Preparation method of high-consistency cerium-doped lutetium silicate crystal

Abstract

The invention belongs to the technical field of inorganic non-metallic materials, and particularly relates to a preparation method of a high-consistency cerium-doped lutetium silicate crystal. The preparation method of the high-consistency cerium-doped lutetium silicate crystal comprises the following steps: (1) processing a cerium-doped lutetium silicate single crystal, so that the size of the cerium-doped lutetium silicate single crystal in at least one dimension is not greater than 20mm; and (2) placing the processed cerium-doped lutetium silicate single crystal in a high-temperature furnace, introducing an oxygen-containing atmosphere into the furnace, raising the temperature of the furnace to 1100-1400 DEG C, keeping the temperature for 30-120 hours, and then cooling to room temperature along with the furnace. Through the method which is simple in process, remarkable in effect and suitable for large-scale production, the cerium-doped lutetium silicate crystal high in consistency is obtained, and the light output and the energy resolution of the cerium-doped lutetium silicate crystal can be stably and repeatedly improved to the high level.

Description

Technical Field

[0001] This invention belongs to the field of inorganic non-metallic materials technology, specifically relating to a method for preparing highly uniform cerium-doped lutetium silicate crystals. Background Technology

[0002] Cerium-doped lutetium silicate (Lu₂SiO₅:Ce, LSO:Ce) crystals are characterized by their high density (7.4 g / cm³). 3 With its excellent comprehensive properties such as rapid decay (approximately 40-50 ns) and non-hygroscopicity, cerium-doped lutetium silicate is an ideal material for high-end detectors such as positron emission tomography (PET). However, its industrial application is limited by the key technical challenge of low uniformity, namely, the crystal scintillation performance, especially light output, which exhibits significant and uncontrollable fluctuations, with huge performance differences between different ingots and even different parts of the same ingot. For applications such as PET, which require hundreds or thousands of crystal pixels to be precisely arranged to form detector modules, the low uniformity of cerium-doped lutetium silicate crystals seriously affects the manufacturing yield and cost of PET detector modules, limiting its application.

[0003] It is generally believed that the low uniformity of cerium-doped lutetium silicate crystals originates from impurities in the raw material lutetium oxide (Lu2O3). However, research has found that even when using raw materials from different sources and with different purities, or even with the intentional addition of impurities, the performance fluctuation problem of cerium-doped lutetium silicate crystals still exists, and there is no clear correlation between the performance and the impurities.

[0004] In-depth analysis of the crystal growth process revealed that cerium-doped lutetium silicate crystals grown under high-temperature (approximately 2150℃) and low-oxygen (oxygen partial pressure <1%) conditions are highly susceptible to oxygen vacancy intrinsic point defects. These oxygen vacancies, acting as deep-level defects, quench scintillation luminescence through non-radiative recombination, leading to reduced light output and performance instability. Understanding these lattice defects provides a new direction for improving the performance of cerium-doped lutetium silicate crystals and is crucial for expanding their applications. Summary of the Invention

[0005] The purpose of this invention is to address the intrinsic point defect—oxygen vacancies—in cerium-doped lutetium silicate crystals grown in a low-oxygen environment using the Czochralski method. This invention provides a simple, effective, and mass-producible method to obtain cerium-doped lutetium silicate crystals with high uniformity, thereby fundamentally improving the light output, energy resolution, and uniformity of cerium-doped lutetium silicate crystals.

[0006] The present invention provides a method for preparing highly uniform cerium-doped lutetium silicate crystals, comprising the following steps: (1) Process the cerium-doped lutetium silicate single crystal so that its size in at least one dimension is no greater than 20 mm; (2) Place the processed cerium-doped lutetium silicate single crystal in a high-temperature furnace, introduce an oxygen-containing atmosphere into the furnace, raise the furnace temperature to 1100~1400°C and hold for 30~120h, and then cool it to room temperature with the furnace.

[0007] This preparation method effectively fills oxygen vacancies by supplementing oxygen atoms into cerium-doped lutetium silicate crystals, thereby significantly improving the crystal's core performance indicators such as light output, energy resolution, performance consistency, and temperature stability. It has crucial application value in fields such as nuclear medicine imaging, high-energy physics experiments, safety detection, and geological exploration.

[0008] Furthermore, the chemical formula of the cerium-doped lutetium silicate single crystal mentioned in step (1) is Ce:Lu₂SiO₃. 5-z Y a , where z > 0, a is 0.02~0.10; z represents oxygen vacancies in the crystal.

[0009] Furthermore, the cerium-doped lutetium silicate single crystal in step (1) is obtained by growing in a low-oxygen environment using the Czochralski method; the low-oxygen environment refers to a nitrogen or argon atmosphere with an oxygen volume fraction greater than 0 and less than 0.001%.

[0010] Furthermore, in step (1), the size of the cerium-doped lutetium silicate single crystal in one dimension is greater than 1 mm and less than or equal to 10 mm; the appropriate size can ensure that oxygen can effectively diffuse into the whole crystal within a reasonable time.

[0011] Furthermore, in step (1), the cerium-doped lutetium silicate single crystal is processed into any one of the following shapes: elongated rod, sheet, or rectangular block.

[0012] Preferably, the oxygen-containing atmosphere in step (2) is one or more of pure oxygen, air, and oxygen-enriched air; in the oxygen-enriched air, 21% < the volume fraction of oxygen < 99%.

[0013] Furthermore, in step (2), the furnace temperature is raised to 1200~1300°C and held for 50~80h. Under high temperature conditions, the thermal vibration of crystal lattice atoms intensifies and the spacing increases, providing excellent kinetic conditions for the diffusion of oxygen ions.

[0014] In step (2), temperature and time must be precisely balanced. If the temperature is too low or the time is too short, the oxygen diffusion depth will be insufficient, and a large number of oxygen vacancies will still exist inside the crystal, resulting in limited performance improvement. If the temperature is too high or the time is too long, it may lead to the luminescence center Ce. 3+ The ions are oxidized to Ce, which has no luminescent properties. 4+Ions cause the crystal to appear yellow, resulting in a permanent decrease in light output.

[0015] The present invention also provides a highly uniform cerium-doped lutetium silicate crystal, which is prepared by the above preparation method.

[0016] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: (1) This invention obtains cerium-doped lutetium silicate crystals with high consistency through a simple process, significant effect and suitable for large-scale production. It can stably and repeatedly improve the light output and energy resolution of cerium-doped lutetium silicate crystals to a high level, fundamentally improving the light output, energy resolution and uniformity of cerium-doped lutetium silicate crystals. (2) Processing cerium-doped lutetium silicate single crystals into suitable sizes can ensure that oxygen can effectively diffuse into the whole crystal within a reasonable time and repair the crystal lattice defects; (3) By using appropriate temperature and time, the oxidation of cerium ions is avoided, while the thermal vibration of the crystal lattice atoms is intensified and the spacing is increased, which provides excellent kinetic conditions for the diffusion of oxygen ions. (4) The preparation method has no special and demanding requirements for the crystal growth process, can be directly applied to the existing industrial chain, has clear process parameters, conventional equipment requirements, is easy to achieve large-scale and automated production, and has high cost-effectiveness. (5) The obtained cerium-doped lutetium silicate crystals have greatly promoted the development of high-end medical imaging equipment and scientific instruments such as PET, and can improve their image quality, scanning speed and reliability. They have vital application value in fields such as nuclear medicine imaging, high-energy physics experiments, safety detection and geological exploration. Detailed Implementation

[0017] The technical solution of the present invention will be further described and illustrated below through specific embodiments. It should be understood that the specific embodiments described herein are only for the purpose of helping to understand the present invention and are not intended to limit the present invention. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commonly used raw materials in the art, and the methods used in the embodiments are all conventional methods in the art. Example 1

[0018] The preparation method of cerium-doped lutetium silicate crystal in this embodiment includes the following steps: (1) Select a Ce:LYSO single crystal with y=0.05 (i.e., the content of yttrium is 5% of the molar mass of lutetium) grown by conventional Czochralski method in a low oxygen environment, and process it into a rectangular pixel block with a size of 4 mm × 6 mm × 30 mm. (2) The processed Ce:LYSO single crystal was placed in a high-temperature furnace and heated to 1100°C in normal air pressure for 60 hours. Then it was cooled to room temperature with the furnace.

[0019] Scintillation performance tests were conducted on 10 Ce:LYSO single crystals and the final obtained cerium-doped lutetium silicate crystals. The light output (LY, expressed as the number of channels) of each pixel and the energy resolution (ER, %) of the 662 keV photoelectric peak were measured using a 137Cs source and a PMT-MCA system. FWHM represents the full width at half maximum (FWHM). The results are shown in Table 1. Table 1. Performance data of Ce:LYSO single crystal and cerium-doped lutetium silicate crystal.

[0020] The obtained cerium-doped lutetium silicate crystals showed significant improvements in light output (LY) and energy resolution (ER%), which improved from generally above 10% (up to 17.8%) to all below 9.1%. At the same time, the FWHM value, which characterizes the photoelectric peak width, was also significantly narrowed, fully demonstrating the effectiveness and consistency of the performance of cerium-doped lutetium silicate crystals. Example 2

[0021] The preparation method of cerium-doped lutetium silicate crystal in this embodiment includes the following steps: (1) Select a pure Ce:LSO single crystal grown in a low-oxygen environment using the conventional Czochralski method (i.e., without yttrium doping) and process it into a rectangular pixel block with a size of 6 mm × 6 mm × 25 mm. (2) Place the processed Ce:LSO single crystal in a high-temperature furnace, raise the furnace temperature to 1100°C and hold it for 60h or 120h in normal air pressure, and then cool it to room temperature with the furnace.

[0022] Scintillation performance tests were conducted on 10 Ce:LYSO crystal blanks and the final cerium-doped lutetium silicate crystals. The results are shown in Table 2. Table 2. Performance data of Ce:LSO crystal blanks and cerium-doped lutetium silicate crystals.

[0023] After 60 hours of treatment, the light output (LY) of the obtained cerium-doped lutetium silicate crystal was significantly improved, jumping from approximately 300 channels initially to approximately 600 channels, almost doubling the performance. This demonstrates that thermo-oxidative diffusion is equally effective for pure Ce:LSO single crystals. However, the energy resolution (ER%) deteriorated significantly, and a bimodal phenomenon appeared in the test spectrum, i.e., the emission peak of the scintillation light split into two. This indicates the non-uniformity of oxidation within the crystal, with some areas of the crystal being effectively oxidized coexisting with incompletely oxidized areas, leading to inconsistencies in light output and decay time, thus displaying a broad energy peak. The reason is that for the more compact pure Ce:LSO single crystal, treatment at 1100℃ for 60 hours is insufficient to achieve complete and uniform oxygen diffusion.

[0024] After treatment at 1100℃ for 120 hours, the light output (LY) was further consolidated and improved, with all samples reaching over 650 channels, and the energy resolution (ER%) was also significantly improved. A comparison of Examples 1-2 shows that for pure Ce:LSO crystals, a longer heat treatment time than Ce:LYSO is required to achieve sufficient oxidation and obtain the best overall performance. Example 3

[0025] The preparation method of cerium-doped lutetium silicate crystal in this embodiment includes the following steps: (1) Select a pure Ce:LSO single crystal and a Ce:LYSO single crystal grown in a low-oxygen environment using the conventional Czochralski method (the content of yttrium element is 5% of the molar mass of lutetium element), and process them into 15 rectangular pixel blocks with a size of 6 mm × 6 mm × 25 mm respectively. (2) Five pixels from the same crystal were divided into three groups to form three Ce:LSO single crystals and three Ce:LYSO single crystals. The three groups of single crystal samples were placed in three different high-temperature furnaces and subjected to thermal oxygen diffusion treatment with different parameters in air atmosphere: the first group (sample number 1-5) was heat-treated at 1400℃ for 30 hours; the second group (sample number 6-10) was heat-treated at 1300℃ for 50 hours; and the third group (sample number 11-15) was heat-treated at 1200℃ for 80 hours.

[0026] The scintillation performance of the final cerium-doped lutetium silicate crystals was tested. The test results for Ce:LSO single crystals are shown in Table 3, and the test results for Ce:LYSO single crystals are shown in Table 4. Table 3 Performance data of the obtained Ce:LSO single crystals

[0027] Table 4 Performance data of the obtained Ce:LYSO single crystal

[0028] For pure Ce:LSO single crystals, only by treating at 1400℃ for 30h can a simultaneous and significant improvement in light output (LY) and energy resolution (ER%) be achieved. At 1300℃ and 1200℃, although light output is improved, energy resolution deteriorates severely, indicating incomplete oxidation, consistent with the bimodal problem in Example 2. In contrast, Ce:LYSO single crystals show excellent overall performance improvement under all three temperature conditions. Even at the lower 1200℃ for 80h, its energy resolution can be optimized to below 8%, showing a more easily diffused oxygen characteristic.

[0029] After complete oxidation, the final light output levels of the resulting Ce:LSO crystal and Ce:LYSO crystal are very close, but Ce:LYSO crystal consistently maintains an advantage in energy resolution. This demonstrates that 1400℃ is a critical temperature threshold for Ce:LSO crystals, enabling efficient and relatively uniform oxygen diffusion. For Ce:LYSO crystals, the process window is wider; excellent performance can be achieved by adjusting the time within the 1200-1400℃ range, highlighting its convenience and reliability in industrial production. Comparative Example 1

[0030] The comparative method for preparing cerium-doped yttrium silicate crystals includes the following steps: (1) Select a Ce:YSO single crystal (completely replace lutetium with yttrium) and process it into a rectangular pixel block with a size of 6 mm × 6 mm × 10 mm; (2) The processed Ce:YSO single crystal was placed in a high-temperature furnace and heated to 1100°C in normal air pressure for 60 hours. Then it was cooled to room temperature with the furnace.

[0031] The initial light yield of the Ce:YSO single crystal (y=1.00) was 397, and the energy resolution was 10.6%. The resulting cerium-doped yttrium silicate crystal turned pale yellow, indicating that at least some Ce... 3+ Converted to Ce 4+ Ce 3+ As a high-efficiency blue light emission center, Ce 4+ It emits no light at all; energy resolution is improved to 10.0%. Although it increases light output to some extent, the improvement is relatively limited.

[0032] Finally, it should be noted that the specific embodiments described herein are merely illustrative of the spirit of the invention and are not intended to limit the implementation of the invention. Those skilled in the art can make various modifications or additions to the described embodiments or use similar methods to replace them; it is neither necessary nor possible to exemplify all embodiments here. However, these obvious variations or modifications derived from the essential spirit of the invention still fall within the scope of protection of the invention, and interpreting them as any additional limitation would contradict the spirit of the invention.

Claims

1. A method for preparing highly uniform cerium-doped lutetium silicate crystals, characterized in that, Includes the following steps: (1) Process the cerium-doped lutetium silicate single crystal so that its size in at least one dimension is no greater than 20 mm; (2) Place the processed cerium-doped lutetium silicate single crystal in a high-temperature furnace, introduce an oxygen-containing atmosphere into the furnace, raise the furnace temperature to 1100~1400°C and hold for 30~120h, then cool it to room temperature with the furnace; The chemical formula of the cerium-doped lutetium silicate single crystal is Ce:Lu₂SiO₃. 5-z Y a , where z > 0, a is 0.02~0.10; z represents oxygen vacancies in the crystal.

2. The preparation method according to claim 1, characterized in that, The cerium-doped lutetium silicate single crystal in step (1) is obtained by growing in a low-oxygen environment by the Czochralski method; the low-oxygen environment refers to a nitrogen or argon atmosphere with an oxygen volume fraction greater than 0 and less than 0.001%.

3. The preparation method according to claim 1, characterized in that, In step (1), the size of the cerium-doped lutetium silicate single crystal in one dimension is greater than 1 mm and less than or equal to 10 mm.

4. The preparation method according to claim 1 or 3, characterized in that, In step (1), the cerium-doped lutetium silicate single crystal is processed into any of the following shapes: elongated rod, sheet, or rectangular block.

5. The preparation method according to claim 1, characterized in that, The oxygen-containing atmosphere mentioned in step (2) is one or more of pure oxygen, air, and oxygen-enriched air; in the oxygen-enriched air, 21% < volume fraction of oxygen < 99%.

6. The preparation method according to claim 1, characterized in that, In step (2), the furnace temperature is raised to 1200~1300°C and held for 50~80 hours.

7. A highly uniform cerium-doped lutetium silicate crystal, characterized in that, The highly uniform cerium-doped lutetium silicate crystal is prepared by the preparation method described in claim 1.

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