Preparation method and application of transition metal ion sensitized rare earth fluoride long-afterglow nano material

Abstract

The invention discloses a preparation method and application of a transition metal ion sensitized rare earth fluoride long-afterglow nano material, and belongs to the technical field of biological nano materials. The NaYF4: Tb, Mn long-afterglow nano scintillator is synthesized through a solvothermal decomposition method, divalent Mn < 2 + > with smaller ion radius and rare earth ions Tb < 3 + > are co-doped in a rare earth fluoride NaYF4 matrix, Tb < 3 + > is used as a luminescence center ion, Mn < 2 + > is used as a sensitizer, doping of heterovalent Mn < 2 + > ions can occupy crystal sites to adjust a local crystal field, and doping of the heterovalent Mn < 2 + > ions is realized. Vacancies or gaps can be generated, so that afterglow emission is enhanced; the obtained nano scintillator is combined with a substrate material PDMS to prepare a flexible transparent film, a clear object image is successfully presented under irradiation of X rays with a low dosage rate of 278 [mu] Gy.s <-1 >, and long-term optical stability can still be maintained after continuous 20 times of cyclic irradiation.

Description

Technical Field

[0001] The present invention belongs to the technical field of biological nanomaterials, and specifically relates to a down-conversion long afterglow nanomaterial, and in particular to a preparation method and application of a transition metal ion sensitized rare earth fluoride long afterglow nanomaterial. Background Art

[0002] Rare earth fluoride scintillators not only have the advantages of low toxicity, low manufacturing cost, convenient device processing and tunable emission wavelength, but also have the characteristics of long afterglow luminescence under X-ray excitation. Long afterglow luminescence refers to the phenomenon that after irradiation with excitation light (ultraviolet-visible light, X-rays, gamma rays, etc.), the excited electrons are captured by the defect state of the crystal, and the electrons overcome the energy barrier and slowly migrate from the defect state to the luminescence center, resulting in luminescence delay. This phenomenon can continue to emit light for seconds or even hours. Therefore, rare earth fluoride scintillators are widely used in the fields of information encryption and storage, multi-color fluorescence anti-counterfeiting, X-ray detectors, and biomedical diagnosis and treatment, especially in flexible X-ray detectors, showing great application potential. In addition, rare earth fluoride scintillators have the characteristics of easy size control, good dispersibility, and excellent afterglow performance. Combining them with flexible substrates can achieve high-resolution X-ray time-delay imaging without the need for electronic circuits, which makes the manufacture of flexible X-ray detectors possible.

[0003] At present, X-ray stimulated long afterglow luminescence of rare earth fluoride nanomaterials has broad application prospects in background-free biomedicine and X-ray time-lapse imaging. In order to minimize the radiation risk, how to achieve high-efficiency afterglow emission is crucial for practical applications using low X-ray radiation doses. This also puts higher requirements on the preparation of long afterglow scintillators, which not only require controllable morphology and uniform monodispersity, but also require a significant increase in the afterglow intensity of X-ray excitation to achieve low-dose X-ray high-resolution imaging. Usually, the crystallographic symmetry, inter-ion distance and phonon energy of the host material will affect the down-conversion emission. Compared with rare earth ions, the radius of transition metal ions is usually much smaller. After doping, it will cause lattice contraction, destroy the local site symmetry, and increase the probability of electronic transition of rare earth ions, thereby enhancing the down-conversion emission. At the same time, lattice distortion will introduce more defect states, which is conducive to afterglow emission. Divalent Mn 2+ It is often used as an inorganic sensitizer due to its low manufacturing cost and environmental friendliness. 2+ It is difficult to achieve high-resolution imaging at low X-ray dose rates by conventional technical means. It is necessary to improve the luminescence performance, size morphology, dispersion and other indicators of nanoparticles through process improvements to meet the actual requirements of background-free biomedicine and X-ray time-lapse imaging.

[0004] Through searching the prior art, there is no 2+With rare earth ion Tb 3+ Co-doped NaYF 4 Literature reports on enhancing its down-conversion emission and improving afterglow intensity. Summary of the invention

[0005] In view of the shortcomings of the prior art, the first object of the present invention is to provide a transition metal ion sensitized rare earth fluoride long afterglow nanoscintillator and a preparation method thereof, so as to comprehensively improve the luminescence performance, size morphology, dispersion and other indicators of the rare earth fluoride scintillator to meet the actual requirements of background-free biomedicine and X-ray time-lapse imaging.

[0006] In order to achieve the above technical purpose, the inventors used divalent Mn with a smaller ionic radius. 2+ With rare earth ion Tb 3+ Co-doped rare earth fluoride NaYF 4 In the matrix, Tb 3+ As the luminescent central ion, Mn 2+ As a sensitizer, heterovalent Mn 2+ The doping of ions can not only occupy crystal sites to adjust the local crystal field, but also generate vacancies or gaps to enhance the afterglow emission. In addition, the present invention prepares uniform monodispersed NaYF with higher luminescence intensity and longer afterglow time by solvent thermal decomposition method. 4 : Tb, Mn nanoparticles.

[0007] Specifically, the technical purpose of the present invention is achieved by using the following technical solution: a transition metal ion sensitized rare earth fluoride long afterglow nano scintillator, the nano scintillator is NaYF 4 :10%Tb,5%Mn, of which Tb 3+ As the luminescent central ion, Mn 2+ As a sensitizer. By doping with heterovalent transition metal ions Mn 2+ The resulting nanoscintillator can regulate the local crystal field, increase the transition probability of the luminescent center ions, and at the same time generate more trap states in the main matrix to capture excited electrons and holes, significantly enhancing the afterglow emission.

[0008] A method for preparing a transition metal ion-sensitized rare earth fluoride long afterglow nano scintillator, the method comprising the following steps: 3 、TbCl 3 、MnCl 2 , oleic acid and 1-octadecene were mixed and heated to 155-165°C under inert gas protection until a clear and transparent solution was formed. The mixture was cooled to 48-55°C and then a mixture containing NH 4F and NaOH methanol solution, stirring to remove methanol, then further heating the mixed solution to 290-320°C at a heating rate of 8-12°C / min, keeping the temperature for 1-2h under the protection of inert gas, and finally cooling to room temperature, centrifuging the cooled reaction product at high speed, separating the precipitate and washing to obtain NaYF 4 :10%Tb,5%Mn nanoparticles.

[0009] Further preferably, in the method for preparing the transition metal ion-sensitized rare earth fluoride long afterglow nano scintillator as described above, the volume ratio of oleic acid to 1-octadecene is 1:(1.5-3).

[0010] Further preferably, in the method for preparing the transition metal ion-sensitized rare earth fluoride long afterglow nano-scintillator as described above, the speed of the reaction product during high-speed centrifugation is 8000-12000 rpm.

[0011] Further preferably, in the method for preparing the transition metal ion-sensitized rare earth fluoride long afterglow nano-scintillator as described above, the precipitate is washed 1 to 5 times with a mixed solution of ethanol / cyclohexane in a volume ratio of 2:1.

[0012] The second object of the present invention is to provide a method for preparing a transition metal ion sensitized rare earth fluoride long afterglow nano film, the method comprising the following steps: 4 :10% Tb, 5% Mn nanoparticles were dispersed in cyclohexane, ultrasonicated for 5-20 min at room temperature, and then heated in NaYF 4 : Polydimethylsiloxane is added to the dispersion of 10% Tb, 5% Mn nanoparticles and ultrasonically treated for 30 to 60 minutes to ensure uniform distribution of the nanoparticles. The resulting mixture is transferred to a mold of an acrylic plate, degassed in a vacuum container to remove bubbles, and finally the mixture is cured until a film is formed. The resulting film can be used to prepare a flexible X-ray detector.

[0013] Further preferably, in the method for preparing the transition metal ion-sensitized rare earth fluoride long afterglow nanofilm as described above, the polydimethylsiloxane is polymerized by a prepolymer and a crosslinking agent in a mass ratio of (9-11):1.

[0014] Further preferably, in the method for preparing the transition metal ion-sensitized rare earth fluoride long afterglow nanofilm as described above, the technical parameters of the curing step are: curing temperature 75-85° C., and curing time 6-18 h.

[0015] In addition, the present invention will prepare NaYF 4: 10% Tb, 5% Mn nanoparticles were dissolved in PDMS (polydimethylsiloxane) to prepare a flexible transparent film. It produces stronger green fluorescence emission under X-ray (80Kv, 0.7mA) excitation. After 20 consecutive cycles of X-ray irradiation, it can still maintain long-term optical stability and -1 A clear image is presented under low-dose rate X-ray irradiation. Therefore, the third object of the present invention is to provide a new product use, namely, the use of the above-mentioned transition metal ion sensitized rare earth fluoride long afterglow nano scintillator in the preparation of persistent luminescent imaging materials; or the use of the above-mentioned transition metal ion sensitized rare earth fluoride long afterglow nano scintillator in the preparation of X-ray sensors, radiation dose testers or fluorescent probes for biological markers.

[0016] Compared with the prior art, the preparation method of the transition metal ion sensitized rare earth fluoride long afterglow nanomaterial provided by the present invention has the following advantages and progress:

[0017] (1) The present invention synthesized NaYF by solvent thermal decomposition method 4 :Tb,Mn long afterglow nano scintillator, to achieve controllable preparation of uniform lattice, size and morphology. And by doping a specific proportion of transition metal Mn 2+ , changing the point symmetry of the crystal structure, increasing the transition probability of the luminescent center ion, thereby enhancing the down-conversion emission. At the same time, the resulting lattice distortion will introduce more defect states, which is beneficial to afterglow emission and significantly improves the luminescence intensity and afterglow duration.

[0018] (2) The present invention adopts the optimal doping ratio of NaYF 4 :10% Tb, 5% Mn nanoparticles combined with PDMS substrate material to prepare a flexible transparent film. -1 Under low-dose rate X-ray irradiation, a clear image is successfully presented, and after 20 consecutive cycles of irradiation, long-term optical stability can still be maintained.

[0019] (3) NaYF of the present invention 4 :Tb,Mn nanoscintillators have the characteristics of excellent X-ray responsiveness, strong afterglow emission, clear imaging, simple preparation process and low cost. They can be used in the fields of X-ray sensors, radiation safety monitoring and fluorescent probes for biomarkers. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 :NaYF 4 : Transmission electron microscopy (TEM) and particle size distribution of 10% Tb, 5% Mn nanoparticles.

[0021] Figure 2:NaYF 4 : XRD patterns of 10% Tb, 5% Mn nanoparticles are similar to those of hexagonal β-NaYF 4 The diffraction peaks of the samples were matched with those of the standard diffraction peaks of (JCPDS No.16-0334).

[0022] Figure 3 :Different Mn 2+ NaYF with doping concentrations (x = 0, 2, 5, 10, 15 and 20 mol%) 4 : X-ray excitation emission spectrum of 10% Tb, x% Mn.

[0023] Figure 4 : After 5 minutes of X-ray excitation, NaYF 4 : Afterglow decay curves of 10% Tb, x% Mn (x = 0, 2, 5, 10, 15 and 20 mol%) at 545 nm.

[0024] Figure 5 :NaYF 4 :The luminescence stability of 10% Tb, 5% Mn nanoparticles was tested under X-ray (80Kv, 0.7mA) irradiation for 20 consecutive cycles (400s).

[0025] Figure 6 :Put the capsule with coil spring and ballpoint pen in NaYF 4 :10% Tb, 5% Mn films, at a dose rate of 278 μGy·s -1 Imaging is performed under X-ray irradiation.

[0026] Figure 7 :Mn 2+ NaYF with optimal doping luminescence 4 :10%Tb, 5%Mn thin film and undoped NaYF 4 :10%Tb film at a dose rate of 278μGy·s -1 After the X-ray irradiation stops, the afterglow changes with time. DETAILED DESCRIPTION

[0027] The present invention is doped with heterovalent transition metal ions Mn 2+ , regulating the local crystal field, increasing the transition probability of the luminescent center ion, and at the same time generating more trap states in the main matrix to capture excited electrons and holes, significantly enhancing the afterglow emission. The synthesis conditions of this preparation method are easy to control, and the prepared rare earth fluoride nanoparticles have regular morphology, uniform size and good dispersibility. It is combined with the substrate material PDMS (polydimethylsiloxane) to prepare a flexible transparent film. At 278μGy·s -1Under X-ray irradiation with a high dose rate, the prepared flexible transparent film presents a clear image, providing a new idea for the manufacture of new flexible X-ray detectors.

[0028] The present invention is further described in detail below through specific embodiments. The specific technical operation steps or conditions not specified in the examples are all conventional methods, which can be carried out according to the general techniques or conditions described in the literature in this field or according to the product instructions. The reagents or instruments used without indicating the manufacturer are all conventional products that can be purchased commercially. The specific experimental process is as follows:

[0029] (1) NaYF with different doping concentrations 4 Preparation of 10% Tb, x% Mn (x = 0, 2, 5, 10, 15 and 20 mol%)

[0030] First, YCl 3 (0.9-x mmol), TbCl 3 (0.1mmol), MnCl 2 A mixed solution of 1-octadecene (x mmol), oleic acid OA (12 mL) and 1-octadecene ODE (28 mL) was added to a 100 mL round-bottom flask. The mixture was heated to 160°C under argon protection until a clear transparent solution was formed, and then cooled to 50°C. Next, 10 mL of NH 4 A methanol solution of F (4 mmol) and NaOH (2.5 mmol) was added to the mixture and stirred for 30 min to remove methanol. Then, the solution was further heated to 290-320 ° C at a heating rate of 10 ° C / min, heated for 1-2 h under an argon atmosphere, and cooled to room temperature. The cooled solution was centrifuged at 10000 rpm to obtain a precipitate product, and the precipitate was washed 3 times with an ethanol / cyclohexane mixture (2: 1, v / v), and finally dispersed in 10 mL of cyclohexane for further use.

[0031] The NaYF prepared by the solvent thermal decomposition method in this example 4 : Transmission electron microscopy (TEM) images and particle size distribution of 10% Tb, 5% Mn nanoparticles, such as Figure 1 As shown. The NaYF prepared by the solvent thermal decomposition method in this example 4 : XRD pattern of 10% Tb, 5% Mn nanoparticles, such as Figure 2 As shown. Figure 1 and Figure 2 It can be seen that the transition metal Mn 2+ Doped NaYF 4 :10% Tb, 5% Mn are spherical particles with good uniformity and dispersion, and the particle size is about 33.8nm. ; The crystal structure is a typical hexagonal β phase, and the XRD diffraction pattern is clear, proving that it has good crystallinity.

[0032] (2) Different concentrations of Mn 2+ Doping to achieve NaYF 4 :Luminescence Control of 10%Tb,x%Mn Nanoparticles

[0033] A series of Mn 2+ / Tb 3+ Co-doped NaYF 4 Nanoparticles, including Tb 3+ As the luminescent central ion, Mn 2+ As a sensitizer, the emission spectra and afterglow decay spectra of NaYF4:10%Tb,x%Mn (x=0,2,5,10,15 and 20mol%) nanocrystals under X-ray excitation (80Kv, 0.7mA) were recorded, and the luminescence intensity of the nanoparticles was observed to increase with the increase of Mn 2+ The trend of doping concentration variation.

[0034] like Figure 3 As shown, the prepared NaYF 4 :10%Tb,x%Mn nanoparticles show Tb under X-ray excitation 3+ The characteristic emission peaks are 490, 545, 586 and 625nm, respectively, and the strongest emission peak is in the 545nm green light range. 2+ With the increase of doping amount, the displacement of emission peak has not changed, but the overall luminescence intensity shows a trend of increasing first and then decreasing. It reaches the optimum when the doping amount is 5%, and the luminescence intensity is 4.3 times that of the undoped state. The reason is: Mn 2+ The radius is larger than Y 3+ The radius is much smaller, and doping will cause the lattice to shrink, destroy the symmetry of the local site, and increase the luminescence center Tb 3+ ions, thereby enhancing the luminescence. 2+ The doping amount will lead to the luminescence center Tb 3+ The energy transfer between them produces harmful cross relaxation and self-quenching effect, which leads to a decrease in luminescence intensity.

[0035] In order to explore Mn 2+ The effect of doping concentration on afterglow decay, such as Figure 4 As shown, this embodiment measures different Mn 2+ The afterglow decay curve of doping concentration shows that its decay law is basically consistent with the change of luminous intensity. The afterglow decay time is the longest when the doping amount is 5%, and the afterglow intensity is 2.7 times that of the undoped state. This is due to the appropriate concentration of Mn 2+ Doping is beneficial to form a suitable trap depth and concentration in the main matrix, leading to an increase in the afterglow intensity. Figure 5 As shown in the figure, after 20 consecutive cycles of X-ray (80Kv, 0.7mA), X-ray excited NaYF 4 :The luminescence intensity of 10%Tb, 5%Mn nanoparticles has almost no change, proving their excellent optical stability.

[0036] (3)NaYF 4 Preparation of Tb, Mn Nanoscintillator Thin Films

[0037] 60 mg of NaYF 4 : 10% Tb, 5% Mn nanoparticles were dispersed in 1 mL of cyclohexane and sonicated for 10 min at room temperature. Then, 1.1 g of PDMS (the weight ratio of prepolymer and crosslinker was 10:1) was mixed with the above solution and sonicated for 40 min to ensure uniform distribution of the nanoparticles. Then, the mixed solution was transferred to a mold of a square acrylic plate and degassed in a vacuum container to remove bubbles. Finally, the mixture was cured at 80 ° C for 12 h until a film was formed.

[0038] By placing the target object on NaYF 4 :Tb, Mn nanoscintillator films, and place them all directly under the X-ray source. Turn on the X-ray source (80Kv, 0.7mA) for irradiation, and the scintillator film begins to collect and store the internal structure information of the target. After stopping the excitation, place the scintillator film on a constant temperature heating table at 80°C for heating treatment to accelerate the release of carriers in the trap, observe clearer images, and record them with an ordinary digital camera. The scintillator film can erase the recorded images by continuous heating at a higher temperature, and supports multiple and repeated uses.

[0039] The results of X-ray imaging of the capsule with a coil spring and a ballpoint pen as the real object are as follows: Figure 6 As shown in the figure, the internal images of each can be clearly seen; 2+ NaYF with optimal doping luminescence 4 :10%Tb,5%Mn thin film and undoped NaYF 4 :10%Tb film at a dose rate of 278μGy·s -1 Irradiate with X-rays for 5 minutes, and collect images that change over time after irradiation stops. Figure 7 As shown, it can be observed that Mn 2+ The doped scintillator film produces stronger afterglow emission under low-dose rate X-ray irradiation and presents clearer images. Compared with the undoped scintillator film, it shows higher resolution and longer image storage, and has excellent imaging performance.

Claims

1. A transition metal ion sensitized rare earth fluoride long afterglow nano scintillator, characterized in that: The nano scintillator is NaYF4:10% Tb, 5% Mn, wherein Tb 3+ As the luminescent central ion, Mn 2+ As a sensitizer.

2. A method for preparing a transition metal ion-sensitized rare earth fluoride long afterglow nano-scintillator, characterized in that: The method comprises the following steps: mixing YCl3, TbCl3, MnCl2, oleic acid and 1-octadecene, heating to 155-165°C under the protection of an inert gas until a clear and transparent solution is formed, cooling to 48-55°C, then dripping a methanol solution containing NH4F and NaOH, stirring to remove the methanol, then further heating the mixed solution to 290-320°C at a heating rate of 8-12°C / min, keeping the mixture warm for 1-2h under the protection of an inert gas, and finally cooling to room temperature, centrifuging the cooled reaction product at high speed, separating the precipitate and washing to obtain NaYF4:10%Tb,5%Mn nanoparticles.

3. The method for preparing the transition metal ion sensitized rare earth fluoride long afterglow nano scintillator according to claim 2, characterized in that: The volume ratio of oleic acid to 1-octadecene is 1:(1.5-3).

4. The method for preparing the transition metal ion sensitized rare earth fluoride long afterglow nano scintillator according to claim 2, characterized in that: The speed of high-speed centrifugation of the reaction product is 8000-12000 rpm.

5. The method for preparing the transition metal ion sensitized rare earth fluoride long afterglow nano scintillator according to claim 2, characterized in that: The precipitate is washed 1 to 5 times with an ethanol / cyclohexane mixture in a volume ratio of 2:

1.

6. A method for preparing a transition metal ion sensitized rare earth fluoride long afterglow nano film, characterized in that: The method comprises the following steps: dispersing NaYF4:10%Tb,5%Mn nanoparticles prepared by the method of claim 2 in cyclohexane, ultrasonically treating at room temperature for 5 to 20 minutes, then adding polydimethylsiloxane to the dispersion of NaYF4:10%Tb,5%Mn nanoparticles and ultrasonically treating for 30 to 60 minutes to ensure uniform distribution of the nanoparticles, transferring the obtained mixed solution to a mold of an acrylic plate, degassing in a vacuum container to remove bubbles, and finally curing the mixed solution until a film is formed.

7. The method for preparing the transition metal ion sensitized rare earth fluoride long afterglow nano film according to claim 6, characterized in that: The polydimethylsiloxane is polymerized by a prepolymer and a crosslinking agent in a mass ratio of (9-11):

1.

8. The method for preparing the transition metal ion sensitized rare earth fluoride long afterglow nano film according to claim 6, characterized in that: The technical parameters of the curing step are: curing temperature 75-85° C., and curing time 6-18 hours.

9. Use of the transition metal ion sensitized rare earth fluoride long afterglow nano scintillator according to claim 1 or the transition metal ion sensitized rare earth fluoride long afterglow nano scintillator prepared by the method according to claim 2 in the preparation of persistent luminescence imaging materials.

10. Use of the transition metal ion-sensitized rare earth fluoride long afterglow nano scintillator according to claim 1 or the transition metal ion-sensitized rare earth fluoride long afterglow nano scintillator prepared by the method according to claim 2 in the preparation of X-ray sensors, radiation dose testers or fluorescent probes for biological markers.

Images