Preparation and application of Zn-doped zirconium-based metal halide nanocrystal and composite scintillator screen

Abstract

The invention discloses preparation and application of Zn-doped zirconium-based metal halide nanocrystals and a composite scintillator screen, firstly, a Zn < 2 + > heterovalent doping strategy is adopted in an all-inorganic scintillator Cs2ZrCl6, an energy band structure of the Cs2ZrCl6 is successfully regulated and controlled, and defects of the Cs2ZrCl6 are effectively passivated, so that the luminescent property and environmental stability of a material are greatly improved. The preparation method of the zirconium-based metal halide nanocrystalline composite scintillator screen has the advantages of being simple in process, low in cost, green, free of pollution and high in imaging resolution. And finally, the nanocrystals are embedded into the anodic aluminum oxide template by using a low-temperature hydrothermal method, and scattering of scintillation light in the horizontal direction is remarkably inhibited by virtue of a waveguide effect generated by an array structure of the template, so that the spatial resolution of X-ray imaging is effectively improved, and the imaging precision is improved. The X-ray detector can be widely applied to high-sensitivity and high-resolution X-ray detection in the fields of medical imaging, industrial flaw detection, safety inspection and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of scintillator materials, and particularly relates to a preparation method and application of Zn-doped zirconium-based metal halide nanocrystals and composite scintillator screens. Background Art

[0002] X-ray imaging has been widely used in medical imaging, security inspection, industrial non-destructive testing and other fields. Although commercial scintillators (such as CsI:Tl, NaI:Tl, BGO, etc.) are mature, they still have limitations in imaging resolution, environmental stability, low-dose response, etc. In addition, problems such as heavy metal toxicity and difficulty in preparing large-area flexible screens have also led to the demand for new generation scintillation materials.

[0003] Metal halides have become the focus of scintillator research in recent years. Among them, halides based on metals such as manganese, copper, and zinc have attracted much attention due to their strong electron localization and high quantum efficiency. However, such metal atoms have relatively low atomic numbers, and the absorption efficiency for high-energy X-rays is limited. In contrast, zirconium has a relatively higher atomic number, is environmentally friendly and has low toxicity, providing a very promising research direction for scintillation materials.

[0004] At present, the typical zirconium-based metal halide Cs2ZrCl6 shows excellent performance in X-ray detection due to its unique self-trapped exciton (STE) luminescence mechanism and dopant-tunable characteristics. However, there are still huge challenges in further improving the luminescence efficiency of Cs2ZrCl6 in practical imaging applications, reducing the afterglow decay caused by material defects, and achieving high-resolution and large-area imaging. Summary of the Invention

[0005] The first object of the present invention is to provide a Zn-doped zirconium-based metal halide nanocrystal and a preparation method thereof.

[0006] The second object of the present invention is to use the above-mentioned halide nanocrystals to further construct a preparation method of an arrayed high-resolution composite scintillator screen.

[0007] The third object of the present invention is to provide the uses of the halide nanocrystals and the composite scintillator screens.

[0008] I. Scintillator Materials and Their Preparation Methods The chemical general formula of the halide nanocrystals of the present invention is Cs2ZrCl6: x %Zn 2+ (1 ≤x≤ 8), that is, Zn ions are introduced into the Cs2ZrCl6 system through an aliovalent doping strategy, thereby forming zirconium-based metal halide nanocrystals with a zero-dimensional structure. 2+

[0009] Preferably, x %Zn 2+ in x = 3.

[0010] The present invention prepares Cs2ZrCl6: x %Zn 2+ nanocrystals by a thermal injection method, that is, dissolving Cs, Zr, and Zn precursors in a high-boiling organic solvent, maintaining a certain high-temperature environment and then quickly injecting a chlorine source solution, so that the nanocrystals nucleate and grow rapidly. This method can effectively control the crystal size and morphology and ensure uniform doping of Zn. 2+ Specifically as follows: 1) Dissolve zirconium chloride in octadecene, stir and heat at 55 - 70 °C for more than 30 min; then add cesium acetate, zinc acetate, oleic acid, and oleylamine, mix well and vacuum dry at 100 - 110 °C for 1 - 2 h to obtain a precursor solution; 2) Under nitrogen protection, heat the precursor solution to 200 - 210 °C and then inject trimethylchlorosilane, react for 0.1 - 10 min and then cool to room temperature, centrifuge to collect the precipitate, wash, and vacuum dry to obtain Cs2ZrCl6: x %Zn 2+ nanocrystals.

[0011] The molar ratio of the zirconium chloride to the cesium acetate is 1:1 - 2:1, and the molar amount of zinc acetate is 1% - 8% of the molar amount of zirconium chloride.

[0012] The volume ratio of the octadecene to the oleic acid and the oleylamine is (16 - 18):(4 - 6):1.

[0013] II. Constructing an arrayed high-resolution scintillation screen Based on the above Cs2ZrCl6: x %Zn 2+ nanocrystal powder, in order to further improve the spatial resolution and suppress the lateral scattering, the present invention proposes to embed the nanocrystals into an anodic aluminum oxide (AAO) template to form a composite scintillation film. The arrayed pore structure of the AAO can produce a waveguide effect, reduce the scattering of the scintillation light in the horizontal direction, and greatly improve the final imaging resolution. Take an appropriate amount of Cs2ZrCl6: x %Zn 2+Nanocrystalline powders are dispersed in low-polarity organic solvents (such as n-hexane, toluene or their mixture), and ultrasonic treatment or stirring is carried out until a homogeneous dispersion is formed. AAO with a thickness of 50 - 500 μm and a pore diameter of 20 - 200 nm is selected. First, the dust and surface contaminants on the template surface are removed by vacuum filtration or surface pretreatment; using the hydrothermal method, the nanocrystals penetrate into the template pores and deposit on the tube wall; then through the drying and solvent removal process, the nanocrystals are firmly embedded and form Cs2ZrCl6: x %Zn 2+ @AAO composite scintillation screen.

[0014] III. Applications of Scintillator Materials 1. X-ray Detection and Imaging The above-mentioned halide nanocrystals have high luminescence efficiency under X-ray irradiation, and the low afterglow characteristics are beneficial for high-speed imaging; among them, 3%Zn 2+ ion-doped zirconium-based halide nanocrystals achieve efficient blue light emission with a light yield of 31,424 photons / MeV; they can be used to prepare high-resolution X-ray imaging devices, and the imaging clarity and contrast are significantly improved; Due to its stability to environmental humidity and heat, it can be used in multiple scenarios such as medical imaging (such as digital radiography), industrial non-destructive testing (such as weld inspection) and luggage security inspection.

[0015] 2. Anti-counterfeiting and Fluorescent Display This material emits visible light under ultraviolet or high-energy ray irradiation, and can be combined with spectral characteristics for anti-counterfeiting, fluorescent marking, etc.; It can also be applied to optically imaging sensitive to spatial resolution, or composite with other fluorescent materials to achieve multi-color imaging.

[0016] In summary, the beneficial effects of the present invention are as follows: 1. By doping Zn in Cs2ZrCl6 2+ , the internal defects of the material can be effectively passivated and its energy band structure can be finely tuned, greatly improving the luminescence efficiency, light yield and environmental stability of the scintillator, and avoiding the toxicity and easy degradation problems of traditional lead-based halides; 2. The doped Cs2ZrCl6: x %Zn 2+ can be further compounded with anodic aluminum oxide (AAO) template, and the waveguide effect of the arrayed pores is used to effectively suppress lateral scattering, thereby greatly improving the spatial resolution of X-ray imaging; 3. The present invention uses the hot-injection method to prepare Cs2ZrCl6: x %Zn 2+The nanocrystals have a short reaction time, controllable crystal growth, and are easy to achieve mass production. At the same time, the obtained nanocrystal powder can be applied to the preparation of scintillation films or device encapsulation through simple post-treatment. 4. The obtained halide nanocrystals exhibit good stability under both conventional atmospheric environment and humid conditions, are suitable for various application scenarios such as medical imaging, industrial flaw detection, and security inspection, and can be compatible with common optoelectronic detection devices such as CCD / CMOS and α-Si. 5. The obtained halide nanocrystals can still maintain stable and strong radiation-induced luminescence at a low dose level, which helps to reduce the medical or environmental risks brought by X-ray irradiation. At the same time, more refined and rapid detection and identification can be achieved in occasions such as security inspection. Description of the Drawings

[0017] Figure 1 For Cs2ZrCl6 and Cs2ZrCl6 prepared in Examples 1 to 9 of the present invention: x %Zn 2+ (1 ≤ x≤ 8) Comparison chart of the measured XRD and the simulated XRD spectrum of Cs2ZrCl6 (the simulated XRD spectrum is made according to the CIF card (PDF#74-0505) analyzed from the single crystal structure of Cs2ZrCl6, and the measured XRD is obtained from the powder test of Cs2ZrCl6: x %Zn 2+ Powder XRD); Figure 2 For the pre-composite Cs2ZrCl6: 3%Zn prepared in Examples 4 and 10 of the present invention 2+ nanocrystals, AAO empty sample, and the comparison chart of the XRD of the post-composite Cs2ZrCl6: 3%Zn 2+ @AAO and the simulated XRD spectrum of Cs2ZrCl6; Figure 3 For the Cs2ZrCl6: 3%Zn after composite in Example 10 2+ nanocrystals, (a) SEM and EDS diagrams in the radial direction, (b) SEM and EDS diagrams on the side of the Cs2ZrCl6: 3%Zn 2+ @AAO scintillator screen; Figure 4 For the (a) side SEM diagram of Cs2ZrCl6: 3%Zn prepared in Example 10 2+ @AAO; (b) locally enlarged diagram of (a); (c) Cs2ZrCl6: 3%Zn obtained by the thermal injection method 2+TEM and EDS images of nanocrystals; (d) Cs2ZrCl6: 3%Zn 2+ TEM images of nanocrystals; Figure 5 Calculated band diagrams of Cs2ZrCl6 (a) and Cs2ZrCl6: 3%Zn 2+ (b) prepared in Example 1 and Example 4; Figure 6 UV absorption spectra and Tauc plots of Cs2ZrCl6 and Cs2ZrCl6: 3%Zn 2+ prepared in Example 1 and Example 4; Figure 7 (a) Cs2ZrCl6 with different doping concentrations prepared in Example 1 to Example 9; x Zn 2+ Photographs under 254 nm UV lamp irradiation; Cs2ZrCl6 with different doping concentrations; x Zn 2+ PL (b) and PLE (c) diagrams; Figure 8 Cs2ZrCl6 with different doping concentrations prepared in Example 1 to Example 9; x Zn 2+ Time-resolved fluorescence spectra; Figure 9 XRD stability diagram of Cs2ZrCl6: 3%Zn 2+ @AAO stored in nitrogen (N2) environment; Figure 10 Thermogravimetric diagrams of Cs2ZrCl6 (a) and Cs2ZrCl6: 3%Zn 2+ (b) prepared in Example 1 and Example 4 in nitrogen atmosphere; Figure 11 Normalized RL diagrams of Cs2ZrCl6 and Cs2ZrCl6: 3%Zn 2+ prepared in Example 1 and Example 4 and reference sample BGO (tube voltage: 70 kV; dose rate: 48.56 mGy air s -1 ); Figure 12 Signal-to-noise ratio (SNR) of Cs2ZrCl6@AAO and Cs2ZrCl6: 3%Zn 2+ @AAO prepared in Example 10 and Example 11 under different X-ray irradiation dose rates; Figure 13Cs2ZrCl6@AAO (a) and Cs2ZrCl6: 3%Zn prepared in Example 10 and Example 11 2+ @AAO (b) Radiation stability of the screen under intermittent X-ray irradiation (tube voltage: 70 kV; dose rate: 48.56 mGy air s -1 ); Figure 14 Cs2ZrCl6: 3% Zn prepared in Example 10 2+ @AAO scintillator screen in sunlight (a) and 254 nm ultraviolet light (b) Figure 15 Cs2ZrCl6: 3% Zn prepared in Example 10 2+ @AAO The relationship between the spatial frequency and modulation transfer function (MTF) of X-ray imaging measured by the blade method of the scintillator screen; Figure 16 Cs2ZrCl6: 3% Zn prepared in Example 10 2+ @AAO scintillator screen imaging of capacitive pen (a) and Type-C interface (b) under X-ray and its actual picture; Figure 17 Cs2ZrCl6: 3% Zn prepared in Example 10 2+ @AAO scintillator screen imaging of shells and magnetons (a) and magnetons (b) under X-rays and their physical images; Figure 18 Cs2ZrCl6: 3% Zn prepared in Example 10 2+ @AAO scintillator screen imaging of a standard X-ray resolution lead plate under X-rays. DETAILED DESCRIPTION

[0018] The present invention is further explained below with reference to specific embodiments.

[0019] Example 1 Preparation of Cs2ZrCl6 scintillator nanocrystals (1) Grind ZrCl4 and weigh 0.6991 g, place it in a three-necked flask containing 22.3 mL of octadecene, and heat it at 55-70 °C with stirring for more than 30 minutes; (2) Then, 0.2879 g of cesium acetate, 5.926 mL of oleic acid, and 1.3 mL of oleylamine were added in sequence, mixed thoroughly, and dried in vacuum at 105 °C for 1 hour to remove excess water; (3) Switch to nitrogen protection, heat to 205°C, quickly inject TMSCl, react for 10 seconds, and then quickly cool; (4) The obtained crude product suspension was mixed with a mixed solution of acetone and isopropanol in a volume ratio of 1:1 (the ratio of the suspension to the mixed solution was 5:1) for washing, centrifuged at 10,000 rpm for 7 min, the supernatant was discarded, and n-hexane was used to re-disperse and repeat the washing process; (5) The washed powder was placed in a vacuum drying oven and dried for 12 hours to obtain pure Cs2ZrCl6 nanocrystals.

[0020] Example 2 Cs2ZrCl6: 1%Zn 2+ Preparation of Scintillator Nanocrystals (1) Grind ZrCl4 and weigh 0.6921 g, place it in a three-necked flask containing 22.3 mL of octadecene, and heat it at 55-70 °C with stirring for more than 30 minutes; (2) 0.2879 g of cesium acetate, 0.0066 g of zinc acetate, 5.926 mL of oleic acid and 1.3 mL of oleylamine were then added in sequence, mixed thoroughly and dried in vacuum at 105 °C for 1 hour to remove excess water; (3) Switch to nitrogen protection, heat to 205°C, quickly inject TMSCl, react for 10 seconds, and then quickly cool; (4) The obtained crude product suspension was mixed with a mixed solution of acetone and isopropanol in a volume ratio of 1:1 (the ratio of the suspension to the mixed solution was 5:1) for washing, centrifuged at 10,000 rpm for 7 min, the supernatant was discarded, and n-hexane was used to re-disperse and repeat the washing process; (5) The washed powder was placed in a vacuum drying oven and dried for 12 hours to obtain pure Cs2ZrCl6:1%Zn 2+ Nanocrystals.

[0021] Example 3 Cs2ZrCl6: 2%Zn 2+ Preparation of Scintillator Nanocrystals (1) Grind ZrCl4 and weigh 0.6851 g, place it in a three-necked flask containing 22.3 mL of octadecene, and heat it at 55-70 °C with stirring for more than 30 minutes; (2) 0.2879 g of cesium acetate, 0.0132 g of zinc acetate, 5.926 mL of oleic acid and 1.3 mL of oleylamine were then added in sequence, mixed thoroughly and dried in vacuum at 105 °C for 1 hour to remove excess water; (3) Convert to nitrogen protection, heat to 205 °C, quickly inject TMSCl, and quickly cool after reacting for 10 seconds; (4) Mix the obtained crude product suspension with a mixed solution of acetone and isopropanol with a volume ratio of 1:1 (the ratio of the suspension to the mixed solution is 5:1) for washing, centrifuge at 10000 rpm for 7 minutes, discard the supernatant, redisperse with n-hexane and repeat the washing process; (5) Put the washed powder into a vacuum drying oven, and obtain pure Cs2ZrCl6:2%Zn 2+ nanocrystals.

[0022] Example 4 Cs2ZrCl6: 3%Zn 2+ Preparation of scintillator nanocrystals (1) First, grind ZrCl4 and weigh 0.6781 g, place it in a three-necked flask containing 22.3 mL of octadecene, and stir and heat at 55-70 °C for more than 30 minutes; (2) Subsequently, add 0.2879 g of cesium acetate, 0.0198 g of zinc acetate, 5.926 mL of oleic acid and 1.3 mL of oleylamine in sequence, mix well and vacuum dry at 105 °C for 1 hour to remove excess water; (3) Convert to nitrogen protection, heat to 205 °C, quickly inject TMSCl, and quickly cool after reacting for 10 seconds; (4) Mix the obtained crude product suspension with a mixed solution of acetone and isopropanol with a volume ratio of 1:1 (the ratio of the suspension to the mixed solution is 5:1) for washing, centrifuge at 10000 rpm for 7 minutes, discard the supernatant, redisperse with n-hexane and repeat the washing process; (5) Put the washed powder into a vacuum drying oven, and obtain pure Cs2ZrCl6:3%Zn 2+ nanocrystals.

[0023] Example 5 Cs2ZrCl6: 4%Zn 2+ Preparation of scintillator nanocrystals (1) First, grind ZrCl4 and weigh 0.6712 g, place it in a three-necked flask containing 22.3 mL of octadecene, and stir and heat at 55-70 °C for more than 30 minutes; (2) Subsequently, 0.2879 g of cesium acetate, 0.0264 g of zinc acetate, 5.926 mL of oleic acid, and 1.3 mL of oleylamine were added in sequence. After thorough mixing, it was vacuum dried at 105 °C for 1 hour to remove excess moisture; (3) The nitrogen protection was switched on, and after heating to 205 °C, TMSCl was rapidly injected. After reacting for 10 seconds, it was rapidly cooled; (4) The obtained crude product suspension was mixed with a mixed solution of acetone and isopropanol with a volume ratio of 1:1 (the ratio of the suspension to the mixed solution was 5:1) for washing, centrifuged at 10000 rpm for 7 min, the supernatant was discarded, and it was redispersed with n - hexane and the washing process was repeated; (5) The washed powder was placed in a vacuum drying oven and dried for 12 hours to obtain pure Cs2ZrCl6:4%Zn 2+ nanocrystals.

[0024] Example 6 Cs2ZrCl6: 5%Zn 2+ Preparation of scintillator nanocrystals (1) First, 0.6642 g of ZrCl4 was weighed after grinding and placed in a three - necked flask containing 22.3 mL of octadecene, and stirred and heated at 55 - 70 °C for more than 30 minutes; (2) Subsequently, 0.2879 g of cesium acetate, 0.0330 g of zinc acetate, 5.926 mL of oleic acid, and 1.3 mL of oleylamine were added in sequence. After thorough mixing, it was vacuum dried at 105 °C for 1 hour to remove excess moisture; (3) The nitrogen protection was switched on, and after heating to 205 °C, TMSCl was rapidly injected. After reacting for 10 seconds, it was rapidly cooled; (4) The obtained crude product suspension was mixed with a mixed solution of acetone and isopropanol with a volume ratio of 1:1 (the ratio of the suspension to the mixed solution was 5:1) for washing, centrifuged at 10000 rpm for 7 min, the supernatant was discarded, and it was redispersed with n - hexane and the washing process was repeated; (5) The washed powder was placed in a vacuum drying oven and dried for 12 hours to obtain pure Cs2ZrCl6:5%Zn 2+ nanocrystals.

[0025] Example 7 Cs2ZrCl6: 6%Zn 2+ Preparation of scintillator nanocrystals (1) Grind ZrCl4 and weigh 0.6572 g, place it in a three-necked flask containing 22.3 mL of octadecene, and heat it at 55-70 °C with stirring for more than 30 minutes; (2) 0.2879 g of cesium acetate, 0.0395 g of zinc acetate, 5.926 mL of oleic acid and 1.3 mL of oleylamine were then added in sequence, mixed thoroughly and dried in vacuum at 105 °C for 1 hour to remove excess water; (3) Switch to nitrogen protection, heat to 205°C, quickly inject TMSCl, react for 10 seconds, and then quickly cool; (4) The obtained crude product suspension was mixed with a mixed solution of acetone and isopropanol in a volume ratio of 1:1 (the ratio of the suspension to the mixed solution was 5:1) for washing, centrifuged at 10,000 rpm for 7 min, the supernatant was discarded, and n-hexane was used to re-disperse and repeat the washing process; (5) The washed powder was placed in a vacuum drying oven and dried for 12 hours to obtain pure Cs2ZrCl6:6%Zn 2+ Nanocrystals.

[0026] Example 8 Cs2ZrCl6: 7%Zn 2+ Preparation of Scintillator Nanocrystals (1) Grind ZrCl4 and weigh 0.6502 g, place it in a three-necked flask containing 22.3 mL of octadecene, and heat it at 55-70 °C with stirring for more than 30 minutes; (2) 0.2879 g of cesium acetate, 0.0462 g of zinc acetate, 5.926 mL of oleic acid and 1.3 mL of oleylamine were then added in sequence, mixed thoroughly and dried in vacuum at 105 °C for 1 hour to remove excess water; (3) Switch to nitrogen protection, heat to 205°C, quickly inject TMSCl, react for 10 seconds, and then quickly cool; (4) The obtained crude product suspension was mixed with a mixed solution of acetone and isopropanol in a volume ratio of 1:1 (the ratio of the suspension to the mixed solution was 5:1) for washing, centrifuged at 10,000 rpm for 7 min, the supernatant was discarded, and n-hexane was used to re-disperse and repeat the washing process; (5) The washed powder was placed in a vacuum drying oven and dried for 12 hours to obtain pure Cs2ZrCl6:7%Zn 2+ Nanocrystals.

[0027] Example 9 Cs2ZrCl6: 8%Zn 2+Preparation of Scintillator Nanocrystals (1) Grind ZrCl4 and weigh 0.6432 g, place it in a three-necked flask containing 22.3 mL of octadecene, and heat it at 55-70 °C with stirring for more than 30 minutes; (2) 0.2879 g of cesium acetate, 0.0527 g of zinc acetate, 5.926 mL of oleic acid and 1.3 mL of oleylamine were then added in sequence, mixed thoroughly and dried in vacuum at 105 °C for 1 hour to remove excess water; (3) Switch to nitrogen protection, heat to 205°C, quickly inject TMSCl, react for 10 seconds, and then quickly cool; (4) The obtained crude product suspension was mixed with a mixed solution of acetone and isopropanol in a volume ratio of 1:1 (the ratio of the suspension to the mixed solution was 5:1) for washing, centrifuged at 10,000 rpm for 7 min, the supernatant was discarded, and n-hexane was used to re-disperse and repeat the washing process; (5) The washed powder was placed in a vacuum drying oven and dried for 12 hours to obtain pure Cs2ZrCl6:8%Zn 2+ Nanocrystals.

[0028] Example 10 Preparation of composite scintillator screen (1) 2g Cs2ZrCl6: 3%Zn 2+ The nanocrystals were dispersed in 17 mL of n-hexane; (2) Place the single-pass AAO with a center spacing of 450 nm, a pore size of 400 nm, a membrane thickness of 40-60 μm, and a size of 25 × 25 mm in a 50 mL reactor and heat it in a forced air drying oven at 90 °C for 48 h. Take it out and set it aside.

[0029] (3) Use a nitrogen gun to slowly blow away the excess Cs2ZrCl6: 3%Zn attached to AAO 2+ Nanocrystals, and then use tape to repeatedly remove excess attachments to obtain Cs2ZrCl6: 3%Zn with a smooth surface. 2+ @AAO Scintillator Screen.

[0030] Embodiment 11 Preparation of composite scintillator screen (1) Disperse 2 g of Cs2ZrCl6 nanocrystals in 17 mL of n-hexane; (2) It was placed together with a single-pass AAO with a center spacing of 450 nm, a pore diameter of 400 nm, a film thickness of 40 - 60 μm, and a size of 25×25 mm in a 50 mL reactor, and heated in a forced-air drying oven at 90 °C for 48 h, and then taken out for standby.

[0031] (3) The excess Cs2ZrCl6 nanocrystals attached to the AAO were slowly blown off using a nitrogen gun, and then the excess attachments were repeatedly removed using tape to obtain a Cs2ZrCl6@AAO scintillator screen with a smooth surface.

[0032] Structural characterization and performance evaluation of the products prepared in the above Examples 1 - 11: 1. Structural characterization of the products in Examples 1 - 10 The X-ray powder diffraction phase analysis (XRD) of the products was obtained using Cu Kα radiation (λ = 1.54056 Å) on a Bruker D8 Advance X-RAY small-angle powder diffractometer from Bruker Corporation, Germany. It was performed at intervals of 0.04°, and the Bragg angle range was 10° - 80°. X-ray analysis was carried out at room temperature. The test results are as Figure 1 shown. It can be seen that the XRD diffraction pattern obtained by fitting the single-crystal data is highly consistent with the experimentally measured XRD diffraction pattern, proving that the XRD of the Cs2ZrCl6 nanocrystals prepared by thermal injection can correspond to the PDF#74 - 0505 standard card, demonstrating the successful preparation of the samples. By comparing the XRD of Cs2ZrCl6 doped with 0% - 8% Zn 2+ : x %Zn 2+ , we can see that because the difference in ionic radius sizes is not significant (Zn 2+ is 0.74 Å, Zr 4+ is 0.72 Å), the doping of Zn 2+ ions does not significantly change the original crystal structure.

[0033] At the same time, in Figure 2 , the composite Cs2ZrCl6: 3%Zn 2+ @AAO simultaneously exhibits the diffraction peaks of both Cs2ZrCl6: 3%Zn 2+ and AAO, proving the successful composite of the two materials. Because the content of Cs2ZrCl6: 3%Zn 2+ nanocrystals is less than that of AAO and the crystallinity is lower, and AAO has a preferred crystal orientation, the main diffraction peak of AAO can be seen to be much higher than that of the Cs2ZrCl6: 3%Zn 2+ nanocrystals in it.

[0034] As Figure 9 shown, when Cs2ZrCl6: 3%Zn 2+ @AAO is stored in an N2 environment at room temperature (15 - 35°C), no phase transition occurs after nearly 400 days of storage, demonstrating its good phase stability.

[0035] 2. UV - Visible Absorption Spectroscopy Experiment of the Products of Example 1 and Example 4 The UV - visible absorption spectrum of the product was measured using a Shimadzu UV - 3600, with the slowest scanning speed set, an integration time of one second, and a slit width of 5 nm. As Figure 6 shown, the direct band gaps Tauc of Cs2ZrCl6 and Cs2ZrCl6: 3%Zn 2+ obtained from the UV absorption spectrum are 3.92 eV and 3.84 eV respectively, which are almost consistent with the band structure calculation results. The decrease in the band gap of Cs2ZrCl6: 3%Zn 2+ may be due to the introduction of Zn 2+ causing local charge mismatch and lattice distortion in the crystal, thus changing the crystal field environment, bending the energy bands, and resulting in a decrease in the band gap.

[0036] According to theoretical derivation, when the coordination numbers of both were 6 before, the ionic radius of Zn 2+ is slightly larger than that of Zr 4+ (Zn 2+ is 0.74 Å, Zr 4+ is 0.72 Å). When Zn 2+ replaces Zr 4+ and is doped into the lattice, since the coordination numbers of both are 6, the ionic radius of Zn 2+ is slightly larger than that of Zr 4+ (Zn 2+ is 0.74 Å, Zr 4+ is 0.72 Å), which will cause lattice expansion, resulting in an increase in the length of the B - X bond (B is the B - site cation, X is the halogen). The increase in bond length will reduce the degree of overlap of the electron clouds between atoms, thereby weakening the covalent nature of the bond, further reducing the energy difference between the bonding orbital and the antibonding orbital, making the band gap smaller, and thus affecting its luminescence properties after doping. As Figure 5 shown, the band gap size Eg of Cs2ZrCl6 obtained from first - principles is 3.919 eV, slightly larger than that of Cs2ZrCl6: 3%Zn 2+ with Eg = 3.827 eV. This also agrees with the theoretical derivation.

[0037] The thermal stability of the sample was measured on a TGA 4000 from PE Company in an air atmosphere. AsFigure 10 As shown, Cs2ZrCl6 shows an obvious weight loss phenomenon at around 300 °C, while Cs2ZrCl6: 3%Zn 2+ shows no obvious weight loss phenomenon at around 300 °C, indicating that Cs2ZrCl6: 3%Zn 2+ has better thermal stability. Maintaining excellent performance in a high-temperature environment helps to broaden its applications in various complex situations in the field of X-ray imaging.

[0038] 3. Photoluminescence and fluorescence lifetime test experiments of the products of Examples 1-9 Photoluminescence excitation (PLE), photoluminescence (PL), and time-resolved PL (TRPL) decay spectral analysis of the products were performed using an Edinburgh Instruments, FLS920 fully functional steady-state / transient fluorescence spectrophotometer (light source Xe900). The results are shown in Figure 7 、 Figure 8 , and it can be seen that in the metal small bowl, the brightness of Cs2ZrCl6 is relatively low under the irradiation of a 254-nm ultraviolet lamp. As the 2+ doping concentration of Zn increases, the brightness gradually increases, reaching the brightest when the doping concentration reaches 3%, and then gradually decreases. The PL and PLE spectra also reflect the law of the change in luminescence properties. At the same time, through the analysis of its time-resolved PL (TRPL) decay spectrum, it is obtained that the fluorescence decay of Cs2ZrCl6: x %Zn 2+ fits the single-exponential function, and the average lifetime of Cs2ZrCl6 is 30.9 μs, while that of Cs2ZrCl6: 3%Zn 2+ is 25.3 μs. Based on the above preliminary test results, we speculate that Cs2ZrCl6: 3%Zn 2+ has the same luminescence properties as Cs2ZrCl6, and there is only one luminescence center from STE. The reduction in the fluorescence decay time may come from the defect passivation caused by aliovalent doping. In appropriate aliovalent doping, the defects in the crystal are filled by doping ions, resulting in a decrease in the fluorescence lifetime.

[0039] 4. Field emission scanning electron microscope (SEM) experiments on the products of Example 4 and Example 10 The scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS) of the products were taken by a ThermoScientific Apreo 2C field emission scanning electron microscope. Cs2ZrCl6: 3%Zn 2+ @AAO results are shown in Figure 3 、 Figure 4, Cs2ZrCl6: 3%Zn 2+ The nanocrystals are slightly agglomerated on the surface of AAO, but the agglomerated blocks are less distributed, thinner in thickness and smaller in size, so they have little impact on the imaging resolution. It can be seen from the EDS distribution that in both the radial and lateral cross-sections, the elements that should be contained in the scintillator are evenly distributed, proving that Cs2ZrCl6: 3%Zn 2+ is evenly deposited on the AAO tube wall and has a high distribution density.

[0040] 5. Transmission electron microscopy (TEM) test experiment of the product of Example 4 The transmission electron microscopy (TEM) was taken with a Tecnai G2 F20 transmission electron microscope produced by FEI Company. The results are as Figure 4 shown. It can be seen that the size of the Cs2ZrCl6: 3%Zn 2+ nanocrystals prepared by the thermal injection method under the transmission electron microscope is consistent, about 20 - 30 nm. It can be seen from the EDS under the transmission electron microscope that the Cs2ZrCl6: 3%Zn 2+ nanocrystals prepared by the thermal injection method have uniform element distribution.

[0041] 6. X-ray scintillation performance test experiment of the products of Example 10 and Example 11 The X-ray detection of the product uses a micro X-ray tube (MOXTEK Benchtop) with a maximum output power of 12W. The reflection spectrum (RL) is obtained using an integrating sphere (Ф = 10 cm) and an optical fiber spectrometer (omni-λ300i). During the measurement of the stability under X-ray irradiation, the X-ray tube voltage is maintained at 70 kV and 170 μA. The light yield of the sample uses CsI:Tl or BGO as the standard scintillator, and their standard light yields are 40,000 photons / MeV and 8,000 photons / MeV respectively. The X-ray light yield is measured by the reference method. The sample (Sample) and the standard scintillator (Standard) are irradiated with a Mo target X-ray tube (MOXTEK Benchtop 12W), the tube voltage and tube current are 70 kV and 170 μA, and the number of photons is normalized to 100% X-ray attenuation. The results are as Figure 11 , Figure 12 , Figure 13 , Figure 15 shown. Cs2ZrCl6 and Cs2ZrCl6: 3%Zn 2+The normalized RL integral intensities are 192.2% and 329.8% of that of a commercial BGO scintillator (8,000 photons / MeV), respectively, and the calculated light yields are approximately 15,376 and 31,424 photons / MeV, respectively. Cs2ZrCl6: 3%Zn 2+ The lower limit of detection (LoD) of @AAO was determined at a signal-to-noise ratio (SNR) = 3 and was only 3.68 μGy air s -1 , which is much lower than the minimum dose required for traditional computed tomography (5.5 μGy air s -1 ), and helps to reduce the damage to organisms under radiation exposure. The lower limit of detection (LoD) of Cs2ZrCl6 was 7.58 μGy at a signal-to-noise ratio (SNR) = 3 air s -1 , which is higher than 5.5 μGy air s -1 . And after about 30 consecutive on-off cycles (dose rate of 48.56 m y air s -1 , voltage of 70 kV) within 30 minutes, the RL intensity of Cs2ZrCl6@AAO decreased slightly, while that of Cs2ZrCl6: 3%Zn 2+ @AAO hardly changed. The modulation transfer function (MTF = 2) value of the Cs2ZrCl6: 3%Zn 2+ @AAO scintillator was 14.45 lp mm -1 , meeting the resolution criteria specified for most medical imaging systems and having a resolution higher than that of most commercial scintillators. The above scintillation performance indicates that Cs2ZrCl6: 3%Zn 2+ @AAO has strong radiation tolerance and shows its potential in future applications.

[0042] 7. Test the X-ray imaging performance of Example 10 using a self-made X-ray imaging system An X-ray image was taken using a Nikon D7100 camera equipped with a Nikon 18 - 105 mm f / 3.5 - 5.6 VR DX lens, where the focal length was set to 105 mm, ISO 2000, the aperture was f / 5.6, and the exposure time was approximately 90 s. From the test results, it can be seen that the Cs2ZrCl6: 3%Zn 2+ @AAO scintillator screen obtained in Example 10 of the present invention can display a capacitive pen, a Type-C interface ( Figure 16), the clear imaging of three types of objects: the shell and the magnetic plate ( Figure 17 ), and the standard lead plate ( Figure 18 ). It can be seen from Figure 18 that the imaging resolution of the Cs2ZrCl6: 3%Zn 2+ @AAO scintillator film reaches 14 line pairs per millimeter (lp / mm -1 ).

Claims

1. Zn-doped zirconium-based metal halide nanocrystals, characterized in that, The chemical general formula of the halide nanocrystals is Cs2ZrCl6: x %Zn 2+ , 1 ≤ x ≤ 8; and when x = 3, the light yield of the halide nanocrystals is 31,424 photons / MeV.

2. A method for preparing the Zn-doped zirconium-based metal halide nanocrystals as described in claim 1, characterized in that, The Cs2ZrCl6: x %Zn 2+ The halide nanocrystals are prepared by a thermal injection method, and the specific steps are as follows: 1) Dissolve zirconium chloride in octadecene, stir and heat at 55 - 70 °C for more than 30 min; then add cesium acetate, zinc acetate, oleic acid and oleylamine, fully mix and vacuum dry at 100 - 110 °C for 1 - 2 h to obtain a precursor solution; wherein, the molar ratio of zirconium chloride to cesium acetate is (1 - 2):1, the molar amount of zinc acetate is 1% - 8% of the molar amount of zirconium chloride, and the volume ratio of octadecene to oleic acid and oleylamine is (16 - 18):(4 - 6):1; 2) Under nitrogen protection, the precursor solution was heated to 200-210 °C and then trimethylchlorosilane was injected. After reacting for 0.1-10 min, it was cooled to room temperature, the precipitate was collected by centrifugation, washed, and dried under vacuum to obtain Cs2ZrCl6: x %Zn 2+ nanocrystals.

3. Preparation method of composite scintillator screen, characterized in that, Deposit the nanocrystals described in claim 1 on a porous substrate to form a composite scintillator screen.

4. The preparation method of the composite scintillator screen according to claim 3, characterized in that, The porous substrate is an anodic aluminum oxide template with a thickness range of 50 - 500 μm and a pore diameter range of 20 - 200 nm.

5. Composite scintillator screen, characterized in that, Prepared by the method described in claim 3.

6. Application of the composite scintillator screen described in claim 5 in X-ray medical imaging, non-destructive testing, and industrial flaw detection.

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