Fluorescence lifetime adjustable composite superlattice nanospheres, and preparation method and application thereof

Abstract

The application discloses a kind of fluorescent lifetime adjustable composite superlattice nanospheres and its preparation method and application, belong to nanometer luminescent material technical field.The application selects the quantum dot with the transition energy level difference less than the band gap of rare earth nanocrystal luminescent material, makes it and the rare earth nanocrystal luminescent material self-assembly form composite superlattice nanosphere, and realizes the energy transfer between the two based on the composite superlattice nanosphere structure, and then changes the transition probability of rare earth ion in composite superlattice nanosphere;By the selection of different band gap quantum dots, the fluorescent lifetime of composite superlattice nanosphere can be controlled, which is simple to operate and low in cost, and is expected to replace the existing rare earth nanocrystal luminescent material, solve the tailing problem caused by long fluorescent lifetime in stimulated radiation super-resolution imaging, and improve the imaging resolution.

Description

Technical Field

[0001] This invention specifically relates to a composite superlattice nanosphere with tunable fluorescence lifetime, its preparation method and application, belonging to the field of nanoluminescent materials technology. Background Technology

[0002] Rare earth ions possess a rich electronic energy level structure, capable of generating up to millions of intra-state transitions and emitting light across various wavelengths from ultraviolet to visible and near-infrared, earning them the title of a treasure trove of luminescence. Rare earth nanocrystalline luminescent materials, obtained by doping rare earth ions into rare earth nanocrystalline matrices, have become a highly promising functional material with significant development potential and application prospects. They exhibit remarkable characteristics such as good stability, narrow emission bands, strong penetrability, and low toxicity, attracting considerable attention in fields such as micro-nano optical devices, biomedical diagnostics, and super-resolution imaging. In particular, for stimulated emission depletion imaging modes in super-resolution imaging, rare earth nanocrystalline luminescent materials demonstrate great potential as super-resolution imaging probes due to their large Stokes-like shifts, narrow emission peaks, and good biocompatibility.

[0003] The inert rare-earth nanocrystalline matrix of rare-earth nanocrystalline luminescent materials does not emit light itself; its luminescence originates from the doped active rare-earth ions. However, due to the parity-forbidden nature of the transitions between the 4f electron configurations of rare-earth ions, the forbidden transitions are partially unblocked under low-symmetry local crystal fields, resulting in a long fluorescence lifetime for rare-earth ions. In stimulated emission super-resolution imaging, an excessively long fluorescence lifetime not only slows down the scanning imaging speed but also causes image tailing, affecting the imaging resolution. This limits the application of existing rare-earth nanocrystalline luminescent materials in stimulated emission super-resolution imaging. Summary of the Invention

[0004] To address the problem of excessively long fluorescence lifetime in existing rare-earth nanocrystalline luminescent materials, this invention proposes a composite superlattice nanosphere with tunable fluorescence lifetime, its preparation method, and its applications. This invention selects quantum dots with band gaps smaller than the transition energy level difference of rare-earth nanocrystalline luminescent materials, allowing them to self-assemble with the rare-earth nanocrystalline luminescent materials to form a composite superlattice nanosphere. Based on this composite superlattice nanosphere structure, energy transfer between the two is achieved, thereby altering the transition probability of rare-earth ions in the composite superlattice nanosphere. By selecting quantum dots with different band gaps, the fluorescence lifetime of the composite superlattice nanosphere can be regulated, with simple operation and low cost. This composite superlattice nanosphere is expected to replace existing rare-earth nanocrystalline luminescent materials, solving the trailing problem caused by excessively long fluorescence lifetime in stimulated emission super-resolution imaging and improving imaging resolution.

[0005] The technical solution of the present invention is as follows:

[0006] This invention provides a composite superlattice nanosphere with tunable fluorescence lifetime. The composite superlattice nanosphere is formed by the self-assembly of quantum dots with different band gaps and rare earth nanocrystalline luminescent materials. The rare earth nanocrystalline luminescent materials are rare earth ion-doped rare earth nanocrystals. The rare earth ions are +3 valent rare earth ions. The band gap of the quantum dots is smaller than the energy difference of one or more transition levels of the rare earth ions.

[0007] Furthermore, the rare-earth nanocrystalline luminescent material is one of hexagonal rare-earth ion-doped NaLuF4 nanocrystals, rare-earth ion-doped NaGdF4 nanocrystals, or rare-earth ion-doped NaYF4; the chemical formula of the rare-earth ion-doped NaLuF4 nanocrystals is NaLuF4:Ln. 3+ The rare earth ion-doped NaGdF4 nanocrystals have the chemical formula NaGdF4:Ln 3+ The rare earth ion-doped NaYF4 nanocrystals have the chemical formula NaYF4:Ln 3+ Ln 3+ Ln is a rare earth ion. 3+ Including Ce 3+ Yb 3+ Er 3+ Tm 3+ Ho 3+ 、Tb 3+ Dy 3+ 、Sm 3+ 、Nd 3+ and Pr 3+ One or more of them.

[0008] Furthermore, the rare earth nanocrystalline luminescent material is a core-shell structured rare earth nanocrystalline luminescent material formed on the basis of hexagonal rare earth ion-doped NaLuF4 nanocrystals and / or rare earth ion-doped NaGdF4 nanocrystals and / or rare earth ion-doped NaYF4 nanocrystals.

[0009] Furthermore, the chemical formula of the core-shell structured rare-earth nanocrystalline luminescent material is NaLuF4:Yb 3+ @NaLuF4:Er 3+ .

[0010] Furthermore, the quantum dot is a type of II-VI quantum dot.

[0011] Furthermore, the quantum dot is CdSe@CdS@ZnS.

[0012] The luminescence of existing rare-earth luminescent materials originates from the doped rare-earth ions. This invention, based on a composite superlattice nanosphere structure, achieves energy transfer between quantum dots and existing rare-earth nanocrystalline luminescent materials, thereby modulating the fluorescence lifetime of rare-earth ions. When the band gap of the selected quantum dots is smaller than the energy difference of one or more transition levels of rare-earth ions, the fluorescence lifetime of rare-earth ions can be regulated within the composite superlattice nanosphere structure by means of… The resonant energy transfer principle enables energy transfer from rare earth ions (donors) to quantum dots (acceptors), effectively reducing the fluorescence lifetime emitted by electron radiative transitions where the energy level difference is greater than the quantum dot band gap. Since different quantum dots have different band gaps, by selecting different types of quantum dots, the fluorescence lifetime of multi-level radiative transitions in composite superlattice nanospheres can be controllably reduced.

[0013] This invention also provides a method for preparing the above-mentioned composite superlattice nanospheres with tunable fluorescence lifetime, comprising the following steps:

[0014] S1. Dissolve sodium dodecyl sulfate in ultrapure water to obtain solution one;

[0015] S2. Mix oil-soluble rare-earth nanocrystalline luminescent material with quantum dots in cyclohexane, and then add the mixture dropwise to solution one under ultrasonic conditions to obtain solution two.

[0016] S3. Heat and stir the solution under an inert gas atmosphere until the cyclohexane evaporates completely. After the solution cools to room temperature, the product is separated by centrifugation and washed with deionized water to obtain water-soluble composite superlattice nanospheres.

[0017] Furthermore, in step S1, the ratio of sodium dodecyl sulfate dosage to the mass of ultrapure water is 1.5 mg / g.

[0018] Furthermore, in step S2, the molar ratio of the amount of rare earth nanocrystalline luminescent material added to the quantum dots is 1:100.

[0019] Further, in step S3, the temperature is raised to 60°C.

[0020] The composite superlattice nanospheres with tunable fluorescence lifetime provided by this invention can be applied to the preparation of rare-earth nanocrystalline luminescent probes with short fluorescence lifetime.

[0021] Unlike existing technologies, this invention has the following advantages:

[0022] 1. This invention provides a composite superlattice nanosphere with tunable fluorescence lifetime. It has good dispersibility and repeatability, and high degree of order. Interference images of its long-order arrangement can be observed under a transmission electron microscope. It can be applied to the preparation of rare earth nanoluminescent probes with short fluorescence lifetime and has good practical application prospects.

[0023] 2. Compared with existing rare-earth nanocrystalline luminescent materials, the fluorescence lifetime of this composite superlattice nanosphere is significantly reduced. This composite superlattice nanosphere utilizes a process from rare-earth nanocrystalline luminescent material as the donor to quantum dots as the acceptor. Resonant energy transfer effectively reduces the fluorescence lifetime emitted by electrons with transition energy levels greater than the quantum dot band gap as they transition from the excited state back to the ground state. Furthermore, by selecting quantum dots with different band gaps, the fluorescence lifetime of the composite superlattice nanospheres can be controllably reduced. This method is simple to operate and low in cost. The composite superlattice nanospheres are expected to solve the trailing problem caused by excessively long fluorescence lifetimes in existing rare-earth nanocrystalline luminescent materials in stimulated emission super-resolution imaging, thereby improving imaging resolution.

[0024] 3. This invention self-assembles quantum dots and rare-earth nanocrystalline luminescent materials to obtain composite superlattice nanospheres with tunable fluorescence lifetime. The preparation steps are simple and the cost is low. The quantum dots can be any type of group II-VI quantum dots. Thanks to the close packing of rare-earth nanocrystals and quantum dots in the composite superlattice nanosphere structure, the distance between them is... Within the effective range of resonant energy transfer (1-10 nm), energy transfer can be completed through long-range electric dipole-electric dipole interactions simply by the overlap of the fluorescence emission spectrum of the selected donor (rare-earth nanocrystals) and the absorption spectrum of the acceptor (quantum dots). Therefore, when the quantum dots and rare-earth nanocrystal luminescent materials used satisfy the following conditions... Under the premise of resonant energy transfer, this preparation method can use any rare earth nanocrystalline luminescent material prepared by any method as the raw material, and has a wide range of applicability. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the self-assembly of rare-earth nanocrystalline luminescent materials and quantum dots to form superlattice nanospheres in this invention.

[0026] Figure 2 The NaLuF4:50%Yb in the embodiments of the present invention 3+ @NaLuF4:10%Er 3+ Transmission electron microscope image of nanocrystalline luminescent material.

[0027] Figure 3 This is a transmission electron microscope (TEM) image of CdSe@CdS@ZnS quantum dots in an embodiment of the present invention.

[0028] Figure 4 The NaLuF4:50%Yb in the embodiments of the present invention 3+ @NaLuF4:10%Er 3+ Composite superlattice nanospheres formed by the self-assembly of nanocrystalline luminescent materials and CdSe@CdS@ZnS quantum dots.

[0029] Figure 5 The NaLuF4:50%Yb used in the comparative example of this invention 3+ @NaLuF4:10%Er 3+ Transmission electron microscopy image of rare earth nanocrystal self-assembled nanospheres.

[0030] Figure 6 The image shows the emission spectrum of the composite superlattice nanospheres in an embodiment of the present invention, with the inset showing a photograph of the composite superlattice nanosphere solution sample.

[0031] Figure 7 The rare-earth nanocrystalline luminescent material and the Er in the composite superlattice nanospheres in the embodiments of the present invention 3+ ion 4 F 9 / 2 A comparison of fluorescence lifetimes at different energy levels.

[0032] Figure 8 The rare-earth nanocrystalline luminescent material and the Er in the composite superlattice nanospheres in the embodiments of the present invention 3+ ion 4 S 3 / 2 A comparison of fluorescence lifetimes at different energy levels.

[0033] Figure 9 Er in the composite superlattice nanospheres in the embodiments of the present invention 3+ ion 4 S 3 / 2 Comparison of energy level and quantum dot band-edge exciton fluorescence lifetime.

[0034] Figure 10 This is a schematic diagram illustrating the energy transfer between the rare-earth nanocrystalline luminescent material and quantum dots in an embodiment of the present invention. Detailed Implementation

[0035] The present invention will be further described below with reference to the accompanying drawings and preferred embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0036] Unless otherwise specified, all materials and reagents used in the following examples are commercially available; and all methods used in the following examples are conventional methods.

[0037] This invention provides a composite superlattice nanosphere with tunable fluorescence lifetime. The composite superlattice nanosphere is formed by the self-assembly of quantum dots with different band gaps and rare earth nanocrystalline luminescent materials. The rare earth nanocrystalline luminescent materials are rare earth ion-doped rare earth nanocrystals. The rare earth ions are +3 valent rare earth ions. The band gap of the quantum dots is smaller than the energy difference of one or more transition levels of the rare earth ions.

[0038] In some preferred embodiments, the rare-earth nanocrystalline luminescent material may be one of hexagonal rare-earth ion-doped NaLuF4 nanocrystals, rare-earth ion-doped NaGdF4 nanocrystals, or rare-earth ion-doped NaYF4 nanocrystals; the chemical formula of the rare-earth ion-doped NaLuF4 nanocrystals is NaLuF4:Ln. 3+ The rare earth ion-doped NaGdF4 nanocrystals have the chemical formula NaGdF4:Ln 3+ The rare earth ion-doped NaYF4 nanocrystals have the chemical formula NaGdF4:Ln 3+ Ln 3+ Ln is a rare earth ion. 3+ Including Ce 3+ Yb 3+ Er 3+ Tm 3+ Ho 3+ 、Tb 3+ Dy 3+ 、Sm 3+ 、Nd 3+ and Pr 3+ One or more of them.

[0039] In some preferred embodiments, the rare earth nanocrystalline luminescent material may be a core-shell structured rare earth nanocrystalline luminescent material formed on the basis of rare earth ion-doped NaLuF4 nanocrystals and / or rare earth ion-doped NaGdF4 nanocrystals and / or rare earth ion-doped NaYF4 nanocrystals.

[0040] In some preferred embodiments, the core-shell structured rare-earth nanocrystalline luminescent material has the chemical formula NaLuF4:Yb 3+ @NaLuF4:Er 3+ .

[0041] In some preferred embodiments, the quantum dot may be one of the II-VI group quantum dots.

[0042] In some preferred embodiments, the quantum dots are CdSe@CdS@ZnS.

[0043] This invention also provides a method for preparing composite superlattice nanospheres with tunable fluorescence lifetime, comprising the following steps:

[0044] S1. Dissolve sodium dodecyl sulfate in ultrapure water to obtain solution one;

[0045] S2. Mix oil-soluble rare-earth nanocrystalline luminescent material with quantum dots in cyclohexane, and then add the mixture dropwise to solution one under ultrasonic conditions to obtain solution two.

[0046] S3. Heat and stir the solution under an inert gas atmosphere until the cyclohexane evaporates completely. After the solution cools to room temperature, the product is separated by centrifugation and washed with deionized water to obtain water-soluble composite superlattice nanospheres.

[0047] In some preferred embodiments, the ratio of sodium dodecyl sulfate added in step S1 to the mass of ultrapure water is 1.5 mg / g.

[0048] In some preferred embodiments, the molar ratio of rare earth nanocrystalline luminescent material to quantum dots in step S2 is 1:100.

[0049] In some preferred embodiments, the temperature is raised to 60°C in step S3.

[0050] The composite superlattice nanospheres with tunable fluorescence lifetime provided by this invention can be applied to the preparation of rare-earth nanocrystalline luminescent probes with short fluorescence lifetime.

[0051] The following specific embodiments further illustrate the fluorescent lifetime-tunable composite superlattice nanospheres of the present invention:

[0052] Example 1

[0053] This embodiment provides a composite superlattice nanosphere with tunable fluorescence lifetime (structural schematic shown in figure). Figure 1 As shown, the composite superlattice nanosphere is formed by the self-assembly of quantum dots and rare earth nanocrystalline luminescent materials; the rare earth nanocrystalline luminescent materials are rare earth ion-doped rare earth nanocrystals; the rare earth ions are +3 valent rare earth ions; the band gap of the quantum dots is smaller than the energy difference of one or more transition levels of the rare earth ions.

[0054] The rare-earth nanocrystalline luminescent material described in this embodiment is NaLuF4:Yb 3+ @NaLuF4:Er 3+ Yb 3+ The doping level is 50%, Er 3+ The doping amount is 10%, and the chemical formula of the rare earth nanocrystalline luminescent material can be represented as NaLuF4:50%Yb 3+ @NaLuF4:10%Er 3+ .

[0055] The quantum dots used in this embodiment are CdSe@CdS@ZnS, and the band gap of the quantum dots used is smaller than that of Er-doped rare-earth nanocrystalline luminescent materials. 3+ 4S 3 / 2 The energy level difference between energy levels is used in this embodiment to regulate Er. 3+ 4S 3 / 2 The lifetime of fluorescence generated by energy level transitions.

[0056] The method for preparing the fluorescence lifetime-tunable composite superlattice nanospheres includes the following steps:

[0057] S1. At room temperature, 15 mg of sodium dodecyl sulfate was weighed and ultrasonically dispersed in 10 g of ultrapure water to obtain solution one.

[0058] S2, as follows Figure 2 The transmission electron microscope image shows NaLuF4:50%Yb 3+ @NaLuF4:10%Er 3+ Rare earth nanocrystalline luminescent materials and such Figure 3 The CdSe@CdS@ZnS quantum dots shown in the transmission electron microscope image were mixed in a cyclohexane solution at a molar ratio of 1:100. Then, under ultrasonic assistance, the mixture was added dropwise to solution one to obtain solution two.

[0059] S3. The solution is transferred to a flask, heated to 60°C in an inert gas atmosphere, and stirred at a constant temperature for 0.5 to 1 hour. After the cyclohexane has evaporated, the solution is cooled to room temperature. The product is separated by centrifugation and washed with deionized water to obtain composite superlattice nanospheres.

[0060] like Figure 4 As shown, in the transmission electron microscope image of the composite superlattice nanospheres, interference patterns can be observed inside the superlattice nanospheres due to the long-range order of the particles.

[0061] Comparative Example 1

[0062] This comparative example provides a self-assembled nanosphere of rare-earth nanocrystalline luminescent material, which differs from Example 1 in that:

[0063] The nanospheres are formed by the self-assembly of rare-earth nanocrystalline luminescent materials under the influence of amphiphilic molecules; no quantum dots are added.

[0064] The preparation method of the rare earth nanocrystalline luminescent material self-assembled nanospheres differs from that in Example 1 in that:

[0065] CdSe@CdS@ZnS quantum dots were not added in step S2;

[0066] The remaining steps are the same as in Example 1, and will not be repeated here; the transmission electron microscope image of the rare earth nanocrystalline luminescent material self-assembled nanospheres prepared in this comparative example is shown below. Figure 5 As shown.

[0067] Optical performance characterization

[0068] Optical performance testing was conducted on the composite superlattice nanospheres with tunable fluorescence lifetime described in Example 1:

[0069] The composite superlattice nanospheres were dispersed in deionized water (e.g.) Figure 6 (As shown in the illustration), the upconversion emission spectrum of the composite superlattice nanospheres under 980 nm near-infrared laser excitation was monitored using an FLS980 fluorescence spectrometer. Figure 6 As shown, this composite material combines the luminescence characteristics of rare earth ions and quantum dots: it possesses narrow upconversion emission peaks in green (520–570 nm) and red (640–670 nm), which originate from Er₂O₃ and ¹⁴ ... 3+ Ionic 2 H 11 / 2 / 4 S 3 / 2 arrive 4 I 15 / 2 Energy level, and 4 F 9 / 2 arrive 4 I 15 / 2 The energy level configuration transitions; and the broadband emission peak at 600 nm, which belongs to the band-edge exciton radiative recombination luminescence of CdSe@CdS@ZnS quantum dots.

[0070] Furthermore, to verify the energy transfer process between the rare-earth nanocrystalline luminescent material and quantum dots in the composite superlattice nanospheres, the excited-state dynamics of the composite superlattice nanospheres were studied, and the changes in their fluorescence lifetime were compared. An external OPO laser was used with an FLS980 fluorescence spectrometer to monitor the sample under 980nm near-infrared pulsed laser excitation. 4 S 3 / 2 , 4 F 9 / 2 The fluorescence lifetime of band-edge excitons in energy levels. For example... Figure 7 As shown, the composite superlattice nanospheres formed by the self-assembly of rare earth nanocrystals and quantum dots... 4 F 9 / 2 The energy level lifetime is basically consistent with that of the rare-earth nanocrystal self-assembled nanospheres in Comparative Example 1 (which did not self-assemble with quantum dots), both being 450 μs, indicating a mismatch with the quantum dot band gap. 4 F 9 / 2 No energy transfer occurs between the energy level and the energy source; such as Figure 8 As shown, before and after composite 4 S 3 / 2 The fluorescence lifetime of the energy level was shortened from 340 μs to 270 μs, and the fluorescence lifetime of the quantum dot band-edge excitons in the composite superlattice nanospheres was... 4 S 3 / 2 The energy levels are all on the order of μs (e.g.) Figure 9 The above results indicate that the bandgap of quantum dots is matched. 4 S 3 / 2 In addition to the radiative reabsorption (PR) process, there is also an energy level between CdSe@CdS@ZnS quantum dots. The Resonant Energy Transfer Process (FRET) is illustrated in the diagram below. Figure 10 As shown.

[0071] Therefore, based on the composite superlattice structure proposed in this patent, energy transfer between rare earth nanocrystalline luminescent materials and quantum dots can be realized, and its fluorescence lifetime is significantly shortened. It is expected to replace existing rare earth nanocrystalline luminescent materials and be applied to the preparation of various short fluorescence lifetime rare earth nanocrystalline luminescent probes.

Claims

1. A composite superlattice nanosphere with tunable fluorescence lifetime, characterized in that, The composite superlattice nanospheres are formed by the self-assembly of quantum dots with different band gaps and rare earth nanocrystalline luminescent materials. The rare-earth nanocrystalline luminescent material is a rare-earth ion-doped nanocrystal; the rare-earth ions are +3 valent rare-earth ions; the band gap of the quantum dots is smaller than the energy difference of one or more transition levels of the rare-earth ions. The chemical formula of the rare-earth nanocrystalline luminescent material is NaLuF4:Yb 3+ @NaLuF4:Er 3+ ; The quantum dots are CdSe@CdS@ZnS.

2. A method for preparing composite superlattice nanospheres with tunable fluorescence lifetime as described in claim 1, characterized in that, Includes the following steps: S1. Dissolve sodium dodecyl sulfate in ultrapure water to obtain solution one; S2. Mix oil-soluble rare-earth nanocrystalline luminescent material with quantum dots in cyclohexane, and then add the mixture dropwise to solution one under ultrasonic conditions to obtain solution two. S3. Heat and stir the solution under an inert gas atmosphere until the cyclohexane evaporates completely. After the solution cools to room temperature, the product is separated by centrifugation and washed with deionized water to obtain water-soluble composite superlattice nanospheres.

3. The method for preparing a composite superlattice nanosphere with tunable fluorescence lifetime according to claim 2, characterized in that, In step S1, the ratio of sodium dodecyl sulfate to ultrapure water is 1.5 mg / g; in step S2, the molar ratio of rare earth nanocrystalline luminescent material to quantum dots is 1:

100.

4. The method for preparing a composite superlattice nanosphere with tunable fluorescence lifetime according to claim 2, characterized in that, In step S3, heat to 60°C.

5. Applying the composite superlattice nanospheres with tunable fluorescence lifetime as described in claim 1 to the preparation of rare-earth nanocrystalline luminescent probes with short fluorescence lifetime.

Images