CN114561704A - Flux growth method and application of large-size bismuth tungstate crystal - Google Patents
Flux growth method and application of large-size bismuth tungstate crystal Download PDFInfo
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- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/10—Inorganic compounds or compositions
- C30B29/16—Oxides
- C30B29/22—Complex oxides
- C30B29/32—Titanates; Germanates; Molybdates; Tungstates
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- C30B28/00—Production of homogeneous polycrystalline material with defined structure
- C30B28/02—Production of homogeneous polycrystalline material with defined structure directly from the solid state
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- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B9/00—Single-crystal growth from melt solutions using molten solvents
- C30B9/04—Single-crystal growth from melt solutions using molten solvents by cooling of the solution
- C30B9/08—Single-crystal growth from melt solutions using molten solvents by cooling of the solution using other solvents
- C30B9/12—Salt solvents, e.g. flux growth
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- G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
- G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
- G01T1/16—Measuring radiation intensity
- G01T1/20—Measuring radiation intensity with scintillation detectors
- G01T1/202—Measuring radiation intensity with scintillation detectors the detector being a crystal
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Abstract
The invention provides a flux growth method and application of a large-size bismuth tungstate crystal, wherein a crystal growth material is prefabricated, polycrystal of a target crystal is synthesized in advance, and the polycrystal and the flux are fully mixed to obtain the crystal growth material; or directly burdening the raw materials according to the stoichiometric ratio of the target crystal without polycrystalline synthesis of the target crystal, and fully mixing the raw materials with a fluxing agent to obtain a crystal growth material; and (3) growing the fluxing agent of the target crystal, wherein the seedless crystal grows firstly, and then the seed crystal grows to obtain the target crystal. The method has the advantages of easily-achieved required conditions and simple operation, can obtain large-size single crystals of 30mm multiplied by 2mm in the growth period of about 20 days, and basically meets the requirements of processing and physical property characterization. The adopted fluxing agent does not contain high-toxicity elements, can be conveniently obtained in the market, has low price, and produces less pollution and damage to the environment by waste residues in the growth process.
Description
Technical Field
The invention belongs to the technical field of scintillation crystals, and particularly relates to a flux growth method and application of a large-size bismuth tungstate crystal.
Background
Scintillation crystals refer to crystals that can convert high-energy particles and high-energy rays (e.g., high-speed charged particles, X-rays, gamma rays, neutrons, etc.) that are difficult to directly detect into visible or near-ultraviolet light that can be directly detected by a photodetector. According to the photoelectric characteristics of the scintillation crystal, the scintillation crystal can be coupled with photoelectric elements such as a photomultiplier tube (PMT), a Photodiode (PD), an Avalanche Photodiode (APD) and the like to prepare a scintillation detector, and the scintillation detector has important application in the fields of high-energy physics, biomedical detection, industrial exploration, safety inspection and the like. For example, in the aspect of high-energy physics, a core component on the detection satellite "Wukong" of 2015-year emission-rising dark substance particles is a detector consisting of 308 Bi4Ge3O12(BGO) crystals of 25 × 25 × 600mm 3; in the clinical medicine field, the core component is an array composed of scintillation crystals (BGO crystals, LuxY2-xSiO5: Ce (LYSO: Ce) crystals, LaBr3 crystals, Gd3Al2Ga3O12(GAGG) crystals and the like) which are widely used in the field of heart and cerebral vessels and in PET-CT examination for early discovery and diagnosis of serious diseases such as tumors and the like at present, and the performance of the scintillation crystals is a decisive factor influencing the imaging quality; in the field of industrial production, industrial tomography has become an indispensable means for detecting material defects. At present, the scintillation crystal is one of materials with great application prospects in the field of artificial crystal materials, and is also an important field of current research.
In the light emitting mechanism of the scintillation crystal, the scintillation crystal absorbs the energy of high-energy particles or high-energy rays, so that electrons in a ground state in the crystal are transited to an unstable excited state to generate a large number of electrons and holes, the electrons and the holes are transited to a light emitting center and transfer the carried energy to the light emitting center, the electrons and the holes are compounded, fluorescent photons with a certain ultraviolet or visible light wave band are radiated, and the fluorescent photons are detected by a photoelectric detector through a photomultiplier tube. For this reason, the scintillation crystal has different specific response mechanisms to photons of different wavebands, so that the incident photons of different energies can be distinguished. Energy resolution is an important measure of the performance of a scintillation crystal, and a good scintillation crystal should have high energy resolution. In addition, the main parameters characterizing the performance of the scintillation crystal are spectral response, light output (light yield), decay time, optical transmission range, radiation resistance and the like. The spectral response value is that the fluorescence pulse generated by the scintillation crystal under the action of the high-energy particles/rays should be within the detection range of a mature detector, so that the scintillation crystal and the photodetector can be optimally matched. The light output (light yield) is a measure of the ability of the scintillation crystal to convert incident energy into energy of the emitted fluorescent light pulses, and is one of the most important indicators for the scintillation performance of the scintillation crystal. The decay time is the time required for the number of fluorescence photons generated by the scintillation crystal to decay to 1/e of the maximum number of fluorescence photons, and the longer the decay time is, the more serious the detection signal blockage caused by energy accumulation when the scintillation crystal works is, and the poorer the scintillation performance is. Thus, good scintillation crystals generally require as little decay time as possible and either no or very little afterglow. The optical transmission range is directly related to the forbidden bandwidth of the scintillation crystal, and in order to avoid severe self-absorption, the wavelength of the fluorescence emitted by the scintillation crystal should be within the optical transmission range of the crystal. The radiation resistance refers to the ability of the crystal to operate stably for a long time under the action of high-energy particles/rays, and is also called radiation hardness. In addition, a good scintillation crystal should also have a high density and effective atomic number, to maximize the absorption blocking capability for high energy particles/rays; it should also have good environmental stability, not decompose, not deliquesce, can meet the long-term use requirement.
The existing scintillation crystals can be mainly divided into two categories, namely halide crystals and oxide crystals. The halide scintillation crystal is represented by NaI Tl crystal, LaBr3 Ce crystal, CsI Tl crystal, etc. The NaI Tl crystal has higher light output, wide optical transmission range and no obvious self absorption, and is the scintillation crystal which is most widely applied in early PET equipment. However, the NaI Tl crystal absorbs moisture in the air, and the performances such as energy resolution, position resolution, time resolution and the like are poor, so that the current PET equipment based on the NaI Tl is already out of the market. The high output of LaBr3 Ce crystal is very high, and the stability of energy resolution and scintillation property is superior to that of NaI Tl crystal and BGO crystal, thus attracting a lot of research interest. However, the crystal has serious deliquescence in the air, and is easy to crack in the crystal growth and processing processes, so that the price of LaBr3: Ce crystal is high, and the wide application of the crystal is severely limited. The oxide scintillation crystal is represented by BGO crystal, LSO/LYSO crystal, PbWO4 crystal, etc. When used as a scintillator, the BGO crystal has the advantages of strong ray stopping capability, high scintillation efficiency, difficulty in deliquescence and the like, and is easy to realize modularization. However, the time resolution and the energy resolution of the BGO crystal are poor, and particularly, high scattering and random coincidence exist in the three-dimensional (3D) imaging process, the dead time is long, and the influence on the image quality is large. Also due to such disadvantages, current BGO crystal-based PET devices are also gradually coming out of the market. The LYSO Ce crystal is one of the most used scintillation crystals at present, has the advantages of high light output, fast fluorescence attenuation, large irradiation hardness, good matching of emitted light and PMT sensitivity range and the like, and more importantly, a time-of-flight PET system (TOF-PET) designed and manufactured based on the LYSO Ce crystal has the advantages of lower noise level and higher image resolution than BGO-PET, and is the mainstream in the market at present. However, the LSO/LYSO crystal contains expensive rare earth element Lu, which greatly increases the cost of equipment and limits the wide application of the crystal to a certain extent. In addition, tungstate scintillation crystals represented by PbWO4 and CdWO4 have also received attention from researchers due to their advantages such as high density, small irradiation length, large irradiation hardness, and low price. For example, the european nuclear Center (CERN) has adopted PbWO4 as a scintillation crystal material for electromagnetic energy transducers in Large Hadron Colliders (LHC). However, the PbWO4 and CdWO4 crystals which are used more frequently at present contain heavy metal elements such as lead and cadmium which have serious environmental threats, and the light yield of the crystals which are not doped with rare earth is generally low, so that the application of the crystals is limited to a certain extent.
The novel scintillation crystal which has high density, low irradiation length, high light yield, high energy resolution ratio and short fluorescence attenuation life and is stable in physical and chemical properties and not hygroscopic is explored, has important theoretical and application values, and can effectively promote the development of the fields of national nuclear medicine detection, industrial nondestructive detection, safety inspection and high-energy physics.
Disclosure of Invention
In order to solve the technical problems, the invention provides a fluxing agent growth method and application of a large-size bismuth tungstate crystal,
in order to achieve the purpose, the technical scheme adopted by the invention is as follows:
bismuth tungstate, cerium-doped bismuth tungstate, bismuth tungsten molybdate and cerium-doped bismuth tungsten molybdate as scintillation crystals, and the molecular formula is Bi2WO6、Ce:Bi2WO6、Bi2MoxW1-xO6(0≤x≤0.3)、Ce:Bi2MoxW1-xO6(0≤x≤0.3)。
Preferably, Bi2WO6As a scintillation crystal. Bi2WO6The crystal structure at room temperature belongs to the orthorhombic system, P21ab (No.29) space group with unit cell parameters of
Unit cell volume of
Bi determined by our buoyancy method2WO6The density of (a) reaches 9.58g/cm3Exceeds the common metallic iron (the density of industrial pure iron is 7.87 g/cm)3) Density of copper (red copper density 8.93 g/cm)3) In combination with Bi2WO6The crystal has high effective atomic weight and very small irradiation length, and is a scintillation crystal material with excellent performance.
Preferably, Ce: Bi2WO6As a scintillation crystal. Like the BGO crystal, Bi2WO6The crystal can be used as an intrinsic scintillator, but the intrinsic scintillator without rare earth elements has the problem of small light yield. Ce is a common rare earth element as the luminescent center of extrinsic scintillation crystals. Using Ce3+5d → 4f of ion1The transition radiation can realize high light yield and fast attenuation, and greatly improves the performance of the scintillation crystal.
Preferably, Bi2MoxW1-xO6(x is more than or equal to 0 and less than or equal to 0.3) as a scintillation crystal. The mixing occupation of W and Mo at the position of the anionic group can realize the regulation and control of the optical properties (such as optical transmission range, emission peak position, half-peak width and absorption characteristic) of the crystal, and can realize the regulation and control of Bi2WO6And (4) optimizing the scintillation performance of the crystal. In addition, partial substitution of W by Mo reduces the density of the material to some extent, but can optimize the crystal growth habit to obtain a single crystal with a greater thickness. Preferably, Bi2Mo0.15W0.85O6 crystal having a unit cell parameter of
Unit cell volume of
Bi determined by our buoyancy method2WO6The density of (a) reaches 9.42g/cm3. And Bi2WO6Crystal phase ratio of Bi2Mo0.15W0.85O6The crystal maintains high crystal density and small irradiation length, and growth habit is improved to a certain extent, so that a single crystal with larger thickness can be obtained.
Preferably, Ce: Bi2MoxW1-xO6(x is more than or equal to 0 and less than or equal to 0.3) as a scintillation crystal. The series of crystals can fully play the advantages of high light yield, short decay time, good growth habit of Mo and W mixed occupying crystals and convenient regulation and control of optical properties of the cerium-doped crystals, and are beneficial to obtaining single crystals with better properties and larger size.
Bi2WO6、Ce:Bi2WO6、Bi2MoxW1-xO6(0≤x≤0.3)、Ce:Bi2MoxW1-xO6(x is more than or equal to 0 and less than or equal to 0.3) the melting point of the crystal is higher than 980 ℃, and the crystal has structure-building type phase transition near 920 ℃, so the crystal growth temperature is required to be lower than 920 ℃.
The invention provides a fluxing agent growth method and application of a large-size bismuth tungstate crystal, wherein the method comprises the following steps:
step S1, prefabricating a crystal growth material;
growing Bi2WO6、Ce:Bi2WO6、Bi2MoxW1-xO6(0≤x≤0.3)、Ce:Bi2MoxW1-xO6(x is more than or equal to 0 and less than or equal to 0.3) a crystal raw material prefabricating mode: synthesizing polycrystal of a target crystal in advance, and fully mixing the polycrystal and a fluxing agent to obtain a crystal growth material; or directly burdening the raw materials according to the stoichiometric ratio of the target crystal without polycrystalline synthesis of the target crystal, and fully mixing the raw materials with a fluxing agent to obtain a crystal growth material;
step S2, flux growth of the target crystal, which is divided into two steps:
the first step is as follows: seed-free crystal growth: moving the crucible containing the crystal growth material to a programmable control high-temperature molten salt furnace, heating to 950-980 ℃, and keeping the temperature until the raw materials are completely and uniformly melted to form a uniform single-phase solution; then cooling, forming a wafer through spontaneous crystallization, continuously cooling to increase the thickness and the transverse size of the crystal, cooling to the temperature range of 900-800 ℃ in the crystal growth temperature range, wherein the cooling rate is 0.1-5 ℃/d, and the growth period is 5-20 days, so as to obtain seed crystals;
The second step: seed crystal growth: moving the crucible containing the crystal growth material to a programmable control high-temperature molten salt furnace, heating to 950-980 ℃, and keeping the temperature until the raw materials are completely and uniformly melted to form a uniform single-phase solution; then cooling, lightly touching the platinum wire with the liquid surface, observing the temperature of crystals appearing on the platinum wire, and determining a saturation temperature point; then repeatedly heating to 950-980 ℃ to obtain a uniform solution again, and then cooling to saturation temperature and then lightly contacting the seed crystal generated in the first step with the liquid surface; then slowly cooling to the temperature range of 900-800 ℃ in the crystal growth temperature range, wherein the cooling rate is 0.005-1 ℃/d, and the crystal growth period is 10-50 days, thus obtaining the target crystal.
Preferably, Bi2MoxW1-xO6、Ce:Bi2MoxW1-xO6Middle x rangeX is more than or equal to 0 and less than or equal to 0.3.
Preferably, when the raw materials are mixed in a stoichiometric ratio of the target crystal without polycrystalline synthesis of the target crystal in step S1 and then sufficiently mixed with the flux to obtain a crystal growth material and when there is a raw material which emits gas, a low-temperature sintering is added to sinter the emitted gas before heating to 950 ℃.
Preferably, Bi is cultured2WO6Crystal, Ce: Bi2WO6Crystal, Bi2MoxW1-xO6Crystal, Ce: Bi2MoxW1-xO6The high-temperature molten salt furnace for seedless crystal growth of the crystal is configured in a temperature field with a temperature gradient (namely the high-temperature molten salt furnace is required to be adjusted to be configured in the temperature field with a certain temperature gradient); culturing of Bi 2WO6Crystal, Ce: Bi2WO6Crystal, Bi2MoxW1-xO6Crystal, Ce: Bi2MoxW1-xO6The high-temperature molten salt furnace for the seed crystal growth of the crystal is configured by a temperature field with a constant temperature area and good temperature stability.
Preferably, Bi is cultured2WO6Crystal, Ce: Bi2WO6Crystal, Bi2MoxW1-xO6Crystal, Ce: Bi2MoxW1-xO6In the high-temperature molten salt furnace for seedless crystal growth of the crystal, the thickness of the heat-insulating fiber above the crucible is 3-10cm so as to keep the temperature in the hearth stable; the distance between a refractory brick below the crucible and the top of the heating coil is 1/3-1/4 of the height of the furnace body, so that the supercooling degree of the liquid level is maximum, and crystals are ensured to appear at the liquid level position firstly. Culturing large-size block Bi2WO6Crystal, Ce: Bi2WO6Crystal, Bi2MoxW1-xO6Crystal, Ce: Bi2MoxW1-xO6In the high-temperature molten salt furnace for the seed crystal growth of the crystal, the thickness of the heat-insulating fiber above the crucible is not less than 15cm, and the position of the refractory brick is adjusted to ensure that the crucible is positioned above and below the central position of the heating coil so as to keep the crucibleAt a temperature as constant as possible.
Preferably, in step S1, the target crystal polycrystalline material is synthesized by the following steps:
preparation of Bi2WO6Polycrystalline of (2): mixing Bi powder and Bi2O3、Bi(OH)3Or (BiO)2CO3One of them and WO3、H2WO4One of them is mixed according to the stoichiometric ratio and sintered at 600-850 ℃ to generate Bi2WO6Polycrystal; grinding and sintering are repeated for at least two times; pressing before sintering, if not pressing and raw materials containing Bi (OH) 3、H2WO4In one case, the first sintering temperature does not exceed 500 ℃, and the subsequent sintering process temperature can be within the range of 600-850 ℃; ce: Bi2WO6Polycrystalline synthesis step of (3) and preparation of Bi2WO6Is uniform in the polycrystal, Ce source is CeO2The doping concentration does not exceed 2 percent (molar ratio);
the reaction equation is:
or
Or
Preparation of Bi2MoxW1-xO6Polycrystal: mixing Bi powder and Bi2O3、Bi(OH)3Or (BiO)2CO3One of, WO3、H2WO4One of, and MoO3Mixing according to different stoichiometric ratios, and sintering at 550-800 ℃ to generate Bi2MoxW1-xO6Polycrystal; grinding and sintering are repeated for at least two times; pressing before sintering, if not pressing and raw materials containing Bi (OH)3、H2WO4One of themWhen the first sintering temperature is not more than 500 ℃, the temperature of the subsequent sintering process can be carried out within the range of 550 ℃ and 800 ℃; ce is Bi2MoxW1-xO6Polycrystalline synthesis step and preparation of Bi2MoxW1-xO6Polycrystalline, Ce source being CeO2The doping concentration does not exceed 2% (molar ratio).
Preferably, in step S2, the crystal rotates during the growth of the seed crystal, and the crystal rotation parameter: the rotating speed is 5-40rpm, the acceleration time is 1-10s, the single crystal rotation time is 20-200s, and the intermittent time of two crystal rotations is 5-10 s.
Preferably, the cosolvent is one of the following:
(1)Li2B4O7target crystal and Li2B4O7The molar ratio of (1) - (0.2-1.8);
(2)Li2B4O7-Bi2O3target crystal and Li 2B4O7、Bi2O3The molar ratio of (1) - (0.5-2) - (0.2-2);
(3)Li2B4O7-MoO3target crystal and Li2B4O7、MoO3The molar ratio of (1) to (0.5-2) to (0.1-0.5); is suitable for Bi2MoxW1-xO6、Ce:Bi2MoxW1-xO6Growing a crystal;
(4)Bi2O3-MoO3target crystal and Bi2O3、MoO3The molar ratio of (1) - (1-3) to (0.1-1) is suitable for Bi2MoxW1-xO6、Ce:Bi2MoxW1-xO6Growing a crystal;
(5)Li2B4O7-WO3target crystal and Li2B4O7-WO3The molar ratio of (1) to (0.5-2) to (0.1-1).
Preferably, in step S2,
with Li2B4O7Seedless growth as flux: containing polycrystalline raw material and Li2B4O7The crucible is moved into a programmable control high-temperature molten salt furnace, heated to 950 ℃ and kept at constant temperature until the raw materials are completely and uniformly melted to form a uniform single-phase solution, the cooling process is accurately controlled, a wafer is formed through spontaneous crystallization, and the cooling is continued to increase the thickness and the transverse size of the crystal; the temperature range of the crystal growth is 900-840 ℃, the cooling rate is 0.05-1 ℃/d, and the growth period is 5-20 days, so as to obtain the target crystal;
with Li2B4O7Seed growth as flux: with Li2B4O7As a flux, a flux containing polycrystalline raw material and Li2B4O7The crucible is moved into a programmable control high-temperature molten salt furnace, heated to 950 ℃ and kept at constant temperature until the raw materials are completely and uniformly melted to form uniform single-phase solution, the temperature reduction process is accurately controlled, the platinum wire is in light contact with the liquid surface, and the appearance of Bi on the platinum wire is observed 2WO6Determining the temperature of the crystal and determining a saturation temperature point; repeatedly heating to obtain uniform solution again, cooling to saturation temperature, and adding Bi2WO6The seed crystal is in light contact with the liquid level, and the temperature is slowly reduced to carry out crystal growth; the temperature range of the crystal growth is 900-850 ℃ (the specific crystallization temperature range can be controlled by changing the amount of the fluxing agent), the cooling rate is 0.005-1 ℃/d, the growth period is 10-50 days, and the target crystal is obtained.
Preferably, Li is used2B4O7-Bi2O3Crystal growth as flux: li2B4O7∶Bi2O3The molar ratio is 1 to (0.2-2), the target crystal and the fluxing agent are in accordance with Bi2WO6∶Li2B4O7∶Bi2O3The ratio of the powder to the powder is 1 to (0.5-2) to (0.2-2);
with Li2B4O7-MoO3Crystal growth as flux: li2B4O7∶MoO3The molar ratio of the target crystal to the fluxing agent is 1 to (0.1-0.5), and the target crystal and the fluxing agent are in accordance with Bi2WO6∶Li2B4O7∶Bi2O3The ratio of 1 to (0.5-2) to (0.1-0.5) is mixed;
with Bi2O3-MoO3Crystal growth as flux: the molar ratio of Bi2O3 to MoO3 is 1 to (0.1-0.3), the target crystal and the fluxing agent are Bi according to the proportion2WO6∶Li2B4O7∶Bi2O3The ratio of the components is 1 to (1-3) to (0.1-1).
The application of the target crystal obtained by the flux growth method of the large-size bismuth tungstate crystal is as follows: bi2WO6Crystal, Ce: Bi2WO6Crystal, Bi2MoxW1-xO6Crystal, Ce: Bi2MoxW1-xO6The crystal is used as a scintillation crystal, is applied to a scintillation detector, can be detected and amplified by photoelectric elements such as a photomultiplier tube (PMT), a Photodiode (PD), an avalanche diode (APD) and the like under the action of high-energy rays and high-energy particles, and can be used in the fields of high-energy physics, biomedical detection, industrial exploration, safety inspection and the like; bi 2WO6Crystal, Bi2MoxW1-xO6The crystal is used as a second-order nonlinear optical crystal and can be used for frequency conversion of laser, including frequency doubling, difference frequency, sum frequency, optical parametric oscillation and the like; bi2WO6Crystal, Bi2MoxW1-xO6The crystal is used as a Raman laser crystal, and the stimulated Raman scattering effect of the crystal is utilized to transform the frequency of laser; bi2WO6Crystal, Bi2MoxW1-xO6The crystal is used as a piezoelectric crystal and is used for manufacturing piezoelectric transducers, piezoelectric sensors, filters, oscilloscopes and the like; bi2WO6Crystal, Bi2MoxW1-xO6The crystal is used as a laser host crystal; bi2WO6Crystal, Bi2MoxW1-xO6The crystal is used as a pyroelectric crystal.
The invention has the following beneficial effects:
the invention provides a fluxing agent growth method and application of large-size bismuth tungstate crystals, and a Bi growth method adopting the fluxing agent method2WO6Crystal, Ce: Bi2WO6Crystal, Bi2MoxW1-xO6Crystal, Ce: Bi2MoxW1-xO6The required conditions of the crystal are easy to reach, the operation is simple, the large-size single crystal of 30mm multiplied by 2mm can be obtained in the growth period of about 20 days, and the requirements of processing and physical property representation are basically met.
The fluxing agent adopted by the invention does not contain high-toxicity elements, can be conveniently obtained in the market, has low price, and generates less pollution and damage to the environment by waste residues in the growth process.
The invention provides Bi 2WO6Crystal, Ce: Bi2WO6Crystal, Bi2MoxW1-xO6Crystal, Ce: Bi2MoxW1-xO6The crystal can be used as a scintillation crystal, is applied to a scintillation detector, can be detected and amplified by photoelectric elements such as a photomultiplier tube (PMT), a Photodiode (PD), an avalanche diode (APD) and the like under the action of high-energy rays and high-energy particles, and can be used in the fields of high-energy physics, biomedical detection, industrial exploration, safety inspection and the like. The invention provides Bi2WO6Crystal, Bi2MoxW1-xO6The crystal can be used as a second-order nonlinear optical crystal and can be used for frequency conversion of laser, including frequency doubling, difference frequency, sum frequency, optical parametric oscillation and the like; the Raman laser crystal can be used as a Raman laser crystal, and the stimulated Raman scattering effect of the crystal is utilized to transform the frequency of laser; the material can be used as a piezoelectric crystal for manufacturing piezoelectric transducers, piezoelectric sensors, filters, oscilloscopes and the like; can be used as a laser host crystal; can be used as a pyroelectric transistor.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below, and it is apparent that the drawings in the following description are only some embodiments of the present invention.
FIG. 1 shows the seedless growth of Bi according to the invention2WO6A schematic diagram of a device and a temperature field construction of a series of crystals;
FIG. 2 shows the seed crystal growth of Bi according to the present invention2WO6A schematic diagram of the device and the temperature field construction of the series of crystals;
FIG. 3 shows Bi synthesized at 850 ℃ in example 1 of the present invention2WO6Comparing the polycrystal diffraction pattern with a theoretical pattern;
FIG. 4 shows the growth of Bi by the seedless method of example 1 of the present invention2WO6Single crystal;
FIG. 5 shows the growth of Bi by the seed crystal method in example 1 of the present invention2WO6Single crystal (Li)2B4O7Is a fluxing agent);
FIG. 6 shows the growth of Bi by the seed crystal method in example 2 of the present invention2WO6Single crystal (Li)2B4O7-Bi2O3Is a fluxing agent);
FIG. 7 shows the growth of Bi by the seed crystal method in example 3 of the present invention2Mo0.15W0.85O6Single crystal;
fig. 8 is a structural view of a scintillation detector of embodiment 4 of the present invention.
Description of reference numerals:
1. a crucible; 2. a liquid level wafer; 3. a refractory brick; 4. a heating coil; 5. heat-insulating fibers; 6. a thermocouple; 7. a crystal; 8. seed crystal; 9. a quartz tube; 10. a quartz seed rod; 11. a crystal converter; 12. lifting the pull head; 13. a scintillation crystal; 14. a photomultiplier tube; 15. an amplifier; 16. a multi-channel analyzer; 17. and (4) a computer.
Detailed Description
In order to make the technical solutions of the present invention better understood, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.
The invention provides a flux growth method of a large-size bismuth tungstate crystal, and relates to Bi in the method2WO6Crystal, Ce: Bi2WO6Crystal、Bi2MoxW1-xO6Crystal, Ce: Bi2MoxW1-xO6The optimization design of the molten salt furnace temperature field for crystal growth comprises the following steps:
culturing of Bi2WO6Crystal, Ce: Bi2WO6Crystal, Bi2MoxW1-xO6Crystal, Ce: Bi2MoxW1-xO6The growth of the crystal (i.e. seedless growth) requires the adjustment of the high temperature molten salt furnace to a temperature field configuration with a certain temperature gradient. Specifically, as shown in fig. 1, the thickness of the heat-insulating fiber 5 above the crucible 1 should not be too thick, preferably 3-10 cm, and only needs to be used for keeping the temperature in the furnace stable, as shown in fig. 1, the height of the refractory brick 3 below the crucible 1 needs to be adjusted to be about 1/3-1/4 away from the top of the heating coil 4 to be the height of the furnace body, so that the supercooling degree of the liquid surface is maximized, and the liquid surface wafer 2 is ensured to appear at the liquid surface position first.
Large size block Bi2WO6Crystal, Ce: Bi2WO6Crystal, Bi2MoxW1-xO6Crystal, Ce: Bi2MoxW1-xO6The growth process of the crystal seed crystal needs the temperature field configuration of the constant temperature area with good temperature stability. Specifically, as shown in FIG. 2, the thickness of the insulating fiber 5 above the crucible 1 should not be less than 15cm, and the position of the refractory brick 3 is adjusted so that the crucible 1 is positioned above and below the center position of the heating coil 4 to maintain the temperature of the crucible 1 at a constant temperature as much as possible. The seed crystal 8 is provided with a crystal converter 11, a pulling head 12, a quartz seed rod 10 and a quartz tube 9 which are matched for use, so that the adjustment and control of crystal pulling and crystal rotation are realized. The position of the thermocouple needs to be always located near the position of the crucible in order to obtain as true a temperature as possible for the growth of the crystal 7.
Example 1:
the embodiment provides a flux growth method of a large-size bismuth tungstate crystal, which comprises the following steps:
step S1, prefabricating crystal growth materials:
Bi2WO6and (4) polycrystalline synthesis. Adding Bi2O3、WO3Proportioning according to a stoichiometric ratio, performing ball milling and full mixing, pressing by a material pressing machine, transferring into a corundum crucible, sintering in a muffle furnace at 850 ℃ for not less than 8 hours, and cooling to room temperature. The grinding, mixing and sintering processes are repeated for not less than 2 times. After grinding, powder X-ray diffraction experiment is carried out, as shown in figure 3, the result shows that the powder is completely consistent with the theoretical diffraction pattern, no extra diffraction peak exists, and the Bi is obtained2WO6Pure phase polycrystallization of (1).
Step S2, flux growth of the target crystal:
Bi2WO6seed-free crystal growth of (1). Bi synthesized in step S12WO6The polycrystal is mixed with a fluxing agent Li according to the molar ratio of 1: 12B4O7Mixing thoroughly, and packaging
The platinum crucible of (1). And (3) moving the platinum crucible into a programmable high-temperature molten salt furnace, heating to 980 ℃ and keeping the temperature for 5 hours to obtain a clarified and uniform solution. Cooling to 890 ℃ after 2h, slowly cooling, cooling to 860 ℃ for 15d, growing at constant temperature until a centimeter-level single crystal wafer is obtained by growth on the liquid level of the crucible, quickly taking out the wafer by using a platinum rod, keeping the wafer in the furnace, keeping the temperature for 5h, cooling to room temperature after 24h, and taking out the single crystal wafer, as shown in figure 4.
Bi2WO6Growing the seed crystal. With Li2B4O7Bi synthesized in step S1 is used as a flux2WO6The polycrystal is mixed with a fluxing agent Li according to the molar ratio of 1: 12B4O7Mixing thoroughly, and packaging
The platinum crucible of (1). And (3) moving the platinum crucible into a programmable high-temperature molten salt furnace, heating to 980 ℃ and keeping the temperature for 5 hours to obtain a clarified and uniform solution. The platinum wire is lightly touched with the liquid surface, and the saturation temperature of the crystal is accurately determined to be 885 ℃ by observing the temperature point of the crystal generated on the platinum wire in the cooling process. Heating again to obtain clear and uniform solutionAfter the solution is cooled to 885 ℃ for 10 hours, the temperature is kept for 5 hours. The single crystal obtained in example 2 was used as a seed crystal, and the temperature was lowered after touching the liquid surface, and then lowered to 870 ℃ after 30 days of growth, to obtain Bi of a size of 40mm at maximum2WO6Single crystal as shown in fig. 5.
Example 2:
the crystal growth material prepared in step S1 was prepared in the same manner as in example 1.
Step S2, flux growth of the target crystal:
Bi2WO6growing the seed crystal of (1). With Li2B4O7-Bi2O3As flux, Li in flux2B4O7And Bi2O3The molar ratio of (A) to (B) is 1: 0.5. The preparation of the high temperature homogeneous solution was the same as in example 1. The platinum wire is lightly touched with the liquid surface, and the saturation temperature of the crystal is accurately measured to be 873 ℃ by observing the temperature point of the crystal generated on the platinum wire in the cooling process. And after reheating to obtain a clear and uniform solution, cooling to 873 ℃ for 10 hours, and keeping the temperature for 5 hours. The single crystal obtained in example 1 is used as seed crystal, the temperature is reduced after the single crystal touches the liquid surface, and the temperature is reduced to 865 ℃ after the single crystal grows for 20 days to obtain Bi with the size of 10mm at most 2WO6Single crystal, with a thickness exceeding 2mm, as shown in fig. 6.
Example 3:
Bi2Mo0.15W0.85O6and seed crystal growth and crystal structure resolution of the crystal. Bi was synthesized in the manner set forth in example 12Mo0.15W0.85O6Polycrystal, MoO in Synthesis Process3A slight excess. With Li2B4O7-Bi2O3As flux, Li in flux2B4O7And Bi2O3The molar ratio of (A) to (B) is 1: 0.5. The preparation of the high temperature homogeneous solution was the same as in example 1. The platinum wire is touched with the liquid surface, and the saturation temperature of the crystal is accurately determined to be 855 ℃ by observing the temperature point of the crystal generated on the platinum wire in the cooling process. After reheating to obtain a clear and uniform solution, the temperature is reduced to 855 ℃ for 10h, and then the temperature is kept for 5 h. The single crystal obtained in example 1 was used asThe seed crystal is started to be cooled after being lightly touched with the liquid surface, and Bi with the size of nearly 20mm at the maximum is obtained after the temperature is reduced to 845 ℃ after the growth of 15d2Mo0.15W0.85O6Single crystal, approximately 2mm thick, as shown in figure 7.
Example 4: examples of the applications
Bi grown in example 22WO6As a scintillator crystal, a single crystal is processed into a scintillator crystal device according to the prior art, and as shown in FIG. 8, a scintillator crystal 13 (Bi) is irradiated with a high-energy ray or particle2WO6Crystal) passes through the photomultiplier 14 and the amplifier 15 and is received by the multichannel analyzer 16, and the multichannel analyzer can detect and image after being processed by the computer 17 system.
According to the technical scheme, the flux growth method and application of the large-size bismuth tungstate crystal provided by the embodiment adopt a flux method to grow Bi2WO6Crystal, Ce: Bi2WO6Crystal, Bi2MoxW1-xO6Crystal, Ce: Bi2MoxW1-xO6The required conditions of the crystal are easy to reach, the operation is simple, the large-size single crystal of 30mm multiplied by 2mm can be obtained in the growth period of about 20 days, and the requirements of processing and physical property representation are basically met. The fluxing agent adopted by the embodiment does not contain high-toxicity elements, can be conveniently obtained in the market, is low in price, and causes less pollution and damage to the environment by waste residues generated in the growth process. Bi proposed in this example2WO6Crystal, Ce: Bi2WO6Crystal, Bi2MoxW1-xO6Crystal, Ce: Bi2MoxW1-xO6The crystal can be used as a scintillation crystal, is applied to a scintillation detector, can be detected and amplified by photoelectric elements such as a photomultiplier tube (PMT), a Photodiode (PD), an avalanche diode (APD) and the like under the action of high-energy rays and high-energy particles, and can be used in the fields of high-energy physics, biomedical detection, industrial exploration, safety inspection and the like. The invention provides Bi2WO6Crystal, Bi2MoxW1-xO6The crystal can be used asThe second-order nonlinear optical crystal can be used for frequency conversion of laser, including frequency doubling, difference frequency, sum frequency, optical parametric oscillation and the like; the Raman laser crystal can be used as a Raman laser crystal, and the stimulated Raman scattering effect of the crystal is utilized to transform the frequency of laser; the material can be used as a piezoelectric crystal for manufacturing piezoelectric transducers, piezoelectric sensors, filters, oscilloscopes and the like; can be used as a laser host crystal; can be used as a pyroelectric transistor.
The embodiments of the present invention have been described in detail through the embodiments, but the description is only exemplary of the embodiments of the present invention and should not be construed as limiting the scope of the embodiments of the present invention. The scope of protection of the embodiments of the invention is defined by the claims. In the present invention, the technical solutions described in the embodiments of the present invention or those skilled in the art, based on the teachings of the embodiments of the present invention, design similar technical solutions to achieve the above technical effects within the spirit and the protection scope of the embodiments of the present invention, or equivalent changes and modifications made to the application scope, etc., should still fall within the protection scope covered by the patent of the embodiments of the present invention.
Claims (10)
1. A fluxing agent growth method of a large-size bismuth tungstate crystal is characterized by comprising the following steps:
step S1, prefabricating a crystal growth material;
growing Bi2WO6、Ce：Bi2WO6、Bi2MoxW1-xO6(0≤x≤0.3)、Ce：Bi2MoxW1-xO6(x is more than or equal to 0 and less than or equal to 0.3) a crystal raw material prefabricating mode: synthesizing polycrystal of a target crystal in advance, and fully mixing the polycrystal and a fluxing agent to obtain a crystal growth material; or directly burdening the raw materials according to the stoichiometric ratio of the target crystal without polycrystalline synthesis of the target crystal, and fully mixing the raw materials with a fluxing agent to obtain a crystal growth material;
Step S2, flux growth of the target crystal, which comprises two steps:
the first step is as follows: seed-free crystal growth: moving the crucible containing the crystal growth material to a programmable control high-temperature molten salt furnace, heating to 950-980 ℃, and keeping the temperature until the raw materials are completely and uniformly melted to form a uniform single-phase solution; then cooling, forming a wafer through spontaneous crystallization, continuously cooling to increase the thickness and the transverse size of the crystal, cooling to the temperature range of 900-800 ℃ in the crystal growth temperature range, wherein the cooling rate is 0.1-5 ℃/d, and the growth period is 5-20 days, so as to obtain seed crystals;
the second step: seed crystal growth: moving the crucible containing the crystal growth material to a programmable control high-temperature molten salt furnace, heating to 950-980 ℃, and keeping the temperature until the raw materials are completely and uniformly melted to form a uniform single-phase solution; then cooling, lightly touching the platinum wire with the liquid surface, observing the temperature of crystals appearing on the platinum wire, and determining a saturation temperature point; then repeatedly heating to 950-980 ℃ to obtain a uniform solution again, and then cooling to saturation temperature and then lightly contacting the seed crystal generated in the first step with the liquid surface; then slowly cooling to the temperature range of 900-800 ℃ in the crystal growth temperature range, wherein the cooling rate is 0.005-1 ℃/d, and the crystal growth period is 10-50 days, thus obtaining the target crystal.
2. The flux growth method of large-size bismuth tungstate crystal as claimed in claim 1, wherein Bi is added2MoxW1- xO6、Ce：Bi2MoxW1-xO6Wherein x is more than or equal to 0 and less than or equal to 0.3.
3. The flux growth method of large-size bismuth tungstate crystal as claimed in claim 2, wherein Bi is cultured2WO6Crystal, Ce: bi2WO6Crystal, Bi2MoxW1-xO6Crystal, Ce: bi2MoxW1-xO6The high-temperature molten salt furnace for seedless crystal growth of the crystal is configured in a temperature field with a temperature gradient; culturing of Bi2WO6Crystal, Ce: bi2WO6Crystal, Bi2MoxW1-xO6Crystal, Ce: bi2MoxW1-xO6High temperature molten salt for seed crystal growthThe furnace is a temperature field configuration with a constant temperature zone.
4. The flux growth method of large-size bismuth tungstate crystal as claimed in claim 3, wherein Bi is cultured2WO6Crystal, Ce: bi2WO6Crystal, Bi2MoxW1-xO6Crystal, Ce: bi2MoxW1-xO6In the high-temperature molten salt furnace for seedless crystal growth of the crystal, the thickness of the heat-insulating fiber above the crucible is 3-10cm so as to keep the temperature in the hearth stable; the distance between a refractory brick below the crucible and the top of the heating coil is 1/3-1/4 of the height of the furnace body, so that the supercooling degree of the liquid level is maximum, and crystals are ensured to appear at the liquid level position firstly; culturing of Bi2WO6Crystal, Ce: bi2WO6Crystal, Bi2MoxW1-xO6Crystal, Ce: bi2MoxW1-xO6In a high-temperature molten salt furnace for the seed crystal growth of the crystal, the thickness of the heat-insulating fiber above the crucible is not less than 15 cm.
5. The flux growth method of large-size bismuth tungstate crystal according to claim 2, wherein in the step S1, the target crystal polycrystalline material is synthesized by the following steps:
preparation of Bi2WO6The polycrystal of (2): mixing Bi powder and Bi2O3、Bi(OH)3Or (BiO)2CO3One of them and WO3、H2WO4One of them is mixed according to the stoichiometric ratio and sintered at 600-850 ℃ to generate Bi2WO6Polycrystal; grinding and sintering are repeated for at least two times; pressing before sintering, if not pressing and raw materials containing Bi (OH)3、H2WO4In one case, the first sintering temperature does not exceed 500 ℃, and the subsequent sintering process temperature can be within the range of 600-850 ℃; ce: bi2WO6Polycrystalline synthesis step and preparation of Bi2WO6Is a source of CeO2The doping concentration is not more than 2%;
preparation of Bi2MoxW1-xO6Polycrystal: mixing Bi powder and Bi2O3、Bi(OH)3Or (BiO)2CO3One of, WO3、H2WO4One of, and MoO3Mixing according to different stoichiometric ratios, and sintering at 550-800 ℃ to generate Bi2MoxW1-xO6Polycrystal; grinding and sintering are repeated for at least two times; pressing before sintering, if not pressing and raw materials containing Bi (OH)3、H2WO4In one case, the first sintering temperature does not exceed 500 ℃, and the subsequent sintering process temperature can be carried out within the range of 550 ℃ and 800 ℃; ce: bi 2MoxW1- xO6Polycrystalline synthesis step and preparation of Bi2MoxW1-xO6Polycrystalline consistency, Ce source being CeO2The doping concentration does not exceed 2%.
6. The flux growth method of large-size bismuth tungstate crystals as claimed in claim 2, wherein the seed crystal rotates during the growth of the seed crystal in step S2, and the crystal transformation parameters are as follows: the rotating speed is 5-40rpm, the acceleration time is 1-10s, the single crystal rotation time is 20-200s, and the intermittent time of two crystal rotations is 5-10 s.
7. The flux growth method of large-size bismuth tungstate crystals as claimed in claim 2, wherein the flux is one of the following:
(1)Li2B4O7target crystal and Li2B4O7The molar ratio of (1) - (0.2-1.8);
(2)Li2B4O7-Bi2O3target crystal and Li2B4O7、Bi2O3The molar ratio of (1) - (0.5-2) - (0.2-2);
(3)Li2B4O7-MoO3target crystal and Li2B4O7、MoO3The molar ratio of (1) to (0.5-2) 0.1-0.5; is suitable for Bi2MoxW1-xO6、Ce：Bi2MoxW1-xO6Growing a crystal;
(4)Bi2O3-MoO3target crystal and Bi2O3、MoO3The molar ratio of (1) - (1-3) to (0.1-1) is suitable for Bi2MoxW1- xO6、Ce：Bi2MoxW1-xO6Growing a crystal;
(5)Li2B4O7-WO3target crystal and Li2B4O7-WO3The molar ratio of (1) to (0.5-2) to (0.1-1).
8. The flux growth method of large-size bismuth tungstate crystals as recited in claim 7, wherein in step S2,
with Li2B4O7Seedless growth as flux: containing polycrystalline raw material and Li 2B4O7The crucible is moved into a programmable control high-temperature molten salt furnace, heated to 950 ℃ and kept at constant temperature until the raw materials are completely and uniformly melted to form a uniform single-phase solution, the cooling process is accurately controlled, a wafer is formed through spontaneous crystallization, and the cooling is continued to increase the thickness and the transverse size of the crystal; the temperature range of the crystal growth is 900-840 ℃, the cooling rate is 0.05-1 ℃/d, and the growth period is 5-20 days, so as to obtain the target crystal;
with Li2B4O7Seed growth as flux: with Li2B4O7As a flux, a flux containing polycrystalline raw material and Li2B4O7The crucible is moved into a programmable control high-temperature molten salt furnace, heated to 950 ℃ and kept at constant temperature until the raw materials are completely and uniformly melted to form uniform single-phase solution, the temperature reduction process is accurately controlled, the platinum wire is in light contact with the liquid surface, and the appearance of Bi on the platinum wire is observed2WO6Determining the temperature of the crystal and determining a saturation temperature point; repeatedly heating to obtain uniform solution again, cooling to saturation temperature, and adding Bi2WO6The seed crystal is in light contact with the liquid level, and the temperature is slowly reduced to carry out crystal growth; the temperature range of the crystal growth is 900-.
9. The flux growth method of large-size bismuth tungstate crystals as recited in claim 7,
With Li2B4O7-Bi2O3Crystal growth as flux: li2B4O7∶Bi2O3The molar ratio of the target crystal to the fluxing agent is 1 to (0.2-2), and the target crystal and the fluxing agent are in a Bi ratio2WO6∶Li2B4O7∶Bi2O3The ratio of 1 to (0.5-2) to (0.2-2) is mixed;
with Li2B4O7-MoO3Crystal growth as flux: li2B4O7∶MoO3The molar ratio of the target crystal to the fluxing agent is 1 to (0.1-0.5), and the target crystal and the fluxing agent are in accordance with Bi2WO6∶Li2B4O7∶Bi2O3The ratio of 1 to (0.5-2) to (0.1-0.5) is mixed;
with Bi2O3-MoO3Crystal growth as flux: the molar ratio of Bi2O3 to MoO3 is 1 to (0.1-0.3), the target crystal and the fluxing agent are Bi according to the proportion2WO6∶Li2B4O7∶Bi2O3The ratio of the components is 1 to (1-3) to (0.1-1).
10. Use of the target crystal obtained by the flux growth method of large-size bismuth tungstate crystal according to any of claims 1 to 9, wherein Bi is2WO6Crystal, Ce: bi2WO6Crystal, Bi2MoxW1-xO6Crystal, Ce: bi2MoxW1-xO6The crystal is used as scintillation crystal in scintillation detector, and under the action of high-energy ray and high-energy particle, the crystal is producedThe light can be detected and amplified by photoelectric elements such as a photomultiplier, a photodiode, an avalanche diode and the like; bi2WO6Crystal, Bi2MoxW1-xO6The crystal is used as a second-order nonlinear optical crystal; bi2WO6Crystal, Bi2MoxW1-xO6The crystal is used as a Raman laser crystal, and the stimulated Raman scattering effect of the crystal is utilized to transform the frequency of laser; bi 2WO6Crystal, Bi2MoxW1-xO6The crystal is used as a piezoelectric crystal; bi2WO6Crystal, Bi2MoxW1-xO6The crystal is used as a laser host crystal; bi2WO6Crystal, Bi2MoxW1-xO6The crystal is used as a pyroelectric crystal.
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