A rare earth doped perovskite quantum dot / fluoride core-shell hetero-nanomaterial and a preparation method thereof

Abstract

This invention discloses a rare-earth-doped perovskite quantum dot / fluoride core-shell heterostructure nanomaterial and its preparation method, relating to the field of nanomaterial preparation technology. This invention uses Yb 3+ Cesium lead halide perovskite serves as the quantum dot core, with a rare-earth-doped active fluoride shell epitaxially grown on its surface, forming a core-shell heterostructure. Furthermore, an undoped inert fluoride shell is epitaxially grown on the surface of the active fluoride shell, constructing a core-shell-shell multilayer heterogeneous nanomaterial. This invention achieves complementary performance advantages between perovskite and fluorides, broadens the material's spectral response range, improves chemical stability and luminescence efficiency, and combines upconversion luminescence and quantum sizing characteristics. It can be widely applied in near-infrared photodetectors, biofluorescent probes, optical anti-counterfeiting, and spectral conversion thin films.

Description

Technical Field

[0001] This invention relates to the field of nanomaterial preparation technology, and in particular to a rare earth-doped perovskite quantum dot / fluoride core-shell heterostructure nanomaterial and its preparation method. Background Technology

[0002] Halide perovskite nanocrystals are novel semiconductor materials with great application potential in the optoelectronic field in recent years. They possess outstanding advantages such as wide absorption cross-section, high fluorescence quantum yield, tunable emission spectrum, and simple preparation process, showing broad application prospects in fields such as light-emitting displays, photovoltaic cells, photoelectric detection, and bioimaging. Among them, cesium lead halide perovskite quantum dots (CsPbX3, X=Cl, Br, I) have become a research focus of perovskite-based luminescent materials due to their stable crystal structure and excellent optical properties.

[0003] However, traditional lead halide perovskite materials have significant limitations in practical applications: on the one hand, their lattice chemical stability is poor, and they are easily affected by external environmental factors such as moisture, light, and temperature, resulting in decomposition and structural collapse, which leads to a rapid decay in luminescence efficiency; on the other hand, due to the intrinsic band gap, the photoresponse and luminescence range of perovskite quantum dots are mainly concentrated in the ultraviolet-visible light region, making it difficult to cover important functional bands such as near-infrared, which seriously limits their application expansion in scenarios such as near-infrared detection, optical communication, and deep biological imaging.

[0004] Fluorides are ideal doping matrices for rare earth ions, possessing advantages such as low phonon energy, chemical stability, strong compatibility with rare earth doping, and designable core-shell structures. They can efficiently support co-doping with various rare earth ions, enabling multiple nonlinear luminescence processes such as upconversion, quantum trimming, and downtransfer. They have wide applications in optical anti-counterfeiting, laser devices, and biomarkers. Heterogeneous composites of perovskite quantum dots and rare earth-doped fluorides represent an effective way to overcome the performance limitations of single-material composites.

[0005] Currently, perovskite / fluoride composite systems are mostly developed using physical mixing, surface bonding, and porous encapsulation methods. While these methods have improved material stability to some extent, they still suffer from several key technical shortcomings: First, the interfacial bonding is weak, resulting in low energy transfer efficiency and making it difficult to achieve efficient bidirectional energy transfer between perovskite and rare earth fluorides. Second, the types and concentrations of rare earth ion doping are limited, leading to limited optical functions. Third, only one nonlinear luminescence mode, either upconversion or downconversion, can be achieved, making it impossible to integrate multiple optical responses in a single nanoparticle. Fourth, the emission wavelength is still mainly visible light, with weak near-infrared luminescence intensity and poor tunability.

[0006] In summary, existing technologies cannot simultaneously address the issues of insufficient perovskite stability, limited rare-earth doping, single luminescence mode, and narrow spectral range, making it difficult to meet the demands of cutting-edge fields such as multi-mode optical anti-counterfeiting, near-infrared detection, and bioimaging for wide-band, multi-response, and highly stable nanoluminescent materials. Therefore, developing a perovskite-fluoride heterostructure nanomaterial that can achieve efficient rare-earth doping, possesses multiple nonlinear luminescence functions, and covers a wide visible-near-infrared band has become a key technical problem urgently needing to be solved in this field. Summary of the Invention

[0007] The purpose of this invention is to provide a rare earth-doped perovskite quantum dot / fluoride core-shell heterogeneous nanomaterial and its preparation method, so as to solve the problems existing in the prior art.

[0008] To achieve the above objectives, the present invention provides the following solution: This invention provides a rare earth-doped perovskite quantum dot / fluoride core-shell heterogeneous nanomaterial having a core-shell structure, comprising quantum dots and an active fluoride shell coating the surface of the quantum dots; The quantum dot is Yb 3+ The doped cesium lead halide perovskite nanocrystals have the general chemical formula CsPbX3:Yb, where X is selected from at least one of Cl, Br and I. The chemical formula of the active fluoride shell is NaREF4:Ln; where RE is a rare earth element and Ln is a doped active rare earth ion. The corresponding heterogeneous nanomaterial structure has the general formula CsPbX3:Yb@NaREF4:Ln.

[0009] Furthermore, it also includes an inert fluoride shell coating the surface of the active fluoride shell; the chemical formula of the inert fluoride shell is NaREF4; wherein RE is a rare earth element; The corresponding heterogeneous nanomaterial structure has the general formula CsPbX3:Yb@NaREF4:Ln@NaREF4.

[0010] Furthermore, the RE in the active fluoride shell and / or the inert fluoride shell is selected from Y or Gd.

[0011] That is, the matrix material of the active fluoride shell is selected from NaYF4 or NaGdF4; the matrix material of the inert fluoride shell is selected from NaYF4 or NaGdF4.

[0012] Furthermore, the doped active rare earth ion Ln includes a sensitizer and an activator; The sensitizer is Yb. 3+ The activator is selected from Er 3+ Ho 3+ and Tm3+ At least one of them.

[0013] Furthermore, in the active fluoride shell, the sensitizer Yb 3+ The doping molar percentage is 5%~30%; the doping molar percentage of the activator is as follows: Er 3+ 0.2%~95%, Ho 3+ 2%~10%, Tm 3+ 0.1%~2%.

[0014] Furthermore, in the CsPbX3:Yb, X represents Cl and Br, and the molar ratio of Cl:Br = 1:1; the active fluoride shell contains Yb 3+ The molar doping percentage is 15%.

[0015] This invention also provides a method for preparing the above-mentioned rare-earth-doped perovskite quantum dot / fluoride core-shell heterostructure nanomaterials, comprising the following steps: (1) For Yb 3+ Doped cesium lead halide perovskite quantum dots are surface modified to obtain modified perovskite quantum dots. (2) An active fluoride shell is epitaxially grown on the surface of the modified perovskite quantum dots to obtain the rare earth-doped perovskite quantum dot / fluoride core-shell heterogeneous nanomaterial.

[0016] Furthermore, the synthesis of Yb 3+ The doped cesium lead halide perovskite quantum dots include the following steps: A cesium source, a ytterbium source, a lead source, a halogen source, a ligand, and a solvent were mixed and reacted under an inert atmosphere, followed by cooling and separation to obtain the Yb. 3+ Doped cesium lead halide perovskite quantum dots.

[0017] Furthermore, the surface modification treatment includes the following steps: The perovskite quantum dots are treated with a haloorganic amine reagent generated by the reaction of ammonium halide or hydrogen halide with an organic amine. The epitaxial growth of the active fluoride shell includes the following steps: A shell precursor is prepared by mixing rare earth source, fluorine source, alkali source and ligand, and then the modified perovskite quantum dots are added. After removing the solvent, the precursor is heat-treated under an inert atmosphere to allow the active fluoride to grow epitaxially on the surface of the quantum dots.

[0018] Furthermore, the heat treatment includes the following steps: first heating to 270°C and holding at that temperature, then heating to 300~320°C and holding at that temperature.

[0019] Furthermore, the method for epitaxially growing an inert fluoride shell includes: An inert shell precursor is injected into a solution of the rare earth-doped perovskite quantum dot / fluoride core-shell heterogeneous nanomaterial and reacted under an inert atmosphere, allowing the inert fluoride to grow epitaxially on the surface of the active fluoride shell.

[0020] The present invention further provides the application of the above-mentioned rare earth-doped perovskite quantum dot / fluoride core-shell heterogeneous nanomaterials in the preparation of near-infrared photodetectors, biofluorescent probes, anti-counterfeiting inks or spectral conversion films.

[0021] This invention achieves a synergistic improvement in material properties by heterogeneously integrating rare-earth-doped perovskite quantum dots with rare-earth-doped fluoride nanocrystals, resulting in the following significant advantages: This invention fully combines the advantages of perovskite quantum dots, such as large absorption cross-section and high fluorescence quantum yield, with the characteristics of fluoride nanocrystals, such as strong compatibility with rare earth ion doping and flexible composition tunability. It achieves complementary advantages of the two materials, effectively solves the technical bottleneck of limited types and low concentrations of rare earth ion doping in single perovskite materials, and significantly improves the doping efficiency and multi-element doping capability of rare earth ions.

[0022] To address the limitations of traditional perovskite quantum dots, which are restricted by their intrinsic band gap and whose spectral response only covers the ultraviolet-visible region, this invention utilizes heterogeneous integration of rare-earth-doped fluorides. By leveraging the upconversion luminescence properties of these fluorides, near-infrared photons are converted into high-energy photons that can be effectively absorbed by perovskites. This successfully extends the spectral response range of the material from the ultraviolet-visible region to the near-infrared region, significantly broadening the application scenarios of the material.

[0023] This invention utilizes the bidirectional energy transfer mechanism between perovskite and fluorides to achieve tunable emission across a wide visible-near-infrared band. In the visible region, leveraging the tunable bandgap of perovskite quantum dots, the discrete, fixed emission of rare-earth ions in fluorides is transformed into continuous, tunable emission covering the entire visible light range. In the near-infrared region, through efficient energy transfer from perovskite quantum dots to rare-earth ions in fluorides, the emission band is extended into the near-infrared region, and this can be further enhanced by selecting Er... 3+ Ho 3+ Tm 3+ Rare earth ions enable flexible tuning in the 900-1700 nm near-infrared band.

[0024] Furthermore, this invention achieves the synergistic integration of two nonlinear optical responses, upconversion luminescence and quantum cutting, in a single heterogeneous nanoparticle, breaking through the limitation of existing composite materials that can only achieve a single nonlinear luminescence mode. This provides a novel and efficient material platform for cutting-edge fields such as multi-mode optical anti-counterfeiting, near-infrared photoelectric detection, and deep biological imaging.

[0025] The present invention discloses the following technical effects: This invention constructs a core-shell heterostructure of rare-earth-doped perovskite quantum dots and fluorides, enabling synergistic performance and complementary advantages between the two materials. Perovskite quantum dots possess a large light absorption cross-section and high luminescence efficiency, while the fluoride matrix exhibits strong compatibility with rare-earth ions, allowing for high-concentration, multi-type rare-earth ion doping, effectively overcoming the bottleneck of limited rare-earth doping in single perovskite materials. By epitaxially growing an active fluoride shell on the quantum dot surface, upconversion luminescence can be used to convert near-infrared photons into visible light, broadening the material's spectral response range and achieving tunable emission across a wide visible-near-infrared band through bidirectional energy transfer. Further epitaxial growth of an inert fluoride shell on the active fluoride shell significantly improves the material's crystal integrity, chemical stability, and high-temperature resistance, reduces interface defects and non-radiative transitions, and enhances luminescence efficiency and structural stability. The heterogeneous nanomaterials obtained by this invention simultaneously integrate upconversion luminescence and quantum cutting properties, demonstrating outstanding application value in near-infrared photoelectric detection, biofluorescence imaging, optical anti-counterfeiting, and spectral conversion. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This diagram illustrates the structure and bidirectional energy transfer mechanism of the rare-earth-doped perovskite quantum dot / fluoride core-shell heterogeneous nanomaterial of the present invention; wherein, a is a schematic diagram of the energy transfer process from perovskite quantum dots to rare-earth-doped fluorides under ultraviolet light excitation, and b is a schematic diagram of the energy transfer process from rare earth to perovskite quantum dots under 980 nm near-infrared light excitation.

[0028] Figure 2 The CsPbCl prepared in Example 1 of this invention 1.5 Br 1.5 Transmission electron microscopy image of Yb quantum dots.

[0029] Figure 3 The CsPbCl prepared in Example 1 of this invention 1.5 Br 1.5 Optical characterization results of Yb quantum dots, where a is the absorption spectrum and b is the emission spectrum under ultraviolet excitation.

[0030] Figure 4 The CsPbCl prepared in Example 2 of this invention 1.5 Br 1.5Morphological characterization of the Yb@NaYF4:15%Yb,5%Er heterogeneous nanomaterial, where a is a transmission electron microscope image and b is a high-resolution transmission electron microscope image.

[0031] Figure 5 The CsPbCl obtained in Example 2 of this invention 1.5 Br 1.5 X-ray diffraction pattern of heterogeneous nanomaterials: Yb@NaYF4:15%Yb,5%Er.

[0032] Figure 6 The CsPbCl prepared in Example 3 of this invention 1.5 Br 1.5 Transmission electron microscopy image of heterogeneous core-shell nanomaterials: Yb@NaYF4:15%Yb,5%Er@NaYF4.

[0033] Figure 7 The CsPbCl obtained in Example 2 of this invention 1.5 Br 1.5 :Yb@NaYF4:15%Yb,5%Er heterogeneous nanomaterials and CsPbCl obtained in Example 3 1.5 Br 1.5 Comparison of near-infrared emission spectra of heterogeneous core-shell nanocrystals of Yb@NaYF4:15%Yb,5%Er@NaYF4 under UV excitation.

[0034] Figure 8 The different activators Er obtained in Examples 3-5 of this invention 3+ Ho 3+ Tm 3+ Near-infrared emission spectra of doped heterogeneous core-shell nanocrystals under ultraviolet excitation.

[0035] Figure 9 The different activators Er obtained in Examples 3-5 of this invention 3+ Ho 3+ Tm 3+ Emission spectrum of doped heterogeneous core-shell nanocrystals under 980 nm near-infrared excitation. Detailed Implementation

[0036] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0037] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0038] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0039] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0040] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0041] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0042] Figure 1 This diagram illustrates the structure and bidirectional energy transfer mechanism of the rare-earth-doped perovskite quantum dot / fluoride core-shell heterogeneous nanomaterial of the present invention; wherein, a is a schematic diagram of the energy transfer process from perovskite quantum dots to rare-earth-doped fluorides under ultraviolet light excitation, and b is a schematic diagram of the energy transfer process from rare earth to perovskite quantum dots under 980 nm near-infrared light excitation.

[0043] like Figure 1 As shown in Figure a, under ultraviolet light excitation, electrons are excited from the valence band to the conduction band of the perovskite matrix. Some excitons recombine and emit blue photons, while others are trapped by shallow traps through nonradiative transitions and generate twice the amount of Yb through quantum clipping effects. 3+ The excitation ultimately results in the emission of near-infrared light at 980 nm. This energy is transferred to the Yb at the interface in the fluoride matrix due to resonant matching. 3+ After Yb 3+ -Yb3+ Multi-step energy transfer to Er 3+ of 4 I 11 / 2 energy level, through non-radiative relaxation and 4 I 13 / 2→ 4 I 15 / 2 radiative transition produces down-transfer emission at 1550 nm.

[0044] like Figure 1 As shown in b, under 980 nm near-infrared light excitation, Yb 3+ After absorbing energy, it is gradually transferred to Er. 3+ of 4 I 11 / 2、 4 F7 / 2 and 2 Excited states such as G7 / 2 undergo energy transfer upconversion and nonradiative relaxation processes, with electrons in... 4 G 11 / 2 and 2 The population consists of high-energy excited states such as H9 / 2. Since the energy of this excited state matches the perovskite bandgap, it can be determined from Er... 3+ Energy is transferred to the interface of the perovskite host, and electrons are excited from the valence band to the conduction band of the perovskite. After exciton recombination, blue photons are emitted.

[0045] The preferred steps of the method for preparing rare-earth-doped perovskite quantum dot / fluoride core-shell heterogeneous nanomaterials of the present invention are as follows: (1) Yb 3+ Synthesis of doped perovskite quantum dots Add the mixture of cesium carbonate, oleic acid, and 1-octadecene to a three-necked round-bottom flask, heat to 100-150 °C under continuous nitrogen protection, and keep warm for 1 hour until the solid is completely dissolved to obtain a clear cesium oleate precursor solution. Keep the temperature above 100 °C before use to avoid precipitation.

[0046] In another three-necked flask, ytterbium chloride hydrate or ytterbium acetate, lead halide, oleic acid, oleylamine, and 1-octadecene were added. The mixture was heated to 150 °C under nitrogen protection, stirred, and maintained at this temperature for at least 40 minutes. The temperature was then raised to 200-250 °C, and after stabilization, the aforementioned cesium oleate precursor was rapidly injected. The reaction was allowed to proceed for 10-30 seconds, followed by immediate cooling to room temperature in an ice-water bath. The resulting suspension was centrifuged to collect the perovskite powder, which was then washed with cyclohexane. Finally, the perovskite quantum dots were dispersed in cyclohexane for later use.

[0047] (2) Optional anion exchange steps When the prepared perovskite quantum dots contain two or more halogens, anion exchange is performed to precisely control the halogen composition; when the perovskite quantum dots contain only a single halogen, this step is not performed.

[0048] During anion exchange, lead halide and 1-octadecene were placed in a three-necked flask and heated to 120 °C under a nitrogen atmosphere. The mixture was stirred and kept at this temperature for 10 minutes. Then, oleic acid and oleylamine were added, and the mixture was kept at this temperature until the solid was completely dissolved, thus obtaining a halogen source solution. The perovskite solution obtained in step (1) was stirred vigorously at room temperature, while the halogen source solution was added dropwise to carry out the anion exchange reaction. After the reaction was completed, the perovskite nanocrystals were separated by centrifugation, and the precipitate was redispersed in cyclohexane for later use.

[0049] (3) Yb 3+ Surface modification of perovskite quantum dots First, prepare oleylamine bromide: Add oleylamine and hydrobromic acid to a three-necked flask, heat to 80 ℃ and keep warm for 1 hour under nitrogen protection, then raise the temperature to 120 ℃ and keep warm for 2 hours to obtain a pale yellow oleylamine bromide solution.

[0050] The quantum dot solution obtained in step (2) was centrifuged to obtain solid powder. 1-Octadecene and oleylamine bromide were added, and the quantum dots were uniformly dispersed by ultrasonic treatment. The supernatant was removed by centrifugation, and the precipitate was redispersed in cyclohexane to obtain modified perovskite quantum dots, which served as the core material for subsequent heterostructure preparation.

[0051] (4) Preparation of quantum dot-active fluoride shell heterogeneous nanomaterials Rare earth hydrated chlorides required for the active fluoride shell were added to a three-necked flask according to the target molar ratio. Oleic acid and 1-octadecene were added, and the mixture was heated to 150 °C and held for at least 30 minutes under nitrogen protection to obtain a clear precursor solution. After cooling, a methanol solution containing NaOH and NH4F was added, and the temperature was raised to 80-100 °C to remove the methanol. After cooling again, the modified quantum dot solution obtained in step (3) was added, and the mixture was mixed evenly. The mixture was then heated to 90 °C under vacuum to completely remove cyclohexane. The mixture was subjected to segmented heat treatment under reflux conditions: first, the temperature was raised to 270 °C and held for 30 minutes, and then the temperature was raised to 300–320 °C and held for 1.5 hours. After cooling to room temperature, the product was centrifuged and washed alternately with ethanol and cyclohexane. Finally, the product was dispersed in cyclohexane to obtain a quantum dot-active fluoride shell heterogeneous nanomaterial.

[0052] (5) Preparation of quantum dot-active fluoride shell-inert fluoride shell heterogeneous nanomaterials An inert fluoride shell is applied to the heterogeneous nanomaterials obtained in step (4).

[0053] Sodium trifluoroacetate and rare earth hydrated trifluoroacetate were added to a three-necked flask in a 1:1 molar ratio, along with oleic acid and 1-octadecene. The mixture was heated to 120 °C under a nitrogen atmosphere and stirred for 30 minutes to completely dissolve the solid and remove residual moisture. After cooling, an inert shell precursor was obtained.

[0054] The heterogeneous nanocrystal solution obtained in step (4) was added to a three-necked flask containing oleic acid and 1-octadecene, and heated to 90 °C under vacuum to remove cyclohexane. Under nitrogen protection, the temperature was raised to 300 °C, and the above-mentioned inert shell precursor was injected in portions. The epitaxial shell growth was completed after reacting for 1 hour. After cooling to room temperature, the product was collected by centrifugation, washed with ethanol and cyclohexane, and dispersed in cyclohexane to obtain quantum dot-active fluoride shell-inert fluoride shell heterogeneous nanomaterials.

[0055] The present invention will be specifically described below with reference to embodiments: Example 1 This embodiment is used to prepare Yb with controllable composition, precise emission wavelength, and strong surface adaptability. 3+ Doped perovskite quantum dots provide a stable core material for subsequent epitaxial growth of fluoride shells. The resulting quantum dots have the chemical formula CsPbCl. 1.5 Br 1.5 The specific steps are as follows: :Yb@OAmBr (1) Preparation of CsPbCl3:Yb perovskite quantum dots: 0.4 g of cesium carbonate (Cs₂CO₃), 0.7 mL of oleic acid (OA), and 7.5 mL of 1-octadecene (ODE) were added to a 25 mL three-necked flask, where OA served as the acidic ligand and ODE served as the high-boiling noncoordinate solvent to provide the reaction medium. The mixture was heated to 120 °C under continuous nitrogen protection and held at this temperature for 1 h until the solid completely dissolved, yielding a clear cesium oleate precursor solution, which was then maintained at 120 °C for later use. In a 100 mL three-necked flask, add 0.3 mmol of ytterbium chloride hexahydrate (YbCl3•6H2O), 0.3 mmol of lead chloride (PbCl2), 1.5 mL of OA, 3 mL of oleylamine (OAm), and 10 mL of ODE, where OAM acts as a cationic ligand, and both OAM and OA act as surface ligands for the quantum dots. Heat to 150 °C under nitrogen protection and stir for 40 min; then raise the temperature to 240 °C and rapidly inject 0.8 mL of the above-mentioned cesium oleate precursor. After reacting for 10 s, immediately quench the mixture in an ice-water bath to room temperature. Centrifuge the reaction suspension at 9500 r / min for 10 min, collect the solid, wash with cyclohexane, and finally disperse in 5 mL of cyclohexane for later use.

[0056] (2) CsPbCl 1.5 Br 1.5 Preparation of Yb perovskite quantum dots: 0.15 mmol of lead bromide (PbBr2) and 5 mL of 1-octadecene (ODE) were added to a 25 mL three-necked flask. The mixture was heated to 120 °C under a nitrogen atmosphere and held at that temperature for 10 min. Then, 0.2 mL of oleic acid (OA) and 0.2 mL of oleylamine (OAm) were added, and the mixture was kept at that temperature for another 30 min until the solid was completely dissolved, thus obtaining a homogeneous and stable halogen source solution. Under vigorous stirring at room temperature, the above halogen source solution was slowly added dropwise to the CsPbCl3:Yb quantum dot solution obtained in step (1) to carry out anion exchange reaction. The photoluminescence spectrum was monitored in real time during the reaction until the center wavelength of the emission peak was tuned to 450 nm and then the reaction was stopped. After centrifugation to collect the nanocrystals, they were redispersed in 5 mL of cyclohexane for later use. The halogen ratio was precisely controlled to Cl:Br=1:1 by anion exchange to achieve controllable adjustment of the perovskite band gap and emission wavelength, thus obtaining CsPbCl3 with the target visible light emission characteristics. 1.5 Br 1.5 Yb quantum dots. Redispersed in 5 mL of cyclohexane for later use.

[0057] (3) CsPbCl 1.5 Br 1.5 Surface modification of Yb perovskite quantum dots: Add 10 mL of OAm and 1 mL of hydrobromic acid (HBr) to a 50 mL three-necked flask, heat to 80 °C for 1 h under nitrogen protection, then raise the temperature to 120 °C and hold for 2 h to obtain a pale yellow oleylamine bromide (OAmBr) solution. Take the CsPbCl obtained in step (2) 1.5 Br 1.5 Yb quantum dot solution was centrifuged to collect the solid powder. 5 mL of 1-octadecene (ODE) and 50 μL of oleylamine bromide (OAmBr) were added, and the mixture was sonicated for 5 min to ensure uniform dispersion. The supernatant was removed by centrifugation again, and the precipitate was redispersed in 5 mL of cyclohexane to obtain surface-coordinated modified CsPbCl₂. 1.5 Br 1.5 Yb@OAmBr quantum dots, by replacing the oleylamine bromide ligands to optimize the coordination environment of the quantum dot surface, improve high-temperature stability and interfacial compatibility, and provide a stable and suitable reaction interface for subsequent epitaxial growth of fluoride shells.

[0058] Figure 2 The CsPbCl prepared in Example 1 of this invention 1.5 Br1.5 Transmission electron microscopy image of Yb quantum dots. The quantum dots are cubic in phase and have an average particle size of 16 nm.

[0059] Figure 3 The CsPbCl prepared in Example 1 of this invention 1.5 Br 1.5 Optical characterization results of Yb quantum dots, where a is the absorption spectrum and b is the emission spectrum under ultraviolet excitation. Emission sites include intrinsic perovskite emission (exciton emission center at 450 nm) and rare-earth ion Yb. 3+ The emission at 980 nm. Among them, Yb 3+ The emission originates from the perovskite host to Yb 3+ The quantum cutting effect.

[0060] Example 2 This embodiment provides a rare earth-doped perovskite quantum dot / fluoride core-shell heterostructure nanomaterial (CsPbCl). 1.5 Br 1.5 The preparation method of Yb@NaYF4 (15%Yb, 5%Er) yields a quantum dot core-active fluoride shell bilayer heterostructure. This embodiment uses Er... 3+ This example serves as an activator; other rare-earth ion-doped heteromaterials can be constructed by adjusting the types and concentrations of rare-earth elements. The specific steps are as follows: (1) Preparation of rare earth precursor solution: 0.05 mmol of erbium chloride hexahydrate (ErCl3•6H2O), 0.15 mmol of ytterbium chloride hexahydrate (YbCl3•6H2O), and 0.8 mmol of yttrium chloride hexahydrate (YCl3•6H2O) were added to a 100 mL three-necked flask, followed by 6 mL of oleic acid (OA) and 15 mL of 1-octadecene (ODE). The mixture was heated to 150 °C under continuous nitrogen protection and held at this temperature for 40 min until the solids were completely dissolved, yielding a clear rare earth precursor solution. The solution was then cooled to below 50 °C. The 0.8 mmol of YCl3•6H2O was used to provide the Y required for the NaYF4 matrix. 3+ 0.15 mmol YbCl3•6 H2O was used to introduce 15% molar fraction of Yb into the fluoride shell. 3+ As a sensitizer, 0.05 mmol ErCl3•6H2O was used as an activator to achieve upconversion luminescence.

[0061] (2) Preparation of fluoride precursors: Dissolve 2.5 mmol NaOH and 4 mmol NH4F in 8 mL of methanol. After complete dissolution, add the solution dropwise to the above rare earth precursor solution. Heat the mixture to 100 °C and hold for 30 min to completely remove the methanol, then cool it again to below 50 °C. Add CsPbCl prepared in Example 1 to the system. 1.5 Br 1.5 The Yb@OAmBr quantum dot solution was stirred evenly at room temperature, then heated to 90 °C under vacuum and held for 30 min to ensure complete removal of cyclohexane.

[0062] (3) Segmented heat treatment and epitaxial growth of active shell: The mixture was subjected to staged heat treatment under reflux conditions: first, the temperature was raised to 270 °C and held for 30 min, then raised to 300 °C and held for 1.5 h. After the reaction, the mixture was allowed to cool naturally to room temperature, and the product was collected by centrifugation. The product was then washed alternately with ethanol and cyclohexane using ultrasonication. Finally, the obtained solid was dispersed in 5 mL of cyclohexane to obtain heterogeneous nanocrystals, namely CsPbCl. 1.5 Br 1.5 :Yb@NaYF4:15%Yb,5%Er heterogeneous nanomaterials (i.e., CsPbCl) 1.5 Br 1.5 :Yb@NaYF4:Yb,Er).

[0063] Figure 4 In the image, a is a transmission electron microscope (TEM) image of the heterogeneous nanocrystals obtained in this embodiment, showing uniform particles with an average particle size of approximately 26 nm; b is a high-resolution TEM image, in which clear lattice fringes can be observed.

[0064] Figure 5 The X-ray diffraction pattern of the heterostructured nanocrystals obtained in this embodiment (labeled as CsPbX3:Yb@NaYF4:YbEr in the figure) shows that the diffraction peak positions match well with the standard patterns of cubic perovskite and hexagonal NaYF4, indicating that the perovskite-fluoride heterostructure was successfully formed.

[0065] Example 3 This embodiment provides a rare earth-doped perovskite quantum dot / fluoride core-shell heterostructure nanomaterial (CsPbCl). 1.5 Br 1.5 The preparation method of (Yb@NaYF4: 15%Yb, 5%Er@NaYF4) yields a three-layer heterostructure consisting of a quantum dot core, an active fluoride shell, and an inert fluoride shell. This embodiment uses Er... 3+ This example serves as an activator; other rare-earth ion-doped heteromaterials can be achieved by adjusting the types and concentrations of rare-earth elements. The specific steps are as follows: (1) Preparation of inert NaYF4 shell precursor: 1 mmol sodium trifluoroacetate (NaCF3COO) and 1 mmol yttrium trifluoroacetate trihydrate (Y(CF3COO)3•3H2O) were added to a three-necked flask, followed by 5 mL oleic acid (OA) and 5 mL 1-octadecene (ODE); the temperature was raised to 120 °C under a nitrogen atmosphere, stirred and kept warm for 30 min to completely dissolve the solid and remove residual water in the system. After cooling to room temperature, the inert NaYF4 shell precursor was obtained.

[0066] (2) Inert shell epitaxial growth: Take 5 mL of CsPbCl prepared in Example 2 1.5 Br 1.5 A heterocrystalline solution of Yb@NaYF4:15%Yb,5%Er was added to a three-necked flask containing 7.5 mL of OA and 7.5 mL of ODE. The solution was heated to 90 °C under vacuum and held until cyclohexane was completely removed. Under nitrogen protection, the system was heated to 300 °C, and the NaYF4 precursor was injected in four portions, reacting for 15 min after each injection. After all the precursors were added, the reaction continued for 1 h to complete the epitaxial growth of the inert shell. After the reaction, the solution was cooled to room temperature, and the product was collected by centrifugation to obtain heterocrystalline nanocrystals. These nanocrystals were washed alternately with ethanol and cyclohexane and finally dispersed in cyclohexane to obtain CsPbCl. 1.5 Br 1.5 :Yb@NaYF4:15%Yb,5%Er@NaYF4 heterogeneous core-shell nanomaterials (i.e., CsPbCl) 1.5 Br 1.5 :Yb@NaYF4:Yb,Er@NaYF4).

[0067] Example 4 The only difference from Example 3 is that the activator Er is used. 3+ Replace with an equimolar amount of Ho 3+ .

[0068] Example 5 The only difference from Example 3 is that the activator Er is used. 3+ Replace with equimolar amounts of Tm 3+ .

[0069] Figure 6 The image shows a transmission electron microscope (TEM) image of the heterogeneous core-shell nanocrystals obtained in Example 3. The nanoparticles exhibit a regular morphology, with a long axis diameter of approximately 45 nm and a short axis diameter of approximately 33 nm. The outer inert shell has a thickness of 9.5 nm (long axis) to 3.5 nm (short axis).

[0070] Figure 7The near-infrared emission spectrum of the heterogeneous core-shell nanocrystals obtained in Example 3 under ultraviolet excitation shows Yb 3+ Characteristic 980 nm emission and Er 3+ Characterized by emission at 1550 nm. (Similar to CsPbCl) 1.5 Br 1.5 Compared to Yb@NaYF4:15%Yb,5%Er, Yb coated with an inert shell and then heterogeneous core-shell nanocrystals... 3+ and Er 3+ The infrared emission intensity increased by 7.4 times and 8.1 times, respectively.

[0071] Figure 8 The different activators Er obtained in Examples 3-5 3+ Ho 3+ Tm 3+ Near-infrared emission spectra of doped heterogeneous core-shell nanocrystals (labeled Er NPs, Ho NPs, and Tm NPs) under UV excitation. The sensitizer Yb is also present. 3+ and activator Er 3+ Tm 3+ Ho 3+ The down-transfer launch.

[0072] Figure 9 The different activators Er obtained in Examples 3-5 3+ Ho 3+ Tm 3+ The emission spectra of doped heterogeneous core-shell nanocrystals (labeled Er NPs, Ho NPs, and Tm NPs) under 980 nm near-infrared excitation show both perovskite intrinsic exciton emission and rare-earth activator Er 3+ Tm 3+ Ho 3+ The corresponding upconversion transmission.

[0073] In summary, this invention successfully solves the technical problems of existing perovskite / fluoride composite materials, such as the single nonlinear emission mode, insufficient infrared emission extension, and limited types and concentrations of rare earth ion doping. It achieves a synergistic improvement in material performance, and the resulting heterogeneous nanomaterials possess both dual-mode nonlinear emission characteristics and wide-band tunable emission performance, while also exhibiting excellent stability. This provides high-performance new material support for applications in related optical fields.

[0074] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A rare-earth-doped perovskite quantum dot / fluoride core-shell heterostructure nanomaterial, characterized in that, It has a core-shell structure, including quantum dots and an active fluoride shell coating the surface of the quantum dots; The quantum dot is Yb 3+ The doped cesium lead halide perovskite nanocrystals have the general chemical formula CsPbX3:Yb, where X is selected from at least one of Cl, Br and I. The chemical formula of the active fluoride shell is NaREF4:Ln; where RE is a rare earth element and Ln is a doped active rare earth ion.

2. The rare-earth-doped perovskite quantum dot / fluoride core-shell heterostructure nanomaterial according to claim 1, characterized in that, It also includes an inert fluoride shell coating the surface of the active fluoride shell; the chemical formula of the inert fluoride shell is NaREF4; wherein RE is a rare earth element.

3. The rare-earth-doped perovskite quantum dot / fluoride core-shell heterostructure nanomaterial according to claim 2, characterized in that, The RE in the active fluoride shell and / or the inert fluoride shell is selected from Y or Gd.

4. The rare-earth-doped perovskite quantum dot / fluoride core-shell heterostructure nanomaterial according to claim 1, characterized in that, Doping with active rare earth ions Ln includes sensitizers and activators; The sensitizer is Yb. 3+ The activator is selected from Er 3+ Ho 3+ and Tm 3+ At least one of them.

5. A method for preparing rare-earth-doped perovskite quantum dot / fluoride core-shell heterostructure nanomaterials as described in claim 1, characterized in that, Includes the following steps: (1) For Yb 3+ Doped cesium lead halide perovskite quantum dots are surface modified to obtain modified perovskite quantum dots. (2) An active fluoride shell is epitaxially grown on the surface of the modified perovskite quantum dots to obtain the rare earth-doped perovskite quantum dot / fluoride core-shell heterogeneous nanomaterial.

6. The preparation method according to claim 5, characterized in that, Synthetic Yb 3+ The doped cesium lead halide perovskite quantum dots include the following steps: A cesium source, a ytterbium source, a lead source, a halogen source, a ligand, and a solvent were mixed and reacted under an inert atmosphere, followed by cooling and separation to obtain the Yb. 3+ Doped cesium lead halide perovskite quantum dots.

7. The preparation method according to claim 5, characterized in that, The surface modification treatment includes the following steps: The perovskite quantum dots are treated with a haloorganic amine reagent generated by the reaction of ammonium halide or hydrogen halide with an organic amine. The epitaxial growth of the active fluoride shell includes the following steps: A shell precursor is prepared by mixing rare earth source, fluorine source, alkali source and ligand, and then the modified perovskite quantum dots are added. After removing the solvent, the precursor is heat-treated under an inert atmosphere to allow the active fluoride to grow epitaxially on the surface of the quantum dots.

8. The preparation method according to claim 7, characterized in that, The heat treatment includes the following steps: First, raise the temperature to 270℃ and hold it there, then raise the temperature to 300~320℃ and hold it there.

9. The preparation method according to claim 5, characterized in that, It also includes epitaxially growing an inert fluoride shell on the surface of the active fluoride shell: An inert shell precursor is injected into a solution of the rare earth-doped perovskite quantum dot / fluoride core-shell heterogeneous nanomaterial and reacted under an inert atmosphere, allowing the inert fluoride to grow epitaxially on the surface of the active fluoride shell.

10. The application of the rare earth-doped perovskite quantum dot / fluoride core-shell heterogeneous nanomaterial as described in any one of claims 1-4 in the preparation of near-infrared photodetectors, biofluorescent probes, anti-counterfeiting inks, or spectral conversion films.

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