Preparation process of LYSO crystal
By using calcium oxide to stabilize the zirconia crucible and controlling the heat treatment atmosphere during the LYSO crystal preparation process, the problems of oxygen vacancies and Ce3+ oxidation were solved, thereby improving the light output performance of the crystal.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ANHUI CRESTRON CRYSTAL MATERIALS CO LTD
- Filing Date
- 2026-01-20
- Publication Date
- 2026-05-12
AI Technical Summary
In existing LYSO crystal fabrication processes, it is difficult to effectively solve the problems of oxygen vacancies and Ce3+ oxidation at the same time, resulting in poor light output performance.
Crystals were grown using a crucible-lowering method with a calcium oxide-stabilized zirconia crucible. The oxidation state of oxygen vacancies and Ce3+ was controlled by heat treatment in a reducing atmosphere followed by annealing in an oxygen-containing gas. The specific steps included heating, annealing, and cooling.
This effectively reduces defects in the crystal, improves light output performance, and ensures the high-efficiency light emission performance of the LYSO crystal.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of scintillation crystal material preparation technology, specifically to a preparation process for LYSO crystals. Background Technology
[0002] yttrium lutetium silicate crystal (LYSO:Ce) is a novel high-performance scintillation material developed in the last decade, with the chemical formula Ce. 2x (Lu 1-y Y y ) 2(1-x) SiO5 and LYSO crystals are monoclinic crystals with space group C2 / c, and Ce is the dominant element. 3+ As the luminescent center, when high-energy rays (γ / X-rays) excite the crystal, energy is transferred to Ce through the crystal lattice. 3+ The ions trigger the 5d→4f energy level transition, producing ultrafast scintillation fluorescence. Lutetium provides high density and high effective atomic number, enhancing X-ray blocking capability; the introduction of yttrium can tune lattice distortion and optimize Ce. 3+ Luminous efficiency. LYSO crystals have a high density (7.1 g / cm³). 3 It features high effective atomic number (average Z=64), excellent energy resolution (<10%@662keV under Na-22 source), fast light decay (about 40ns), high light output (≥30000ph / MeV), and low afterglow (<0.1%@3ms), and is widely used in fields such as nuclear medicine imaging PET, high-energy physics detection and security inspection equipment.
[0003] Currently, LYSO crystals exhibit some differences in light output. Related studies speculate that this is due to insufficient purity of the raw material lutetium oxide or oxygen vacancies in the crystal. In existing technologies, iridium crucibles are mostly used during the crystal growth stage to resist the high corrosivity of molten raw materials. Chinese patent application CN201410532109.X discloses a process for growing cerium-doped lutetium yttrium silicate scintillation crystals using a molybdenum crucible. It proposes replacing iridium crucibles with molybdenum crucibles to reduce high instrument costs, employing a crucible lowering method. It also introduces a weakly reducing gas during the heating and melting of the raw material and the crystal growth stage, and adds carbon felt to the vacuum furnace to prevent oxidation and corrosion of the molybdenum crucible. However, crystal growth in a weakly reducing atmosphere results in numerous oxygen vacancies and poor light output performance. To address this issue, Chinese patent application CN201510761927.1 discloses a method to improve the scintillation performance of cerium-doped lutetium yttrium silicate crystals grown using the crucible lowering method. This method involves heat-treating the grown crystal under a mixture of nitrogen and oxygen to compensate for oxygen vacancies. However, this method also removes some of the cerium... 3+ Oxidized to Ce 4+ This results in poor light output performance. Therefore, a new design and optimization of the process steps are needed to solve the problem of light output variation in LYSO crystals. Summary of the Invention
[0004] The purpose of this invention is to provide a process for preparing LYSO crystals, thereby solving the following technical problems: Existing crucible lowering techniques present oxygen vacancy problems in LYSO crystals and require measures to prevent Ce formation. 3+ The oxidation problem is difficult to solve perfectly at the same time; it is also difficult to ensure both economy and practicality in the selection of crucible materials.
[0005] The objective of this invention can be achieved through the following technical solutions: A process for preparing LYSO crystals, characterized by comprising the following steps: S1. Add the raw materials to the reaction tank, heat and stir for 4-6 hours, add the mixed solution dropwise to the reaction tank, age overnight, wash alternately with deionized water and anhydrous ethanol, and dry to obtain LYSO precursor; S2. Place the LYSO precursor into a crucible, place the crucible into a reactor, and grow crystals using the crucible lowering method. First, raise the temperature to 600-700℃ at a heating rate of 100℃ / h, then raise the temperature to 80℃ / h until the LYSO precursor melts and crystal growth begins. Maintain the temperature until crystal growth ends, and then lower the temperature to room temperature at a cooling rate of 60℃ / h to obtain the LYSO crystal sample. S3. Place the LYSO crystal sample in a vacuum furnace, evacuate the furnace, introduce a reducing gas, heat the temperature to 600-700℃ at a rate of 100℃ / h and hold for 3-5 hours. Then introduce an oxidizing gas to replace the original atmosphere and heat the temperature to 1400-1500℃ at a rate of 50℃ / h for annealing for 10 hours. Then cool the temperature to 1200-1300℃ at a rate of 100℃ / h for annealing for 10-20 hours. Finally, cool the temperature to room temperature at a rate of 60℃ / h to obtain the LYSO crystal.
[0006] As a further aspect of the present invention: the raw material composition of LYSO crystal is Lu2O3, Y2O3 and CeO2, with a weight ratio of 85-90:5-10:0.3-0.5.
[0007] As a further aspect of the present invention: the mixed solution in S1 is a mixed solution of sodium silicate and ammonia water, with an addition mass ratio of 1:5-6; The mass ratio of raw materials to mixed solution is 101-103:100.
[0008] As a further aspect of the present invention: the crucible in S2 is a calcium oxide stabilized zirconia crucible.
[0009] As a further aspect of the present invention: the reducing gas in S3 is a mixture of 95% N2 / Ar and 5% H2, and the oxidizing gas is a mixture of 97% N2 / Ar and 3% O2.
[0010] As a further aspect of the present invention: the chemical composition of the LYSO crystal is Ce. 2x (Lu 1-y Y y ) 2(1-x) SiO5, wherein x is from 0.00001 to 0.05 and y is from 0.0001 to 0.9999.
[0011] The beneficial effects of this invention are: In this invention, the grown LYSO crystal sample is first heat-treated in a reducing atmosphere to reduce trace amounts of Ce within the crystal sample. 4+ Restored to Ce 3 + Then, a second annealing process is performed in a protective gas containing a small amount of oxygen to fill oxygen vacancies, while preventing excessive oxidation, resulting in fewer defects in the LYSO crystal and higher light output.
[0012] The crucible material used in the crucible lowering method of this invention is calcium oxide stabilized zirconium oxide. Zirconia has a melting point of 2700℃, strong thermal shock resistance, and high chemical inertness. The addition of calcium oxide improves thermal stability, thermal insulation, and upper limit temperature. The calcium oxide stabilized zirconium oxide crucible can continuously operate at temperatures above 2200℃, and has low cost, making it an ideal crucible material. Detailed Implementation
[0013] 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.
[0014] Example 1 The preparation process of LYSO crystal in this example includes the following steps: S1. 2550g Lu2O3, 150g Y2O3 and 9g CeO2 were mixed to obtain raw materials, which were put into a reaction tank and heated and stirred for 4 hours. 2.7kg of a 1:5 mixture of sodium silicate and ammonia was added dropwise to the reaction tank. The mixture was aged overnight, washed alternately with deionized water and anhydrous ethanol, and dried to obtain LYSO precursor. S2. Place the LYSO precursor into a calcium oxide-stabilized zirconia crucible, place the crucible into a reactor, first heat to 600℃ at a heating rate of 100℃ / h, then heat to 80℃ / h until the LYSO precursor melts and begins to grow crystals, hold the temperature until the crystal growth ends, and cool to room temperature at a cooling rate of 60℃ / h to obtain the LYSO crystal sample. S3. Place the LYSO crystal sample in a vacuum furnace, evacuate the furnace, and then introduce a mixed gas of 95% N2 and 5% H2. Heat the sample to 600℃ at a heating rate of 100℃ / h and hold for 3 hours. Then, introduce a mixed gas of 97% N2 and 3% O2 to replace the original atmosphere and heat the sample to 1400℃ at a heating rate of 50℃ / h for annealing for 10 hours. Finally, anneal the sample to 1200℃ at a cooling rate of 100℃ / h for 10 hours and then cool the sample to room temperature at a cooling rate of 60℃ / h to obtain the LYSO crystal.
[0015] Example 2 The preparation process of LYSO crystal in this example includes the following steps: S1. 2610g Lu2O3, 210g Y2O3 and 12g CeO2 were mixed to obtain raw materials, which were put into a reaction tank and heated and stirred for 5 hours. 2.8kg of a 1:5 mixture of sodium silicate and ammonia was added dropwise to the reaction tank. The mixture was aged overnight, washed alternately with deionized water and anhydrous ethanol, and dried to obtain LYSO precursor. S2. Place the LYSO precursor into a calcium oxide-stabilized zirconia crucible, place the crucible into a reaction furnace, first heat to 650℃ at a heating rate of 100℃ / h, then heat to 80℃ / h until the LYSO precursor melts and begins to grow crystals, hold the temperature until the crystal growth ends, and cool to room temperature at a cooling rate of 60℃ / h to obtain the LYSO crystal sample. S3. Place the LYSO crystal sample in a vacuum furnace, evacuate the furnace, and then introduce a mixed gas of 95% N2 and 5% H2. Heat the sample to 600-700℃ at a heating rate of 100℃ / h and hold for 3-5 hours. Then, introduce a mixed gas of 97% N2 and 3% O2 to replace the original atmosphere and heat the sample to 1450℃ at a heating rate of 50℃ / h for annealing for 10 hours. Finally, anneal the sample to 1250℃ at a cooling rate of 100℃ / h for 15 hours and then cool the sample to room temperature at a cooling rate of 60℃ / h to obtain the LYSO crystal.
[0016] Example 3 The preparation process of LYSO crystal in this example includes the following steps: S1. 2700g Lu2O3, 300g Y2O3 and 15g CeO2 were mixed to obtain raw materials, which were put into a reaction tank and heated and stirred for 6 hours. 3kg of a 1:6 mixture of sodium silicate and ammonia was added dropwise to the reaction tank. The mixture was aged overnight, washed alternately with deionized water and anhydrous ethanol, and dried to obtain LYSO precursor. S2. Place the LYSO precursor into a calcium oxide-stabilized zirconia crucible, place the crucible into a reactor, first heat to 700℃ at a heating rate of 100℃ / h, then heat to 80℃ / h until the LYSO precursor melts and begins to grow crystals, hold the temperature until the crystal growth ends, and cool to room temperature at a cooling rate of 60℃ / h to obtain the LYSO crystal sample. S3. Place the LYSO crystal sample in a vacuum furnace, evacuate the furnace, and then introduce a mixed gas of 95% N2 and 5% H2. Heat the sample to 700℃ at a heating rate of 100℃ / h and hold for 5 hours. Then, introduce a mixed gas of 97% N2 and 3% O2 to replace the original atmosphere and heat the sample to 1500℃ at a heating rate of 50℃ / h for annealing for 10 hours. Finally, anneal the sample to 1300℃ at a cooling rate of 100℃ / h for 20 hours and then cool the sample to room temperature at a cooling rate of 60℃ / h to obtain the LYSO crystal.
[0017] Performance testing: 1. Crystal appearance: The crystal color was recorded by visual inspection and color comparison with color chart. The results are shown in Table 1.
[0018] 2. Relative light output: According to GB / T 13181-2024 "Methods for measuring the performance of solid-state scintillators", a NaI(Tl) standard sample was used, and the output was measured by... 137 Excitation was performed using a Cs source (661.6keV). The Compton edge channel addresses of the standard sample and the crystal under test were measured. The relative pulse amplitude ratio was calculated to obtain the light output of the crystal under test. The results are shown in Table 1.
[0019] 3. Scintillation decay time: According to GB / T 13181-2024 "Methods for measuring the performance of solid scintillators", the scintillation decay time was detected by single-photon method using a pulsed X-ray fluorescence lifetime tester. The results are shown in Table 1.
[0020] Table 1: Performance Test Data Statistics for Examples 1-3
[0021] As shown in Table 1, the LYSO crystal obtained by the process of this invention is colorless and transparent, has high light output, and short scintillation decay time, reaching a leading level and meeting the application requirements of the next generation of detectors.
[0022] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.
Claims
1. A process for preparing LYSO crystals, characterized in that, It includes the following steps: S1. Add the raw materials to the reaction tank, heat and stir for 4-6 hours, add the mixed solution dropwise to the reaction tank, age overnight, wash alternately with deionized water and anhydrous ethanol, and dry to obtain LYSO precursor; S2. Place the LYSO precursor into a crucible, place the crucible into a reactor, and grow crystals using the crucible lowering method. First, raise the temperature to 600-700℃ at a heating rate of 100℃ / h, then raise the temperature to 80℃ / h until the LYSO precursor melts and crystal growth begins. Maintain the temperature until crystal growth ends, and then lower the temperature to room temperature at a cooling rate of 60℃ / h to obtain the LYSO crystal sample. S3. Place the LYSO crystal sample in a vacuum furnace, evacuate the furnace, introduce a reducing gas, heat the temperature to 600-700℃ at a rate of 100℃ / h and hold for 3-5 hours. Then introduce an oxidizing gas to replace the original atmosphere and heat the temperature to 1400-1500℃ at a rate of 50℃ / h for annealing for 10 hours. Then cool the temperature to 1200-1300℃ at a rate of 100℃ / h for annealing for 10-20 hours. Finally, cool the temperature to room temperature at a rate of 60℃ / h to obtain the LYSO crystal.
2. The preparation process of LYSO crystal according to claim 1, characterized in that, The raw material composition of LYSO crystals is Lu2O3, Y2O3 and CeO2, with a weight ratio of 85-90:5-10:0.3-0.
5.
3. The preparation process of LYSO crystal according to claim 1, characterized in that, The mixed solution in S1 is a mixture of sodium silicate and ammonia water, with an addition mass ratio of 1:5-6; The mass ratio of raw materials to mixed solution is 101-103:
100.
4. The preparation process of LYSO crystal according to claim 1, characterized in that, The crucible in S2 is a calcium oxide stabilized zirconia crucible.
5. The preparation process of LYSO crystal according to claim 1, characterized in that, S3 contains a mixture of 95% N2 / Ar and 5% H2 as reducing gases and a mixture of 97% N2 / Ar and 3% O2 as oxidizing gases.
6. The preparation process of LYSO crystal according to claim 1, characterized in that, The chemical composition of the LYSO crystal is Ce. 2x (Lu 1-y Y y ) 2(1-x) SiO5, wherein x is from 0.00001 to 0.05 and y is from 0.0001 to 0.9999.