High-quality and large-size Cs2ZnCl4 single crystal as well as aqueous solution growth method and application thereof

Abstract

The invention provides a high-quality and large-size Cs2ZnCl4 single crystal as well as an aqueous solution growth method and application thereof. The Cs2ZnCl4 single crystal which is high in quality and large in size (gt, 30 * 30 * 30 mm < 3 >) and has a natural crystal face is successfully grown in deionized water by adjusting parameters such as solution pH, growth temperature, growth speed and the like, and the Cs2ZnCl4 single crystal is remarkably characterized in that almost all solvent components are water. The single crystal has excellent scintillation performance, slow attenuation components completely disappear, nearly 100% ultrafast attenuation is presented, and the attenuation time is 1.8 ns (99%). In addition, the scintillation wavelength of the crystal is 321 nm, and single-peak emission is presented. Meanwhile, the single crystal has excellent permeability, has ultrahigh transmittance (about 90%) in an ultra-wide wavelength range (260 nm to 15 m) of an ultraviolet-visible-infrared spectrum, can be used as a high-performance permeable window material, and has huge application potential.

Description

TECHNICAL FIELD

[0001] The present application relates to a high-quality, large-size Cs2ZnCl4 single crystal and its aqueous solution growth method and application, belonging to the technical field of optoelectronic material preparation. BACKGROUND

[0002] Scintillation crystals refer to crystals that can emit flashes of light by converting energy into light energy under the impact of high-energy particles such as X-rays, gamma rays, etc. X X-rays, gamma gamma rays, etc. As the core component of scintillation detectors, scintillation crystals with excellent performance are widely used in medical detection, safety detection, space exploration, nuclear medicine, and high-energy physics, and have become an important cornerstone for national security, social stability, and economic development in China. Ultrafast scintillators are a class of functional materials that can convert energy into detectable optical signals in a very short time (usually nanoseconds or even picoseconds) after absorbing high-energy particles or rays. Their core feature is the extremely short light emission decay time, which can accurately capture the motion trajectory or instantaneous energy deposition of high-speed particles, and is widely used in high-energy physics, nuclear medical imaging, and other fields that require high time resolution.

[0003] Currently, ultrafast scintillators are divided into three categories based on the scintillation light emission mechanism: cross-luminescence scintillators, direct band gap semiconductors, and luminescence with strong thermal quenching scintillators. The scintillation decay time is less than 3 ns, which can well meet the stringent requirements of high time resolution and high count rate in different application scenarios. Currently, three types of ultrafast scintillators such as BaF2, ZnO:Ga, YAP:Yb have been widely used in many fields. However, despite their excellent time performance, each of these ultrafast scintillators still has some difficult problems to overcome: (1) Slow components exist in scintillation light. Cross-luminescence scintillators generally have slow-decaying self-trapped exciton (STE) light components, such as the slow component (~630 ns) in BaF2 scintillation light, which accounts for more than 85%. This can cause serious signal stacking and increase the dead time of the detection system, greatly limiting its application.

[0004] (2) Strong volume dependence. Direct band gap semiconductors rely on near-band edge luminescence to achieve ultrafast scintillation, but the small Stokes shift resulting from this luminescence mechanism leads to strong self-absorption of the crystal to scintillation light. For example, the light yield and energy resolution of ZnO:Ga will decrease rapidly with increasing volume, which means that large-size ZnO:Ga does not have high application value.

[0005] (3) Poor stability of scintillation performance. Luminescence with strong thermal quenching scintillators have a strong temperature quenching effect. For example, YAP:Yb crystals cannot produce ultrafast scintillation at low temperatures. At higher temperatures, the scintillation decay time is sub-nanosecond, but the light yield is very low, and the application value is also not high.

[0006] (4) High cost. Growing high-quality, large-size ultrafast scintillation crystals using traditional methods (such as the Bridgman method) requires high-purity, water-free raw materials, and high requirements for equipment, which directly leads to high cost of traditional method for preparing ultrafast scintillation crystals, making it difficult to achieve large-scale application. Therefore, it is of great significance to explore new ultrafast scintillation crystals with ultrafast decay, high light yield, stable performance and low cost.

[0007] Based on the above problems, researchers are seeking a new type of ultrafast scintillation crystal, aiming to achieve an ultrafast scintillator with excellent ultrafast scintillation performance, no volume dependence, stable performance and low cost. In recent years, cross luminescence scintillator Cs2ZnCl4 single crystal has attracted great attention in the field of scintillation due to its excellent physical properties, and is expected to replace BaF2 as a new generation of ultrafast scintillator. The crystal has obvious advantages such as high effective atomic number, no deliquescence, no radioactive background, no toxic elements, colorless and transparent, etc. And its scintillation performance is stable, with a large Stokes shift and a fast decay component with a proportion close to 100%, which means it does not have the mechanism defect of cross luminescence. Such excellent ultrafast scintillator not only ensures the ultra-high time resolution and high count rate of the detection system, but also does not produce self-absorption, ensuring the accuracy of the detection signal, which is very suitable for scintillation detection.

[0008] In view of the above excellent physical indicators, in recent years, domestic and foreign researchers have rapidly carried out research work on the growth of large bulk Cs2ZnCl4 single crystals and their scintillation performance. In 2022, Shandong University and the University of Tennessee reported the growth of large bulk Cs2ZnCl4 single crystals, both of which exhibited excellent scintillation performance. Among them, the crystal obtained by the Bridgman method of the University of Tennessee is the most outstanding in terms of performance, with a scintillation decay time of only 1.66 ns, and the fast component luminescence is > 90%, which means that almost no slow component is detected, and the time resolution can reach 136 ps FWHM, surpassing almost all scintillators at present. In 137 Under the action of Cs γ-ray radiation, the light yield of Cs2ZnCl4 single crystal is 1980 ph. / MeV, which surpasses the currently widely used BaF2 (fast component light yield about 1400 ph. / MeV). Due to the almost no interference of slow component, Cs2ZnCl4 can be comparable to the ultrafast scintillator of the tip. After that, Cs2ZnCl4:Cu nanocrystal, Cs2ZnCl4:Mn 2+ crystal, Cs2ZnCl4:Sb 3+ microcrystal, Cs2ZnCl4:Zr 4+Crystal and so on are also grown successively, researchers add new energy level by doping activation ions, introduce STE emission in scintillation light, successfully optimize the light yield, quantum yield and other performances of Cs2ZnCl4. Among them, Cs2ZnCl4:Zr 4+ Under the premise of maintaining 100% ultrafast decay, the light yield is successfully improved to 28000 ph. / MeV, and excellent scintillation performance is exhibited. However, due to the limitation of growth technology, the Cs2ZnCl4 with optimized performance is still limited to low-quality, small-size powder-like grains, which greatly limits the industrial application of Cs2ZnCl4.

[0009] The above research shows that the Cs2ZnCl4 single crystal has excellent scintillation performance, and has great application potential as an ultrafast scintillator. However, there are still major problems in the growth of high-quality, large-size single crystals. At present, the growth method of the crystal is the Bridgman method, and the size of the grown Cs2ZnCl4 single crystal is small, the quality is poor, there are obvious bad faces and cracks, and the crystal quality has not reached the ideal level, which is difficult to meet the needs of practical application. In the process of crystal growth by the Bridgman method, the Cs2ZnCl4 single crystal is prone to cracking due to uneven temperature distribution and internal thermal stress. At the same time, the inconsistent solute segregation coefficient and uneven temperature field destroy the composition uniformity of the crystal, causing serious composition segregation problem, resulting in a large number of defects in the crystal, and thus the quality of the crystal is poor. There are defect energy levels in the energy band of such low-quality Cs2ZnCl4, which leads to slow component light emission, which directly affects the application value of Cs2ZnCl4. Therefore, it is of great significance to explore a method for growing high-quality, large-size Cs2ZnCl4 single crystals. SUMMARY

[0010] In view of the shortcomings of the prior art, the first object of the present application is to provide a new aqueous solution growth method of high-quality, large-size Cs2ZnCl4 single crystal. The present application successfully grows high-quality, large-size (>30×30×30 mm 3 ), natural crystal face Cs2ZnCl4 single crystal by adjusting the solution pH, growth temperature, growth rate and other parameters in the solvent (deionized water). The significant feature is that the solvent composition is almost water.

[0011] The second object of the present application is to provide a Cs2ZnCl4 single crystal. The Cs2ZnCl4 single crystal has excellent scintillation performance. The slow decay component of the crystal disappears completely, showing nearly 100% ultrafast decay with a decay time of 1.8 ns (99%). In addition, the scintillation light wavelength of the crystal is 321 nm, showing single peak emission.

[0012] Meanwhile, the Cs2ZnCl4 single crystal has excellent transmission performance. The crystal has ultrahigh transmittance (~90%) in an ultraviolet-visible-infrared spectrum in an ultrawide wavelength range (260 nm-15 µm). It is emphasized that the Cs2ZnCl4 single crystal can be used as a high-performance transmission window material, and has great application potential.

[0013] A third object of the present application is to provide application of the Cs2ZnCl4 single crystal in a high-performance optical window material or a scintillation detector.

[0014] To achieve the above objects, the present application is implemented by the following technical solutions: A high-quality and large-size Cs2ZnCl4 single crystal, which has an ultrafast decay time of 1.8 ns, a fast decay time of 5.8 ns, and no slow decay; a rocking curve half-width value of 50.4'', a band gap of 5.0 eV, and a size of >30×30×30 mm 3 ; a transmittance of 85%-95% in a range of 260 nm-15 µm; a single peak emission centered at 321 nm at room temperature 137 ; a light yield of 1320 Photons / MeV under Cs excitation, and an energy resolution of 15.3%.

[0015] The aqueous solution growth method of the high-quality and large-size Cs2ZnCl4 single crystal comprises the following steps: 1) mixing a chloride containing Zn 2+ , a chloride containing Cs + , and a hydrochloric acid-water solution, and fully dissolving to obtain a mixed solution; 2) fixing a seed crystal on a seed crystal holder, and placing it in the mixed solution obtained in step 1) for temperature reduction growth to obtain the high-quality and large-size Cs2ZnCl4 single crystal.

[0016] According to the present application, preferably, in step 1), the chloride containing Zn 2+ is ZnCl2, and the chloride containing Cs + is CsCl.

[0017] According to the present application, preferably, in step 1), the molar ratio of the chloride containing Zn 2+ to the chloride containing Cs + is 2:1.

[0018] According to the present application, preferably, in step 1), the hydrochloric acid-water solution is prepared by adding a hydrochloric acid aqueous solution with a mass concentration of 36%-38% into deionized water dropwise; and the pH of the hydrochloric acid-water solution is 0.5-0.6.

[0019] According to the application, preferably, in step 1), the molar amount of the chloride containing Zn 2+ and the volume ratio of the hydrochloric acid-water solution is 0.4-0.6 mol / L.

[0020] According to the application, preferably, in step 1), the sufficient dissolution is performed under stirring at 65-75℃.

[0021] According to the application, preferably, in step 2), the seed crystal growth method comprises the steps of: stirring the mixed solution obtained in step 1) at 70℃ for 2 days; obtaining a saturation temperature point of 50℃ by repeated cooling; stirring at 50℃ for 2 days to obtain a uniform and stable solution; setting the cooling program to decrease at a constant speed of 0.1℃ per day, and obtaining the seed crystal after 3 days of cooling growth.

[0022] According to the application, preferably, in step 2), the cooling growth comprises the steps of: naturally cooling to 51℃, at which time the seed crystal starts to grow; then cooling at a rate of 0.1-0.5℃ / day, and the seed crystal rotating at a speed of 45-55 hz, to obtain a high-quality and large-size Cs2ZnCl4 single crystal after 40-60 days of cooling growth.

[0023] The above high-quality and large-size Cs2ZnCl4 single crystal is applied to high-performance optical window materials or scintillation detectors.

[0024] The technical features and excellent effects of the application are as follows: 1. The Cs2ZnCl4 single crystal of the application has a large size (>30×30×30 mm 3 ), not only has natural crystal faces and more regular zero-dimensional structures in line with crystal habits, but also has a high consistency of atomic proportions at different positions and good crystallinity.

[0025] 2. The Cs2ZnCl4 single crystal of the application is the first perovskite single crystal successfully grown in water, breaking the long-held cognition that perovskite crystals are incompatible with water environment.

[0026] 3. The Cs2ZnCl4 single crystal of the application is the first Cs2ZnCl4 single crystal grown by an innovative aqueous solution method. The single crystal exhibits unique and adjustable growth behavior, and the half-height width value of the rocking curve is only 50.4'', and the crystal quality is significantly improved.

[0027] 4. The Cs2ZnCl4 single crystal in the prior art has a significant slow decay component, which is the technical "pain point" to be solved by the application. The Cs2ZnCl4 single crystal of the application has a complete fast scintillation decay characteristic at room temperature, i.e., the fast decay component accounts for 100%, and the ultrafast scintillation decay component (1.8 ns) accounts for 99%. Compared with the previous reports, the application completely eliminates the slow decay. The ultrafast decay time approaches the theoretical limit of 100%, setting a new record.

[0028] 5. The Cs₂ZnCl₄ single crystal of this invention exhibits single-peak emission characteristics at room temperature, with a peak position of 321 nm. Compared with previous reports, this represents an optimization from multi-peak emission to single-peak emission. Single-peak emission offers higher color purity and more stable light color compared to multi-peak emission. Single-peak emission refers to the luminescent material exhibiting only one distinct emission peak in the spectrum, corresponding to high color purity, suitable for applications such as displays and lighting where high color accuracy is required. Multi-peak emission, on the other hand, with multiple emission peaks, easily leads to mixed light colors, reducing color saturation and visual experience. Single-peak emission reduces the need for filters or optical correction, simplifies device structure, and improves luminous efficiency and system stability. Multi-peak emission often requires additional optical processing to separate or suppress extraneous peaks, increasing system complexity and cost.

[0029] 6. The Cs2ZnCl4 single crystal of the present invention has excellent environmental stability. It does not absorb moisture even after being placed at 40 °C and 70% relative humidity for 20 days.

[0030] 7. The Cs2ZnCl4 single crystal of the present invention has ultra-high transmittance (~90%) in an ultra-wide wavelength range (260 nm-15 µm), indicating that the crystal can be used as a high-performance transmission window material.

[0031] 8. The growth method of this invention is an aqueous solution method, which utilizes the high solubility of cesium chloride and zinc chloride in water. Only deionized water is used as the solvent. By adjusting parameters such as solution pH, growth temperature, and growth rate, high-quality, large-sized (>30×30×30 mm) cesium chloride has been successfully grown. 3 This invention produces Cs₂ZnCl₄ single crystals with natural crystal faces. The raw materials required are only conventional zinc chloride and cesium chloride, eliminating the need for high-purity raw materials. The growth equipment is mature and simple, significantly reducing costs. The preparation method of this invention is simple, has low equipment dependence, is economical, and is easy to implement for industrial application.

[0032] 9. The growth method of this invention allows for device design based on the target crystal size, enabling the growth of large-size single crystals. The crystal growth process can be observed in real time, achieving precise control over crystal growth.

[0033] 10. The Cs₂ZnCl₄ single crystal of the present invention in a gamma-ray source ( 241 Am、 137 Under Cs irradiation, they exhibit excellent light yield and energy resolution, and have great application potential in the field of scintillation detection.

[0034] 11. In the growth method of this invention, suitable temperature, seed crystal, and cooling rate are relatively important.

[0035] The growth temperature needs to be appropriate. The temperature should be in the metastable zone range of the solution, which is the "golden region of crystal nucleation and growth": a temperature higher than the metastable zone is easy to cause the supersaturation to be too low, the crystal growth to be slow or not to grow; below the metastable zone, the supersaturation increases suddenly, and a large number of spontaneous nucleation is triggered (forming polycrystals, powder, rather than single crystals).

[0036] The seed crystal is a "template for single crystal growth": the orientation, purity and defect state of the seed crystal directly determine the lattice integrity of the grown single crystal (such as seed crystal orientation deviation will cause twin crystal of single crystal, and defects will be transferred to the finished crystal). Influence performance consistency: for ultrafast scintillators, the luminescent center distribution and optical uniformity of the seed crystal will directly affect the scintillation decay time and light output intensity of the finished product (such as high-purity seed crystal can reduce luminescence quenching center). The seed crystal prepared by the method of the present application has high lattice matching degree with the target single crystal, high purity, no dislocation and no cracking, which is beneficial to obtain high-quality target single crystal.

[0037] The cooling rate control is the core process condition to protect the lattice integrity of the ultrafast scintillator single crystal and reduce the generation of defects, and its importance and specific description are as follows: ① Technical principle level: the cooling process is the "solidification stage" of the transition of crystal atoms from molten state to ordered lattice state, and the cooling rate directly determines the order degree of atomic arrangement - slow and accurate cooling can give atoms enough time to arrange in the direction of the seed crystal lattice, avoiding defects such as vacancies and dislocations caused by insufficient atomic migration; ② Influence on process: the rationality of the cooling rate range of the present application is reflected in: if the cooling rate is too fast: the atoms cannot arrange in order, and a large stress will be generated in the crystal, leading to single crystal cracking and increasing twin crystal defects; if the cooling rate is too slow: the crystal growth period is greatly prolonged, and the raw material composition is easy to segregate, forming impurities. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 It is a physical picture of the Cs2ZnCl4 crystal obtained in Example 2.

[0039] Figure 2 It is a rocking curve diagram of the Cs2ZnCl4 crystal obtained in Example 2.

[0040] Figure 3 It is a solubility-super saturation curve diagram of the Cs2ZnCl4 crystal obtained in Example 2.

[0041] Figure 4 It is a UV-Vis-IR transmission spectrum diagram of the Cs2ZnCl4 crystal obtained in Example 2.

[0042] Figure 5 It is a crystal growth equipment diagram of aqueous solution method.

[0043] Figure 6 A growth process diagram for the Cs2ZnCl4 crystal obtained in Example 2 by the aqueous solution method.

[0044] Figure 7 A crystal structure diagram for the Cs2ZnCl4 crystal obtained in Example 2.

[0045] Figure 8 An X-ray diffraction pattern for the Cs2ZnCl4 crystal obtained in Example 2.

[0046] Figure 9 An elemental energy dispersive surface analysis diagram for the Cs2ZnCl4 crystal obtained in Example 2.

[0047] Figure 10 A band structure diagram for the Cs2ZnCl4 crystal obtained in Example 2.

[0048] Figure 11 A density of states distribution diagram for the Cs2ZnCl4 crystal obtained in Example 2.

[0049] Figure 12 An ultraviolet-visible diffuse reflectance spectrum diagram for the Cs2ZnCl4 crystal obtained in Example 2.

[0050] Figure 13 A core band-valence band-conduction band wave function isosurface diagram for the Cs2ZnCl4 crystal obtained in Example 2.

[0051] Figure 14 An X-ray photoelectron spectroscopy valence band spectrum diagram for the Cs2ZnCl4 crystal obtained in Example 2.

[0052] Figure 15 A transmission spectrum diagram for the Cs2ZnCl4 crystal obtained in Example 2.

[0053] Figure 16 A refractive index diagram for the Cs2ZnCl4 crystal obtained in Example 2.

[0054] Figure 17 A light yield and energy resolution diagram for the Cs2ZnCl4 crystal obtained in Example 2.

[0055] Figure 18 A scintillation decay time diagram for the Cs2ZnCl4 crystal obtained in Example 2.

[0056] Figure 19 An X-ray excited luminescence spectrum diagram for the Cs2ZnCl4 crystal obtained in Example 2.

[0057] Figure 20Mass change diagram of Cs2ZnCl4 crystals obtained in Example 2 at 40 °C, 70 % relative humidity for 20 days.

[0058] Figure 21 Cs2ZnCl4 crystals obtained in Example 2 137 Temperature dependence test diagram under Cs excitation. DETAILED DESCRIPTION

[0059] The specific embodiments of the present application will be further described with the following examples. It is to be understood that the examples are merely described for the purpose of illustration and are not to be construed as limiting the present application as described in the detailed description of the application.

[0060] Example 1: Obtaining of seed crystal First, deionized water (700 ml) was added to a beaker, and then the pH value was adjusted to about 0.58 by adding hydrochloric acid solution with a mass concentration of 38% dropwise and stirring uniformly. Then, cesium chloride (125.002 g, 0.742 mol) and zinc chloride (50.605 g, 0.371 mol) were added, and the temperature was heated to 70 °C for stirring to achieve complete dissolution of the raw materials. Then, the mixed solution was transferred to a crystal growth flask, and the temperature was kept at 70 °C for stirring for 2 days (stirring speed 50 hz). Then, by repeatedly lowering the temperature, the saturation temperature point was obtained as 50 °C, and the temperature was kept at 50 °C for stirring for 2 days (stirring speed 50 hz) to obtain a uniform and stable solution. The temperature controller was set to have a lowering program of 0.1 °C per day at a constant speed. After 3 days, a plurality of small-size Cs2ZnCl4 seed crystals with high gloss were obtained.

[0061] Example 2: Growth of large-size Cs2ZnCl4 crystals 1) Small-size single crystals obtained in Example 1 were used as seed crystals, deionized water solution (700 ml) was added to a beaker, and then the pH value was adjusted to 0.58 by adding hydrochloric acid solution with a mass concentration of 38% dropwise and stirring uniformly. Then, cesium chloride (125.002 g, 0.742 mol) and zinc chloride (50.605 g, 0.371 mol) were added, and the temperature was heated to 70 °C for stirring to achieve complete dissolution of the raw materials. Then, the mixed solution was transferred to a crystal growth flask; the seed crystal was stuck on a seed crystal holder and placed in the mixed solution in the growth flask for temperature lowering growth.

[0062] 2) Natural temperature lowering to 51 °C, at which time the seed crystal started to grow. After temperature lowering growth for 40 days at a temperature lowering rate of 0.1 °C per day and a seed crystal rotation speed of 50 hz, large-size and transparent Cs2ZnCl4 single crystals were obtained.

[0063] Preparation of seed crystal for Comparative Example 1 Firstly, deionized water (700 ml) was added into a beaker, then the pH value was adjusted to about 0.58 by adding hydrochloric acid solution with a mass concentration of 38% dropwise and stirring uniformly. Then cesium chloride (125.002 g, 0.742 mol) and zinc chloride (50.605 g, 0.371 mol) were added, and the temperature was heated to 70°C for stirring to achieve complete dissolution of the raw materials. Then the above mixed solution was transferred to a crystal growth flask, and constant temperature stirring was carried out at 70°C for 2 days (stirring speed 50 hz). Then, by repeatedly lowering the temperature, the saturation temperature point was 50°C, and constant temperature stirring was carried out at 50°C for 2 days (stirring speed 50 hz) to obtain a uniform and stable solution. The temperature controller was set to a cooling program of 0.5°C per day at a constant speed. After 3 days, several large-size low-quality Cs2ZnCl4 seed crystals were obtained. The seed crystal had poor quality and no practical significance.

[0064] Test Example 1. Habit of Cs2ZnCl4 crystal Figure 3 The solubility-super-saturation curve of the Cs2ZnCl4 crystal obtained in Example 2 has a metastable zone affected by temperature, indicating that the growth habit in the aqueous solution of the crystal is controllable.

[0065] Figure 5 The aqueous solution method crystal growth equipment for the Cs2ZnCl4 crystal obtained in Example 2 realizes controllable growth of the crystal by controlling the solution environment conditions.

[0066] Figure 6 The aqueous solution method growth process for the Cs2ZnCl4 crystal obtained in Example 2.

[0067] The above shows that the Cs2ZnCl4 crystal grown by the aqueous solution method of the present application is completely appropriate and feasible, and has great application potential. In addition, the aqueous solution method is expected to be expanded into an effective method for growing such metal halide scintillation crystals.

[0068] 2. Quality of Cs2ZnCl4 crystal Figure 1 The Cs2ZnCl4 crystal obtained in Example 2 has complete natural crystal faces and a large size (~30x30x30 mm 3 ).

[0069] Figure 2 The rocking curve measured after the Cs2ZnCl4 crystal obtained in Example 2 was processed into a wafer, and the full width at half maximum value was only 50.4''.

[0070] Figure 7The crystal structure of the Cs2ZnCl4 crystal obtained in Example 2 has a more regular zero-dimensional structure.

[0071] Figure 8 The X-ray diffraction pattern of the Cs2ZnCl4 crystal obtained in Example 2 is highly consistent with the PDF card.

[0072] Figure 9 The elemental energy distribution area analysis of the wafer processed from the Cs2ZnCl4 crystal obtained in Example 2 shows that the atomic ratios in different directions are highly consistent.

[0073] The above data show that the Cs2ZnCl4 single crystal grown by the method has extremely high quality and great application value.

[0074] 3. Optical properties of Cs2ZnCl4 crystal Figure 12 The ultraviolet-visible diffuse reflectance spectrum of the Cs2ZnCl4 crystal obtained in Example 2 shows that the band gap value is about 5.0 eV.

[0075] Figure 16 The refractive index of the Cs2ZnCl4 crystal obtained in Example 2 shows that it has a relatively low refractive index surface suitable for application in optoelectronic devices.

[0076] Figure 15 The transmission spectrum of the Cs2ZnCl4 crystal obtained in Example 2 is consistent with the theoretical value.

[0077] Figure 4 The ultraviolet-visible-infrared transmission spectrum of the Cs2ZnCl4 crystal obtained in Example 2 shows that the transmittance in the range of 260 nm-15 µm is about 90%, which is superior to commercially available CaF2, Si, Al2O3, ZnS and ZnSe wafer. This shows that the Cs2ZnCl4 crystal grown by the aqueous solution of the application not only has the advantages of high quality and large size, but also exhibits high transmittance in a super wide frequency band, and has great application potential in the field of high-performance transmittance window materials.

[0078] 4. Electronic structure properties of Cs2ZnCl4 crystal Figure 10 The energy band structure of the Cs2ZnCl4 crystal obtained in Example 2 shows that the optical band gap is about 4.9 eV and 3.8 eV, and the band gap is about 5.1 eV.

[0079] Figure 12 The ultraviolet-visible diffuse reflectance spectrum of the Cs2ZnCl4 crystal obtained in Example 2 shows that the band gap is about 5.0 eV, which is consistent with the theoretical value.

[0080] Figure 11 The crystal state density of states plot of Cs2ZnCl4 obtained in Example 2, where Cl - The top of the valence band is composed of Zn 2+ The top of the core band is composed of Zn.

[0081] Figure 13 The core band-valence band-conduction band wave function contour plot of Cs2ZnCl4 crystal obtained in Example 2, showing the electronic structure.

[0082] Figure 14 The X-ray photoelectron spectroscopy valence band spectrum of Cs2ZnCl4 crystal obtained in Example 2, with an optical band gap of about 4.8 eV and 3.8 eV.

[0083] The above data show that the electronic structure of the Cs2ZnCl4 crystal grown by this method is highly consistent with the theoretical prediction, fully meeting the theoretical expectation.

[0084] 5. Scintillation performance characterization of Cs2ZnCl4 crystal Figure 19 The X-ray excitation luminescence spectrum of Cs2ZnCl4 crystal obtained in Example 2, compared with previous reports, its emission peak changes from multi-peak emission to single-peak emission centered at 321 nm. It has more excellent luminescence performance, completely eliminating impurity and defect luminescence.

[0085] Figure 18 The scintillation decay time of Cs2ZnCl4 crystal obtained in Example 2 is 1.8 ns (99%) and 5.8 ns (1%), without any slow decay.

[0086] Figure 17 The light yield and energy resolution of Cs2ZnCl4 crystal obtained in Example 2, at room temperature 137 The light yield of this crystal under Cs excitation is 1320 ph. / MeV, and the energy resolution is 15.3 %.

[0087] Figure 21 Cs2ZnCl4 crystal obtained in Example 2 137 Temperature dependence test under Cs excitation. The light yield changes by ~2700 to ~1300 photons / MeV in the temperature range of 75 K to 300 K.

[0088] These data show that this Cs2ZnCl4 crystal grown by aqueous solution method of the present application has excellent scintillation properties, and has great potential for application in the field of scintillation detection.

[0089] 6. Cs2ZnCl4 crystal has excellent environmental stability Figure 20The results of the hygroscopicity evaluation of the Cs2ZnCl4crystals obtained in Example 2 show that the mass change of five Cs2ZnCl4single crystal samples within 20 days at 40 °C, 75% relative humidity is close to zero, meeting most of the criteria for non-hygroscopic materials. This shows that the Cs2ZnCl4single crystals grown by this method have excellent environmental stability and do not have the phenomenon of deliquescence.

[0090] From the above, compared with previous reports, the Cs2ZnCl4single crystal is closer to the theoretical prediction in terms of crystal structure, electronic structure and scintillation properties: its band gap value reaches 5.0 eV, surpassing all previous reported values; its luminescence spectrum presents a single peak emission (321 nm), which is significantly different from previous reports; the ultrafast decay time approaches the theoretical limit of 100% - setting a new record. The Cs2ZnCl4single crystal of the present application has ultra-high transmittance (~ 90%) in an ultra-wide wavelength range (260 nm-15 µm), and other technical patents do not have the highest transmittance value.

Claims

1. A high-quality, large-size Cs₂ZnCl₄ single crystal, characterized in that, The Cs₂ZnCl₄ single crystal exhibits an ultrafast decay time of 1.8 ns (accounting for 99%), a fast decay time of 5.8 ns (accounting for 1%), and no slow decay. Its rocking curve has a full width at half maximum (FWHM) of 50.4'', a band gap of 5.0 eV, and dimensions >30×30×30 mm. 3 The transmittance is 85%-95% in the 260 nm-15 µm range; it exhibits single-peak emission centered at 321 nm at room temperature; room temperature 137 The Cs-excited light yield is 1320 Photons / MeV, with an energy resolution of 15.3%.

2. The method for growing high-quality, large-size Cs₂ZnCl₄ single crystals in aqueous solution as described in claim 1, comprising the following steps: 1) Containing Zn 2+ Chlorides, containing Cs + The chloride and hydrochloric acid-water solution are mixed and dissolved completely to obtain a mixed solution; 2) Fix the seed crystal on the seed crystal holder and place it in the mixed solution obtained in step 1) for cooling growth to obtain high-quality, large-size Cs2ZnCl4 single crystals.

3. The method for growing high-quality, large-size Cs₂ZnCl₄ single crystals in aqueous solution according to claim 2, characterized in that, Step 1) contains Zn 2+ The chloride is ZnCl2, which contains Cs. + The chloride is CsCl.

4. The method for growing high-quality, large-size Cs₂ZnCl₄ single crystals in aqueous solution according to claim 2, characterized in that, Step 1) contains Zn 2+ Chlorides, containing Cs + The molar ratio of chlorides is 2:

1.

5. The method for growing high-quality, large-size Cs₂ZnCl₄ single crystals in aqueous solution according to claim 2, characterized in that, In step 1), the hydrochloric acid-water solution is prepared by adding a 36%-38% hydrochloric acid-water solution dropwise to deionized water; the pH of the hydrochloric acid-water solution is 0.5-0.

6.

6. The method for growing high-quality, large-size Cs₂ZnCl₄ single crystals in aqueous solution according to claim 2, characterized in that, Step 1) contains Zn 2+ The molar amount of chloride and the volume ratio of hydrochloric acid to aqueous solution are 0.4-0.6 mol / L.

7. The method for growing high-quality, large-size Cs₂ZnCl₄ single crystals in aqueous solution according to claim 2, characterized in that, In step 1), complete dissolution is carried out under stirring conditions at 65-75℃.

8. The method for growing high-quality, large-size Cs₂ZnCl₄ single crystals in aqueous solution according to claim 2, characterized in that, In step 2), the seed crystal growth method includes the following steps: stirring the mixed solution obtained in step 1) at 70°C for 2 days; obtaining a saturation temperature of 50°C by repeatedly cooling; and stirring at 50°C for 2 days to obtain a uniform and stable solution. The cooling program was set to decrease at a constant rate of 0.1℃ per day, and seed crystals were obtained after 3 days of cooling growth.

9. The method for growing high-quality, large-size Cs₂ZnCl₄ single crystals in aqueous solution according to claim 2, characterized in that, In step 2), the cooling growth includes the following steps: naturally cooling to 51℃, at which point the seed crystal begins to grow; then cooling at a rate of 0.1-0.5℃ / day and a seed crystal rotation speed of 45-55 Hz for 40-60 days to obtain high-quality, large-size Cs2ZnCl4 single crystals.

10. The application of the high-quality, large-size Cs2ZnCl4 single crystal as described in claim 1 in high-performance optical window materials or scintillation detectors.

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