Preparation method of cerium-doped lutetium yttrium silicate crystal

Abstract

The invention relates to a preparation method of a cerium-doped lutetium yttrium silicate crystal, and relates to the technical field of scintillation crystal preparation. Compared with a traditional Czochralski method, the cerium-doped lutetium yttrium silicate is prepared through a flame fusion method, the growth speed of the flame fusion method is 15-20 mm / h, the growth rate is higher, consumable items such as an iridium crucible are not needed, mutual reaction between a high-temperature melt and the crucible is avoided, the cost is effectively reduced, and the cerium-doped lutetium yttrium silicate is obtained. The limitation of a crucible material on preparation of high-melting-point oxide crystals is eliminated, the crystal quality is improved, and the growth period is short.

Description

Technical Field

[0001] The invention relates to the technical field of scintillation crystal preparation, and in particular to a method for preparing a cerium-doped yttrium-lutetium silicate crystal. Background Art

[0002] Scintillator crystals play an important role in radiation detection. They achieve the scintillation effect by emitting ultraviolet or visible light, and measure radiation information such as energy, intensity, and propagation. They are widely used. Ce: LYSO scintillator crystals are valued for their large light yield, short fluorescence time, good gamma-ray detection efficiency, high energy resolution, stable chemical properties, and mechanical strength. They have been successfully used in high-energy physics, nuclear medicine, and oil exploration. Many companies or research institutions such as Crystal Photonics Inc., Siemens Medical Solutions USA Inc., Saint-Gobain, Hitachi, the 26th Institute of China Science and Technology Electronics Group Corporation, and the Shanghai Institute of Ceramics, Chinese Academy of Sciences have conducted research on the growth and application of Ce: LYSO crystals.

[0003] However, there are some technical difficulties in the process of growing Ce:LYSO crystals by the widely used Czochralski method. The high melting point of Ce:LYSO exceeds 2000°C, and the iridium crucible used is easy to volatilize or oxidize, which increases the growth cost and leads to the formation of scattering centers. High temperature causes loss of insulation materials, and the thermal field stability cannot be ensured. In addition, Ce:LYSO crystals belong to the monoclinic system, which is prone to cracking when the temperature drops, and it is difficult to adjust the temperature field. Finally, the crystal needs to be annealed twice to remove oxygen vacancies to improve the scintillation performance. And when Ce:LYSO crystals are prepared by the Czochralski method, the growth rate is low. For example, in the "Study on the Growth and Performance of Cerium-doped Yttrium Lutetium Silicate Scintillating Crystal Materials", the maximum growth rate of the Czochralski method is 3.5mm / h. In summary, the quality of Ce:LYSO crystals grown by the traditional Czochralski method is not as expected, and the cost is high, the growth rate is low, and the growth cycle is long. Therefore, it is necessary to propose a new preparation method to solve the above technical problems. Summary of the invention

[0004] In order to solve the above technical problems, the purpose of the present invention is to provide a method for preparing cerium-doped yttrium-lutetium silicate crystals. The preparation method of the present invention is used to prepare Ce:LYSO crystals, with a faster growth rate, a shorter growth cycle, effectively reducing costs, and no pollution to the crystals. It effectively solves the limitation of crucible materials on the preparation of high-melting-point oxide crystals when using the pulling method to prepare Ce:LYSO crystals, thereby improving the quality of the crystals.

[0005] The technical solution of the present invention to solve the above technical problems is as follows:

[0006] The purpose of the present invention is to provide a method for preparing cerium-doped yttrium lutetium silicate crystals, the specific steps of which are as follows:

[0007] (1) Lu2O3 powder, Y2O3 powder, SiO2 powder and Ce(NO3)3·6H2O powder are mixed to obtain a mixed powder, and the mixed powder is dried and sieved before solid phase synthesis to obtain a polycrystalline block for later use;

[0008] (2) after introducing inner oxygen, outer oxygen and hydrogen to obtain a mixed gas, ignite the mixed gas for preheating, and adjust the introduction increment of the inner oxygen and the hydrogen at the same time; after preheating, add LYSO:Ce seed crystal for heating, and then drop the polycrystalline material block onto the LYSO:Ce seed crystal;

[0009] (3) adjusting the LYSO:Ce seed crystal to start descending, keeping the internal oxygen and hydrogen introduction increments unchanged, and adjusting the external oxygen introduction increment separately, and after the crystal melt cap is formed, keeping the descending rate of the LYSO:Ce seed crystal unchanged, adjusting the dripping amount of the polycrystalline material block and the internal oxygen and hydrogen introduction increments, so that the crystal expands and grows;

[0010] (4) After the crystal overflows, the shoulder expansion growth of the crystal is stopped, and the crystal is cooled to room temperature to obtain a cerium-doped yttrium lutetium silicate crystal.

[0011] The beneficial effects of the present invention are as follows: compared with the traditional pulling method, the growth rate of the flame melting process of the present invention is 15 to 20 mm / h, and the growth rate is faster; there is no need to use consumables such as iridium crucibles, thereby avoiding the mutual reaction between the high-temperature melt and the crucible, effectively reducing costs, getting rid of the limitations of crucible materials on the preparation of high-melting-point oxide crystals, improving the crystal quality, and having a shorter growth cycle; and the doping element cerium in the cerium-doped yttrium lutetium silicate crystals prepared by the present invention can replace other rare earth elements, including lanthanum, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, and ytterbium.

[0012] Preferably, the mixed powder is dried at a temperature of 70 to 90° C. for a drying time of 22 to 26 hours, and the mixed powder is sieved through a 200-mesh sieve.

[0013] Preferably, after the crystal stops expanding its shoulders and growing, the furnace is wrapped with heat-insulating cotton to allow the crystal to cool slowly and prevent the crystal from breaking.

[0014] Based on the above technical solution, the present invention can also be improved as follows.

[0015] Furthermore, the mass ratio of the Lu2O3 powder, the Y2O3 powder, the SiO2 powder and the Ce(NO3)3·6H2O powder in step (1) is (0.8-0.9):(0.09-0.1):(0.8-1.2):(0.002-0.006), and the purity is all 4N grade.

[0016] The beneficial effect of adopting the above further scheme is that the present invention meets the requirements of the flame melting method for powder purity and fluidity, and excessive addition of SiO2 powder prevents the volatilization of SiO2 from the melt during the subsequent heating and melting process due to different melting points, thereby accelerating the decomposition of the LYSO melt, thereby causing excessive Lu2O3 components in the melt, and ultimately causing inclusions to appear in the crystal.

[0017] Furthermore, in step (1), zirconium oxide balls are added to the mixed powder during mixing, and the mass ratio of the mixed powder to the zirconium oxide balls is 5:1; and the specific process of the solid phase reaction is: sintering at 1200-1500° C. for 240-480 min.

[0018] Furthermore, in step (2), the initial amount of the external oxygen introduced is 3 to 4 L / min; the initial amount of the internal oxygen introduced is 4 to 5 L / min; and the initial amount of the hydrogen introduced is 7 to 9 L / min.

[0019] The beneficial effect of adopting the above further scheme is: by controlling the amount of internal oxygen and hydrogen introduced, the chemical formula 2H2+O2→2H2O is satisfied, and by selecting a three-tube burner, external oxygen can be increased to adjust the flame shape and form a large temperature difference temperature zone.

[0020] Furthermore, in step (2), the amount of the internal oxygen and the amount of the hydrogen introduced is adjusted in a specific manner as follows: the amount of the internal oxygen and the amount of the hydrogen introduced is increased at a ratio of 1:2 to 2.5 every 10 to 20 minutes.

[0021] Furthermore, the preheating temperature in step (2) is 500-700° C., and heating is continued for 20-40 minutes after preheating.

[0022] Furthermore, the specific steps of placing the LYSO:Ce seed crystal in the single crystal furnace for heating in step (2) are: first baking it in the single crystal furnace hearth for 10 to 20 minutes, then raising the LYSO:Ce seed crystal to the crystal growth zone located in the single crystal furnace hearth, keeping the increase in the introduction of the hydrogen and the internal oxygen unchanged, heating the single crystal furnace hearth, and when the temperature of the single crystal furnace hearth reaches 2000 to 2200°C, the LYSO:Ce seed crystal melts.

[0023] Furthermore, step (2) of dropping the polycrystalline material block onto the LYSO:Ce seed crystal is specifically as follows: dropping the polycrystalline material block onto the LYSO:Ce seed crystal via a powder feeding funnel, wherein the initial knocking amplitude of the powder feeding funnel is 10 to 25 mm.

[0024] The beneficial effect of adopting the above further solution is to ensure that the position of the solid-liquid interface remains unchanged.

[0025] Furthermore, in step (3), the descending rate of the LYSO:Ce seed crystal is 15-20 mm / h; and the increment of the external oxygen is adjusted separately: the increment of the external oxygen is increased by 0.05-0.15 L / min every 5-10 minutes.

[0026] The beneficial effects of adopting the above further scheme are: adjusting the flame shape, forming a larger temperature gradient, and ensuring that the position of the solid-liquid interface remains unchanged. Since there are more elements in the synthetic powder during the growth of LSYO:Ce, and LYSO is a solid solution of LSO and YSO, the uneven temperature requires a larger temperature gradient to be created during the growth process. The role of the internal oxygen and hydrogen is mainly to provide heat for crystal growth, and the role of the external oxygen is mainly to reduce the temperature of the inner wall of the furnace to form a larger temperature gradient.

[0027] Furthermore, the step (3) of adjusting the dripping amount of the polycrystalline material block and the incremental amount of the internal oxygen and hydrogen introduced is specifically as follows: adjusting the tapping amplitude of the powder feeding funnel to increase by 5 to 10 mm every 30 minutes; and increasing the amount of the internal oxygen and the hydrogen introduced by a ratio of 1:2.5 to 3.5 every 5 to 10 minutes.

[0028] The beneficial effect of adopting the above further solution is: expanding the area of ​​the isothermal zone to ensure the shoulder expansion growth of the crystal.

[0029] Preferably, during the growth of the crystal shoulder, if the growth interface is not clear, it is necessary to increase the amount of hydrogen and external oxygen introduced and the seed crystal descent rate in real time to reduce the crystal growth temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is an X-ray diffraction pattern of the lutetium yttrium silicate powder of Example 1 of the present invention;

[0031] Figure 2 This is a SEM image of the yttrium lutetium silicate powder of Example 1 of the present invention;

[0032] Figure 3 This is a picture of the lutetium yttrium silicate single crystal of Example 1 of the present invention;

[0033] Figure 4 This is the X-ray diffraction pattern of lutetium yttrium silicate. DETAILED DESCRIPTION

[0034] The principles and features of the present invention are described below, and the examples are only used to explain the present invention and are not used to limit the scope of the present invention. If no specific technology or conditions are specified in the embodiments, the technology or conditions described in the literature in this field or the product instructions are used. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased through regular channels.

[0035] Example 1: Preparation of cerium-doped yttrium-lutetium silicate crystals

[0036] (1) 49 g Lu2O3, 3.1 g Y2O3, 8.2 g SiO2 and 0.3 g Ce(NO3)3·6H2O powders of 4N purity were mixed at room temperature in a ball mill equipped with zirconium oxide balls and a jar to obtain a mixed powder, wherein the mass ratio of the balls to the mixed powder was 5:1. The mixed powder was dried at 80°C for 24 h, passed through a 200 mesh sieve, and sintered at 1300°C for 360 min for solid phase synthesis to generate a polycrystalline block for use;

[0037] (2) introducing inner oxygen, outer oxygen and hydrogen into a three-tube burner to obtain a mixed gas, wherein the initial introduction amounts of inner oxygen, outer oxygen and hydrogen are 4 L / min, 3 L / min and 8.5 L / min respectively, igniting the mixed gas to heat the single crystal furnace, and at the same time, increasing the inner oxygen by 0.1 L / min and hydrogen by 0.2 L / min every 15 min on the basis of the initial introduction amount, and heating the furnace to 500° C.; heating for another 20 min after reaching the temperature, placing the LYSO:Ce seed crystal into the single crystal furnace and baking it for 10 min, and then slowly raising the LYSO:Ce seed crystal to the crystal growth zone, and continuously increasing the introduction amount of inner oxygen by 0.1 L / min and hydrogen by 0.2 L / min every 15 min. As the temperature of the single crystal furnace increases, when the temperature reaches 2150° C., the upper surface of the seed crystal gradually melts, and when a liquid phase is formed, the powder feeding funnel is knocked with an initial knocking amplitude of 10 mm to feed the polycrystalline material block;

[0038] (3) Adjusting LYSO: The Ce seed crystal begins to descend at a rate of 15 mm / h, and the internal oxygen and hydrogen are increased by 0.1 L / min and 0.2 L / min respectively every 15 min. At the same time, the external oxygen is increased once every 7 minutes, and the increment is 0.05 L / min. After the crystal melt cap is formed, the descending rate of the seed crystal is kept unchanged, and the tapping amplitude of the powder feeding colander is adjusted by an increment of 5 mm every 30 min. The increment of external oxygen is kept unchanged, and the internal oxygen and hydrogen are adjusted to increase by 0.05 L / min and 0.15 L / min respectively every 5 min to expand the isothermal area to ensure the shoulder expansion growth of the crystal.

[0039] (4) After the crystal overflows, the shoulder expansion growth of the crystal is stopped, and the furnace is wrapped with insulation cotton to allow the crystal to slowly cool to room temperature to obtain LYSO:Ce crystal.

[0040] Example 1 The LYSO:Ce crystals prepared as Figure 3As shown, the prepared LYSO:Ce crystals are colorless, transparent, and crack-free. Scanning electron microscope (JEM-2100F; JEOL) and X-ray diffractometer (Smartlab (9); Rigaku) ​​were used for SEM and XRD analysis. The results are shown in Figure 2 , Figure 4 shown.

[0041] Figure 2 The particles show almost no agglomeration and are almost spherical and uniform.

[0042] Figure 4 This is the XRD pattern of the LYSO:Ce crystal of Example 1, from which it can be seen that the LYSO:Ce crystal was successfully synthesized.

[0043] Example 2: Preparation of cerium-doped yttrium-lutetium silicate crystals

[0044] (1) 49 g Lu2O3, 3.1 g Y2O3, 8.2 g SiO2 and 0.3 g Ce(NO3)3·6H2O powders of 4N purity were mixed at room temperature using a ball mill with zirconium oxide balls and a jar to obtain a mixed powder, wherein the mass ratio of the balls to the mixed powder was 5:1. The mixed powder was dried at 80°C for 24 h, passed through a 200 mesh sieve, and sintered at 1500°C for 240 min for solid phase synthesis to generate a polycrystalline block for use;

[0045] (2) introducing inner oxygen, outer oxygen and hydrogen into a three-tube burner to obtain a mixed gas, wherein the initial introduction amounts of inner oxygen, outer oxygen and hydrogen are 5 L / min, 4 L / min and 9 L / min respectively, igniting the mixed gas to heat the furnace of the single crystal furnace, and at the same time, increasing the inner oxygen by 0.1 L / min and hydrogen by 0.25 L / min every 10 min on the basis of the initial introduction amount, and heating the furnace temperature to 700°C; heating for another 20 min after reaching the temperature, placing the LYSO:Ce seed crystal into the furnace of the single crystal furnace for baking for 20 min, and then slowly raising the LYSO:Ce seed crystal to the crystal growth zone, and continuously increasing the introduction amount of inner oxygen by 0.1 L / min and hydrogen by 0.25 L / min every 10 min. As the temperature of the furnace of the single crystal furnace increases, when the temperature reaches 2200°C, the upper surface of the seed crystal gradually melts, and when a liquid phase is formed, the powder feeding funnel is knocked with an initial knocking amplitude of 25 mm to feed the polycrystalline material block;

[0046] (3) Adjusting LYSO: The Ce seed crystal begins to descend at a rate of 20 mm / h, and the inner oxygen and hydrogen are increased by 0.1 L / min and 0.25 L / min respectively every 10 min. At the same time, the outer oxygen is increased once every 10 minutes, and the increment is 0.15 L / min. After the crystal melt cap is formed, the descending rate of the seed crystal is kept unchanged, and the tapping amplitude of the powder feeding colander is adjusted by an increment of 10 mm every 30 min. The increment of the outer oxygen is kept unchanged, and the inner oxygen and hydrogen are adjusted to increase by 0.08 L / min and 0.28 L / min respectively every 10 min to expand the isothermal area to ensure the shoulder expansion growth of the crystal.

[0047] (4) After the crystal overflows, the shoulder expansion growth of the crystal is stopped, and the furnace is wrapped with insulation cotton to allow the crystal to slowly cool to room temperature to obtain LYSO:Ce crystal.

[0048] Example 3: Preparation of cerium-doped yttrium-lutetium silicate crystals

[0049] (1) 49 g Lu2O3, 3.1 g Y2O3, 8.2 g SiO2 and 0.3 g Ce(NO3)3·6H2O powders of 4N purity were mixed at room temperature in a ball mill equipped with zirconium oxide balls and a jar to obtain a mixed powder, wherein the mass ratio of the balls to the mixed powder was 5:1. The mixed powder was dried at 80°C for 24 h, passed through a 200 mesh sieve, and sintered at 1200°C for 480 min for solid phase synthesis to generate a polycrystalline block for later use;

[0050] (2) introducing inner oxygen, outer oxygen and hydrogen into a three-tube burner to obtain a mixed gas, wherein the initial introduction amounts of inner oxygen, outer oxygen and hydrogen are 4.5 L / min, 3.5 L / min and 7 L / min respectively, igniting the mixed gas to heat the single crystal furnace, and at the same time, increasing the inner oxygen by 0.1 L / min and hydrogen by 0.20 L / min every 10 min on the basis of the initial introduction amount, and heating the furnace to 500°C; heating for another 40 min after reaching the temperature, placing the LYSO:Ce seed crystal into the single crystal furnace and baking it for 10 min, and then slowly raising the LYSO:Ce seed crystal to the crystal growth zone, and continuously increasing the introduction amount of inner oxygen by 0.1 L / min and hydrogen by 0.20 L / min every 10 min, as the temperature of the single crystal furnace increases, when the temperature reaches 2000°C, the upper surface of the seed crystal gradually melts, and when a liquid phase is formed, knocking the powder feeding funnel with an initial knocking amplitude of 10 mm to feed the polycrystalline material block;

[0051] (3) Adjusting LYSO: The Ce seed crystal begins to descend at a rate of 18 mm / h, and the internal oxygen and hydrogen are increased by 0.1 L / min and 0.20 L / min respectively every 10 min. At the same time, the external oxygen is increased once every 5 minutes, and the increment is 0.05 L / min. After the crystal melt cap is formed, the descending rate of the seed crystal is kept unchanged, and the tapping amplitude of the powder feeding colander is adjusted by an increment of 5 mm every 30 min. The increment of external oxygen is kept unchanged, and the internal oxygen and hydrogen are adjusted to increase by 0.1 L / min and 0.25 L / min respectively every 5 min to expand the isothermal area to ensure the shoulder expansion growth of the crystal.

[0052] (4) After the crystal overflows, the shoulder expansion growth of the crystal is stopped, and the furnace is wrapped with insulation cotton to allow the crystal to slowly cool to room temperature to obtain LYSO:Ce crystal.

[0053] Comparative Example 1: Preparation of Cerium-doped Lutetium Yttrium Silicate Crystals

[0054] This comparative example is the same as Example 1, except that the initial amounts of internal oxygen, external oxygen and hydrogen introduced in step (2) are different, and the remaining conditions and preparation steps are the same. The specific step (2) is as follows:

[0055] (2) Inner oxygen, outer oxygen and hydrogen are introduced into a three-tube burner to obtain a mixed gas, wherein the initial introduction amounts of inner oxygen, outer oxygen and hydrogen are 6 L / min, 5 L / min and 10 L / min respectively, and the mixed gas is ignited to heat the furnace of the single crystal furnace. At the same time, on the basis of the initial introduction amount, 0.1 L / min of inner oxygen and 0.2 L / min of hydrogen are increased every 15 minutes to heat the furnace temperature to 500°C; after reaching the temperature, the mixture is heated for another 20 minutes, and the LYSO:Ce seed crystal is placed in the furnace of the single crystal furnace for baking for 10 minutes, and then the LYSO:Ce seed crystal is slowly raised to the crystal growth zone, and the introduction amount of inner oxygen and hydrogen is continuously increased by 0.1 L / min and 0.2 L / min every 15 minutes. As the temperature of the single crystal furnace increases, when the temperature reaches 2150°C, the upper surface of the seed crystal gradually melts, and when a liquid phase is formed, the powder feeding funnel is knocked with an initial knocking amplitude of 10 mm to feed the polycrystalline material block.

[0056] Comparative Example 2: Preparation of Cerium-doped Lutetium Yttrium Silicate Crystals

[0057] This comparative example is the same as Example 1, except that the increments of oxygen and hydrogen introduced in step (2) are different, and the other conditions and preparation steps are the same. The specific step (2) is as follows:

[0058] (2) Inner oxygen, outer oxygen and hydrogen are introduced into a three-tube burner to obtain a mixed gas, wherein the initial introduction amounts of inner oxygen, outer oxygen and hydrogen are 4 L / min, 3 L / min and 8.5 L / min respectively, and the mixed gas is ignited to heat the furnace of the single crystal furnace. At the same time, on the basis of the initial introduction amount, 0.1 L / min of inner oxygen and 0.4 L / min of hydrogen are increased every 7 minutes to heat the furnace temperature to 500°C; after reaching the temperature, the mixture is heated for another 20 minutes, and the LYSO:Ce seed crystal is placed in the furnace of the single crystal furnace for baking for 10 minutes, and then the LYSO:Ce seed crystal is slowly raised to the crystal growth zone, and the introduction amount of inner oxygen and hydrogen is continuously increased by 0.1 L / min and 0.2 L / min every 15 minutes. As the temperature of the single crystal furnace increases, when the temperature reaches 2150°C, the upper surface of the seed crystal gradually melts, and when a liquid phase is formed, the powder feeding funnel is knocked with an initial knocking amplitude of 10 mm to feed the polycrystalline material block.

[0059] Comparative Example 3: Preparation of Cerium-doped Lutetium Yttrium Silicate Crystals

[0060] This comparative example is the same as Example 1, except that the initial tapping amplitude in step (2) is different, and the other conditions and preparation steps are the same. The specific step (2) is as follows:

[0061] (2) Inner oxygen, outer oxygen and hydrogen are introduced into a three-tube burner to obtain a mixed gas, wherein the initial introduction amounts of inner oxygen, outer oxygen and hydrogen are 4 L / min, 3 L / min and 8.5 L / min respectively, and the mixed gas is ignited to heat the furnace of the single crystal furnace. At the same time, on the basis of the initial introduction amount, 0.1 L / min of inner oxygen and 0.2 L / min of hydrogen are increased every 15 minutes to heat the furnace temperature to 500°C; after reaching the temperature, the mixture is heated for another 20 minutes, and the LYSO:Ce seed crystal is placed in the furnace of the single crystal furnace for baking for 10 minutes, and then the LYSO:Ce seed crystal is slowly raised to the crystal growth zone, and the introduction amount of inner oxygen and hydrogen is continuously increased by 0.1 L / min and 0.2 L / min every 15 minutes. As the temperature of the single crystal furnace increases, when the temperature reaches 2150°C, the upper surface of the seed crystal gradually melts, and when a liquid phase is formed, the powder feeding funnel is knocked with an initial knocking amplitude of 5 mm to feed the polycrystalline material block.

[0062] Comparative Example 4: Preparation of Cerium-doped Lutetium Yttrium Silicate Crystals

[0063] This comparative example is the same as Example 1, except that the amount of external oxygen introduced in step (3) is different, and the other conditions and preparation steps are the same. The specific step (3) is as follows:

[0064] (3) Adjusting LYSO: The Ce seed crystal begins to descend at a rate of 10 mm / h, and the internal oxygen and hydrogen are increased by 0.1 L / min and 0.2 L / min respectively every 15 min. At the same time, the external oxygen is increased once every 4 minutes, with an increase of 0.01 L / min. After the crystal melt cap is formed, the seed crystal descent rate is kept unchanged, and the tapping amplitude of the powder feeding colander is adjusted by an increase of 5 mm every 30 min. The external oxygen increment is kept unchanged, and the internal oxygen and hydrogen are adjusted to increase by 0.05 L / min and 0.15 L / min respectively every 5 min to expand the isothermal area to ensure the shoulder growth of the crystal.

[0065] Comparative Example 5: Preparation of Cerium-doped Lutetium Yttrium Silicate Crystals

[0066] This comparative example is the same as Example 1, except that the increment of the tapping amplitude in step (3) is different, and the other conditions and preparation steps are the same. The specific step (3) is as follows:

[0067] (3) Adjusting LYSO: The Ce seed crystal begins to descend at a rate of 10 mm / h, and the internal oxygen and hydrogen are increased by 0.1 L / min and 0.2 L / min respectively every 15 min. At the same time, the external oxygen is increased once every 7 minutes, with an increase of 0.05 L / min. After the crystal melt cap is formed, the seed crystal descent rate is kept unchanged, and the tapping amplitude of the powder feeding colander is adjusted by an increase of 10 mm every 30 min. The external oxygen increase is kept unchanged, and the internal oxygen and hydrogen are adjusted to increase by 0.05 L / min and 0.15 L / min respectively every 5 min to expand the isothermal area to ensure the shoulder growth of the crystal.

[0068] Comparative Example 6: Preparation of Cerium-doped Lutetium Yttrium Silicate Crystals

[0069] This comparative example is the same as Example 1, except that the increments of oxygen and hydrogen introduced in step (3) are different, and the other conditions and preparation steps are the same. The specific step (3) is as follows:

[0070] (3) Adjusting LYSO: The Ce seed crystal begins to descend at a rate of 10 mm / h, and the internal oxygen and hydrogen are increased by 0.1 L / min and 0.2 L / min respectively every 15 min. At the same time, the external oxygen is increased once every 7 minutes, with an increase of 0.05 L / min. After the crystal melt cap is formed, the seed crystal descent rate is kept unchanged, and the tapping amplitude of the powder feeding colander is adjusted by an increase of 5 mm every 30 min. The external oxygen increment is kept unchanged, and the internal oxygen and hydrogen are adjusted to increase by 0.05 L / min and 0.1 L / min respectively every 15 min to expand the isothermal area to ensure the shoulder growth of the crystal.

[0071] Test example: performance testing

[0072] The average growth rate and vernier caliper detection were performed on the LYSO:Ce crystals of Examples 1 to 3 and Comparative Examples 1 to 7 respectively. The average growth rate of the crystal was characterized by the descending rate of the seed crystal, and the crystal size was measured by a vernier caliper. The detection method was as follows. The detection results are shown in Table 1:

[0073] Table 1

[0074]

[0075] From Table 1, we can get:

[0076] In Example 1-3, LYSO:Ce scintillator single crystals can be prepared by flame melting method. Compared with the traditional pulling method, the growth rate of the flame melting method of the present invention is 15-20 mm / h, the growth rate is faster, and the growth cycle is shorter.

[0077] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for preparing cerium-doped yttrium-lutetium silicate crystals, characterized in that: The specific steps of the preparation method are as follows: (1) Lu2O3 powder, Y2O3 powder, SiO2 powder and Ce(NO3)3·6H2O powder are mixed to obtain a mixed powder, and the mixed powder is dried and sieved before solid phase synthesis to obtain a polycrystalline block for later use; (2) after introducing inner oxygen, outer oxygen and hydrogen to obtain a mixed gas, ignite the mixed gas for preheating, and adjust the introduction increment of the inner oxygen and the hydrogen at the same time; after preheating, add LYSO:Ce seed crystal for heating, and then drop the polycrystalline material block onto the LYSO:Ce seed crystal; (3) adjusting the LYSO:Ce seed crystal to start descending, keeping the internal oxygen and hydrogen introduction increments unchanged, and adjusting the external oxygen introduction increment separately, and after the crystal melt cap is formed, keeping the descending rate of the LYSO:Ce seed crystal unchanged, adjusting the dripping amount of the polycrystalline material block and the internal oxygen and hydrogen introduction increments, so that the crystal expands and grows; (4) After the crystal overflows, the shoulder expansion growth of the crystal is stopped, and the crystal is cooled to room temperature to obtain a cerium-doped yttrium lutetium silicate crystal.

2. The method for preparing a cerium-doped yttrium-lutetium silicate crystal according to claim 1, characterized in that: The molar ratio of the Lu2O3 powder, the Y2O3 powder, the SiO2 powder and the Ce(NO3)3·6H2O powder in step (1) is (0.8-0.9):(0.09-0.1):(0.8-1.2):(0.002-0.006), and the purity is all 4N grade.

3. The method for preparing a cerium-doped yttrium-lutetium silicate crystal according to claim 2, characterized in that: In step (1), zirconium oxide balls are added to the mixed powder during mixing, and the mass ratio of the mixed powder to the zirconium oxide balls is 5:1; the specific process of the solid phase reaction is: sintering at 1200-1500°C for 240-480min.

4. The method for preparing a cerium-doped yttrium-lutetium silicate crystal according to claim 1, characterized in that: In step (2), the initial amount of the external oxygen introduced is 3-4 L / min; the initial amount of the internal oxygen introduced is 4-5 L / min; and the initial amount of the hydrogen introduced is 7-9 L / min.

5. The method for preparing a cerium-doped yttrium-lutetium silicate crystal according to claim 4, characterized in that: The method of adjusting the amount of the internal oxygen and the hydrogen introduced in step (2) is specifically as follows: increasing the amount of the internal oxygen and the hydrogen introduced in a ratio of 1:2 to 2.5 every 10 to 20 minutes.

6. The method for preparing a cerium-doped yttrium-lutetium silicate crystal according to claim 5, characterized in that: The preheating temperature in step (2) is 500-700° C., and heating is continued for 20-40 minutes after preheating.

7. The method for preparing a cerium-doped yttrium-lutetium silicate crystal according to claim 6, characterized in that: The specific steps of placing the LYSO:Ce seed crystal in the single crystal furnace for heating in step (2) are: first baking it in the single crystal furnace hearth for 10 to 20 minutes, then raising the LYSO:Ce seed crystal to the crystal growth zone located in the single crystal furnace hearth, keeping the hydrogen and internal oxygen introduction increments unchanged, heating the single crystal furnace hearth, and when the single crystal furnace hearth temperature reaches 2000 to 2200°C, the LYSO:Ce seed crystal melts.

8. The method for preparing cerium-doped yttrium-lutetium silicate crystals according to claim 7, characterized in that: In step (2), the polycrystalline material block is dropped onto the LYSO:Ce seed crystal by using a powder feeding funnel, and the initial knocking amplitude of the powder feeding funnel is 10 to 25 mm.

9. The method for preparing cerium-doped yttrium-lutetium silicate crystals according to claim 8, characterized in that: The descending rate of the LYSO:Ce seed crystal in step (3) is 15-20 mm / h; the increment of the external oxygen is adjusted separately: the increment of the external oxygen is increased by 0.05-0.15 L / min every 5-10 minutes.

10. The method for preparing cerium-doped yttrium-lutetium silicate crystals according to claim 9, characterized in that: The method of adjusting the dripping amount of the polycrystalline material block and the incremental amount of the internal oxygen and hydrogen introduced in step (3) is specifically as follows: adjusting the tapping amplitude of the powder feeding funnel to increase by 5 to 10 mm every 30 minutes; and increasing the amount of the internal oxygen and the hydrogen introduced by a ratio of 1:2.5 to 3.5 every 5 to 10 minutes.

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