High-luminous-efficiency rare earth luminous nanocrystal as well as preparation method and application thereof

Abstract

The invention provides a high-luminous-efficiency rare earth luminous nanocrystal as well as a preparation method and application thereof. According to the invention, the up-conversion (visible region) emission and the down-conversion (NIR-II, 1000-1700nm) emission of the same particle are enhanced at the same time by reconstructing the competitive relationship between ETU and CR in the NaREF4: Yb, Er nanocrystal. The in-vivo penetration depth and the imaging definition of the material are improved, and the material is suitable for small animal deep organ imaging and intraoperative navigation. Under the condition that the basic structure of the material is not changed, the same particle can be seen deeper, treated better and used more safely at the same time, and the material can be used for preparing an NIR II / visible dual-mode imaging probe, a light-operated drug-loaded nano platform, a visible excitation driven antibacterial / anti-tumor functional dressing, high-contrast anti-counterfeiting and display ink and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of nanomaterials, in particular to a rare earth luminescent nanocrystal with high luminescent efficiency and a preparation method and application thereof. BACKGROUND

[0002] Upconversion Nanoparticles (UCNPs) are a class of nanomaterials that can convert low-energy photons (such as near-infrared light) into high-energy photons (such as visible or ultraviolet light). This process is called "upconversion luminescence" and belongs to the anti-Stokes luminescence phenomenon, which is achieved through nonlinear optical mechanisms (such as excited-state absorption, energy transfer upconversion). UCNPs are usually composed of an inorganic matrix (such as NaYF4) doped with rare earth ions (such as Yb 3+ , Er 3+ , Tm 3+ ). They have the characteristics of narrow-band emission, good light stability, high biocompatibility, strong tissue penetration, and no background fluorescence interference. Their applications cover biological imaging, targeted therapy, solar cells, optical anti-counterfeiting, and super-resolution microscopy.

[0003] Upconversion Nanoparticles are widely used in biological imaging, sensing, and display due to their resistance to spontaneous fluorescence, deep penetration, and multi-color emission. Improving their luminescent brightness and channel selectivity usually relies on: enhancing energy transfer upconversion (ETU) by increasing rare earth doping concentration (such as high Er or high Yb), but high concentration easily introduces strong cross relaxation (CR) leading to quenching; inhibiting surface quenching by constructing core-shell structure, but the fine regulation of energy level energy diversion is limited; changing the local field by changing the ligand or solvent polarity, but lacking strategies for programmable regulation of internal energy network.

[0004] Cetyltrimethylammonium bromide (CTAB) is a cationic quaternary ammonium salt surfactant, its molecular structure contains both hydrophilic head and hydrophobic long-chain alkyl tail, which can form micelles in aqueous solution and significantly reduce surface tension. The most important property of CTAB is that its cationic head can strongly adsorb negatively charged substances through electrostatic interaction, such as binding with DNA molecules and precipitating them, or guiding the ordered nucleation and growth of negatively charged noble metal salts on the micelle template. Based on these characteristics, CTAB is widely used in molecular biology as a component of lysis buffer for DNA extraction to isolate genomic DNA; in nanomaterial synthesis, it is often used as a structure-directing agent to prepare specific nanostructures such as gold nanorods and mesoporous silica with controllable morphology. SUMMARY

[0005] The purpose of the present application is to overcome the shortcomings and deficiencies of the prior art, and to provide a rare earth luminescent nanocrystal with high luminescent efficiency.

[0006] Another object of the present application is to provide the preparation method of the high luminescent efficiency rare earth luminescent nanocrystal.

[0007] Another object of the present application is to provide the application of the high luminescent efficiency rare earth luminescent nanocrystal.

[0008] The object of the present application is achieved by the following technical solutions:

[0009] The preparation method of the high luminescent efficiency rare earth luminescent nanocrystal comprises the following steps:

[0010] (1) heating the aqueous solution of rare earth salt to dryness, adding oleic acid and 1-octadecene, and then reacting after temperature rising and keeping, to obtain a rare earth-oleic acid complex;

[0011] (2) adding a surfactant into the rare earth-oleic acid complex, mixing, and then removing the solvent by temperature rising, to obtain a surfactant-rare earth complex mixed solution;

[0012] (3) adding a methanol solution containing ammonium fluoride and sodium hydroxide into the surfactant-rare earth complex mixed solution, mixing, making the particles nucleate, removing the solvent by temperature rising, and excluding air and filling a protective atmosphere;

[0013] (4) heating and continuously stirring under the protective atmosphere, making the particles gradually grow, cooling after the reaction is completed, adding anhydrous ethanol to precipitate the product, centrifugally collecting the precipitate, and washing, to obtain the high luminescent efficiency rare earth luminescent nanocrystal.

[0014] The rare earth salt in step (1) comprises at least one of erbium salt, ytterbium salt, thulium salt and yttrium salt; and preferably comprises at least one of erbium salt or ytterbium salt.

[0015] The rare earth salt is all chloride hexahydrate, which is prepared into an aqueous solution before use.

[0016] The ratio of the rare earth salt to the oleic acid in step (1) is 1 mmol: 6-60 mL.

[0017] The heating in step (1) is heating to 100-120℃.

[0018] The reaction condition after temperature rising in step (1) is temperature rising to 140-170℃ for 10-30 min.

[0019] The surfactant in step (2) comprises at least one of CTAB, CTAC and NaBr; and preferably is CTAB.

[0020] The surfactant in step (2) is prepared into an ethanol solution before adding.

[0021] The ratio of the surfactant to the rare earth atom in the rare earth-oleic acid complex in step (2) is 0.5-80 mg: 1 mmol; preferably 2.5 mg: 1 mmol.

[0022] The temperature rising and solvent evaporation condition in step (2) is to heat to 110-130°C for 10-30 min.

[0023] The methanol solution containing ammonium fluoride and sodium hydroxide in step (3) is a methanol solution containing 4.0 mmol of ammonium fluoride and 2.5 mmol of sodium hydroxide.

[0024] The ratio of the methanol solution containing ammonium fluoride and sodium hydroxide to the rare earth atom in the surfactant-complex mixed solution in step (3) is 3-10 mL: 1 mmol.

[0025] The temperature rising and solvent evaporation condition in step (3) is to heat to 110-130°C for 10-30 min.

[0026] The protective atmosphere in steps (3) and (4) is one of argon or high-purity nitrogen atmosphere.

[0027] The heating and continuous stirring condition in step (4) is to stir at 200-500 rpm for 40-90 min at 300-310°C.

[0028] The cooling in step (4) is to cool to room temperature.

[0029] The centrifugation condition in step (4) is to centrifuge at 8000-12000 rpm for 5-20 min.

[0030] A high-luminous-efficiency rare earth luminescent nanocrystal prepared by the above preparation method.

[0031] A preparation method of a high-luminous-efficiency rare earth luminescent nanocrystal with an inert shell structure, comprising the following steps:

[0032] (5) heating a rare earth salt aqueous solution to dryness, adding oleic acid and 1-octadecene, heating and then holding for reaction, and cooling to obtain a rare earth-oleic acid complex;

[0033] (6) dissolving the high-luminous-efficiency rare earth luminescent nanocrystal in cyclohexane, adding the rare earth-oleic acid complex, mixing, heating and evaporating the solvent to obtain a nanocrystal-complex mixed solution;

[0034] (7) adding a methanol solution containing ammonium fluoride and sodium hydroxide to the nanocrystal-complex mixed solution, mixing, heating and evaporating the solvent, and excluding air and filling a protective atmosphere;

[0035] (8) After the reaction is completed, the product is precipitated by adding anhydrous ethanol under heating and continuous stirring, and the precipitate is collected by centrifugation and washed to obtain the high-luminous-efficiency rare earth luminescent nanocrystal with inert shell structure.

[0036] The molar ratio of the rare earth element in the rare earth salt to the rare earth element in the high-luminous-efficiency rare earth luminescent nanocrystal is 1:1-10; preferably 1:5.

[0037] The rare earth salt in step (5) includes yttrium salt.

[0038] The yttrium salt is yttrium chloride hexahydrate.

[0039] The ratio of the rare earth salt in step (5) to oleic acid is 1 mmol: 6-200 mL.

[0040] The heating in step (5) is heating to 100-120°C.

[0041] The reaction condition of the temperature rising and holding after the temperature rising in step (5) is rising the temperature to 140-170°C and holding for 10-30 min.

[0042] The condition of the solvent evaporation by temperature rising in step (6) is rising the temperature to 110-130°C and holding for 10-30 min.

[0043] The methanol solution containing ammonium fluoride and sodium hydroxide in step (7) is a methanol solution containing 4.0 mmol of ammonium fluoride and 2.5 mmol of sodium hydroxide.

[0044] The ratio of the methanol solution containing ammonium fluoride and sodium hydroxide in step (7) to the surfactant-complex mixed solution of rare earth atoms is 3-10 mL: 1 mmol.

[0045] The condition of the solvent evaporation by temperature rising in step (7) is rising the temperature to 110-130°C and holding for 10-30 min.

[0046] The protective atmosphere in steps (7) and (8) is one of argon or high-purity nitrogen atmosphere.

[0047] The condition of the heating and continuous stirring in step (8) is stirring at 200-500 rpm for 60-120 min at 300-310°C.

[0048] The cooling in step (8) is cooling to room temperature.

[0049] The centrifugation in step (8) is centrifugation at 8000-12000 rpm for 5-20 min.

[0050] A high luminescent efficiency rare earth luminescent nanocrystal with an inert shell structure is prepared by the above preparation method.

[0051] The application of the above high luminescent efficiency rare earth luminescent nanocrystal and / or high luminescent efficiency rare earth luminescent nanocrystal with an inert shell structure in preparing light-controlled drug-loaded particles.

[0052] The application of the above high luminescent efficiency rare earth luminescent nanocrystal and / or high luminescent efficiency rare earth luminescent nanocrystal with an inert shell structure in preparing imaging probes.

[0053] The present application has the following advantages and effects relative to the prior art:

[0054] The present application provides a high luminescent efficiency rare earth luminescent nanocrystal and a preparation method and application thereof. Under the premise of not changing the host crystal phase and particle size level, the competition relationship between the internal ETU and CR of NaREF4:Yb,Er nanocrystals is reconstructed, the up-conversion (visible region) and down-conversion (NIR-II, 1000-1700 nm) emissions of the same particle are simultaneously enhanced, and a dual-optimal combination window of UC and NIR-II is obtained. The NIR II signal is stronger, and the in vivo penetration depth and imaging clarity are improved, which is suitable for small animal deep organ imaging and intraoperative navigation. The UC enhancement can more effectively activate the red light response photosensitizer and photothermal material, improve the photodynamic / photothermal treatment efficiency, and reduce the excitation power requirement. The present application can be used for preparing NIR II / visible dual-mode imaging probes, light-controlled drug-loaded nanometer platforms, visible excitation driven antibacterial / antitumor functional dressings, and high-contrast anti-counterfeiting and display inks, etc. without changing the basic structure of the material. BRIEF DESCRIPTION OF DRAWINGS

[0055] Figure 1 Figure 1 is a transmission electron microscope photo of the CTAB-modified NaErF4:CTAB particles prepared in Example 1 and the NaErF4 particles without CTAB modification, and the scale is 200 nm.

[0056] Figure 2 Figure 2 is an elemental analysis of the CTAB-modified NaErF4:CTAB particles prepared in Example 1.

[0057] Figure 3 Figure 3 is the up-conversion luminescence and near-infrared two-region luminescence spectral curve of the NaErF4:CTAB (doping concentration is 0, 0.5, 2.5, 5, 25, 50, and 80 mg CTAB / mmol Er) nanoparticles under 980 nm excitation in Example 3.

[0058] Figure 4is the upconversion luminescence spectra curve of NaErF4:CTAB and NaErF4:NaBr nanoparticles under 980 nm excitation in Example 5.

[0059] Figure 5 is the TEM image of the particles synthesized with different holding time (20, 40, 90 min) in Example 6, the scale is 200 nm.

[0060] Figure 6 is the upconversion luminescence and near-infrared two-region luminescence spectra curve of pure NaErF4 (Er), NaErF4:CTAB (Er+CTAB), core-shell structured NaErF4@NaYF4, core-shell structured NaErF4:CTAB@NaYF4 (Er+CTAB@Y) under 980 nm excitation in Example 7.

[0061] Figure 7 is the upconversion luminescence picture of pure NaErF4 (Er), NaErF4:CTAB (Er+CTAB), core-shell structured NaErF4@NaYF4, core-shell structured NaErF4:CTAB@NaYF4 (Er+CTAB@Y) under 980 nm excitation in Example 7.

[0062] Figure 8 is the luminescence enhancement multiple of NaYbF4:2%Er particles doped with different CTAB concentration (0, 2.5, 5, 25 mg / mmol RE) relative to undoped NaYbF4:2%Er particles at different wavelengths (407, 539, 659, 803, 1540 nm) in Example 8.

[0063] Figure 9 is the upconversion luminescence and near-infrared two-region luminescence spectra curve of NaYbF4:Er,CTAB particles (the mole fraction of Er is 1%, 2%, 4%, 8%, 16%, 32% respectively) under 980 nm excitation in Example 9. DETAILED DESCRIPTION

[0064] The application will be further described in conjunction with the examples and the drawings, but the embodiments of the application are not limited thereto.

[0065] In the following examples, if the specific experimental conditions are not specified, the general experimental conditions or the experimental conditions suggested by the reagent company are usually used. The materials, reagents, etc. used, if not specifically stated, are reagents and materials obtained from commercial channels.

[0066] Example 1 Synthesis of CTAB-doped NaErF4 upconversion nanoparticles

[0067] (1) Add an aqueous solution containing 0.2 mmol of ErCl3-6H2O [erbium (III) chloride hexahydrate] into a 100 mL three-necked flask, and heat to 110°C under continuous stirring (at a speed of about 300 rpm) until the water is completely evaporated; add 6 mL of oleic acid and 15 mL of 1-octadecene in sequence, heat to 156°C and keep for 20 min, so that the Er 3+ is fully complexed with the oleic acid to form a stable Er oleate complex, and then cool to room temperature.

[0068] (2) Dissolve cetyltrimethylammonium bromide (CTAB) powder in deionized water to prepare a CTAB stock solution with a concentration of 20 mg / mL, take an appropriate amount of the stock solution and add to anhydrous ethanol to prepare a 5 mL ethanol solution containing 0.5 mg of CTAB (2.5 mg of CTAB per mmol of Er), and then add the Er oleate complex obtained in step (1), mix thoroughly, heat to 120°C and keep for 20 min, and evaporate the ethanol until the solution is clear.

[0069] (3) Add 5 mL of a methanol solution containing 4.0 mmol of ammonium fluoride (NH4F) and 2.5 mmol of sodium hydroxide (NaOH) to the reaction system, mix thoroughly, heat to 120°C and keep for 20 min to completely remove the methanol; alternately perform vacuum pumping and argon filling three times at 120°C to remove residual methanol and dissolved oxygen, and finally maintain an argon protection environment.

[0070] (4) Under an argon protection atmosphere, heat the reaction system to 304°C and keep for 60 min to promote the crystallization and growth of the NaErF4 nanocrystals, and maintain stable stirring (at a speed of about 500 rpm) during the process; after the reaction is completed, cool to room temperature, add an equal volume of anhydrous ethanol to precipitate the product, centrifuge at a speed of 10000 rpm for 10 min to collect the precipitate, and perform resuspension-centrifugation washing three times with anhydrous ethanol to remove unreacted precursors and surface residual small molecules; finally, disperse the precipitate in cyclohexane for standby, and obtain NaErF4:CTAB nanoparticles.

[0071] In addition, the NaErF4 nanoparticles for comparison are prepared by referring to the above method but omitting step (2).

[0072] It should be noted that water and oxygen should be strictly avoided from re-entering the high-temperature system during the entire reaction process, so as to ensure the crystal phase structure and luminescent performance of the final product.

[0073] Example 2 Characterization of Nanoparticles

[0074] 2.1 Conventional characterization experiments

[0075] The NaErF4and NaErF4:CTAB nanoparticles prepared in Example 1 were characterized using TEM, EDS, XRD and other common methods.

[0076] 2.2 Luminescence performance detection

[0077] To verify the upconversion luminescence effect of the nanoparticles, the nanoparticles were dispersed in cyclohexane (or deionized water) and loaded into a 1 cm quartz cuvette. A 980 nm continuous wave (CW) laser (0-1500 mW) was used for excitation, and a fiber-coupled spectrometer was used to detect the visible light emission (detection range 300-900 nm). An InGaAs array spectrometer was used to detect the near-infrared emission (detection range 900-1700 nm).

[0078] 2.3 Characterization results

[0079] The experimental results are shown in Table 1, and the specific analysis results are as follows: Figures 1-2

[0080] (1) Morphological characteristics: The particle morphology changed from 30-40 nm spherical particles without CTAB doping to disc-shaped particles with a diameter of 69.82 nm and a thickness of 29.53 nm;

[0081] (2) Structural characteristics: HRTEM analysis showed that there were multiple lattice fringes on the surface of the particles, and the "twisted braid" structure was clearly visible on the surface, with a fringe spacing of 0.2132 nm (larger than the 0.1831 nm of pure NaErF4particles);

[0082] (3) Composition characteristics: Elemental mapping results showed that the atomic concentrations of Na (7.07%), Er (9.71%), F (82.66%), Br (0.42%), and Cl (0.14%) in the particles;

[0083] (4) Crystal structure: The XRD peak position was the same as that of the NaErF4particles without CTAB doping, showing a β-NaYF4structure with the same hexagonal lattice;

[0084] (5) Luminescence performance: Under 980 nm excitation, the visible light emission (400-750 nm) and near-infrared two-region emission (1400-1700 nm) intensity significantly increased, and the red-green ratio improved, with the 660 nm red light peak as the dominant.

[0085] Example 3 Effect of CTAB dopant amount on performance of NaErF4nanoparticles

[0086] 3.1 Preparation of nanoparticles by adjusting the CTAB dopant amount

[0087] ​NaErF4:CTAB nanoparticles were prepared according to the method of Example 1, except that the concentration of CTAB in step (2) was adjusted to 0, 0.5, 2.5, 5, 25, 50, 60, 70, 80 mg CTAB / mmol Er.

[0088] 3.2 Characterization results

[0089] The characterization test was performed according to the method of Example 2, and the experimental results are shown in Figure 3 , and the specific results are as follows:

[0090] (1) Morphological characteristics: At low doping concentrations (0.5, 2.5, 5, 25, 50 mg CTAB / mmol NaErF4), the particles changed from 30-40 nm spherical shape to 140 nm in diameter and 60 nm in thickness disc-shaped, and spontaneously formed linear assemblies on the TEM copper mesh; at high doping concentrations (60, 70, 80 mg CTAB / mmol NaErF4), the particles returned to 30 nm or so spherical shape with spiky ligands on the surface;

[0091] (2) Luminescence performance: The visible light emission (400-750 nm) intensity of all doped samples under 980 nm excitation was significantly higher than that of the undoped sample, and the near-infrared two-zone emission (1400-1700 nm) intensity of some samples was also enhanced. Among them, the doped sample of 2.5 mg CTAB / mmol Er exhibited the strongest visible light emission.

[0092] Example 4 Removal of surface ligands of NaErF4:CTAB nanoparticles

[0093] 4.1 Removal of surface ligands

[0094] 5 mL of NaErF4:CTAB cyclohexane solution doped with different concentrations of CTAB prepared in Example 1 and Example 3 was mixed with 5 mL of 1 mol / L hydrochloric acid aqueous solution, and after shaking for 1 minute, water bath ultrasonic treatment was performed for 20 minutes; stand for 20 minutes until the solution is layered, carefully suck the upper aqueous solution and transfer to a new test tube, discard the lower liquid; add an equal volume of ethanol to the aqueous solution for washing, centrifuge at 10000 rpm for 20 minutes to collect the precipitate; redispersed the precipitate in aqueous solution, repeated washing three times, finally the particles were dispersed in 5 mL of aqueous solution for spectral test.

[0095] 4.2 Experimental results

[0096] NaErF4:CTAB nanoparticles after removing surface ligands still keep good luminescent properties, and the visible light (400-750 nm) and near-infrared two-region light (1400-1700 nm) intensities under 980 nm excitation are significantly higher than those of pure NaErF4 particles without doping.

[0097] Example 5 Comparison of doping of CTAB with other surfactants

[0098] 5.1 Doping treatment using different surfactants

[0099] NaErF4 nanoparticles were prepared according to the same method of Example 1, except that CTAB doping was replaced by cetyltrimethylammonium chloride (CTAC) or sodium bromide (NaBr), and the molar fraction of the added amount was equivalent to the amount of CTAB introduced in Example 1, i.e. 2.5 mg CTAB / mmol NaErF4.

[0100] 5.2 Experimental results

[0101] The experimental results are shown in Table 1. Figure 4 As shown in Table 1, the results show that, under the condition of CTAC, the prepared NaErF4:CTAC particles are disc-shaped with a diameter of 55.52 nm and a thickness of 21.28 nm; under the condition of NaBr, the particles are spherical with a diameter of 23.15 nm. However, both of the particles do not show obvious luminescence enhancement.

[0102] Example 6 Control of particle morphology by holding time

[0103] 6.1 Preparation using different holding times

[0104] Nanoparticles were prepared according to the method of Example 1, except that the holding time in step (1) was adjusted to 20, 40 and 90 minutes, respectively, and then the particles were characterized according to the method of Example 2.

[0105] 6.2 Experimental results

[0106] The experimental results are shown in Table 2. Figure 5 As shown in Table 2, the results show that, when the holding time is 20 minutes, the particles are basically spherical with a diameter of 20.69 nm; when the holding time is 40 minutes, the particles are disc-shaped with a diameter of 32.86 nm and a thickness of 19.33 nm; and when the holding time is 90 minutes, the particles are further increased to disc-shaped with a diameter of 54.41 nm and a thickness of 25.06 nm.

[0107] Example 7 Synthesis of CTAB-doped NaErF4 core / inert shell upconversion nanoparticles

[0108] 7.1 Preparation method

[0109] (1) Add 0.04 mmol YCl3.6H2O (0.2 times the molar equivalent of the core particles) into a 100 mL three-necked flask, and dehydrate at about 110°C. Add 6 mL of oleic acid and 15 mL of 1-octadecene in turn, heat to 156°C and keep for 10 min to form a Y oleate precursor solution. Cool to room temperature;

[0110] (2) Add the pre-prepared NaErF4:CTAB core particles dispersed in cyclohexane (different CTAB-doped nanoparticles obtained in Example 3, equivalent to 0.2 mmol of rare earth) into the Y oleate precursor at room temperature. Heat to 120°C and keep until the solution is clear and no solvent is volatilized;

[0111] (3) Add 5 mL of a methanol solution containing 4.0 mmol of NH4F and 2.5 mmol of NaOH into the system, mix thoroughly, heat to 120°C and keep, and completely remove the methanol; alternately perform vacuum pumping and argon filling three times at about 120°C to remove residual solvents and oxygen, and finally maintain an argon protection environment;

[0112] (4) Under argon protection, heat the system to 304°C and keep for 1.5 hours to promote the epitaxial growth of an inert shell (such as NaYF4) on the core surface; after the reaction is cooled to room temperature, add anhydrous ethanol to precipitate the product, and centrifuge at a speed of 10000 rpm to collect the precipitate. After ethanol washing, disperse the product in 20 mL of cyclohexane to obtain NaErF4:CTAB@NaYF4 core / shell structure nanoparticles.

[0113] It should be noted that the entire reaction process should be kept dry and inert atmosphere to avoid undercrystallization or surface defects of the shell.

[0114] 7.2 Characterization results

[0115] The characterization was performed according to the method of Example 2, and the experimental results are shown in Table 1. Figures 6-7 The results show that the prepared NaErF4:CTAB@NaYF4 core / shell structure nanoparticles have the following characteristics:

[0116] (1) For the core particles doped with a low concentration of CTAB (2.5 mg of CTAB per mmol of NaErF4), NaYF4 can form a core-shell structure on the surface of the particles, and significantly enhance the upconversion luminescence performance of the particles;

[0117] (2) For the core particles doped with a high concentration of CTAB (60, 80 mg of CTAB per mmol of NaErF4), the Y oleate precursor cannot form a core-shell structure with the core particles due to the blocking effect of the ligands on the surface of the core particles, but instead forms NaYF4 particles by self-nucleation;

[0118] (3) The upconversion luminescence intensity of NaErF4:CTAB@NaYF4 composite particles at 660 nm is 149.3 times higher than that of pure NaErF4 particles, and the near-infrared two-region luminescence intensity at 1523 nm is 10.7 times higher. The obtained core / shell structure further improves the luminescence quantum efficiency by reducing the surface quenching effect, while retaining the energy micro-region effect introduced by CTAB, which significantly promotes red light and near-infrared two-region emission.

[0119] Example 8 Synthesis and luminescence performance of NaYbF4:Er,CTAB particles

[0120] 8.1 Preparation of Yb, Er doped nanoparticles by adjusting different CTAB addition amounts

[0121] NaYbF4:Er,CTAB particles were prepared according to the same method of Example 1, except that the rare earth element composition of the particles was adjusted. In Example 1, 0.2 mmol of ErCl3·6H2O was adjusted to 0.196 mmol of YbCl3·6H2O and 0.04 mmol of ErCl3·6H2O (specifically NaYbF4:2% Er). The doping concentration of CTAB was also changed, specifically set to 0, 2.5, 5, and 25 mg of CTAB per mmol of RE (RE is the total moles of Yb and Er).

[0122] 8.2 Experimental results

[0123] The experimental results are shown in Table 8.2. Figure 8 As shown in Table 8.2, the results show that the upconversion luminescence and near-infrared luminescence intensity of all CTAB doped NaYbF4:2% Er,CTAB particles are significantly higher than that of pure NaYbF4:2% Er without doping. The doping concentration of 5 mg of CTAB per mmol of RE produces the strongest visible light enhancement (main emission peaks at 407 nm, 539 nm, 659 nm, and 803 nm). The doping concentration of 2.5 mg of CTAB per mmol of RE corresponds to particles with the strongest near-infrared two-region luminescence (1540 nm), which is 63.2 times higher than that of pure NaYbF4:2% Er.

[0124] Example 9 Luminescence performance of NaYbF4:Er,CTAB particles

[0125] 9.1 Preparation of Yb, Er doped nanoparticles by adjusting different rare earth raw material ratios

[0126] NaYbF4:Er, CTAB particles were prepared in the same way as in Example 7, except that the rare earth element composition of the particles was adjusted, specifically NaYbF4:Er (molar fraction of Er was 1%, 2%, 4%, 8%, 16%, 32%, respectively), while the doping amount of CTAB was fixed at 2.5 mg CTAB / mmol RE (RE is the total amount of Yb and Er in moles). Undoped NaYbF4:Er (molar fraction of Er was 2%, 4%, 8%) was also synthesized as a control group.

[0127] 9.2 Experimental results

[0128] The experimental results are shown in Table 1, and the specific analysis results are as follows: Figure 9

[0129] (1) Compared with NaYbF4:Er without CTAB doping, the CTAB-modified particles with the same rare earth doping ratio showed obvious upconversion luminescence (main emission peaks at 545 nm and 660 nm) and near-infrared two-region (1540 nm) luminescence enhancement. The particles emitted bright red light under excitation conditions;

[0130] (2) The particles with 8% Er molar fraction showed the strongest near-infrared two-region (NIR-II) and visible light luminescence;

[0131] (3) The power-dependent curve of NaYbF4:8% Er, CTAB particles showed a phenomenon similar to photon avalanche;

[0132] (4) With the increase of the molar fraction of Er, the red-to-green ratio (R / G) of the NaYbF4:Er, CTAB particles gradually increased. The red-to-green ratio of the three NaYbF4:Er particles (2%, 4%, 8%) without CTAB doping was less affected by the excitation power; after modification with CTAB, the red-to-green ratio of the particles of the three components showed obvious power dependence, generally showing that the red-to-green ratio increased continuously with the increase of the excitation power. When the molar fraction of Er reached 32%, the red-to-green ratio of the NaYbF4:Er, CTAB particles was no longer affected by the excitation power. Similarly, the red-to-green ratio of the NaErF4:CTAB particles was also not affected by the excitation power. It can be considered that when the doping concentration of Er is greater than 32%, the cross-relaxation (CR) process dominates in the particles, and the red-to-green ratio is no longer regulated by the excitation power.

[0133] The above examples are the preferred embodiments of the present application, but the embodiments of the present application are not limited to the above examples, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application should be equivalent replacement methods, which are all included in the protection scope of the present application.​

Claims

1. A method for preparing high-luminescence-efficiency rare-earth luminescent nanocrystals, characterized in that... Includes the following steps: (1) Heat the rare earth salt aqueous solution until it evaporates to dryness, add oleic acid and 1-octadecene, raise the temperature and keep it at the temperature to react, and obtain the rare earth-oleic acid complex. (2) Add the surfactant to the rare earth-oleic acid complex, mix well, and heat to remove the solvent to obtain a surfactant-rare earth complex mixed solution. (3) Add a methanol solution containing ammonium fluoride and sodium hydroxide to the surfactant-rare earth complex mixture, mix well, nucleate the particles, heat up to remove the solvent, remove the air and fill with a protective atmosphere; (4) Heating and stirring under a protective atmosphere to allow the particles to grow gradually. After the reaction is complete, cooling is performed, anhydrous ethanol is added to precipitate the product, the precipitate is collected by centrifugation, washed, and high-efficiency rare earth luminescent nanocrystals are obtained.

2. The method for preparing high-luminescence-efficiency rare-earth luminescent nanocrystals according to claim 1, characterized in that: The rare earth salts mentioned in step (1) include at least one of erbium salts, ytterbium salts, thulium salts, and yttrium salts; All rare earth salts mentioned are chloride hexahydrates and should be prepared as aqueous solutions before use.

3. The method for preparing high-luminescence-efficiency rare-earth luminescent nanocrystals according to claim 1, characterized in that: The ratio of rare earth salt to oleic acid in step (1) is 1 mmol: 6-60 mL; The heating described in step (1) is heating to 100-120°C; The conditions for the heating and holding reaction described in step (1) are to heat to 140-170 degrees Celsius and hold for 10-30 minutes.

4. The method for preparing high-luminescence-efficiency rare-earth luminescent nanocrystals according to claim 1, characterized in that: The surfactant mentioned in step (2) includes at least one of CTAB, CTAC, and NaBr; The surfactant mentioned in step (2) is prepared as an ethanol solution before being added; The ratio of rare earth atoms in the surfactant and rare earth-oleic acid complex described in step (2) is 0.5–80 mg: 1 mmol; The conditions for removing the solvent by heating in step (2) are to heat to 110-130℃ and hold for 10-30 minutes.

5. The method for preparing high-luminescence-efficiency rare-earth luminescent nanocrystals according to claim 1, characterized in that: The methanol solution containing ammonium fluoride and sodium hydroxide mentioned in step (3) is a methanol solution containing 4.0 mmol of ammonium fluoride and 2.5 mmol of sodium hydroxide; In step (3), the ratio of rare earth atoms in the methanol solution containing ammonium fluoride and sodium hydroxide to the surfactant-complex mixture is 3-10 mL: 1 mmol. The conditions for removing the solvent by heating in step (3) are to heat to 110-130℃ and hold for 10-30 minutes; The protective atmosphere described in steps (3) and (4) is either argon or high-purity nitrogen.

6. The method for preparing high-luminescence-efficiency rare-earth luminescent nanocrystals according to claim 1, characterized in that: The heating and continuous stirring conditions described in step (4) are: stirring at 200-500 rpm for 40-90 min at 300-310℃; The cooling described in step (4) is cooling to room temperature; The centrifugation conditions described in step (4) are centrifugation at 8000-12000 rpm for 5-20 min.

7. A high-luminescence-efficiency rare-earth luminescent nanocrystal, prepared by any one of the preparation methods described in claims 1 to 6.

8. A method for preparing high-efficiency rare-earth luminescent nanocrystals with an inert shell structure, characterized in that... Includes the following steps: (5) Heat the rare earth salt aqueous solution until it evaporates to dryness, add oleic acid and 1-octadecene, heat up and keep the temperature to react, and then cool to obtain the rare earth-oleic acid complex. (6) Dissolve the high luminous efficiency rare earth luminescent nanocrystals according to any one of claims 1 to 7 in cyclohexane, add them to the rare earth-oleic acid complex, mix well, heat up to evaporate the solvent, and obtain a nanocrystal-complex mixed solution. (7) Add a methanol solution containing ammonium fluoride and sodium hydroxide to the nanocrystal-complex mixed solution, mix well, heat to remove the solvent, remove air, and then fill with a protective atmosphere. (8) Under a protective atmosphere, heat and stir continuously. After the reaction is completed, cool and add anhydrous ethanol to precipitate the product. Centrifuge to collect the precipitate, wash and obtain high-efficiency rare earth luminescent nanocrystals with an inert shell structure. The molar ratio of rare earth elements in the rare earth salt to rare earth elements in the high-efficiency rare earth luminescent nanocrystals is 1:1 to 10. The rare earth salts mentioned in step (5) include yttrium salts; The yttrium salt mentioned is yttrium chloride hexahydrate; The ratio of rare earth salt to oleic acid in step (5) is 1 mmol: 6-200 mL; The heating described in step (5) is to heat to 100-120°C; The conditions for the heating and holding reaction described in step (5) are to heat to 140-170 degrees Celsius and hold for 10-30 minutes; The conditions for removing the solvent by heating in step (6) are to heat to 110-130℃ and hold for 10-30 minutes; The methanol solution containing ammonium fluoride and sodium hydroxide mentioned in step (7) is a methanol solution containing 4.0 mmol of ammonium fluoride and 2.5 mmol of sodium hydroxide; The ratio of rare earth atoms in the methanol solution containing ammonium fluoride and sodium hydroxide and the surfactant-complex mixture in step (7) is 3-10 mL: 1 mmol; The conditions for removing the solvent by heating in step (7) are to heat to 110-130℃ and hold for 10-30 minutes; The protective atmosphere described in steps (7) and (8) is either argon or high-purity nitrogen. The heating and continuous stirring conditions described in step (8) are: stirring at 200-500 rpm for 60-120 min at 300-310°C; The cooling described in step (8) is cooling to room temperature; The centrifugation conditions described in step (8) are centrifugation at 8000-12000 rpm for 5-20 min.

9. A high-efficiency rare-earth luminescent nanocrystal with an inert shell structure, prepared by the preparation method described in claim 8.

10. The application of the high luminescence efficiency rare earth luminescent nanocrystals of claim 7 and / or the high luminescence efficiency rare earth luminescent nanocrystals with an inert shell structure of claim 9 in the preparation of light-controlled drug-loaded particles or imaging probes.

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