A method for preparing a bismuth silicate scintillation crystal by a guided mode method

Abstract

The application belongs to the technical field of scintillation crystal preparation, and particularly discloses a method for preparing bismuth silicate scintillation crystal by a guided mode method. Raw materials are sequentially mixed, pre-sintered, compacted and sintered to obtain bismuth silicate polycrystal material, and then the bismuth silicate polycrystal material is melted to determine a suitable longitudinal temperature gradient and design a pulling speed. Through the determination of the above parameters, the bismuth silicate scintillation crystal is prepared by the guided mode method through a guided mode mold (10). The preparation method of the bismuth silicate scintillation crystal disclosed by the application is simple in process and easy to implement, and the prepared bismuth silicate scintillation crystal has the characteristics of high quality, few defects, good component uniformity and the like.

Description

Technical Field

[0001] This invention relates to the field of scintillation crystal preparation technology, and in particular to a method for preparing bismuth silicate scintillation crystals using a guided mode method. Background Technology

[0002] Bismuth silicate (Bi4Si3O) 12 Bismuth germanate (BSO) crystal is a novel type of scintillation crystal with excellent mechanical and chemical stability, as well as photoelectric and pyroelectric properties. BSO is combined with bismuth germanate (Bi₄Ge₃O₄) crystal. 12 Lead tungstate (BSO) and lead tungstate (BGO) crystals share many similar physicochemical properties. Both belong to the cubic crystal system and have similar structures. The decay time (100 ns) of BSO crystal is only one-third that of BGO crystal, while the light output of BSO can reach several times that of lead tungstate (PbWO4, PWO), especially exhibiting superior performance in key areas such as afterglow decay. Furthermore, the low cost of BSO crystal raw materials makes it an ideal alternative to BGO, and it is more suitable for important applications in nuclear physics and high-energy physics.

[0003] Several high-energy physics projects in Europe and the United States are also focusing on BSO crystals. In particular, CERN and the University of Texas Tech are researching the application of BSO crystals in dual-readout calorimeters. Preliminary experimental conclusions indicate that BSO crystals currently outperform other crystals such as BGO and PWO crystals in dual-readout calorimeter applications. Furthermore, BSO crystals have also shown good performance in light-emitting diodes (LEDs) and lasers, attracting considerable attention.

[0004] Bismuth sulfide (BSO) crystal is a stable compound in the Bi₂O₃-SiO₂ pseudobinary system, belonging to the cubic crystal system and having a bismuth sphalerite structure. BSO and BGO crystals have the same structure and similar melting points, but their phase diagrams are completely different. BGO is a uniformly melting stable compound with relatively simple crystallization behavior; BSO, on the other hand, is a heterogeneous melting compound, with crystallization occurring in a metastable state, making it prone to compositional segregation. This leads to macroscopic defects such as inclusions and cross-linking in the later stages of growth, and the resulting crystal surface is usually covered with yellow Bi₂O₃ extrusions. Due to the significant difference in melting points and densities between Bi₂O₃ and SiO₂, and the complexity of the correlation system in the Bi₂O₃-SiO₂ binary system, the chemical composition homogeneity and crystallization behavior of BSO melt are more difficult to control than those of BGO crystal. Although the crucible lowering method and the Czochralski method can grow BSO crystals of a certain size, both methods have defects to varying degrees during crystal growth. During crystal growth, silicon oxide melt precipitates in the upper layer of the melt, bismuth oxide melt precipitates in the lower layer, and only the middle layer is bismuth silicate melt. This severely affects the quality and compositional uniformity of the grown crystal. To grow high-quality BSO single crystals suitable for applications, it is necessary to improve the technical parameters of these two growth methods or develop new BSO single crystal growth methods to effectively suppress compositional segregation during single crystal growth and grow high-quality crystals suitable for applications.

[0005] Therefore, improving the quality and compositional uniformity of bismuth silicate scintillation crystals and reducing the preparation difficulty of bismuth silicate scintillation crystals are urgent problems to be solved in this field. Summary of the Invention

[0006] In view of this, the present invention provides a method for preparing bismuth silicate scintillation crystals by a guided mode method, so as to solve the problems of low quality and poor composition uniformity of bismuth silicate scintillation crystals prepared by existing methods.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing bismuth silicate scintillation crystals by a guided mold method includes the following steps: first, preparing bismuth silicate polycrystalline material, and then using a guided mold (10) to prepare bismuth silicate scintillation crystals from the bismuth silicate polycrystalline material by a guided mold method.

[0009] Preferably, the preparation steps of the bismuth silicate polycrystalline material include: sequentially mixing, pre-sintering, compacting, and sintering the raw materials to obtain the bismuth silicate polycrystalline material.

[0010] Preferably, when the raw materials are bismuth oxide and silicon oxide, the molar ratio of bismuth oxide to silicon oxide is 2:3;

[0011] When the raw materials are bismuth oxide, silicon oxide and rare earth oxides, the molar ratio of bismuth oxide, silicon oxide and rare earth oxides is 2-x:3:x, where 0 < x < 2; the rare earth oxides include one or more of Gd2O3, Tm2O3, Eu2O3, Dy2O3 and Ho2O3.

[0012] Preferably, the pre-sintering temperature is 650-700℃ and the pre-sintering time is 5-10h; the sintering temperature is 800-950℃ and the sintering time is 12-18h.

[0013] Preferably, the guide mold (10) includes a mold cover plate (11) and a mold body (12) that are fixedly connected.

[0014] Preferably, the mold body (12) contains a capillary tube (121), which has a lower through-hole (122) and an upper through-hole (123).

[0015] Preferably, the diameter of the capillary (121) is 0.2-1 mm, the height of the guide mold (10) is 50-200 mm, and the opening angle of the upper through-hole (123) is 45-90°.

[0016] Preferably, the guide mold (10) is made of platinum.

[0017] Preferably, the guided-mode method involves pulling a seed crystal that is in contact with the upper through-hole (123) under heating conditions to prepare a bismuth silicate scintillation crystal.

[0018] Preferably, the heating conditions are as follows: the temperature of the bismuth silicate polycrystalline material is 1100-1250℃, the temperature difference between the bismuth silicate polycrystalline material flush with the liquid surface in the capillary and the through-hole (123) is 20-150℃, the temperature of the bismuth silicate polycrystalline material flush with the liquid surface in the capillary is greater than that of the bismuth silicate polycrystalline material at the through-hole (123), and the longitudinal temperature gradient is 10-20℃ / cm; the pulling speed is 5-10mm / h.

[0019] In this invention, the convection of the melt in the capillary during crystal growth via the guided-mode method is extremely weak. Excess solute discharged during crystal growth due to segregation can only diffuse back into the melt bulk. This weak convection effectively suppresses component segregation, which is beneficial for the growth of bismuth silicate single crystals. Furthermore, the absence of stirring in the melt makes it easier to reach stable thermal equilibrium at the solid-liquid interface, ensuring that crystal growth occurs in a stable state. This characteristic also effectively suppresses component segregation, making it easier to obtain bismuth silicate scintillation crystals with uniform composition.

[0020] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The method for preparing bismuth silicate scintillation crystals using the guided mode method disclosed in this invention can directly grow slab-shaped bismuth silicate crystals, and the thickness is adjustable within a certain range;

[0022] 2. This invention can effectively suppress the segregation of bismuth silicate melt and ensure consistent growth composition, that is, it can grow high-quality lath-shaped bismuth silicate crystals with consistent composition throughout. In principle, it can grow crystals with any ratio of bismuth oxide to silicon oxide around 2:3.

[0023] 3. It can grow high-quality bismuth silicate crystals with uniform rare earth ion doping, and its various properties can be effectively controlled through uniform rare earth ion doping.

[0024] 4. Due to the characteristics of the mold-guided method, crystals of different mold shapes can be easily grown, that is, different molds can be made according to the needs, so as to grow irregular crystals of arbitrary shapes;

[0025] 5. The preparation method disclosed in this invention is simple to operate, low in cost, and easy to industrialize. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the bismuth silicate crystal preparation apparatus of the present invention;

[0028] Among them, 10 is the guide mold, 11 is the mold cover plate, 12 is the mold body, 121 is the capillary tube, 122 is the lower through-hole, 123 is the upper through-hole, 20 is the crucible, and 30 is the heating device. Detailed Implementation

[0029] The present invention provides a method for preparing bismuth silicate scintillation crystals by a guided mold method, comprising the following steps: first, preparing bismuth silicate polycrystalline material, and then using a guided mold (10) to prepare bismuth silicate scintillation crystals from the bismuth silicate polycrystalline material by a guided mold method.

[0030] In this invention, the obtained bismuth silicate scintillation crystal is a lath-shaped crystal.

[0031] In this invention, the preparation steps of the bismuth silicate polycrystalline material include: mixing raw materials sequentially, pre-sintering, compacting, and sintering to obtain bismuth silicate polycrystalline material.

[0032] In this invention, when the raw materials are bismuth oxide and silicon oxide, the molar ratio of bismuth oxide to silicon oxide is 2:3.

[0033] In this invention, when the raw materials are bismuth oxide, silicon oxide, and rare earth oxides, the molar ratio of bismuth oxide, silicon oxide, and rare earth oxides is 2-x:3:x, where 0 < x < 2, and x can specifically be 0.005, 0.01, 0.02, 0.04, or 0.06; the rare earth oxides include one or more of Gd2O3, Tm2O3, Eu2O3, Dy2O3, and Ho2O3.

[0034] In this invention, the pre-sintering temperature is 650–700°C, specifically 660°C, 670°C, 680°C, or 690°C; the pre-sintering time is 5–10 hours, specifically 6 hours, 7 hours, 8 hours, or 9 hours; the sintering temperature is 800–950°C, specifically 820°C, 850°C, 860°C, 880°C, 900°C, or 920°C; and the sintering time is 12–18 hours, specifically 13 hours, 14 hours, 15 hours, 16 hours, or 17 hours.

[0035] In this invention, the guide mold (10) includes a mold cover plate (11) and a mold body (12) that are fixedly connected.

[0036] In this invention, the mold body (12) contains a capillary tube (121), which has a lower through-hole (122) and an upper through-hole (123).

[0037] In this invention, the diameter of the capillary tube (121) is 0.2–1 mm, specifically 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, or 0.9 mm; the height of the guide mold (10) is 50–200 mm, specifically 55 mm, 60 mm, 65 mm, 70 mm, 80 mm, 90 mm, 100 mm, 120 mm, 140 mm, 150 mm, or 180 mm. The angle of the upper through-hole (123) is 45–90°, specifically 50°, 55°, 60°, 65°, 70°, 75°, 80°, or 85°.

[0038] In this invention, if the diameter of the capillary (121) is too large, it will affect the diffusion of the melt in the capillary; if it is too small, it will result in slow growth. The size of the upper through-hole (123) determines the thickness of the strip-shaped crystal. The upper through-hole (123) is the through-hole adjacent to the mold cover plate (11).

[0039] In this invention, the height h of the guide mold (10) and the diameter d of the capillary tube (121) satisfy the formula: h = 2γcosθ / dρg; where γ is the surface tension coefficient of the bismuth silicate polycrystalline melt (N / cm); θ is the solid-liquid wetting angle; and ρ is the density of the bismuth silicate polycrystalline material (g / cm³). 3 ); g is a constant (gravitational acceleration, N / g); in this invention, the smaller d is, the larger h will be; the larger θ is, the thicker the grown lath-shaped crystals will be, and the smaller the mold height will be.

[0040] In this invention, the raw material for preparing the guide mold (10) is platinum. The raw materials for making the guide mold (10) in this invention must be able to be wetted by bismuth silicate melt but must not react chemically with each other.

[0041] In this invention, the guided model method is to prepare bismuth silicate scintillation crystal by pulling a seed crystal that is in contact with the upper through-hole (123) under heating conditions.

[0042] In this invention, a schematic diagram of the bismuth silicate crystal preparation apparatus is shown below. Figure 1 As shown.

[0043] In this invention, the heating conditions are as follows: the temperature of the bismuth silicate polycrystalline material is 1100–1250°C, specifically 1120°C, 1150°C, 1160°C, 1180°C, 1200°C, 1220°C, or 1240°C; the bismuth silicate polycrystalline material is in a molten state at this temperature; the temperature difference between the bismuth silicate polycrystalline material flush with the liquid surface inside the capillary and the through-hole (123) is 20–150°C, specifically 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 60°C, 80°C, 100°C, or 120°C. The temperature of the bismuth silicate polycrystalline material flush with the liquid surface in the capillary is higher than that of the bismuth silicate polycrystalline material at the upper through-hole (123). The longitudinal temperature gradient is 10-20℃ / cm, specifically 12℃ / cm, 14℃ / cm, 15℃ / cm, 16℃ / cm, and 18℃ / cm. The pulling speed is 5-10mm / h, specifically 5.5mm / h, 6mm / h, 6.5mm / h, 7mm / h, 7.5mm / h, 8mm / h, 8.5mm / h, 9mm / h, and 9.5mm / h.

[0044] In this invention, the temperature of the bismuth silicate polycrystalline material below the liquid surface in the capillary is the same as that of the bismuth silicate polycrystalline material in the container.

[0045] In this invention, as the growth time increases, the liquid level difference between the upper through-hole (123) and the bismuth silicate polycrystalline material in the container will become larger and larger. At this time, the temperature difference remains constant, while the temperature gradient gradually decreases.

[0046] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] Example 1

[0048] Platinum was selected as the guide mold material, along with a corresponding insulation layer. Bismuth oxide and silicon oxide were mixed in a molar ratio of 2:3, thoroughly blended using a ball mill, and pre-sintered at 670℃ for 8 hours. The raw material was then removed and compacted. Sintering at 800℃ for 18 hours yielded BSO polycrystalline material. The guide mold was placed in a crucible with a capillary diameter of 0.2 mm and a through-hole angle of 45°. The temperature of the bismuth silicate polycrystalline material in the crucible was maintained at 1200℃, keeping the temperature at the through-hole in the capillary 100℃ lower than the liquid surface. The pulling speed was 7 mm / h. Finally, a strip-shaped BSO crystal with a thickness of 1 mm, a width of 50 mm, and a length of 100 mm was obtained.

[0049] Three samples were taken from the top, middle, and bottom parts of the crystal. After grinding and polishing, micro Raman analysis was performed. The [Bi] / [Bi+Si] ratios of the crystal were 57.139%, 57.143%, and 57.145%, respectively, which are very close to the theoretical value of [Bi] / [Bi+Si] = 4 / 7. This indicates that the method can effectively suppress the segregation of BSO crystal composition and grow uniform and high-quality BSO crystals.

[0050] Example 2

[0051] Platinum was selected as the guide mold material, along with a corresponding insulation layer. Bismuth oxide and silicon oxide were mixed at a molar ratio of 2:3.1, thoroughly blended using a ball mill, and pre-sintered at 660℃ for 10 hours. The material was then removed and compacted. Sintering at 800℃ for 18 hours yielded BSO polycrystalline material. The guide mold was placed in a crucible with a capillary diameter of 0.2 mm and a through-hole angle of 45°. The temperature of the bismuth silicate polycrystalline material in the crucible was maintained at 1200℃, keeping the temperature at the through-hole in the capillary 100℃ lower than the liquid surface. The pulling speed was 6 mm / h. Finally, a plate-shaped BSO crystal with a thickness of 1 mm, a width of 50 mm, and a length of 100 mm was obtained.

[0052] Three samples were taken from the top, middle, and bottom parts of the crystal. After grinding and polishing, micro Raman analysis was performed. The [Bi] / [Bi+Si] ratios of the crystal were 56.333%, 56.339%, and 56.346%, respectively. These values ​​are very close to the theoretical value of [Bi] / [Bi+Si] = 4 / 7.1, indicating that this method can effectively suppress the segregation of BSO crystal components and can adjust the ratio of Bi to Si ions in the crystal.

[0053] Example 3

[0054] Platinum was selected as the guide mold material, along with a corresponding insulation layer. Bismuth oxide and silicon oxide were mixed in a molar ratio of 2:3, thoroughly blended using a ball mill, and pre-sintered at 650℃ for 7 hours. The raw material was then removed and compacted. Sintering at 920℃ for 12 hours yielded BSO polycrystalline material. The guide mold was placed in a crucible with a capillary diameter of 0.5 mm and a through-hole angle of 50°. The temperature of the bismuth silicate polycrystalline material in the crucible was maintained at 1180℃, with the temperature at the through-hole in the capillary kept 90℃ lower than the liquid surface. The pulling speed was 8 mm / h. Finally, a plate-shaped BSO crystal with a thickness of 1.5 mm, a width of 50 mm, and a length of 100 mm was obtained.

[0055] Three samples were taken from the upper, middle and lower parts of the crystal. After grinding and polishing, micro Raman analysis was performed. The composition [Bi] / [Bi+Si] of the crystal was 57.135%, 57.140% and 57.148% respectively, which is very close to the theoretical value [Bi] / [Bi+Si] = 4 / 7. This shows that the method can effectively suppress the compositional segregation of BSO crystal.

[0056] Example 4

[0057] Platinum was selected as the guide mold material, along with a corresponding insulation layer. Bismuth oxide and silicon oxide were mixed in a molar ratio of 2:3, thoroughly blended using a ball mill, and pre-sintered at 700℃ for 5 hours. The material was then removed and compacted. Sintering at 920℃ for 12 hours yielded BSO polycrystalline material. The guide mold was placed in a crucible with a capillary diameter of 0.5 mm and a through-hole angle of 60°. The temperature of the bismuth silicate polycrystalline material in the crucible was maintained at 1250℃, with the temperature at the through-hole in the capillary kept 120℃ lower than the liquid surface. The pulling speed was 6 mm / h. Finally, a plate-shaped BSO crystal with a thickness of 2 mm, a width of 50 mm, and a height of 100 mm was obtained.

[0058] Three samples were taken from the upper, middle, and lower parts of the crystal. After grinding and polishing, micro Raman analysis was performed. The [Bi] / [Bi+Si] ratios of the wafer were 57.130%, 57.141%, and 57.152%, respectively, which are very close to the theoretical value of [Bi] / [Bi+Si] = 4 / 7. This indicates that the method can effectively suppress the segregation of BSO crystal composition. Compared with Examples 1 to 4, the present invention can adjust the thickness of the grown BSO plate crystal by adjusting the angle of the through-hole and the thickness of the capillary.

[0059] Example 5

[0060] Platinum was selected as the guide mold material, along with a corresponding insulation layer. Bismuth oxide, silicon oxide, and rare earth oxide (Gd₂O₃) were mixed in a molar ratio of 1.98:3:0.02 using a ball mill. The mixture was pre-sintered at 670℃ for 8 hours, then removed and compacted. Finally, it was sintered at 900℃ for 15 hours to obtain (Bi₂O₃). 3.96 Gd 0.04 Si3O 12 Bismuth silicate (BGSO) polycrystalline material was used. A guide mold was placed in a crucible with a capillary diameter of 0.5 mm and a through-hole angle of 60°. The temperature of the bismuth silicate polycrystalline material in the crucible was 1180℃, and the temperature at the through-hole in the capillary was maintained 90℃ lower than the liquid surface. The pulling speed was 7 mm / h. Finally, a plate-shaped BGSO crystal with a thickness of 2 mm, a width of 50 mm, and a height of 100 mm was obtained.

[0061] Taking x = 0.02 as an example, samples from the upper, middle, and lower parts of the BGSO crystal were taken respectively. After grinding and polishing, micro Raman analysis was performed. The composition [Gd] / [Bi+Si+Gd] of the crystal was 0.57132%, 0.57141%, and 0.57152%, respectively, which are very close to the theoretical value [Gd] / [Bi+Si+Gd] = 2x / 7. This indicates that the method can effectively suppress the compositional segregation of BSO crystal and grow uniform rare earth-doped BSO crystal.

[0062] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0063] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a bismuth silicate scintillation crystal by a Littrow method, characterized in that, The method comprises the following steps: preparing a bismuth silicate polycrystal material, and then preparing a bismuth silicate scintillation crystal by using a mode guide mold (10) through a mode guide method. The preparation of the bismuth silicate polycrystal material comprises sequentially mixing raw materials, pre-sintering, compacting and sintering to obtain the bismuth silicate polycrystal material. The pre-sintering temperature is 650-700 DEG C, and the pre-sintering time is 5-10 h; the sintering temperature is 800-950 DEG C, and the sintering time is 12-18 h. The mode guide mold (10) comprises a mold cover plate (11) and a mold main body (12) fixedly connected. The mold main body (12) comprises a capillary tube (121) having a lower through hole (122) and an upper through hole (123). The diameter of the capillary tube (121) is 0.2-1 mm, the height of the mode guide mold (10) is 50-200 mm, and the opening angle of the upper through hole (123) is 45-90 DEG. The mode guide method comprises pulling a bismuth silicate scintillation crystal by using a seed crystal in contact with the upper through hole (123) under heating. The heating condition is that the temperature of the bismuth silicate polycrystal material is 1100-1250 DEG C, the temperature difference between the bismuth silicate polycrystal material in the capillary tube and the upper through hole (123) is 20-150 DEG C, the temperature of the bismuth silicate polycrystal material in the capillary tube is higher than that of the bismuth silicate polycrystal material in the upper through hole (123), and the longitudinal temperature gradient is 10-20 DEG C / cm; the pulling speed is 5-10 mm / h.

2. The method of claim 1, wherein the method of fabricating a bismuth silicate scintillation crystal by the LSG process is characterized by, When the raw materials are bismuth oxide and silicon oxide, the molar ratio of bismuth oxide to silicon oxide is 2:

3. When the raw materials are bismuth oxide, silicon oxide and rare earth oxide, the molar ratio of bismuth oxide, silicon oxide and rare earth oxide is 2-x:3:x, wherein 0 < x < 2; the rare earth oxide comprises one or more of Gd2O3, Tm2O3, Eu2O3, Dy2O3 and Ho2O3.

3. The method of claim 1, wherein the method of fabricating a bismuth silicate scintillation crystal by the LSG process is characterized by, The raw material for the mode guide mold (10) is platinum.

Images