Metal nanocluster, preparation method and application thereof

Abstract

The application belongs to the technical field of material, and provides a metal nanocluster, a preparation method and application thereof, wherein the preparation method of the metal nanocluster comprises the following steps: adding a metal salt aqueous solution into ultrapure water, adding a 3-mercaptopropionic acid solution after uniform stirring, and continuing to stir and react until a precipitate is generated; adjusting the pH value of the solution to 7.70-8.40, adding a zinc salt aqueous solution, and performing a reaction under the condition of ultraviolet light irradiation to induce self-assembly of the metal nanocluster; adding the zinc salt aqueous solution into the obtained metal nanocluster to perform a stirring reaction, discarding supernatant after centrifugation, performing freeze-drying treatment, exposing the metal nanocluster after the freeze-drying treatment to an environment with a relative humidity of not less than 2%, and enabling water molecules to interact with metal oxygen bonds through hydrogen bonds. The application passivates structural oxygen vacancy defects in the metal nanocluster through water molecules, significantly improves the light-emitting quantum efficiency of the metal nanocluster, and realizes rapid color regulation.

Description

Technical Field

[0001] The present application belongs to the field of material technology, and in particular relates to a metal nanocluster and a preparation method and application thereof. Background Art

[0002] Structural defects play a crucial role in modulating the optical and electronic properties of materials, particularly in diverse applications such as energy storage, catalysis, photovoltaics, and optoelectronics. Defects typically include vacancies, interstitial atoms, and substitutional impurities, which are generated during synthesis, purification, modification, storage, and application. In luminescent materials, structural defects often introduce intermediate energy levels, affecting electron transport pathways and the relaxation of excited-state electrons, thereby impacting photoluminescence (PL) performance. Therefore, the controlled introduction of structural defects has become an important approach for modulating the optical properties of materials.

[0003] Metal nanoclusters (NCs) exhibit a strong reliance on structural defects due to their ultrasmall size (typically less than 3 nanometers) and abundant dangling bonds or exposed surfaces. The high crystal index, topological complexity, and interactions between NCs and their ligands promote the formation of structural defects. In recent years, surface metal vacancies and point defects have been discovered in NCs, and these structural defects play a key role in regulating the optical and electronic properties of NCs. However, current research on structural defects in NCs is still insufficient. On the one hand, the formation of structural defects reduces the stability of NCs, resulting in their characterization only in single crystals or solutions. On the other hand, research on optimizing PL performance by passivating structural defects is relatively limited. In particular, how to improve PL quantum yield (PLQY) by tuning surface defect chemistry and electron relaxation dynamics has not been fully explored.

[0004] Therefore, developing a method that can effectively regulate the structural defects of metal nanoclusters and significantly improve their luminescence performance, especially improving PLQY and adjusting the luminescence color, has become an important topic in this field. Summary of the Invention

[0005] The purpose of the embodiments of the present application is to provide a method for preparing metal nanoclusters, aiming to develop a method that can effectively regulate the structural defects of metal nanoclusters and significantly improve their luminescence performance.

[0006] The embodiment of the present application is achieved by providing a method for preparing metal nanoclusters, characterized by comprising:

[0007] Adding a metal salt aqueous solution to ultrapure water, stirring evenly, then adding a 3-mercaptopropionic acid solution and continuing to stir and react until precipitation occurs, adjusting the pH value of the solution to 7.70-8.40, adding a zinc salt aqueous solution, and reacting under ultraviolet light to induce self-assembly of metal nanoclusters;

[0008] A zinc salt aqueous solution is added to the obtained metal nanoclusters for stirring reaction, centrifuged and the supernatant is discarded, and then freeze-dried. The freeze-dried metal nanoclusters are exposed to an environment with a relative humidity of not less than 2% to allow water molecules to interact with metal oxygen bonds through hydrogen bonds, thereby obtaining;

[0009] Wherein, the metal salt aqueous solution is a chloroauric acid aqueous solution or a mixture of a chloroauric acid aqueous solution and a silver nitrate aqueous solution or a copper chloride aqueous solution.

[0010] The embodiment of the present application further provides a metal nanocluster, which is prepared by the above-mentioned method for preparing the metal nanocluster.

[0011] The embodiments of the present application also provide an application of the above-mentioned metal nanoclusters in the fields of optoelectronic devices, sensors, and photocatalysts.

[0012] The embodiment of the present application introduces water molecules into metal nanoclusters to form metal-oxygen bonds with exposed metal atoms, thereby suppressing the defect state luminescence caused by structural oxygen vacancies and promoting the dominant role of the cluster's intrinsic state luminescence, thereby increasing the radiation rate; in addition, the introduction of water molecules also enhances the stability of the metal nanoclusters through hydrogen bonds, suppresses non-radiative losses, and reduces electron-optical phonon coupling. Through the method of the present application, the quantum efficiency of the metal nanoclusters is significantly improved from 5.3% (defect state luminescence) to 91.6% (intrinsic state luminescence), and the luminescence color can be adjusted within milliseconds, quickly adjusting from 536nm to 480nm, which has important application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 The scanning electron microscope image and elemental energy spectrum analysis diagram of the AuAg-D nanoclusters before water absorption provided in Example 1 of the present application;

[0014] Figure 2 Mass spectra of the AuAg-S nanocluster solution at different laser powers provided in Example 1 of the present application;

[0015] Figure 3 The emission spectra of AuAg nanoclusters under 365nm light excitation and the corresponding CIE color coordinates in different relative humidity environments provided in Example 1 of the present application;

[0016] Figure 4Absolute quantum efficiency test graphs of AuAg-D, AuAg-H, and AuAg-S nanoclusters provided in Example 1 of the present application under 430, 410, and 410 nm light excitation, respectively;

[0017] Figure 5 The peak fitting diagram of the emission spectrum of AuAg nanoclusters under 365nm light excitation in different relative humidity environments provided in Example 1 of the present application and the change in the proportion of emitters I and II with relative humidity;

[0018] Figure 6 The changing trend and fitting diagram of the emission peak integrated intensity of AuAg nanoclusters under different excitation powers provided in Example 1 of the present application;

[0019] Figure 7 The fluorescence lifetime and fitting diagram of AuAg-D, AuAg-H and AuAg-S nanoclusters provided in Example 1 of the present application;

[0020] Figure 8 (a) Streak camera spectra of AuAg-D, AuAg-H, and AuAg-S nanoclusters under 400nm femtosecond laser excitation, provided in Example 1 of the present application; (b) lifetime decay and fitting diagram at 480nm in the streak camera spectra of AuAg-D, AuAg-H, and AuAg-S nanoclusters

[0021] Figure 9 (a) Transient absorption spectra of AuAg-D, AuAg-H, and AuAg-S nanoclusters under 365 nm femtosecond laser excitation, provided in Example 1 of the present application; (b) Lifetime decay and fitting plots of the transient absorption spectra of AuAg-D, AuAg-H, and AuAg-S nanoclusters at monitoring wavelengths of 488 and 520 nm, 480 and 490 nm, and 475 and 570 nm, respectively;

[0022] Figure 10 Electron paramagnetic resonance spectra of AuAg-D, AuAg-H, and AuAg-S nanoclusters provided in Example 1 of the present application;

[0023] Figure 11 The Au L3-edge X-ray absorption near-edge structure spectra of (a) AuAg-D and (b) AuAg-H nanoclusters, and the Au L3-edge Fourier transform extended X-ray absorption fine structure spectra and fitting diagrams of (c) AuAg-D and (d) AuAg-H nanoclusters provided in Example 1 of the present application;

[0024] Figure 12 Fourier transform infrared spectra of AuAg-D and AuAg-H nanoclusters provided in Example 1 of the present application;

[0025] Figure 13 This is the emission spectra of the powder under 365nm excitation before and after water absorption of AuAg nanoclusters synthesized with different HAuCl4 and AgNO3 feed ratios provided in Example 2 of the present application;

[0026] Figure 14 Emission spectra of the Au and AuCu nanocluster powders provided in Examples 3 and 4 of the present application under 365nm excitation;

[0027] Figure 15 The emission spectra of the powders of AuAg nanoclusters synthesized at different solution pH values ​​before and after water absorption under 365nm excitation provided in Example 5 of the present application;

[0028] Figure 16 This is the emission spectrum of the powder of AuAg nanoclusters synthesized with different zinc salts before and after water absorption under 365nm excitation provided in Example 6 of the present application. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0030] The present invention provides a method for preparing metal nanoclusters, comprising the following steps:

[0031] A metal salt aqueous solution is added to ultrapure water, stirred evenly, and then a 3-mercaptopropionic acid (MPA) solution is added and the stirring reaction is continued until a precipitate is produced. The pH value of the solution is adjusted to 7.70-8.40, and then a zinc salt aqueous solution is added. The reaction is carried out under ultraviolet light irradiation to induce the self-assembly of metal nanoclusters;

[0032] A zinc salt aqueous solution is added to the obtained metal nanoclusters for stirring reaction, and after centrifugation and discarding the supernatant, the metal nanoclusters are freeze-dried. The freeze-dried metal nanoclusters are exposed to an environment with a relative humidity of not less than 2% so that water molecules interact with metal oxygen bonds through hydrogen bonds to obtain the obtained metal nanoclusters.

[0033] The metal salt aqueous solution is a chloroauric acid (HAuCl4) aqueous solution or a mixture of a chloroauric acid aqueous solution and a silver nitrate aqueous solution or a copper chloride aqueous solution; preferably, the volume ratio of the chloroauric acid aqueous solution to the silver nitrate aqueous solution or the copper chloride aqueous solution is (0.64-0.76):(0.04-0.16).

[0034] The concentrations of the chloroauric acid aqueous solution, the silver nitrate aqueous solution, and the copper chloride aqueous solution are all 50 mM.

[0035] Preferably, the air humidity to which the metal nanoclusters are exposed is 60%, and the time for adsorbing water molecules in the air is 30 minutes.

[0036] Preferably, the molar mass ratio of MPA to HAuCl4 is 4:1.

[0037] Preferably, the pH is 7.90.

[0038] Optionally, the zinc salt is one or more of Zn(OAc)2, ZnCl2, ZnBr2, ZnI2, Zn(ClO4)2, and Zn(CF3SO3)2.

[0039] Wherein, in the reaction under ultraviolet light irradiation conditions, the wavelength of the ultraviolet light is 365-410 nm, and the reaction time is 18-30 hours, so as to promote the assembly process and structure formation of the metal nanoclusters.

[0040] Optionally, the step of adding a metal salt aqueous solution to ultrapure water, stirring uniformly, adding a 3-mercaptopropionic acid solution, and continuing to stir and react until a precipitate is generated, adjusting the pH value of the solution to 7.70-8.40, adding a zinc salt aqueous solution, and reacting under ultraviolet light to induce self-assembly of metal nanoclusters comprises:

[0041] To 9.2 mL of ultrapure water, 0.64-0.76 mL of aqueous chloroauric acid and 0.04-0.16 mL of aqueous silver nitrate or copper chloride were added and stirred at 600 rpm at room temperature to ensure uniform distribution of the metal ions. Subsequently, 138 μL of 3-mercaptopropionic acid (MPA) solution was added and stirring continued until the solution changed from light yellow to white and a precipitate formed. The MPA molecules act as surface modifiers, stabilizing the metal nanoclusters and providing active sites for the reaction. In this step, MPA stabilizes and protects the nanoclusters while also adjusting the pH of the reaction solution, ensuring the stability of the AuAg NCs / AuCu NCs / Au NCs.

[0042] The pH of the solution is adjusted to 7.70-8.40 using 1M sodium hydroxide solution. During this process, the precipitate gradually dissolves, and the solution becomes transparent and colorless. For example, a non-photoluminescent AuAg NCs solution is obtained, indicating that the metal ions have been successfully reduced to metal nanoclusters. Then, 2 mL of a zinc salt aqueous solution is added to the solution, and the solution is irradiated with UV light at 365-410 nm for 18-30 hours. The luminescence color of the solution changes from no light to orange-red, indicating that the metal nanoclusters have begun to self-assemble. The addition of the zinc salt in this step is crucial for triggering the self-assembly of the AuAg NCs / AuCu NCs / Au NCs. During this step, the zinc salt reacts with the AuAg NCs / AuCu NCs / Au NCs, promoting the self-assembly of the structures. This reaction occurs at room temperature and lasts for 18-30 hours. As the reaction proceeds, the AuAg NCs / AuCu NCs / Au NCs undergo structural changes to form AuAg-S NCs / AuCu-S NCs / Au-S NCs, which exhibit bright sky blue luminescence. The core of this process is the introduction of Zn on the surface of AuAg NCs / AuCu NCs / Au NCs. 2+ Ions promote their assembly to form stable nanostructures.

[0043] Optionally, the step of adding a zinc salt aqueous solution to the obtained metal nanoclusters for stirring and reacting, centrifuging and discarding the supernatant, and then freeze-drying the metal nanoclusters, and exposing the freeze-dried metal nanoclusters to an environment with a relative humidity of not less than 2% so that water molecules interact with metal oxygen bonds through hydrogen bonds comprises:

[0044] 2 mL of zinc salt aqueous solution was added to the obtained metal nanoclusters and stirred for 5 minutes, followed by centrifugation at 3000 rpm for 5 minutes, and the supernatant was discarded;

[0045] The obtained metal nanoclusters were solidified using liquid nitrogen and freeze-dried at -65 °C and 5 Pa for 3 days;

[0046] The freeze-dried metal nanoclusters are exposed to an environment with a relative humidity of not less than 2% so that water molecules interact with metal oxygen bonds through hydrogen bonds.

[0047] Specifically, to further improve the structure and stabilize the morphology of the AuAg NCs / AuCu NCs / Au NCs, 2 mL of an aqueous zinc salt solution was added to the AuAg-S NCs / AuCu-S NCs / Au-S NCs solution obtained in the above steps. After uniform mixing, the mixture was stirred for 5 minutes. The resulting mixture was then transferred to a centrifuge tube and centrifuged at 3000 rpm for 5 minutes, with the supernatant discarded. The AuAg NCs / AuCu NCs / Au NCs assembly was completely stabilized by freezing with liquid nitrogen. The frozen AuAg NCs / AuCu NCs / Au NCs were lyophilized at -65°C and 5 Pa in a vacuum environment for 3 days to obtain AuAg-DNCs / AuCu-DNCs / Au-D NCs. This step helps stabilize the luminescence properties by removing the solvent and fixing the structure of AuAg NCs / AuCu NCs / Au NCs under low temperature conditions and prepares for the subsequent passivation step.

[0048] Furthermore, in the AuAg-D NCs / AuCu-D NCs / Au-D NCs samples obtained in the above steps, defect state emission occurs due to the presence of structural oxygen vacancies. To address this problem, these structural oxygen vacancies are passivated by the adsorption of water molecules in this step. The AuAg-D NCs / AuCu-D NCs / Au-D NCs are exposed to air to allow them to adsorb water molecules in the air. Water molecules bind to Au-O and Ag-O / Cu-O bonds through hydrogen bonds, effectively passivating these oxygen vacancies and thus reducing the transfer of electrons from the ground state to the defect state. In this process, the adsorption of water molecules not only improves the photoluminescence quantum yield (PLQY) of the AuAg NCs / AuCu NCs / Au NCs, but also changes the luminescence color from 536nm green emission to 480nm sky blue emission. In addition, water molecules interact with the protective ligands through hydrogen bonding, further stabilizing the structure of AuAg NCs / AuCuNCs / Au NCs, making them more stable under light irradiation and reducing the non-radiative relaxation process, resulting in AuAg-H NCs / AuCu-H NCs / Au-HNCs with 480 nm sky blue emission.

[0049] Furthermore, after water molecules adsorbed and passivated structural defects, the photoluminescence performance of AuAg NCs / AuCu NCs / Au NCs was significantly improved. Through passivation treatment, the emission peak of AuAg NCs / AuCu NCs / Au NCs was continuously blue-shifted from 536nm to 480nm, and the luminescence quantum yield was increased from 5.3% to 91.6%. The successful implementation of this process not only demonstrates the important role of water molecules in improving the photoluminescence performance of nanoclusters, but also shows that this method can significantly improve the stability of luminescent materials. Ultimately, the resulting AuAg NCs have tunable luminescence color and luminescence quantum efficiency at room temperature, and can be widely used in optoelectronics, display technology, sensors and other fields.

[0050] During water adsorption, the luminescence color of AuAg NCs / AuCu NCs / Au NCs changes from green to sky blue, indicating that water adsorption affects their luminescence properties. Water molecules interact with Au-O and Ag-O / Cu-O bonds through hydrogen bonds, effectively passivating structural oxygen vacancies in the metal nanoclusters, suppressing defect-state luminescence caused by structural oxygen vacancies and accelerating the rate of radiative luminescence from intrinsic states. Furthermore, the addition of water molecules boosts the luminescence quantum efficiency of AuAgNCs / AuCu NCs / Au NCs by 15-20 times. Water molecules enhance the structural stability of the metal nanoclusters through hydrogen bonding, suppress non-radiative losses, and reduce the rate of electron-optical phonon coupling, thereby significantly improving the luminescence quantum efficiency of the metal nanoclusters.

[0051] The synthesis method of metal nanoclusters in this application is simple and easy, and by precisely controlling the reaction conditions, it can maintain consistency and efficiency in large-scale production. The introduction of water molecules not only effectively suppresses the effects of oxygen vacancies but also enhances the stability of the metal nanoclusters through hydrogen bonding, reducing non-radiative losses and improving overall optical performance. The metal nanoclusters obtained in this application can significantly improve luminescence efficiency in a short period of time through the passivation effect of water molecules, thus providing a new technical path for applications in various fields.

[0052] The present invention also provides a metal nanocluster prepared by the above-described method for preparing metal nanoclusters. The metal nanocluster exhibits significantly improved luminescence quantum efficiency (PLQY), from 5.3% (defect-state luminescence) to 91.6% (intrinsic-state luminescence), and can rapidly adjust the luminescence color from 536 nm to 480 nm, demonstrating fast and adjustable luminescence properties.

[0053] The metal nanoclusters provided in the embodiments of the present application can be used in applications such as optoelectronic devices, sensors, and photocatalysts, wherein their excellent luminescence properties give them important application prospects in the above-mentioned fields.

[0054] The following examples describe metal nanoclusters and their preparation methods in detail. The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials and reagents used are commercially available unless otherwise specified.

[0055] Example 1: Synthesis of AuAg-H NCs

[0056] 1) Synthesis of AuAg Nanoclusters: First, a 50 mM aqueous solution of HAuCl4 and a 50 mM aqueous solution of AgNO3 were added to ultrapure water at a molar ratio of 4:1. The mixture was stirred at room temperature to obtain Solution 1. Then, 138 μL of 3-mercaptopropionic acid (MPA) was added to Solution 1. Stirring was continued until a white precipitate appeared. The pH of the solution was then adjusted to 7.90 by adding 1 M NaOH solution. The precipitate gradually dissolved, forming a transparent solution, resulting in a non-luminescent AuAg NCs solution.

[0057] 2) Self-assembly of AuAg-S nanoclusters: 2 mL of Zn(OAc)2 aqueous solution (concentration of 0.1 M) was added to the AuAg NCs solution obtained in step 1). The reaction was carried out at room temperature and continued for 24 hours to form AuAg-S NCs.

[0058] 3) Preparation of AuAg-D Nanoclusters: To further improve the structure and stabilize the morphology of AuAg NCs, 2 mL of aqueous Zn(OAc)2 solution was added to the AuAg-S NCs solution obtained in step 2). After thorough mixing, the mixture was stirred for 5 minutes. The resulting mixture was then transferred to a centrifuge tube and centrifuged at 3000 rpm for 5 minutes, with the supernatant discarded. The AuAg NCs were then frozen in liquid nitrogen to completely stabilize the assembly. The frozen AuAg NCs were then freeze-dried at -65°C and 5 Pa in a vacuum environment for 3 days to yield AuAg-D NCs.

[0059] 4) Water molecule passivation treatment of AuAg-D nanoclusters: The AuAg-D NCs sample obtained in step 3) was exposed to air to allow it to adsorb water molecules in the air. The water molecules combined with the Au-O and Ag-O bonds, passivating the structural oxygen vacancies and preventing electron transfer from the cluster eigenstate to the defect state. The cluster eigenstate became the main channel for radiative relaxation, and AuAg-H NCs with a sky-blue emission of 480 nm were obtained.

[0060] 5) Luminescence Color and Efficiency Control: After water molecule adsorption and passivation of structural defects, the photoluminescence performance of AuAg NCs is significantly enhanced. Through passivation, the emission peak of AuAg NCs continuously blue-shifts from 536nm to 480nm, and the luminescence quantum yield increases from 5.3% to 91.6%.

[0061] like Figure 1 As shown, scanning electron microscopy (SEM) images reveal that the unique water absorption properties of AuAg-D nanoclusters are driven by their intrinsic porous microstructure.

[0062] like Figure 2 As shown, the positive ion mode matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry of the AuAg-S nanoclusters showed that their composition was Au8Ag2(MPA)6.

[0063] like Figure 3 As shown in the figure, under 365nm light excitation, the AuAg-D nanoclusters exhibit a green emission peak at 536nm. The continuous absorption of water molecules by the AuAg-D nanoclusters continuously blue-shifts their emission band and significantly enhances the emission intensity. As a result, the final AuAg-S nanoclusters exhibit a sky-blue emission at 480nm. Correspondingly, the International Commission on Illumination (CIE) chromaticity coordinates of the AuAg nanoclusters can be adjusted over a wide range, from (0.23, 0.67) for AuAg-D nanoclusters to (0.10, 0.17) for AuAg-S nanoclusters.

[0064] like Figure 4 As shown, under the excitation of band edge energy, the absolute photoluminescence quantum yields of AuAg-D, AuAg-H and AuAg-S nanoclusters were determined to be 5.3%, 79.5% and 91.6%, respectively.

[0065] like Figure 5 As shown in the figure, Gaussian fitting of the emission peaks of AuAg-D and AuAg-D nanoclusters under different relative humidity environments found that emitters I (2.55 eV) and II (about 2.42 eV) could be fitted. In addition, as the relative humidity (RH) conditions increase, the proportion of emitter I increases, while the proportion of emitter II decreases, indicating that water molecules can change the radiation channel in AuAg nanoclusters.

[0066] like Figure 6As shown in Figure 2, the power-dependent photoluminescence spectra of three AuAg-D, AuAg-H, and AuAg-S nanoclusters were measured under 350nm pulsed laser pumping and the data were fitted. The corresponding k values ​​obtained from the fitting results for the AuAg-D, AuAg-H, and AuAg-S nanoclusters were 0.439, 0.966, and 0.974, respectively, demonstrating that emitter I in all AuAg nanoclusters is an intrinsic emission center of the cluster, while emitter II is a defect emission center.

[0067] like Figure 7 As shown in Figure 2, three time components are extracted from the luminescence decay of AuAg-D nanoclusters, namely 16.9 ns (τ1, 56%), 302.4 ns (τ2, 21%) and 4241.4 ns (τ3, 23%). The average PL lifetime (τ ave ) is 1048.5 ns. However, for the luminescence decay of AuAg-H nanoclusters, only two time components can be fitted, namely 29.5 ns (τ1, 73%) and 72.8 ns (τ2, 27%), and its τ ave The luminescence decay of the AuAg-S nanoclusters exhibits a single exponential radiative decay with a time of 69.5 nanoseconds. τ1 and τ2 are attributed to the non-radiative and radiative relaxation of excitons in the AuAg nanoclusters, respectively. Furthermore, it is important to note that the τ1 and τ2 in the luminescence lifetime of the AuAg-D nanoclusters indicate that their defect state emission originates from electron transfer from the eigenstates of the AuAg nanoclusters.

[0068] like Figure 8 As shown, a 480 nm luminescence band was detected in the streak camera images of all AuAg nanoclusters, while defect-state emission at 536 nm was only detected in the AuAg-D and AuAg-H nanoclusters. Lifetime fitting of the 480 nm luminescence decay of the three nanoclusters revealed that only the AuAg-S nanocluster contained a single decay component (>1 ns), corresponding to radiative relaxation of the intrinsic emission state of the AuAg nanocluster. In contrast, the luminescence decay of the AuAg-D and AuAg-H nanoclusters contained an ultrafast decay component (32.9 ps and 78.5 ps, respectively) and a radiative relaxation component (>1 ns). Therefore, the 32.9 ps and 78.5 ps decays are attributed to electron transfer processes in the AuAg-D and AuAg-H nanoclusters, respectively. Therefore, the introduced H2O molecules can suppress the electron transfer process from the intrinsic emission state of the AuAg nanocluster to the defect emission state.

[0069] like Figure 9As shown, the ESA kinetic fitting results of the AuAg-D nanoclusters at 488nm and 520nm showed two decay time components: 29.1 nanoseconds and >1 nanosecond, corresponding to the electron injection process and the radiative relaxation of excited electrons in the defect state, respectively. In addition, the ESA kinetic fitting results of the AuAg-H nanoclusters at 480nm and 490nm showed three decay components: 6.8 picoseconds, 81.3 picoseconds and >1 nanosecond, corresponding to the structural relaxation (SR) in the S1 sublevel, the electron transfer process from the native AuAg nanocluster luminescent state to the defect luminescent state, and the radiative relaxation of excited electrons in the S1 state in the AuAg nanoclusters, respectively. Finally, the ESA kinetic fitting results of the AuAg-S nanoclusters at 475nm and 570nm also showed three decay components: 0.9 picoseconds, 8.5 picoseconds and >1 nanosecond, corresponding to the hot electrons from the S n The internal transition from the S1 state to the S1 state, the structural relaxation process, and the radiative relaxation process are observed. The water molecules initially adsorbed in the AuAg-H nanoclusters significantly slow down the electron transfer process and transform the emission from the defect state to the intrinsic state emission of the AuAg nanoclusters. The continued adsorption of water molecules in the AuAg-S nanoclusters completely suppresses the electron transfer process and inhibits non-radiative structural relaxation, ultimately leading to the enhanced luminescence of the AuAg nanoclusters.

[0070] like Figure 10 As shown in the EPR spectrum of the AuAg-D nanoclusters, a significant EPR signal is shown at g = 2.003, which is attributed to the oxygen vacancy defect near the metal atoms in the AuAg nanoclusters. The intensity of the defect signal gradually decreases from the AuAg-D nanoclusters, indicating that water molecules can effectively passivate the oxygen vacancy defect.

[0071] like Figure 11 As shown in Figure 3, the data fitting of the X-ray absorption near-edge structure spectra of AuAg-D and AuAg-H nanoclusters at the Au L3 edge and Ag K edge showed that there were no Au-O and Ag-O paths in the Au L3 edge and Ag K edge FT-EXAFS fitting of AuAg-D nanoclusters, while these paths existed in AuAg-H nanoclusters, which further confirmed that the adsorbed water molecules can generate Au-O and Ag-O bonds, thereby passivating oxygen vacancy defects.

[0072] like Figure 12 As shown in the Fourier transform infrared spectra of AuAg-D and AuAg-H nanoclusters, the stretching vibration of -C=O group has a significant red shift, indicating that hydrogen bonding has formed between water molecules and -C=O group in MPA ligand. In addition, the -C=O group in AuAg-D nanoclusters at 2933cm -1 The methylene stretching vibration peaks in AuAg-H nanoclusters are split into 2987, 2962, 2934, and 2913 cm-1 The sub-peak of is attributed to the vibrational coupling of adjacent methylene groups in the MPA ligand induced by the newly formed hydrogen bonds.

[0073] In summary, the preparation method of metal nanoclusters proposed in this application can regulate the luminescence properties of metal nanoclusters. Adsorbed water molecules in AuAg nanoclusters can blue-shift the luminescence peak from 536 nm to 480 nm and significantly increase the absolute photoluminescence quantum yield from 5.3% to 91.6%. The green PL at 536 nm in AuAg-D nanoclusters is shown to be emitted by slow radiative defect states at oxygen vacancy centers, originating from electron transfer from the intrinsic emitting states of the AuAg nanocluster. Water molecules can anchor themselves to the exposed Au and Ag atoms in the metal core by forming Au-O and Ag-O bonds. The passivation of oxygen vacancy defects by water molecules inhibits the electron transfer process and transforms the rapidly radiative intrinsic emitting states of the AuAg nanocluster into the primary luminescence pathway. Excess adsorbed water molecules also help stabilize the AuAg nanoclusters, suppressing the intensity and energy of non-radiative electron-optical phonon coupling. Finally, an ultra-high absolute luminescence quantum efficiency of 91.6% was achieved in AuAg-S nanoclusters.

[0074] Example 2: Synthesis of AuAg nanoclusters with different HAuCl4 and AgNO3 feed ratios

[0075] This embodiment is similar to the above embodiment 1, and the only difference is step 1):

[0076] 1) Synthesis of AuAg nanoclusters: To 9.2 mL of ultrapure water, add 0.64-0.76 mL of HAuCl4 (50 mM) and 0.04-0.16 mL of AgNO3 (50 mM) aqueous solution and stir at 600 rpm at room temperature to ensure uniform distribution of metal ions. Subsequently, 138 μL of 3-mercaptopropionic acid (MPA) solution was added and stirring continued until the solution changed from light yellow to white and a precipitate was produced. Next, the pH value of the solution was adjusted to 7.90 by adding 1 M NaOH solution. The precipitate gradually dissolved and formed a transparent solution, resulting in an AuAg NCs solution without luminescence properties.

[0077] Figure 13 The emission spectra of the powder under 365nm excitation before and after water absorption of AuAg nanoclusters synthesized with different HAuCl4 and AgNO3 feed ratios are shown.

[0078] Example 3: Synthesis of Au-H NCs

[0079] 1) Synthesis of Au Nanoclusters: To 9.2 mL of ultrapure water, 0.8 mL of HAuCl4 (50 mM) aqueous solution was added and stirred at 600 rpm at room temperature to ensure uniform distribution of the metal ions. Subsequently, 138 μL of 3-mercaptopropionic acid (MPA) solution was added and stirring continued until the solution changed from light yellow to white and a precipitate formed. Next, the pH of the solution was adjusted to 7.90 by adding 1 M NaOH solution. The precipitate gradually dissolved to form a transparent solution, resulting in a non-luminescent Au NCs solution.

[0080] 2) Self-assembly of Au-S nanoclusters: 2 mL of Zn(OAc)2 aqueous solution (concentration of 0.1 M) was added to the Au NCs solution obtained in step 1). The reaction was carried out at room temperature and continued for 24 h to form Au-S NCs.

[0081] 3) Preparation of Au-D Nanoclusters: To further improve the structure of Au NCs and stabilize their morphology, 2 mL of aqueous Zn(OAc)2 solution was added to the Au-S NCs solution obtained in step 2). After thorough mixing, the mixture was stirred for 5 minutes. The mixture was then transferred to a centrifuge tube and centrifuged at 3000 rpm for 5 minutes, and the supernatant was discarded. The Au NCs were then frozen in liquid nitrogen to completely stabilize the assembly. The frozen Au NCs were then freeze-dried at -65°C and 5 Pa in a vacuum environment for 3 days to obtain Au-D NCs.

[0082] 4) Water molecule passivation treatment of Au-D nanoclusters: The Au-D NCs sample obtained in step 3) was exposed to an environment with a relative humidity of 56% to allow it to adsorb water molecules in the air for 30 minutes. The water molecules combined with the Au-O bonds, passivating the structural oxygen vacancies and preventing electron transfer from the cluster eigenstate to the defect state. The cluster eigenstate became the main channel for radiative relaxation, resulting in Au-H NCs with a sky-blue emission of 480 nm.

[0083] Example 4: Synthesis of AuCu-H NCs

[0084] 1) Synthesis of AuCu nanoclusters: To 9.2 mL of ultrapure water, 0.67 mL of HAuCl4 (50 mM) and 0.13 mL of CuCl2 (50 mM) aqueous solution were added and stirred at 600 rpm at room temperature to ensure uniform distribution of the metal ions. 138 μL of 3-mercaptopropionic acid (MPA) solution was then added and stirred until the solution changed from light yellow to white and a precipitate formed. The pH of the solution was then adjusted to 7.90 by adding 1 M NaOH solution. The precipitate gradually dissolved to form a transparent solution, resulting in a non-luminescent AuCu NCs solution.

[0085] 2) Self-assembly of AuCu-S nanoclusters: 2 mL of Zn(OAc)2 aqueous solution (concentration of 0.1 M) was added to the AuCu NCs solution obtained in step 1). The reaction was carried out at room temperature and continued for 24 h to form AuCu-S NCs.

[0086] 3) Preparation of AuCu-D Nanoclusters: To further improve the structure and stabilize the morphology of AuCu NCs, 2 mL of aqueous Zn(OAc)2 solution was added to the AuCu-S NCs solution obtained in step 2). After uniform mixing, the mixture was stirred for 5 minutes. The mixture was then transferred to a centrifuge tube and centrifuged at 3000 rpm for 5 minutes, and the supernatant was discarded. The AuCu NCs were then frozen in liquid nitrogen to completely stabilize the assembly. The frozen AuCu NCs were lyophilized at -65°C and 5 Pa in a vacuum environment for 3 days to obtain AuCu-D NCs.

[0087] 4) Water molecule passivation treatment of AuCu-D nanoclusters: The AuCu-D NCs sample obtained in step 3) was exposed to an environment with a relative humidity of 56% to allow it to adsorb water molecules in the air for 30 minutes. The water molecules bonded with the Au-O and Cu-O bonds, passivating the structural oxygen vacancies and preventing electron transfer from the cluster eigenstate to the defect state. This made the cluster eigenstate the main channel for radiative relaxation, resulting in AuCu-H NCs with a sky-blue emission of 480 nm.

[0088] Figure 14 Shown are the emission spectra of Au and AuCu nanocluster powders under 365 nm excitation.

[0089] Example 5: Synthesis of AuAg nanoclusters at different solution pH values

[0090] This embodiment is similar to the above embodiment 1, and the only difference is step 1):

[0091] 1) Synthesis of AuAg nanoclusters: To 9.2 mL of ultrapure water, 0.67 mL of HAuCl4 (50 mM) and 0.13 mL of AgNO3 (50 mM) aqueous solution were added and stirred at 600 rpm at room temperature to ensure uniform distribution of metal ions. Subsequently, 138 μL of 3-mercaptopropionic acid (MPA) solution was added and stirring continued until the solution changed from light yellow to white and a precipitate was produced. Next, the pH value of the solution was adjusted to 7.70-8.40 by adding 1 M NaOH solution. The precipitate gradually dissolved and formed a transparent solution, resulting in an AuAg NCs solution without luminescence properties.

[0092] Figure 15The emission spectra of the powder under 365nm excitation before and after water absorption of AuAg nanoclusters synthesized at different solution pH values ​​are shown.

[0093] Example 6: Synthesis of AuAg nanoclusters using different zinc salts

[0094] This embodiment is similar to the above-mentioned embodiment 1, except that the zinc salt is replaced from Zn(OAc)2 to ZnCl2, ZnBr2, ZnI2, Zn(ClO4)2, and Zn(CF3SO3)2 respectively.

[0095] Figure 16 The emission spectra of the powders under 365nm excitation before and after water absorption of AuAg nanoclusters synthesized with different zinc salts are shown.

[0096] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

[0097] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A method for preparing metal nanoclusters, characterized in that: include: A metal salt aqueous solution is added to ultrapure water, stirred evenly, and then a 3-mercaptopropionic acid solution is added and the reaction is continued with stirring until a precipitate is produced. The pH value of the solution is adjusted to 7.70-8.40, and then a zinc salt aqueous solution is added. The reaction is carried out under ultraviolet light irradiation conditions with a wavelength of 365-410 nm and a reaction time of 18-30 hours to induce self-assembly of metal nanoclusters; A zinc salt aqueous solution is added to the obtained metal nanoclusters for stirring reaction, and after centrifugation and discarding the supernatant, the metal nanoclusters are freeze-dried. The freeze-dried metal nanoclusters are exposed to an environment with a relative humidity of not less than 2% to allow water molecules to interact with metal oxygen bonds through hydrogen bonds, thereby obtaining; Wherein, the metal salt aqueous solution is a chloroauric acid aqueous solution or a mixture of a chloroauric acid aqueous solution and a silver nitrate aqueous solution or a copper chloride aqueous solution.

2. The method for preparing metal nanoclusters according to claim 1, wherein: The zinc salt is one or more of Zn(OAc)2, ZnCl2, ZnBr2, ZnI2, Zn(ClO4)2, and Zn(CF3SO3)2.

3. The method for preparing metal nanoclusters according to claim 1, wherein: The volume ratio of the chloroauric acid aqueous solution to the silver nitrate aqueous solution or the copper chloride aqueous solution is (0.64-0.76):(0.04-0.16).

4. The method for preparing metal nanoclusters according to claim 3, wherein: The concentrations of the chloroauric acid aqueous solution, the silver nitrate aqueous solution, and the copper chloride aqueous solution are all 50 mM.

5. The method for preparing metal nanoclusters according to claim 1, wherein: The method comprises adding a metal salt aqueous solution to ultrapure water, stirring uniformly, adding a 3-mercaptopropionic acid solution, continuing to stir and react until a precipitate is generated, adjusting the pH value of the solution to 7.70-8.40, adding a zinc salt aqueous solution, and reacting under ultraviolet light to induce self-assembly of metal nanoclusters, comprising: To 9.2 mL of ultrapure water, add 0.64-0.76 mL of chloroauric acid aqueous solution and 0.04-0.16 mL of silver nitrate or copper chloride aqueous solution and stir at 600 rpm at room temperature to ensure uniform distribution of metal ions. Then add 138 μL of 3-mercaptopropionic acid solution and continue stirring until the solution changes from light yellow to white and a precipitate is produced. The pH value of the solution was adjusted to 7.70-8.40 using 1 M sodium hydroxide solution, 2 mL of zinc salt aqueous solution was added to the solution, and the reaction was carried out under 365-410 nm ultraviolet light irradiation to induce the self-assembly of metal nanoclusters.

6. The method for preparing metal nanoclusters according to claim 5, characterized in that: The method comprises adding a zinc salt aqueous solution to the obtained metal nanoclusters, stirring the mixture, centrifuging and discarding the supernatant, and then freeze-drying the metal nanoclusters. The freeze-dried metal nanoclusters are exposed to an environment with a relative humidity of not less than 2% so that water molecules interact with metal oxygen bonds through hydrogen bonds, including: 2 mL of zinc salt aqueous solution was added to the obtained metal nanoclusters and stirred for 5 minutes, followed by centrifugation at 3000 rpm for 5 minutes, and the supernatant was discarded; The obtained metal nanoclusters were solidified using liquid nitrogen and freeze-dried at -65 °C and 5 Pa for 3 days; The freeze-dried metal nanoclusters are exposed to an environment with a relative humidity of not less than 2% to allow water molecules to interact with metal oxygen bonds through hydrogen bonds.

7. A metal nanocluster, characterized in that: The metal nanoclusters are prepared by the preparation method of the metal nanoclusters according to any one of claims 1 to 6.

8. The metal nanocluster according to claim 7, characterized in that The luminescence quantum efficiency of the metal nanoclusters is as high as 91.6%, and the luminescence color can be adjusted within milliseconds, quickly adjusting from 536 nm to 480 nm.

9. Use of the metal nanoclusters according to claim 7 in the fields of optoelectronic devices, sensors, and photocatalysts.

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