPs, a photodetector with relatively high performance was obtained. The results show that when the size of UCNPs is 150 nm, the performance of the near-infrared narrow-band photodetector reaches the extreme value, and the optimized photo response ability, detection ability and external quantum efficiency are 0.51 A / W, 6.9×109 Jones and 64.9%, respectively. The present invention provides a new design idea for the application of large-size upconversion nanoparticles in the field of photodetection. To achieve the above object, the present invention adopts the following technical solutions:

[0006] A preparation method for applying large-size upconversion nanoparticles to a near-infrared narrow-band photodetector, the specific steps are as follows:

[0007] Step 1: Prepare an upconversion nanoparticle (UCNPs) solution (NaYF 4 : 20% Yb 3+ , 2% Er 3+ )

[0008] Under vacuum conditions at 100 - 200 °C, ErCl 3 , YbCl 3 and YCl 3 are dispersed in a mixed solution of octadecene and oleylamine in a molar ratio of (0.01 - 0.1):(0.1 - 1):1 and dissolved at high temperature to obtain solution A; then, when naturally cooled to 30 - 70 °C, NaOH and NH 4 F are dispersed in a methanol solution in a molar ratio of (1 - 10):1 to obtain solution B; under a nitrogen environment at 50 - 100 °C, solution B is slowly added to solution A and degassed for 0.5 - 2 hours to remove unreacted methanol in the mixed solution; after the methanol is removed, it is maintained at 250 °C - 350 °C under nitrogen conditions and continuously reacted for 1 - 3 hours to prepare upconversion nanoparticles NaYF 4 : 20% Yb 3+ , 2% Er 3+ ; finally, after the reaction is completed and cooled to room temperature, NaYF 4 : 20% Yb 3+ , 2% Er 3+ is collected, centrifuged and washed twice with ethanol - cyclohexane in a volume ratio of (1 - 3):1, the centrifugation speed is 5000 - 15000 rpm, and the centrifugation time is 10 - 40 min; the collected centrifuged product is dispersed in ethanol with a mass fraction of 1 - 90% to obtain a UCNPs solution.

[0009] Step 2: Preparation of gold - silver nanocore - shell nanorod solution (Au@Ag NRs)

[0010] First, prepare a gold seed solution. Cetyltrimethylammonium chloride (CTAC), sodium citrate NaBH 4 and HAuCl 4 are stirred vigorously at room temperature in a molar ratio of (100 - 900):(10 - 130):(10 - 200):1 for 1 - 5 minutes and then transferred to an oil bath at 50 - 100 °C and stirred slowly for 2 - 6 hours; after the reaction is completed, a gold seed solution C is obtained.

[0011] Then, prepare a gold nanobipyramid solution. Cetyltrimethylammonium bromide (CTAB), HAuCl 4 , AgNO 3, HCl and ascorbic acid are mixed in a molar ratio of (20 - 100):(1 - 20):(5 - 60):(1 - 100):1 to obtain solution D; then solution D and the gold seed solution C are mixed in a volume ratio of (1 - 100):1, and left standing for 0.5 - 4 h under the condition of 20 - 80 °C; the product is collected by centrifugation, the centrifugation speed is 4000 - 10000 rpm, and the centrifugation time is 20 - 40 min; the collected centrifuged product is dispersed in deionized water with a mass fraction of 1 - 90% to obtain a gold nanobipyramid solution.

[0012] Finally, the preparation of Au@Ag NRs. CTAC, AgNO 3 and ascorbic acid are mixed in a molar ratio of (20 - 100):(1 - 50):1, and then mixed with the gold nanobipyramid solution in a volume ratio of (1 - 50):1. Under the condition of 20 - 100 °C, left standing for 0.5 - 8 h; the product is collected by centrifugation, the centrifugation speed is 2000 - 15000 rpm, and the centrifugation time is 10 - 40 min; the collected centrifuged product is dispersed in deionized water with a mass fraction of 1 - 90% to obtain an Au@Ag NRs solution.

[0013] Step 3: Preparation of polyethylene pyrrolidone (PVP)-coated UCNPs and Au@Ag NRs solution

[0014] PVP and ethanol are mixed in a mass ratio of (0.01 - 0.2):1 to obtain an ethanol solution of PVP with a mass fraction of 1 - 20%; hydrochloric acid and water are mixed in a mass ratio of (0.01 - 0.2):1 to obtain a dilute hydrochloric acid solution with a mass fraction of 1 - 20%.

[0015] The UCNPs solution and the dilute hydrochloric acid are mixed in a volume ratio of (1 - 5):1 and ultrasonicated for 0.5 - 2 h to remove the oleic acid molecules on the surface of the upconversion nanoparticles; then the mixed solution is centrifuged at a high speed, the centrifugation speed is 3000 - 10000 rpm, and the centrifugation time is 20 - 40 min; the collected centrifuged product is dispersed in the ethanol solution of PVP; after the precipitate is completely dispersed, it is centrifuged again to remove PVP in the solution; finally, the precipitate is dispersed in the ethanol solution to obtain a PVP-coated upconversion nanoparticle solution, denoted as the PVP-coated UCNPs solution.

[0016] Mix the Au@Ag NRs solution and the ethanol solution of PVP in a volume ratio of (1 - 5):1 and dissolve them using ultrasonic waves for 0.5 - 2 h; then perform high-speed centrifugation on the mixed solution, with a centrifugation speed of 3000 - 8000 rpm and a centrifugation time of 20 - 40 min; take the collected centrifugation product and disperse it in an ethanol solution to obtain a PVP-coated Au@Ag NRs solution, denoted as the PVP-coated Au@Ag NRs solution.

[0017] Step 4: Prepare a monolayer of UCNPs film, a monolayer of Au@Ag NRs film, a bilayer of Au@Ag NRs / UCNPs composite film, and a four-layer of Au@Ag NRs / UCNPs / Au@Ag NR / UCNPs composite film using the method of self-assembly at the three-phase interface.

[0018] Preparation of monolayer UCNPs: Mix the PVP-coated UCNPs solution prepared in Step 3, dichloromethane, and deionized water in a volume ratio of (0.01 - 0.1):(0.1 - 1):1 to obtain Solution E; then mix Solution E with n-hexane in a volume ratio of (2 - 100):1 and let it stand for 1 - 30 min. At this time, the UCNPs are driven to the interface between water and n-hexane; use the dip-coating method to transfer the UCNPs onto a silicon wafer to obtain a monolayer UCNPs film.

[0019] Preparation of monolayer Au@Ag NRs: Mix the PVP-coated Au@Ag NRs solution prepared in Step 3, dichloromethane, and deionized water in a volume ratio of (0.01 - 0.1):(0.1 - 1):1 to obtain Solution F; then mix Solution F with n-hexane in a volume ratio of (2 - 100):1 and let it stand for 1 - 30 min. At this time, the UCNPs are driven to the interface between water and n-hexane; use the dip-coating method to transfer the UCNPs onto a silicon wafer to obtain a monolayer UCNPs film.

[0020] Preparation of bilayer Au@Ag NRs / UCNPs: On the basis of the preparation of monolayer Au@Ag NRs, transfer the monolayer UCNPs film to the surface of the silicon wafer containing the monolayer Au@Ag NRs film to prepare a bilayer Au@Ag NRs / UCNPs composite film.

[0021] Preparation of four-layer Au@Ag NRs / UCNPs / Au@Ag NR / UCNPs: On the basis of the preparation of bilayer Au@Ag NRs / UCNPs, repeat the preparation process of bilayer Au@Ag NRs / UCNPs again to obtain a four-layer Au@Ag NRs / UCNPs / Au@Ag NR / UCNPs composite film.

[0022] Step 5: UCNPs / MAPbI3 、 Au@Ag NRs / UCNPs / MAPbI 3 、 Au@Ag NRs / UCNPs / Au@Ag NRs / UCNPs / MAPbI 3 Fabrication of Composite Photodetectors

[0023] Based on the single-layer UCNPs film, double-layer Au@Ag NRs / UCNPs composite film, and four-layer Au@Ag NRs / UCNPs / Au@Ag NRs / UCNPs composite film prepared in Step 4, photodetectors are fabricated under the conditions of a vacuum glove box. First, prepare the perovskite precursor solution: Mix DMF and DMSO in a volume ratio of (1 - 8):1 to obtain Solution G; mix PbI 2 and MAI in a molar ratio of (0.1 - 10):1 and add them to Solution G, then let it stand for 1 - 20 h until PbI 2 and MAI are completely dissolved to obtain the perovskite precursor solution; transfer the perovskite precursor solution, single-layer UCNPs, double-layer Au@Ag NRs / UCNPs, and four-layer Au@Ag NRs / UCNPs / Au@Ag NRs / UCNPs composite films into the glove box; take the perovskite precursor solution and drop it onto the UCNPs, Au@Ag NRs / UCNPs, and Au@Ag NRs / UCNPs / Au@Ag NRs / UCNPs composite films respectively. Turn on the spin coater and set it to a low speed of 200 - 1000 rpm for 2 - 10 s, then a high speed of 2000 - 8000 rpm for 20 - 100 s to obtain UCNPs / perovskite precursor, Au@Ag NRs / UCNPs / perovskite precursor, and Au@Ag NRs / UCNPs / Au@Ag NRs / UCNPs / perovskite precursor composite films respectively; start timing when the spin coater changes from low speed to high speed. After 10 - 40 s, drop chlorobenzene onto the UCNPs / perovskite precursor, Au@Ag NRs / UCNPs / perovskite precursor, and Au@Ag NRs / UCNPs / Au@Ag NRs / UCNPs / perovskite precursor composite films respectively. The volume ratio of chlorobenzene to the perovskite precursor solution is (2 - 20):1; after the spin coater stops, transfer the silicon wafer to a heating stage and heat it in a segmented manner. First, heat it to a low temperature of 10 - 100 °C for 1 - 20 min, then raise the temperature to a high temperature of 100 - 260 °C for 1 - 20 min to obtain UCNPs / MAPbI 3 、 Au@AgNRs / UCNPs / MAPbI 3 、 Au@AgNRs / UCNPs / Au@Ag NRs / UCNPs / MAPbI 3Composite films; these composite films were respectively transferred to a vacuum evaporation coater, and an Ag electrode was evaporated on the composite films to obtain three near-infrared narrow-band photodetectors.

[0024] Advantages of the present invention:

[0025] (1) A monolayer film of UCNPs was prepared by the three-phase interface self-assembly method and was combined with the plasmonic layer Au@Ag NRs. The local surface plasmon resonance effect of Au@Ag NRs can significantly enhance the upconversion fluorescence intensity. As the size of UCNPs increased from 50 nm to 400 nm, the enhancement factor of upconversion fluorescence gradually decreased from 25-fold to 2-fold. Moreover, the introduction of the "sandwich" structure of Au@Ag NRs / UCNPs / Au@AgNRs / UCNPs did not significantly improve the upconversion fluorescence intensity. In the "sandwich" structure, as the size of UCNPs increased, the enhancement factor of upconversion fluorescence decreased from 8-fold to 2-fold.

[0026] (2) The near-infrared narrow-band photodetector is based on the UCNPs / MAPbI 3 、Au@AgNRs / UCNPs / MAPbI 3 、Au@Ag NRs / UCNPs / Au@Ag NRs / UCNPs / MAPbI 3 composite structure. The three-phase self-assembly method used is suitable for applying UCNPs of different sizes to the near-infrared narrow-band photodetectors of MAPbI 3 , and the maximum size of UCNPs can reach 400 nm. In addition, the diameter of UCNPs is positively correlated with the dark current. By changing the size of UCNPs, the competitive relationship between the size of UCNPs and the performance of the near-infrared photodetector was verified. When using UCNPs with a size of 150 nm to prepare the Au@Ag NRs / UCNPs / MAPbI 3 photodetector, the performance of the near-infrared narrow-band photodetector reaches an extreme value. The optimized photodetector's optical response ability, detection ability, and external quantum efficiency are 0.51 A / W, 6.9×109 Jones, and 64.9%, respectively. This provides a new design idea for the application of large-sized upconversion nanoparticles in the field of photodetection. Description of the drawings

[0027] Figure 1 is the transmission electron microscopy image of UCNPs with a size of 150 nm.

[0028] Figure 2 is the transmission electron microscopy image, where (a) is the transmission electron microscopy image of gold nanobipyramids, and (b) is the transmission electron microscopy image of Au@Ag NRs.

[0029] Figure 3Scanning electron microscopy image of a monolayer of UCNPs with a size of 150 nm.

[0030] Figure 4 Scanning electron microscopy image of a monolayer of Au@Ag NRs.

[0031] Figure 5 Scanning electron microscopy image of a composite film of Au@Ag NRs / UCNPs (150 nm).

[0032] Figure 6 Scanning electron microscopy image of a composite film of Au@Ag NRs / UCNPs / Au@Ag NRs / UCNPs (150 nm).

[0033] Figure 7 Upconversion fluorescence enhancement factors of the composite films of Au@Ag NRs / UCNPs and Au@Ag NRs / UCNPs / Au@Ag NRs / UCNPs.

[0034] Figure 8 For Au@Ag NRs / UCNPs / MAPbI 3 And Au@Ag NRs / UCNPs / Au@Ag NRs / UCNPs / MAPbI 3 Performance tests of the composite film photodetectors, where (a) sensitivity, (b) external quantum efficiency, (c) detectivity. Detailed implementation manners

[0035] The present invention will be specifically described below by way of examples, but the present invention is not limited by the following examples.

[0036] Example 1:

[0037] (1) Under vacuum conditions at 100 °C, ErCl 3 (0.0071 g), YbCl 3 (0.076 g) and YCl 3 (0.24 g) were dispersed in a mixed solution of 15 mL of octadecene and 6 mL of oleylamine and dissolved at high temperature;

[0038] (2) When naturally cooled to 30 °C, NaOH (0.1 g) and NH 4 F (0.15 g) were dispersed in 5 mL of methanol solution;

[0039] (3) Under a nitrogen environment at 50 °C, the liquid obtained in step (2) was slowly added to the solution obtained in step (1) and degassed for 0.5 hour to remove unreacted methanol in the mixed solution; heated to 250 - 280 °C under nitrogen conditions and reacted for 1 hour to prepare upconversion nanoparticles NaYF 4 : 20% Yb3+ , 2% Er 3+ ;

[0040] (4) Centrifuge and wash the sample twice with a mixed solution of ethanol - cyclohexane with a volume ratio of 1:1, the centrifuge speed is 5000 - 8000 rpm, and the centrifuge time is 10 min. Disperse the collected centrifuged product in ethanol to obtain UCNPs solutions of different sizes; as Figure 1 shown, the transmission electron microscope image shows that UCNPs of 150 nm have been successfully prepared. Determination by transmission electron microscope: The transmission electron microscope was tested using a Hitachi H - 8100IV transmission electron microscope at an acceleration voltage of 200 kV

[0041] (5) Take 100 mM of CTAC, 10 mM of citric acid and 1 mM of HAuCl 4 and dissolve them by mixing. Rapidly add 10 mM of NaBH 4 under vigorous stirring. After 1 minute, transfer the mixed solution to a condition of 50 °C and stir slowly for 2 h;

[0042] (6) Take 20 mM of CTAB, 1 mM of HAuCl 4 , 5 mM of AgNO 3 and 1 mM of HCl and mix and stir. Rapidly add 20 mM of ascorbic acid under vigorous stirring conditions and continue to stir vigorously for 30 s;

[0043] (7) Mix the mixed solution in step (5) with the mixed solution in step (6) at a volume ratio of 1:1 under vigorous stirring, and then let the obtained mixed solution stand at 20 °C for 0.5 h;

[0044] (8) Centrifuge to collect the product. After centrifuging at a speed of 4000 rpm for 20 min, take the precipitate and disperse it in 10 mL of deionized water. At this time, a gold nanobipyramid solution is obtained;

[0045] (9) Take 10 mM of CTAC, 10 mM of AgNO 3 , 10 mM of ascorbic acid and mix them. After vigorous stirring, mix them with the gold nanobipyramid solution obtained in step (8) at a volume ratio of 1:1. After vigorous stirring for 2 min, let it stand at 20 °C for 0.5 h;

[0046] (10) Centrifuge to collect the product. After centrifuging at a speed of 2000 rpm for 10 min, take the precipitate and disperse it in 10 mL of deionized water. At this time, an Au@Ag NRs solution is obtained. As Figure 2 shown, the transmission electron microscope image shows that the prepared Au@Ag NRs consists of a gold nanobipyramid as the core and a silver rod as the shell. The Au@Ag NRs are about 180 nm long and about 25 nm wide.

[0047] (11) Mix PVP and ethanol in a mass ratio of 0.01:1 to obtain an ethanol solution of PVP with a mass fraction of 1%. Mix hydrochloric acid and water in a mass ratio of 0.01:1 to obtain a dilute hydrochloric acid solution with a mass fraction of 1%;

[0048] (12) Mix the UCNPs solution and the dilute hydrochloric acid in a volume ratio of 1:1 and use ultrasonic waves to dissolve for 0.5 h to remove the oleic acid molecules on the surface of UCNPs. Perform high-speed centrifugation on the mixed solution, with a centrifugation speed of 3000 rpm and a centrifugation time of 20 min;

[0049] (13) Take the centrifuged product collected and disperse it in the ethanol solution of PVP. After the precipitate is completely dispersed, centrifuge it again under the conditions of a centrifugation speed of 3000 rpm and a centrifugation time of 20 min to remove PVP in the solution;

[0050] (14) Disperse the precipitate obtained in step (13) in the ethanol solution to obtain a solution of PVP-coated upconversion nanoparticles;

[0051] (15) Mix the Au@Ag NRs solution obtained in step (10) and the ethanol solution of PVP in a volume ratio of 1:1, use ultrasonic waves to dissolve for 0.5 h, and then perform high-speed centrifugation, with a centrifugation speed of 3000 rpm and a centrifugation time of 20 min;

[0052] (16) Take the centrifuged product collected and disperse it in the ethanol solution to obtain a solution of PVP-coated Au@Ag NRs;

[0053] (17) Take dichloromethane, deionized water, and the PVP-coated UCNPs solution obtained in step (14) and mix them in a volume ratio of 10:10:1, and then mix them with n-hexane in a volume ratio of 2:1 again, and let it stand for 1 min. During the standing process, the UCNPs are driven to the water / n-hexane interface. Using the lifting method, pick up the silicon wafer with tweezers to transfer the UCNPs to the silicon wafer, and the preparation of the monolayer UCNPs film is completed. As Figure 3 shown, the scanning electron microscope image of the 150-nm UCNPs film demonstrates that a large-area, flat, and monolayer film can be prepared using this three-phase interface self-assembly method;

[0054] (18) Mix dichloromethane, deionized water, and the PVP-coated Au@Ag NRs solution obtained in step (16) in a volume ratio of 10:10:1; then mix it with n-hexane again in a volume ratio of 2:1 and let it stand for 1 min. During the standing process, the Au@Ag NRs are driven to the water / n-hexane interface. Using the lifting method, pick up the silicon wafer with tweezers to transfer the Au@Ag NRs onto the silicon wafer, and thus the Au@Ag NRs thin film is prepared. As Figure 4 shown, the scanning electron microscope image of the monolayer Au@Ag NRs thin film demonstrates that a large-area, flat, and monolayer thin film can be prepared using this three-phase interface self-assembly method;

[0055] (19) Repeat step (17) on the basis of the monolayer Au@Ag NRs thin film prepared in step (18), and transfer the prepared UCNPs monolayer film onto the thin film containing Au@Ag NRs, and thus the Au@Ag NRs / UCNPs composite thin film is obtained. As Figure 5 shown, the scanning electron microscope image of the Au@Ag NRs / UCNPs (150 nm) composite thin film shows that a large-area, flat, and stacked composite thin film has been successfully prepared using the three-phase interface self-assembly method;

[0056] (20) Repeat steps (17) and (18) on the basis of step (19), and transfer the Au@Ag NRs and UCNPs monolayer films onto the Au@Ag NRs / UCNPs composite thin film, and thus the Au@Ag NRs / UCNPs / Au@Ag NRs / UCNPs composite thin film is obtained. As Figure 6 shown, the scanning electron microscope image of the Au@Ag NRs / UCNPs / Au@Ag NRs / UCNPs (150 nm) composite thin film shows that the stacking of any number of layers of thin films can be easily achieved using three-phase interface self-assembly; Figure 7 is the upconversion fluorescence enhancement factor of the Au@Ag NRs / UCNPs and Au@Ag NRs / UCNPs / Au@Ag NRs / UCNPs composite thin films. As the size of the UCNP increases from 50 nm to 400 nm, the upconversion fluorescence enhancement factor gradually decreases from 25 times to 2 times. Moreover, the introduction of the "sandwich" structure of Au@Ag NRs / UCNPs / Au@Ag NRs / UCNPs does not significantly improve the upconversion fluorescence intensity. As the UCNP size increases, the upconversion fluorescence enhancement factor decreases from 8 times to 2 times;

[0057] (21) Prepare a 1 mL mixed solution of DMF and DMSO in a volume ratio of 1:1 for DMF and DMSO, and then add 0.1 mmol of PbI 2and 1 mmol of MAI, and allowed to stand for 1 hour. 2 After complete dissolution with MAI, it indicates that the preparation of perovskite precursor solution is complete;

[0058] (22) The perovskite precursor solution obtained in step (21) is transferred into the glove box together with the UCNPs, Au@Ag NRs / UCNPs, and Au@Ag NRs / UCNPs / Au@Ag NRs / UCNPs composite films prepared in steps (17), (18), and (19). Taking Au@Ag NRs / UCNP as an example, 80 μL of the perovskite precursor solution is dripped on the Au@Ag NRs / UCNP composite film. The spin coater is set to a low speed of 200 rpm for 2 seconds and a high speed of 2000 rpm for 20 seconds. The timing starts when the spin coater changes from low speed to high speed. After 10 seconds, 160 μL of chlorobenzene is dripped onto the Au@Ag NRs / UCNPs / perovskite precursor composite film.

[0059] (23) After the spin coating was stopped, the silicon wafer was transferred to the heating stage and heated in stages, first at a low temperature of 10 °C for 1 min, then at a high temperature of 100 °C for 1 min. 3 The composite film is prepared;

[0060] (24) Similarly, UCNPs / MAPbI 3 With Au@Ag NRs / UCNPs / Au@Ag NRs / UCNPs / MAPbI 3 The composite films were prepared using exactly the same process;

[0061] (25) The composite film prepared in steps (23) and (24) is transferred to a vacuum evaporator, and a Ag electrode is evaporated on the composite film. At this point, the near-infrared narrow-band photodetector with a plasma composite upconversion structure is completed. Figure 8 UCNPs / MAPbI 3 、Au@Ag NRs / UCNPs / MAPbI 3 and Au@Ag NRs / UCNPs / Au@Ag NRs / UCNPs / MAPbI 3 Performance test of composite thin film photodetector. When Au@Ag NRs / UCNPs / MAPbI was prepared using 150nm upconversion nanoparticles 3 When the photodetector is used, the performance of the near-infrared narrow-band photodetector reaches the extreme value. The optimized light response capability, detection capability and external quantum efficiency are 0.51A / W, 6.9×109Jones and 64.9% respectively.

[0062] Embodiment 2:

[0063] (1) Under vacuum conditions at 150 °C, ErCl 3 (0.0071 g), YbCl 3 (0.0783 g) and YCl 3 (0.2367 g) were dispersed in a mixed solution of 15 mL of octadecene and 6 mL of oleylamine and dissolved at high temperature;

[0064] (2) When naturally cooled to 50 °C, NaOH (0.5 g) and NH 4 F (0.15 g) were dispersed in 5 mL of methanol solution;

[0065] (3) Under a nitrogen environment at 50 °C, the liquid obtained in step (2) was slowly added to the solution obtained in step (1) and degassed for 1.5 h to remove unreacted methanol in the mixed solution; heated to 270 - 310 °C under nitrogen conditions and reacted for 2 hours to prepare upconversion nanoparticles NaYF 4 : 20% Yb 3+ , 2% Er 3+ ;

[0066] (4) The sample was centrifugally washed twice with a mixed solution of ethanol - cyclohexane with a volume ratio of 2:1, the centrifugation speed was 7000 - 10000 rpm, and the centrifugation time was 30 min. The centrifuged product collected was dispersed in ethanol to obtain UCNPs solutions of different sizes;

[0067] (5) 500 mM of CTAC, 50 mM of citric acid and 1 mM of HAuCl 4 were mixed and dissolved. 100 mM of NaBH 4 was quickly added under vigorous stirring. After 1 minute, the mixed solution was transferred and slowly stirred at 60 °C for 4 h;

[0068] (6) 50 mM of CTAB, 10 mM of HAuCl 4 , 20 mM of AgNO 3 and 10 mM of HCl were mixed and stirred. 20 mM of ascorbic acid was quickly added under vigorous stirring conditions and continuously stirred vigorously for 30 s;

[0069] (7) The mixed solution in step (5) and the mixed solution in step (6) were mixed at a volume ratio of 10:1 under vigorous stirring, and the resulting mixed solution was left standing at 60 °C for 2 h;

[0070] (8) The product was centrifugally collected. After centrifugation at a speed of 6000 rpm for 30 min, the precipitate was taken and dispersed in 10 mL of deionized water, and at this time, a gold nanobipyramid solution was obtained;

[0071] (9) Mix 100 mM CTAC, 100 mM AgNO 3 , and 10 mM ascorbic acid, stir vigorously, and then mix with the gold nanobipyramid solution obtained in step (8) at a volume ratio of 10:1. After stirring vigorously for 2 min, let it stand for 2 h at 40 °C;

[0072] (10) Centrifuge to collect the product. After centrifuging at 5000 rpm for 30 min, take the precipitate and disperse it in 10 mL of deionized water to obtain the Au@Ag NRs solution at this time;

[0073] (11) Mix PVP and ethanol at a mass ratio of 0.1:1 to obtain an ethanol solution of PVP with a mass fraction of 10%. Mix hydrochloric acid and water at a mass ratio of 0.1:1 to obtain a hydrochloric acid solution with a mass fraction of 10%;

[0074] (12) Mix the UCNPs solution and hydrochloric acid at a volume ratio of 2:1 and use ultrasonic waves to dissolve for 1 h to remove the oleic acid molecules on the surface of UCNPs. Perform high-speed centrifugation on the mixed solution, with a centrifugation speed of 5000 rpm and a centrifugation time of 30 min;

[0075] (13) Take the collected centrifuged product and disperse it in the ethanol solution of PVP. After the precipitate is completely dispersed, centrifuge it again at a centrifugation speed of 5000 rpm and a centrifugation time of 30 min to remove PVP in the solution;

[0076] (14) Disperse the precipitate obtained in step (13) in the ethanol solution to obtain the PVP-coated upconversion nanoparticle solution;

[0077] (15) Mix the Au@Ag NRs solution obtained in step (10) and the ethanol solution of PVP at a volume ratio of 2:1, use ultrasonic waves to dissolve for 0.5 h, and then perform high-speed centrifugation, with a centrifugation speed of 5000 rpm and a centrifugation time of 30 min;

[0078] (16) Take the collected centrifuged product and disperse it in the ethanol solution to obtain the PVP-coated Au@Ag NRs solution;

[0079] (17) Take dichloromethane, deionized water, and the PVP-coated UCNPs solution obtained in step (14) and mix them at a volume ratio of 20:20:1. Then mix them with n-hexane at a volume ratio of 10:1 again, and let it stand for 5 min. During the standing process, the UCNPs are driven to the water / n-hexane interface. Using the lifting method, pick up the silicon wafer with tweezers to transfer the UCNPs to the silicon wafer, and the single-layer UCNPs film is prepared;

[0080] (18) Mix dichloromethane, deionized water, and the PVP-coated Au@Ag NRs solution obtained in step (16) in a volume ratio of 20:20:1; then mix again with n-hexane in a volume ratio of 10:1 and let it stand for 5 min. During the standing process, the Au@Ag NRs are driven to the water / n-hexane interface. Using the lifting method, pick up the silicon wafer with tweezers to transfer the Au@Ag NRs onto the silicon wafer, and the Au@Ag NRs thin film is thus prepared;

[0081] (19) Repeat step (17) on the basis of the single-layer Au@Ag NRs thin film prepared in step (18), and transfer the prepared UCNPs single-layer film onto the thin film containing Au@Ag NRs to obtain the Au@Ag NRs / UCNPs composite thin film;

[0082] (20) Repeat steps (17) and (18) on the basis of step (19), and transfer the Au@Ag NRs and UCNPs single-layer films onto the Au@Ag NRs / UCNPs composite thin film to obtain the Au@Ag NRs / UCNPs / Au@Ag NRs / UCNPs composite thin film;

[0083] (21) Prepare a 1 mL mixed solution of DMF and DMSO in a volume ratio of 4:1, and then add 1 mmol of PbI 2 and 1 mmol of MAI, and let it stand for 10 h. After the PbI 2 and MAI are completely dissolved, it indicates that the perovskite precursor solution is prepared;

[0084] (22) Transfer the perovskite precursor solution obtained in step (21) and the UCNPs, Au@Ag NRs / UCNPs, and Au@Ag NRs / UCNPs / Au@Ag NRs / UCNPs composite thin films prepared in steps (17), (18), and (19) into the glove box. Taking Au@Ag NRs / UCNP as an example, take 80 μL of the perovskite precursor solution and drop it on the Au@Ag NRs / UCNP composite thin film. Set the spin coater to a low speed of 500 rpm for 5 s, a high speed of 5000 rpm for 50 s, and start timing when the spin coater changes from low speed to high speed. After 15 s, drop 800 μL of chlorobenzene onto the Au@Ag NRs / UCNPs / perovskite precursor composite thin film;

[0085] (23) After stopping the spin coating, transfer the silicon wafer to the heating stage and use a segmented heating method. First, heat at a low temperature of 50 °C for 5 min, and then raise the temperature to a high temperature of 150 °C and heat for 5 min. After that, the Au@Ag NRs / UCNPs / MAPbI 3 composite thin film is prepared;

[0086] (24) Similarly, UCNPs / MAPbI 3 With Au@Ag NRs / UCNPs / Au@Ag NRs / UCNPs / MAPbI 3 The composite films were prepared using exactly the same process;

[0087] (25) The composite film prepared in steps (23) and (24) is transferred to a vacuum evaporator, and a Ag electrode is evaporated on the composite film. At this point, the near-infrared narrow-band photodetector with a plasma composite upconversion structure is completed.

[0088] Embodiment 3:

[0089] (1) Under vacuum conditions at 150°C, ErCl 3 (0.071 g), YbCl 3 (0.78 g) and YCl 3 (0.24 g) was dispersed in a mixture of 15 mL of octadecene and 6 mL of oleylamine and dissolved at high temperature;

[0090] (2) When naturally cooled to 70°C, NaOH (1 g) and NH 4 F (0.15 g) was dispersed in 5 mL of methanol solution;

[0091] (3) Slowly adding the liquid obtained in step (2) to the solution obtained in step (1) under a nitrogen environment at 100° C. and degassing for 2 h to remove unreacted methanol in the mixed solution; heating to 290-350° C. under nitrogen conditions and continuing the reaction for 3 h to prepare upconversion nanoparticles NaYF of different sizes 4 : 20% Yb 3+ , 2%Er 3+ ;

[0092] (4) Wash the sample twice by centrifugation with a mixed solution of ethanol and cyclohexane with a volume ratio of 3:1, the centrifugal speed is 9000-15000 rpm, and the centrifugal time is 40 min. The collected centrifugal product is dispersed in ethanol to obtain UCNPs solutions of different sizes;

[0093] (5) Take 900 mM CTAC, 130 mM citric acid and 1 mM HAuCl 4 Mix and dissolve. Quickly add 200 mM NaBH 4 After 1 minute, the mixed solution was transferred to 80°C and slowly stirred for 6 hours;

[0094] (6) Take 100mM CTAB and 20mM HAuCl 4 , 60 mM AgNO3 Mix it with 100 mM HCl and stir. Rapidly add 1 mM ascorbic acid under vigorous stirring and continue vigorous stirring for 30 s;

[0095] (7) Mix the mixed solution in step (5) and the mixed solution in step (6) at a volume ratio of 10:1 under vigorous stirring. Then, let the resulting mixed solution stand at 80 °C for 4 h;

[0096] (8) Centrifuge to collect the product. After centrifuging at 10000 rpm for 40 min, take the precipitate and disperse it in 10 mL of deionized water. At this time, a gold nanobipyramid solution is obtained;

[0097] (9) Take 200 mM CTAC, 50 mM AgNO 3 3, and 1 mM ascorbic acid, mix them, and after vigorous stirring, mix them with the gold nanobipyramid solution obtained in step (8) at a volume ratio of 50:1. After vigorous stirring for 2 min, let it stand at 100 °C for 8 h;

[0098] (10) Centrifuge to collect the product. After centrifuging at 15000 rpm for 40 min, take the precipitate and disperse it in 10 mL of deionized water. At this time, an Au@Ag NRs solution is obtained;

[0099] (11) Mix PVP and ethanol at a mass ratio of 0.2:1 to obtain an ethanol solution of PVP with a mass fraction of 20%. Mix hydrochloric acid and water at a mass ratio of 0.2:1 to obtain a hydrochloric acid solution with a mass fraction of 20%;

[0100] (12) Mix the UCNPs solution and hydrochloric acid at a volume ratio of 5:1 and use ultrasonic waves to dissolve for 2 h to remove the oleic acid molecules on the surface of UCNPs. Perform high-speed centrifugation on the mixed solution at a centrifugation speed of 8000 rpm for 40 min;

[0101] (13) Take the centrifuged product collected and disperse it in the ethanol solution of PVP. After the precipitate is completely dispersed, centrifuge it again at a centrifugation speed of 10000 rpm for 40 min to remove PVP in the solution;

[0102] (14) Disperse the precipitate obtained in step (13) in the ethanol solution to obtain a PVP-coated upconversion nanoparticle solution;

[0103] (15) Mix the Au@Ag NRs solution obtained in step (10) and the ethanol solution of PVP at a volume ratio of 5:1 and use ultrasonic waves to dissolve for 2 h, and then perform high-speed centrifugation at a centrifugation speed of 10000 rpm for 40 min;

[0104] (16) Disperse the collected centrifuged product in an ethanol solution to obtain a PVP-coated Au@Ag NRs solution;

[0105] (17) Mix dichloromethane, deionized water, and the PVP-coated UCNPs solution obtained in step (14) in a volume ratio of 50:50:1, and then mix it with n-hexane in a volume ratio of 100:1 again. After standing for 30 min, during the standing process, the UCNPs are driven to the water / n-hexane interface. Using the lifting method, pick up the silicon wafer with tweezers to transfer the UCNPs onto the silicon wafer, and thus the monolayer UCNPs film is prepared;

[0106] (18) Mix dichloromethane, deionized water, and the PVP-coated Au@Ag NRs solution obtained in step (16) in a volume ratio of 50:50:1; then mix it with n-hexane in a volume ratio of 100:1 again and stand for 30 min. During the standing process, the Au@Ag NRs are driven to the water / n-hexane interface. Using the lifting method, pick up the silicon wafer with tweezers to transfer the Au@Ag NRs onto the silicon wafer, and thus the Au@Ag NRs film is prepared;

[0107] (19) Repeat step (17) on the basis of the monolayer Au@Ag NRs film prepared in step (18), and transfer the prepared UCNPs monolayer film onto the film containing Au@Ag NRs, and thus the Au@Ag NRs / UCNPs composite film is obtained;

[0108] (20) Repeat steps (17) and (18) on the basis of step (19), and transfer the Au@Ag NRs and UCNPs monolayer films onto the Au@Ag NRs / UCNPs composite film, and thus the Au@Ag NRs / UCNPs / Au@Ag NRs / UCNPs composite film is obtained;

[0109] (21) Prepare a 1 mL mixed solution of DMF and DMSO in a volume ratio of 8:1 for DMF and DMSO. Subsequently, add 10 mmol of PbI 2 and 1 mmol of MAI, and stand for 20 h. After the PbI 2 and MAI are completely dissolved, it indicates that the perovskite precursor solution is prepared;

[0110] (22) The perovskite precursor solution obtained in step (21) is transferred into the glove box together with the UCNPs, Au@Ag NRs / UCNPs, and Au@Ag NRs / UCNPs / Au@Ag NRs / UCNPs composite films prepared in steps (17), (18), and (19). Taking Au@Ag NRs / UCNP as an example, 80 μL of the perovskite precursor solution is dripped on the Au@Ag NRs / UCNP composite film. The spin coater is set to a low speed of 1000 rpm for 10 seconds and a high speed of 8000 rpm for 100 seconds. The timing starts when the spin coater changes from low speed to high speed. After 40 seconds, 1600 μL of chlorobenzene is dripped onto the Au@Ag NRs / UCNPs / perovskite precursor composite film.

[0111] (23) After the spin coating was stopped, the silicon wafer was transferred to the heating stage and heated in stages, first at a low temperature of 100 °C for 20 min, then at a high temperature of 260 °C for 20 min. 3 The composite film is prepared;

[0112] (24) Similarly, UCNPs / MAPbI 3 With Au@Ag NRs / UCNPs / Au@Ag NRs / UCNPs / MAPbI 3 The composite films were prepared using exactly the same process;

[0113] (25) The composite film prepared in steps (23) and (24) is transferred to a vacuum evaporator, and a Ag electrode is evaporated on the composite film. At this point, the near-infrared narrow-band photodetector with a plasma composite upconversion structure is completed.

Claims

1. A preparation method for applying large-sized upconversion nanoparticles to a near-infrared narrow-band photodetector, characterized in that, the specific steps are as follows: Step 1: Prepare an upconversion nanoparticle solution UCNPs using a solvothermal method Under vacuum conditions at 100 - 200 °C, ErCl 3 , YbCl 3 and YCl 3 are dispersed in a mixed solution of octadecene and oleylamine in a molar ratio of (0.01 - 0.1) : (0.1 - 1) : 1 and dissolved at high temperature to obtain solution A; then when naturally cooled to 30 - 70 °C, NaOH and NH 4 F are dispersed in a methanol solution in a molar ratio of (1 - 10) : 1 to obtain solution B; in a nitrogen environment at 50 - 100 °C, solution B is slowly added to solution A and degassed for 0.5 - 2 hours to remove unreacted methanol in the mixed solution; after the methanol is removed, at 250 °C - 350 °C under nitrogen conditions and continuously reacted for 1 - 3 hours to prepare upconversion nanoparticles NaYF 4 : 20% Yb 3+ , 2% Er 3+ ; finally, after the reaction is completed and cooled to room temperature, NaYF 4 : 20% Yb 3+ , 2% Er 3+ is collected, centrifugally washed twice with ethanol - cyclohexane in a volume ratio of (1 - 3) : 1, the centrifugal speed is 5000 - 15000 rpm, and the centrifugal time is 10 - 40 min; the collected centrifuged product is dispersed in ethanol with a mass fraction of 1 - 90% to obtain a UCNPs solution; Step 2: Prepare a gold-silver nanocore-shell nanorod solution Au@Ag NRs First, prepare the gold seed solution: Cetyltrimethylammonium chloride CTA, sodium citrate NaBH 4 and HAuCl 4 are stirred vigorously at room temperature for 1 - 5 minutes in a molar ratio of (100 - 900):(10 - 130):(10 - 200):1, and then transferred to an oil bath at 50 - 100 °C and stirred slowly for 2 - 6 hours; after the reaction is completed, the gold seed solution C is obtained; Then, prepare the gold nanobipyramid solution: Mix cetyltrimethylammonium bromide (CTAB), HAuCl 4 , AgNO 3 , HCl, and ascorbic acid in a molar ratio of (20 - 100):(1 - 20):(5 - 60):(1 - 100):1 to obtain solution D; then mix solution D and the gold seed solution C in a volume ratio of (1 - 100):1, and let it stand at 20 - 80 °C for 0.5 - 4 h; centrifuge to collect the product, with a centrifugation speed of 4000 - 10000 rpm and a centrifugation time of 20 - 40 min; disperse the collected centrifuged product in deionized water with a mass fraction of 1 - 90% to obtain the gold nanobipyramid solution; Finally, the preparation of Au@Ag NRs: CTAC, AgNO 3 and ascorbic acid were mixed in a molar ratio of (20 - 100):(1 - 50):1, and then mixed with the gold nanobipyramid solution in a volume ratio of (1 - 50):1; under the condition of 20 - 100 °C, it was allowed to stand for 0.5 - 8 h; the product was collected by centrifugation, the centrifugation speed was 2000 - 15000 rpm, and the centrifugation time was 10 - 40 min; the collected centrifuged product was dispersed in deionized water with a mass fraction of 1 - 90% to obtain the Au@Ag NRs solution; Step 3: Preparation of UCNPs and Au@Ag NRs solutions coated with polyvinylpyrrolidone PVP Mix PVP and ethanol in a mass ratio of (0.01 - 0.2):1 to obtain an ethanol solution of PVP with a mass fraction of 1 - 20%; mix hydrochloric acid and water in a mass ratio of (0.01 - 0.2):1 to obtain a dilute hydrochloric acid solution with a mass fraction of 1 - 20%; Mix the UCNPs solution and the dilute hydrochloric acid in a volume ratio of (1 - 5):1 and use ultrasonic waves to dissolve for 0.5 - 2 h to remove oleic acid molecules on the surface of the upconversion nanoparticles; then perform high-speed centrifugation on the mixed solution, with a centrifugation speed of 3000 - 10000 rpm and a centrifugation time of 20 - 40 min; take the collected centrifugation product and disperse it in the ethanol solution of PVP; After the precipitate is completely dispersed, centrifuge again to remove PVP in the solution; finally, disperse the precipitate in an ethanol solution to obtain a PVP-coated upconversion nanoparticle solution, denoted as the PVP-coated UCNPs solution; Mix the Au@Ag NRs solution and the ethanol solution of PVP in a volume ratio of (1 - 5):1 and use ultrasonic waves to dissolve for 0.5 - 2 h; then perform high-speed centrifugation on the mixed solution, with a centrifugation speed of 3000 - 8000 rpm and a centrifugation time of 20 - 40 min; take the collected centrifugation product and disperse it in an ethanol solution to obtain a PVP-coated Au@Ag NRs solution, denoted as the PVP-coated Au@AgNRs solution; Step 4: Use a three-phase interface self-assembly method to prepare a monolayer UCNPs film, a monolayer Au@Ag NRs film, and a bilayer Au@Ag NRs / UCNPs composite film, and a four-layer Au@Ag NRs / UCNPs / Au@Ag NR / UCNPs composite film Preparation of monolayer UCNPs: Mix the PVP-coated UCNPs solution prepared in Step 3, dichloromethane, and deionized water in a volume ratio of (0.01 - 0.1):(0.1 - 1):1 to obtain solution E; then mix solution E and n-hexane in a volume ratio of (2 - 100):1 and let it stand for 1 - 30 min. At this time, the UCNPs are driven to the water / n-hexane interface; use the dip-coating method to transfer the UCNPs to a silicon wafer to obtain a UCNPs monolayer film; Preparation of single-layer Au@Ag NRs: The PVP-coated Au@Ag NRs solution prepared in step 3, dichloromethane, and deionized water were mixed at a volume ratio of (0.01 - 0.1):(0.1 - 1):1 to obtain solution F; then solution F and n-hexane were mixed at a volume ratio of (2 - 100):1 and allowed to stand for 1 - 30 min. At this time, UCNPs were driven to the water / n-hexane interface; using the dip-coating method, the UCNPs were transferred onto a silicon wafer to obtain a single-layer UCNPs film; Preparation of double-layer Au@Ag NRs / UCNPs: On the basis of the preparation of single-layer Au@Ag NRs, the single-layer UCNPs film was transferred onto the surface of a silicon wafer containing a single-layer Au@Ag NR film to prepare a double-layer Au@Ag NRs / UCNPs composite film; Preparation of four-layer Au@Ag NRs / UCNPs / Au@Ag NR / UCNPs: On the basis of the preparation of double-layer Au@Ag NRs / UCNPs, the preparation process of double-layer Au@Ag NRs / UCNPs was repeated again to obtain a four-layer Au@Ag NRs / UCNPs / Au@Ag NR / UCNPs composite film; Step 5: Preparation of UCNPs / MAPbI 3 、Au@Ag NRs / UCNPs / MAPbI 3 、Au@Ag NRs / UCNPs / Au@Ag NRs / UCNPs / MAPbI 3 Preparation of Composite Photoelectric Detector Based on the monolayer UCNPs thin film, bilayer Au@Ag NRs / UCNPs composite thin film, and four-layer Au@Ag NRs / UCNPs / Au@Ag NRs / UCNPs composite thin film prepared in step 4, a photodetector is prepared under the condition of a vacuum glove box; First, prepare the perovskite precursor solution: Mix DMF and DMSO in a volume ratio of (1 - 8):1 to obtain solution G; Mix PbI 2 and MAI in a molar ratio of (0.1 - 10):1 and add them to solution G, and let it stand for 1 - 20 h until PbI 2 and MAI are completely dissolved to obtain the perovskite precursor solution; Transfer the perovskite precursor solution, monolayer UCNPs, bilayer Au@Ag NRs / UCNPs, and four-layer Au@Ag NRs / UCNPs / Au@Ag NRs / UCNPs composite thin film into the glove box; Take the perovskite precursor solution and drop it on the UCNPs, Au@Ag NRs / UCNPs, and Au@Ag NRs / UCNPs / Au@Ag NRs / UCNPs composite thin film respectively. Turn on the spin coater and set it to a low speed of 200 - 1000 rpm for 2 - 10 s, and then a high speed of 2000 - 8000 rpm for 20 - 100 s to obtain UCNPs / perovskite precursor, Au@Ag NRs / UCNPs / perovskite precursor, and Au@Ag NRs / UCNPs / Au@Ag NRs / UCNPs / perovskite precursor composite thin film respectively; Start timing when the spin coater changes from low speed to high speed. After 10 - 40 s, drop chlorobenzene on the UCNPs / perovskite precursor, Au@Ag NRs / UCNPs / perovskite precursor, and Au@Ag NRs / UCNPs / Au@Ag NRs / UCNPs / perovskite precursor composite thin film respectively. The volume ratio of chlorobenzene to the perovskite precursor solution is (2 - 20):1; After the spin coater stops, transfer the silicon wafer to a heating stage and heat it in a segmented manner. First, heat it to a low temperature of 10 - 100 °C and maintain it for 1 - 20 min, then heat it to a high temperature of 100 - 260 °C and maintain it for 1 - 20 min to obtain UCNPs / MAPbI 3 , Au@AgNRs / UCNPs / MAPbI 3 , and Au@Ag NRs / UCNPs / Au@Ag NRs / UCNPs / MAPbI 3 composite thin film; Transfer the composite thin film to a vacuum evaporator respectively, and evaporate an Ag electrode on the composite thin film to obtain three near-infrared narrow-band photodetectors.

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