CN113512757B - A kind of bulk high-quality scintillation crystal and its preparation method and application - Google Patents

Abstract

The invention relates to a high-quality flash blockScintillation crystal and preparation method and application thereof, wherein the scintillation crystal is CsMgX ₃ The crystal is a substrate, and is doped or not doped with rare earth elements and/or alkali metals; the rare earth element is one of Eu and Pr; the alkali metal is ⁶ Li, the bulk, high quality, crack-free single crystals were first grown using the Bridgman method. The scintillation crystal obtained by the invention is a novel all-inorganic halogen perovskite block crystal, and the scintillation crystal is a novel all-inorganic halogen perovskite block crystal, and has the advantages of large block crystal size, crystal diameter of 10-25mm, good crystal quality, high transmittance and small refractive index. The decay time is very short, only a few nanoseconds, the scintillation crystal with the luminescence can realize double detection of neutrons and gamma rays, has high atomic number and smaller band gap, and is a scintillation crystal with great application prospect.

Description

A kind of bulk high-quality scintillation crystal and its preparation method and application

technical field

The invention relates to a bulk high-quality scintillation crystal, a preparation method and application thereof, and belongs to the technical field of crystal growth.

Background technique

Scintillator is a kind of material that can emit visible light after absorbing high-energy particles or rays, and plays a very important role in the field of radiation detection. Under the irradiation of high-energy rays, the visible light emitted by the scintillator is converted into electrical signals through photomultiplier tubes, photodiodes or avalanche photodiodes, etc., so as to detect or image high-energy particles or rays. In medicine, scintillator is the core component of nuclear medicine imaging equipment, through which the lesions of various organs of the human body, the size and location of tumor tissue can be quickly diagnosed. It also plays an irreplaceable role in baggage security inspection, non-destructive testing, radioactive detection and other fields. At the same time, the scintillator is also an important material for the manufacture of electromagnetic calorimeters in various colliders. It can capture the information of various particles generated after nuclear reactions, and is an important tool for mankind to explore the mysteries of the microscopic world and the evolution of the universe. Ultrafast scintillator materials refer to scintillator materials with a response time of less than 4ns (10 ^-9 s). Such materials play a pivotal role in pulsed radiation detection, solar neutrino detection, reaction dynamics, inertial confinement fusion, and cosmic ray research.

Although different applications have different requirements for scintillators, scintillators are used to detect ionizing radiation in most applications, so scintillators are required to have high blocking ability to ionizing radiation, that is, scintillators are required to have high Density and contains elements with large atomic numbers.

At present, the commonly used scintillator materials can be divided into three categories: organic scintillators, inorganic scintillators, and composite scintillators. It has the characteristics of high light yield, fast response speed, short decay time and good stability. Composite scintillator is a new type of scintillator prepared by dispersing inorganic scintillator as solute in organic scintillator.

Inorganic scintillators are divided into oxide scintillators and halide scintillators according to different compositions. Oxide scintillators have large effective atomic numbers, stable physical and chemical properties but large band gaps, generally low light yields, and poor energy resolution. Therefore, At present, halide scintillation crystals have become a research hotspot as new scintillation materials with high light yield and high energy resolution.

The advantages of halide scintillation crystals are high light yield, good energy resolution, and simple components. With the development of ABX3-type perovskite compounds, perovskite scintillation crystal materials with scintillation properties have been gradually discovered. The substitution of the halogen at the X position in A BX3 can realize the regulation of the crystal band gap and meet the application in different situations. The halogen perovskite material has quickly become the next generation of new light-emitting materials due to its structural diversity and excellent optoelectronic properties.

SUMMARY OF THE INVENTION

Aiming at the advantages of high light yield, excellent energy resolution and fast decay time of the existing halogen perovskite scintillation crystals, the present invention provides a generally bulk high-quality scintillation crystal and a preparation method and application thereof. The scintillation crystal obtained by the invention is a novel all-inorganic halogen perovskite bulk crystal, the bulk crystal is large in size, has CVL luminescence, and meets the requirements of medical imaging for rapid decay.

By improving the process, the present invention uses the Bridgman method to grow a bulk high-quality crack-free single crystal for the first time.

The technical scheme of the present invention is as follows:

A bulk high-quality scintillation crystal, the scintillation crystal is based on a CsMgX ₃ crystal, doped or not doped with rare earth elements and/or alkali metals.

Preferably according to the present invention, the rare earth element may be one of Eu, Pr, and Pr.

Preferably in the present invention, the rare earth element is Eu.

Eu ion has a 5d-4f transition, and the 5d orbital is completely exposed, which is greatly affected by the environment, which is beneficial to improve the scintillation response ability, and Eu ion can be equivalently substituted with Mg, so Eu ion is the most preferred.

Preferably in the present invention, the alkali metal is ⁶ Li.

该反应使得该晶体可以实现对热中子的探测。The presence of ⁶ Li will cause a nuclear reaction with neutrons:

The reaction allows the crystal to detect thermal neutrons.

On the basis that the above-mentioned rare earth element is Eu and the alkali metal is ⁶ Li, it is further preferred:

The general chemical formula of scintillation crystals is:

Cs _x ⁶ Li _1-x Mg _y Eu _1-y X ₃ ; wherein 0≤x≤1, 0≤y≤1, and X is selected from one of I, Br, and Cl.

The crystal is a perovskite crystal, and the change of the elements (I, Br, Cl) in the X position will affect the band gap of the crystal, and then affect other properties of the crystal.

When X is selected from I, the rare earth element-doped perovskite crystal is Cs _x ⁶ Li _1-x Mg _y Eu _1-y I ₃ . This type of crystal has a small band gap, is expected to have high light yield and low energy resolution, and is a very potential scintillation crystal.

When X is selected from Br, the rare earth element-doped perovskite crystal is Cs _x ⁶ Li _1-x Mg _y Eu _1-y Br ₃ .

When X is selected from Cl, the rare earth element-doped perovskite crystal is Cs _x ⁶ Li _1-x Mg _y Eu _1-y Cl ₃ .

Preferably according to the present invention, when x=1, 0<y<1, the scintillation crystal is a rare earth element doped perovskite crystal.

Preferably according to the present invention, when x=1, 0<y<1, the rare earth element-doped perovskite crystal is selected from one of the following: CsMg _y I ₃ :Eu _1-y , CsMg _y Br ₃ :Eu _1-y , CsMg _y Cl ₃ :Eu _1-y .

Preferably according to the present invention, when 0<x<1 and y=1, the scintillation crystal is an alkali metal-doped perovskite crystal.

When X is selected from I, the alkali metal-doped perovskite crystal is Cs _x MgI ₃ : ⁶ Li _1-x .

When X is selected from Br, the alkali metal-doped perovskite crystal is Cs _x MgBr ₃ : ⁶ Li _1-x .

When X is selected from Cl, the alkali metal-doped perovskite crystal is Cs _x MgCl ₃ : ⁶ Li _1-x .

_CsMgCl3 possesses CVL luminescence with extremely fast decay time. After doping with ⁶ Li, double detection of γ-ray and neutron can be realized.

Preferably according to the present invention, when 0<x<1, y=1, the rare earth element-doped perovskite crystal is selected from one of the following: Cs _x MgI ₃ : ⁶ Li _1-x , Cs _x MgBr ₃ : ⁶ Li _1-x , Cs _x MgCl ₃ : ⁶ Li _1-x .

Preferably according to the present invention, when x=1, y=1, the scintillation crystal is CsMgX ₃ , and X is selected from one of I, Br, and Cl.

Preferably according to the present invention, when 0≤x≤1, 0≤y≤1, x≠1, y≠1, the scintillation crystal Cs _x ⁶ Li _1-x Mg _y Eu _1-y X ₃ is a rare earth element and an alkali metal Co-doped crystals can emit light under the irradiation of neutrons and gamma rays, realizing dual detection of neutrons and gamma rays.

The second object of the present invention is to provide a method for preparing a substantially bulk high-quality scintillation crystal.

Aiming at the strong deliquescence of the existing scintillation crystal and easy periodic cracking along the vertical growth plane, the present invention uses the Bridgman method to grow a bulk high-quality crack-free single crystal for the first time by improving the process.

A method for preparing a bulk high-quality scintillation crystal, comprising the following steps:

1) According to the stoichiometric ratio, mix CsX and MgX ₂ uniformly in a glove box, with or without ⁶ LiX and/or EuX ₂ , to obtain a mixed material, put the mixed material into a quartz tube, and then pump vacuum, sealing;

2) put the sealed quartz tube in a resistance furnace, circulate three times in a heating-cooling-heating manner, keep a constant temperature at 400-680°C for 8-15 hours, and cool down to room temperature to obtain a polycrystalline material;

3) Put the quartz tube containing the polycrystalline material into the crucible descending furnace, heat up to 300-680 ° C, keep the temperature for 8-15 hours, adjust the position of the quartz tube, so that the temperature of the spontaneous nucleation zone or the inoculation zone at the bottom of the quartz tube is high. At the melting point of 1-5°C, the temperature gradient in the single crystal growth furnace is 5-15°C/cm, and then the quartz tube is slowly lowered at a speed of 0.03-0.05mm/h. At the same time, the growth temperature is kept unchanged. After the growth is completed , the temperature of the growth furnace is first cooled to 180-220° C., and then naturally cooled to room temperature, so as to obtain roughly high-quality scintillation crystals.

Preferably according to the present invention, in step 1), the degree of vacuum after vacuuming is 10 ⁻⁶ mbar.

Preferably according to the present invention, in step 2), the heating-cooling-heating method is specifically: firstly heating up to 400-650°C at a rate of 50-100°C/h, and then cooling down 100°C at a rate of 30-50°C/h -150°C, and then heated to 500-650°C at a rate of 50-100°C/h for three cycles. Allow the reaction to proceed sufficiently to ensure that the composition of the polycrystalline material is uniform.

Preferably according to the present invention, in step 2), the cooling rate of cooling to room temperature is 1-15°C/h.

The preparation method of the present invention obtains a bulk single crystal with a diameter of 10-20 mm, no crack and no deliquescence.

The utility model relates to an application of a high-quality scintillation crystal of a large block, and is used in the fields of national defense, medical treatment, security inspection, nuclear non-proliferation and the like to realize neutron detection or neutron and gamma ray dual detection.

The luminescence principle of the novel all-inorganic halogen perovskite bulk crystal of the present invention:

When the CsMgI3 crystal is excited by external γ-rays, electron transitions will occur. The electrons transition from the valence band to the conduction band and absorb the energy of the γ-rays. The electrons after the transition belong to high-energy electrons and are in an unstable state, and de-excitation to the valence band will occur. At the same time, the energy is released in the form of photons, and this process is the scintillation process of the crystal. According to the analysis of the photons emitted by this process, the analysis of gamma rays can be realized.

CsMgI ₃ : The entry of Eu ions in the Eu crystal will form a new impurity energy level between the valence band and the conduction band of the crystal, so that when the crystal is excited, it will transition to a lower energy impurity energy level, and the electrons excited by the same energy More, the more photons are released when de-excited, the greater the light yield of the crystal, the higher the scintillation efficiency, and the better the responsiveness.

CsMgCl3 crystal not only has the same transition between electron valence band and conduction band as CsMgI3 crystal, but also has electronic transition between core band and valence band. This process also produces energy absorption and release, and because the region that occurs is in the core band and the valence band, so the time is very short, this process is the CVL luminescence process of CsMgCl3 crystal.

该反应会将中子的能量转化为电子的能量并在随后的退激过程中放出光子，由于该过程涉及的步骤较多通常时间跨度较CVL的时间长，通过对两种信号的时间分析就可以实现对于中子/γ信号的区分，从而实现中子/γ双探测。When the crystal is ⁶ Li xCs1-xMgCl3, due to the existence of 6Li, the crystal will undergo a nuclear reaction with thermal neutrons:

This reaction converts the energy of neutrons into the energy of electrons and emits photons in the subsequent de-excitation process. Because this process involves more steps, the time span is usually longer than that of CVL. The differentiation of neutron/gamma signals can be achieved, thereby realizing neutron/gamma dual detection.

Advantages and technical features of the present invention:

1. The scintillation crystal of the present invention is a novel all-inorganic halogen perovskite bulk crystal, the bulk crystal size is large, the crystal diameter is 10-25mm, the crystal quality is good, the transmittance is high, and the refractive index is small.

2. The scintillation crystal of the present invention has core-valence luminescence, and the decay time is extremely short, only a few nanoseconds. The scintillation crystal with such luminescence can realize double detection of neutrons and gamma rays.

3. The scintillation crystal of the present invention contains heavy ions, has a high atomic number and a small band gap, and is a very promising scintillation crystal.

Description of drawings

Fig. 1 is the CsMg _0.99 Eu _0.01 I ₃ crystal with a diameter of 15 mm obtained in Example 1 and the photo of the cross-sectional slice, a is the photo of the CsMg _0.99 Eu _0.01 I ₃ scintillation crystal, and b is the photo of the wafer after cutting;

Fig. 2 is the powder XRD pattern measured by grinding the _{CsMg 0.99} Eu _0.01 I crystal with a diameter of 15 mm obtained in Example 1 into powder;

Fig. 3 is the CsMg _0.99 Eu _0.01 I ₃ crystal 1% photoluminescence spectrum with a diameter of 15 mm obtained in Example 1;

Fig. 4 is the crystal photograph of CsMg _0.95 Eu _0.05 Cl ₃ obtained in Example 2;

Fig. 5 is the CsMg _0.95 Eu _0.05 Cl ₃ crystal photoluminescence spectrum obtained in Example 2;

Fig. 6 is the CsMgCl crystal photograph of the diameter 12mm obtained in Example ₃ ;

Fig. 7 is the powder XRD pattern measured by grinding the CsMgCl crystal with a diameter of 12 mm obtained in Example ₃ into powder;

8 is a photograph of the Cs _0.99 ⁶ Li _0.01 MgI ₃ scintillation crystal obtained in Example 4.

Detailed ways

The present invention will be further described below with reference to the embodiments and the accompanying drawings.

Example 1

The preparation of CsMg _0.99 Eu _0.01 I ₃ bulk crystal, the steps are as follows:

1) Mix CsI, MgI ₂ and EuI ₂ uniformly in a stoichiometric ratio in a glove box, put into a quartz tube and seal, and the vacuum degree reaches 10 ^-6 mbar.

2) Put the sealed quartz tube into a resistance furnace, heat up to 450°C at a rate of 100°C/h, then cool down by 100°C at a rate of 50°C/h, and then heat up to 450°C at a rate of 100°C/h , after three cycles, the temperature was kept at 450 °C for 10 hours, and then decreased to 25 °C at a rate of 15 °C/h to obtain CsMg _0.99 Eu _0.01 I ₃ polycrystalline;

3) Put the quartz tube containing CsMg _0.99 Eu _0.01 I ₃ polycrystalline into the crucible descending furnace, heat up to 420 ° C, keep the temperature for 10 hours, adjust the position of the quartz tube, and make the temperature of the spontaneous nucleation zone at the bottom of the quartz tube or the temperature of the inoculation zone. Above the melting point of 1-5 °C, the temperature gradient in the single crystal growth furnace is 5 °C/cm, and then the quartz tube is slowly lowered at a speed of 0.3 mm/h, while keeping the growth temperature unchanged. After the growth, the temperature of the growth furnace was lowered to 200°C at 15°C/h, and then cooled to 30°C naturally.

The quartz tube was taken out, and the tube wall was cut with a wire cutting machine to obtain a high-quality CsMg _0.99 Eu _0.01 I ₃ scintillation crystal with a diameter of 15 mm.

Figure 1 shows the CsMg _0.99 Eu _0.01 I ₃ crystal obtained in Example 1 and the photo of its cross-section. It can be seen from the photographs that the crystals obtained by the present invention are bulk crystals and are large in size.

The results obtained by grinding the obtained crystals into powders and performing powder XRD diffraction are shown in FIG. 2 .

The photoluminescence spectrum of the crystal is shown in FIG. 3 , and it can be seen from FIG. 3 that the luminescence peak around 560 nm is caused by the 5d-4f transition of Eu ²⁺ ions.

Example 2

The preparation of bulk crystal of CsMg _0.95 Eu _0.05 Cl ₃ is as follows:

1) Mix CsCl, MgCl2 and EuCl2 uniformly in a stoichiometric ratio in a glove box, put it into a quartz tube and seal it, and the vacuum degree can reach 10 ^-6 mbar.

2) Put the sealed quartz tube into a resistance furnace, heat up to 650°C at a rate of 100°C/h, then cool down by 100°C at a rate of 50°C/h, and then heat up to 650°C at a rate of 100°C/h , after three cycles, the temperature was kept at 650 °C for 10 hours, and then decreased to 25 °C at a rate of 15 °C/h to obtain CsMg _0.95 Eu _0.05 Cl ₃ polycrystalline;

3) Put the quartz tube containing CsMg _0.95 Eu _0.05 Cl ₃ polycrystalline into the crucible descending furnace, heat up to 615 ° C, keep the temperature for 10 hours, adjust the position of the quartz tube, and make the temperature of the spontaneous nucleation zone at the bottom of the quartz tube or the temperature of the inoculation zone. Above the melting point of 1-5 °C, the temperature gradient in the single crystal growth furnace is 5 °C/cm, and then the quartz tube is slowly lowered at a speed of 0.3 mm/h, while keeping the growth temperature unchanged. After the growth, the temperature of the growth furnace was lowered to 200°C at 15°C/h, and then cooled to 30°C naturally.

4) Take out the quartz tube and cut the tube wall with a wire cutting machine to obtain a 15mm diameter, high-quality CsMg _0.95 Eu _{0.05 Cl} scintillation crystal;

The crystal photo of CsMg _0.95 Eu _0.05 Cl ₃ prepared in Example 2 is shown in FIG. 4 .

The photoluminescence spectrum of CsMg _0.95 Eu _0.05 Cl ₃ crystal is shown in Figure 5. It can be seen from the figure that CsMg _0.95 Eu _0.05 Cl ₃ has only one luminescence peak, which is located at about 480 nm, which is a typical Eu ²⁺ ion luminescence peak.

Example 3

The preparation of _CsMgCl bulk crystal, the steps are as follows:

1) Mix CsCl and MgCl2 uniformly according to the stoichiometric ratio in the glove box, put it into a quartz tube and seal it, and the vacuum degree can reach 10 ^-6 mbar.

2) Put the sealed quartz tube in a resistance furnace, heat up to 650°C at a rate of 100°C/h, then cool down by 100°C at a rate of 50°C/h, and then heat up to 650°C at a rate of 100°C/h , after three cycles, keep the temperature at 650 °C for 10 hours, and then drop to 25 °C at a rate of 15 °C/h to obtain CsMgCl3 polycrystalline;

3) Put the quartz tube containing CsMgCl polycrystalline into the crucible descending furnace, heat up to 615 ° C, keep the temperature for 10 hours, adjust the position of the quartz tube, so that the temperature of the spontaneous nucleation zone at the bottom of the quartz tube or the position of the inoculation zone is higher than the melting point by 1- 5 °C, the temperature gradient in the single crystal growth furnace is 5 °C/cm, and then the quartz tube is slowly lowered at a speed of 0.3 mm/h, and at the same time, the growth temperature is kept unchanged. After the growth, the temperature of the growth furnace was lowered to 200°C at 15°C/h, and then cooled to 30°C naturally.

4) Take out the quartz tube and cut the tube wall with a wire cutting machine to obtain a CsMgCl scintillation crystal with a diameter of 15mm and high quality;

The photo of the CsMgCl3 scintillation crystal prepared in Example 3 is shown in FIG. 6 .

The crystals were ground into powder and the powder XRD diffraction results were shown in Figure 7.

Example 4

The preparation of bulk crystal of Cs _0.99 ⁶ Li _0.01 Mg _0.99 Eu _0.01 I ₃ is as follows:

1) Mix CsI, MgI2, EuI2 and 6LiI according to the stoichiometric ratio uniformly in the glove box, put it into a quartz tube and seal it with a vacuum of 10–6 mbar.

2) Put the sealed quartz tube into a resistance furnace, heat it up to 600-650°C at a rate of 50-100°C/h, then cool it down by 100-150°C at a rate of 30-50°C/h, and then at a rate of 50- The temperature was raised to 600-650°C at a rate of 100°C/h, and after three cycles, the temperature was kept at 600-650°C for 10 hours, and then lowered to 25°C at a rate of 1-15°C/h to obtain Cs _0.99 ⁶ Li _0.01 Mg _0.99 Eu _0.01 I ₃ polycrystalline;

3) Put the quartz tube containing Cs _0.99 ⁶ Li _0.01 Mg _0.99 Eu _0.01 I ₃ polycrystalline into the crucible descending furnace, heat it up to 450-650° C., keep the temperature for 10 hours, adjust the position of the quartz tube, and make the bottom of the quartz tube spontaneously nucleate The temperature or seeding temperature is around the melting point, the temperature gradient is 5–15 °C/cm, and then the quartz tube is slowly lowered at a rate of 0.3–0.5 mm/h, while keeping the growth temperature constant. After the growth, the temperature of the growth furnace was lowered to 200°C at 15°C/h, and then cooled to 30°C naturally.

4) Take out the quartz tube and cut the tube wall with a wire cutting machine to obtain a high-quality Cs _0.99 ⁶ Li _0.01 Mg _0.99 Eu _0.01 I ₃ scintillation crystal with a diameter of 10-20 mm.

The photo of the Cs _0.99 ⁶ Li _0.01 Mg _0.99 Eu _0.01 I ₃ scintillation crystal prepared in Example 4 is shown in FIG. 8 .

Claims (1)

1. A method for preparing a large-block high-quality scintillation crystal comprises the following steps:

1) CsX and MgX were mixed in a stoichiometric ratio in a glovebox ₂ Mixing uniformly, and mixing ⁶ LiX and EuX ₂ Filling the mixed material into a quartz tube, and then vacuumizing and sealing; the vacuum degree after vacuum pumping is 10 ^–6 mbar；

2) Placing the sealed quartz tube into a resistance furnace, circulating for three times in a heating-cooling-heating mode, keeping the temperature at 400-680 ℃ for 8-15 hours, and cooling to room temperature to obtain a polycrystalline material; the heating-cooling-heating mode comprises the following specific steps: heating to 500-650 deg.C at a rate of 50-100 deg.C/h, cooling to 100-150 deg.C at a rate of 30-50 deg.C/h, heating to 500-650 deg.C at a rate of 50-100 deg.C/h, and circulating for three times; the cooling rate of cooling to room temperature is 1-15 ℃/h; obtaining a quartz tube containing a polycrystalline material;

3) Putting a quartz tube containing polycrystalline materials into a crucible descending furnace, heating to 300-680 ℃, preserving heat for 8-15 hours, adjusting the position of the quartz tube, enabling the temperature of a spontaneous nucleation area or an inoculation area at the bottom of the quartz tube to be 1-5 ℃ higher than a melting point, enabling the temperature gradient in a single crystal growth furnace to be 5-15 ℃/cm, then slowly descending the quartz tube at the speed of 0.03-0.05mm/h, keeping the growth temperature unchanged, after the growth is finished, cooling the temperature of the growth furnace to 180-220 ℃, and then naturally cooling to room temperature to obtain a large block of high-quality scintillation crystals;

the scintillation crystal has the chemical formula:

Cs _x ⁶ Li _1-x Mg _y Eu _1-y X ₃ (ii) a Wherein 0<x<1，0<y<1, X is selected from one of I, br and Cl, and can realize double detection of neutron signals and gamma rays.

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