Ultrafast high-brightness extremely low-fluorescent rare earth orthosilicate scintillator material and method of making same

Abstract

The application provides an ultrafast high-brightness extremely low-fluorescence rare earth orthosilicate scintillation material, a preparation method and application thereof. 2(1‑x‑y‑a) Ce 2x Ca 2y A 2a Si (1‑z) Al z O5,0

Description

Technical Field

[0001] This invention relates to the field of scintillation materials technology, specifically to an ultrafast, high-brightness, extremely low-fluorescence rare-earth orthosilicate scintillation material, its preparation method, and its applications. Background Technology

[0002] Inorganic scintillation materials are energy converters that can transform the energy carried by high-energy rays (X / γ rays) or particles (protons, neutrons, etc.) into pulses in the ultraviolet-visible band. They are core sensitive elements in radiation detection and can be combined with photodetectors (which convert ultraviolet-visible photons into electrical signals) to form scintillation detectors. Ultrafast scintillation crystals have narrow time-domain distributions of scintillation pulses, resulting in radiation detectors using these crystals exhibiting ultra-high time resolution and detection repetition rate. With the development of my country's manufacturing technology for high-end medical imaging equipment and key components, higher demands are being placed on the resolving power of ultrafast, high-brightness scintillation crystals used in key detection components of radiation detection systems.

[0003] Due to the high atomic numbers and complex extranuclear electronic structures of rare earth elements, the development of ultrafast scintillation crystals has largely focused on rare earth or rare earth-doped scintillation crystals. Currently, ultrafast (rare earth) scintillation crystals that have been put into application include BaF2, BaF2:Y, and Y3Al5O. 12 High-yield ultrafast scintillation crystals are currently being developed, including Yb (YAG:Yb), ZnO:Ga, and PbWO4:Y (PWO:Y). However, while these materials have short decay times, their light yield is too low. Therefore, the performance of existing ultrafast scintillation crystals cannot meet the needs of new ultrafast detectors in critical fields such as major engineering projects and medical imaging equipment, which are vital to national welfare. Thus, there is an urgent need to develop ultrafast scintillation crystals with high light yield.

[0004] On the other hand, rare-earth orthosilicate scintillation materials exhibit high light yields. These materials include YSO:Ce, GSO:Ce, LSO:Ce, and their solid solutions LYSO:Ce, LGSO:Ce, and GYSO:Ce. Among these, LYSO:Ce scintillation crystal is currently the best candidate material for achieving ultrafast high-speed scintillation emission; it is a monoclinic crystal with space group C. 2 / c The Lu / Y atoms have two coordination environments (RE1 and RE2) in the crystal, with coordination numbers of 7 and 6, respectively. RE1 is associated with 5 O atoms of [SiO4]. 2- and 2 isolated O atoms that are not bonded to silicon 2- Coordination forms a distorted decahedron, RE2 with 4 [SiO4] O 2- and 2 isolated O atoms that are not bonded to silicon 2- Coordination forms pseudooctahedrons; the distorted [ORE4] tetrahedra are arranged parallel to the c-axis and linked by [SiO4]. This is achieved with rare earth ions Ce. 3+ As an activator, Ce 3+The 5d→4f parity-allowed transition is used to obtain high-intensity, fast-decay luminescence.

[0005] However, rare-earth orthosilicate scintillator materials, represented by LYSO:Ce, have high light yields but relatively long decay times. To accelerate the scintillator decay rate of LYSO:Ce crystals, Wu et al. (Crystal Growth & Design, 2019, 19(7):4081-4089; ACS Applied Materials & Interfaces, 2019, 11(8):8194-8201.) reported on Li... + Cu 2+ The doping effect in Lu2SiO5:Ce shows that, under low doping concentration, although the light yield is improved to a certain extent (about 20%), the scintillation decay time is only accelerated by 1 to 3 ns; under high doping concentration, although the decay time is significantly accelerated (from 45.4 ns to 25.0 ns), the light yield is significantly sacrificed (about 100 times).

[0006] Therefore, there is an urgent need to provide a scintillating material with high light yield and ultrafast scintillation. Summary of the Invention

[0007] To improve the scintillation decay of LYSO:Ce, research on Ca co-doped LYSO:Ce materials revealed that surface Ca co-doping does not alter the energy level structure of Ce1 or Ce2, but it reduces the amount of Ce2 relative to Ce1. LYSO:Ce luminescence is composed of a combination of 5d-4f transitions at two lattice sites of seven-coordinate Ce1 and six-coordinate Ce2. The emission peaks at 393 nm and 425 nm are attributed to Ce1 luminescence, while Ce2 luminescence has a longer wavelength (approximately 550 nm). Based on this, the inventors conducted extensive experiments to verify that Ce1 has higher luminescence efficiency and a shorter decay time compared to Ce2. In other words, Ce2 luminescence is suppressed, which contributes to the rapid scintillation decay of Ca co-doped LYSO:Ce. However, Ca co-doped LYSO:Ce materials exhibit photoluminescence properties; if exposed to ultraviolet light during use and transportation, it will generate extremely strong background noise during detection.

[0008] Further research also found that Ca 2+ and Mg 2+ When divalent cations are co-doped at rare earth sites, in order to maintain valence balance, a portion of Ce... 3+ It will transform into a stable Ce 4+ This results in the formation of stable Ce in the crystal lattice. 4+ Its scintillation emission process bypasses Ce 3+ The initial hole trapping process is improved, and charge carrier trapping at defects is suppressed, thereby improving scintillation time performance. Among these, Ce... 4+The 4f ground state is empty, and there is no 5d-4f emission under ultraviolet light excitation, which means that the higher the content of stable Ce 4+ , the lower the photoluminescence intensity. That is to say, in order to improve the photoluminescence phenomenon, a large amount of stable Ce 4 + needs to be introduced. However, if a large amount of stable Ce 4+ is introduced only by increasing the doping concentration of the rare earth site, the light yield will deteriorate.

[0009] On the other hand, Chinese Patent Application CN112630818A discloses a method for improving rare earth orthosilicate scintillation materials by silicon lattice doping, their preparation methods and applications. The doping of the silicon lattice can affect the activation centers on the rare earth lattice through oxygen ions and oxygen vacancies on [SiO4], and the doping of low-valent cations may introduce Ce 4+ , thereby accelerating the decay time. However, for the rare earth orthosilicate scintillation material doped only by the silicon lattice, in order not to greatly affect the scintillation decay performance and light yield, the introduced Ce 4+ is still limited, and the material still has strong photoluminescence characteristics.

[0010] On this basis, the inventor found that for LYSO:Ce materials, by simultaneously introducing silicon lattice doping and rare earth site doping and controlling the doping amount, without affecting the light yield and scintillation performance, on the one hand, the number of Ce2 relative to Ce1 can be reduced, and at the same time, a large amount of stable Ce 4+ can be introduced. Under the synergistic effect of the two, a scintillation material with high light yield, ultrafast scintillation decay, and extremely low fluorescence performance can be obtained, and the present invention is completed on this basis.

[0011] According to the first aspect of the present invention, there is provided an ultrafast, high-brightness, and extremely low-fluorescence rare earth orthosilicate scintillation material, and the chemical formula of the ultrafast, high-brightness, and extremely low-fluorescence rare earth orthosilicate scintillation material is RE 2(1-x-y-a) Ce 2x Ca 2y A 2a Si (1-z) Al z O5, where 0 < x ≤ 0.05, 0 < y ≤ 0.02, 0 < z ≤ 0.05, 0 ≤ a ≤ 0.01, the RE represents a rare earth element, and the rare earth element is selected from at least one of lanthanum, lutetium, yttrium, and gadolinium, the A represents other doping elements, and the other doping elements are selected from at least one of lithium Li, sodium Na, potassium K, rubidium Rb, cesium Cs, magnesium Mg, strontium Sr, scandium Sc, and copper Cu.

[0012] Further, the rare earth element is a solid solution of lutetium or yttrium or both.

[0013] Furthermore, the rare earth element is a solid solution of lutetium and yttrium, wherein the molar ratio of lutetium to yttrium is 9:1.

[0014] In some embodiments, in the chemical formula of the ultrafast high-brightness, ultra-low fluorescence rare-earth orthosilicate scintillation material, 0.0001≤x≤0.003, 0.001≤y<0.003, and 0.001≤z≤0.01.

[0015] In other embodiments, the chemical formula of the ultrafast high-brightness, extremely low-fluorescence rare-earth orthosilicate scintillation material contains 0.0001≤x≤0.003, 0.003≤y≤0.005, and 0.001≤z≤0.01.

[0016] Furthermore, the scintillation yield of the ultrafast, high-brightness, extremely low-fluorescence rare-earth orthosilicate scintillation material is >10. 4 The scintillation light decay time is within 35 ns, and the fluorescence response is within 5% of that of LYSO:Ce scintillation materials.

[0017] Furthermore, the absorption coefficient at 358 nm in the optical absorption spectrum is <2.5 cm⁻¹. -1 .

[0018] According to a second aspect of the present invention, a method for preparing an ultrafast, high-brightness, extremely low-fluorescence rare-earth orthosilicate scintillation material is provided, wherein the chemical formula of the ultrafast, high-brightness, extremely low-fluorescence rare-earth orthosilicate scintillation material is RE. 2(1-x-y-a) Ce 2x Ca 2y A 2a Si (1-z) Al z O5, where 0 <x≤0.05,0<y≤0.02,0<z≤0.05,0≤a≤0.01,

[0019] RE represents a rare earth element, which is selected from at least one of lanthanum, lutetium, yttrium, and gadolinium.

[0020] The A represents other doping elements, which are selected from at least one of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), magnesium (Mg), strontium (Sr), scandium (Sc), and copper (Cu).

[0021] The ultrafast, high-brightness, extremely low-fluorescence rare-earth orthosilicate scintillation material is a single crystal, and the preparation method includes the following steps:

[0022] S1, as raw material, weigh rare earth oxides, CeO2, SiO2, Al2O3, oxides of other doped elements, CaCO3 or CaO according to the chemical formula of the ultrafast high brightness ultra-low fluorescence rare earth orthosilicate scintillation material, and mix them thoroughly to obtain a mixed powder.

[0023] S2, after the mixed powder is pressed into shape, it is subjected to solid-phase reaction at 1000-2000℃ for 5-200 hours to obtain a polycrystalline material with a single phase composition;

[0024] S3, the polycrystalline material is placed in a container and heated to melt it, and the melt is controlled to cool and crystallize slowly to obtain a single crystal crude product;

[0025] S4. The single crystal crude product is annealed at 1000-1400℃ for 10-200 hours to obtain the ultrafast high-brightness ultra-low fluorescence rare earth orthosilicate scintillation material.

[0026] Further, step S4 specifically includes:

[0027] The crude single crystal is placed in a muffle furnace, and air or a mixture of inert gas and oxygen is introduced into it.

[0028] Next, the muffle furnace is heated to 1000-1400°C at a heating rate of less than 300°C / hour, and held at that temperature for 10-200 hours.

[0029] Subsequently, the temperature was reduced to room temperature at a rate of less than 150°C / hour to obtain the ultrafast high-brightness, extremely low-fluorescence rare-earth orthosilicate scintillation material.

[0030] According to a third aspect of the present invention, the application of the ultrafast high-brightness, extremely low-fluorescence rare-earth orthosilicate scintillation material of any embodiment of the first aspect described above is provided in any field including mixed field radiation detection, high-energy physics detection and particle discrimination, and nuclear medicine imaging.

[0031] The above-described technical solution of the present invention has at least one of the following beneficial effects:

[0032] According to embodiments of the present invention, an ultrafast, high-brightness, extremely low-fluorescence rare-earth orthosilicate scintillation material is prepared by Ca reaction in the rare-earth orthosilicate scintillation material. 2+ With Al 3+ Simultaneous doping, Ca 2+ Due to its large ionic radius and strong electron-withdrawing properties, Al mainly occupies RE1 lattice sites. 3+ Due to Si 4+ With similar ionic radii and Al-O bonds that are very similar to Si-O bonds, Al-O primarily occupies Si lattice sites, meaning it has undergone simultaneous doping with both rare-earth and silicon lattice sites. Both can form... and These composite defects reduce the number of oxygen vacancies during scintillation. The carrier trapping capability optimizes scintillation output and afterglow performance. Furthermore, the inventors discovered that Ca... 2+ And Al 3+ The dual-lattice co-doping of Ce makes Ce3+ The emission peak exhibits a blue shift and broadening, a significant increase in Ce1 content, a markedly shortened emission decay time, and improved scintillation yield and afterglow performance; furthermore, due to point defects in Al... Si 'and Ca Lu The simultaneous formation of ' led to a large amount of Ce 3+ Transformation into stable Ce 4+ To maintain charge balance, thereby bypassing Ce 3+ The initial hole-capturing process of the emission further shortens the scintillation decay time; simultaneously, due to Ce 4+ With an empty 4f ground state, this material exhibits extremely low fluorescence response and complete resistance to ultraviolet interference. In other words, the ultrafast, high-brightness, extremely low-fluorescence rare-earth orthosilicate scintillation material according to embodiments of the present invention can simultaneously achieve high light yield, rapid scintillation decay, and extremely low fluorescence response.

[0033] In some embodiments, lower (<0.3%) Ca 2+ And Al 3+ Co-doping significantly increases light yield while accelerating decay time (~35ns).

[0034] In other embodiments, higher (≥0.3%) Ca 2+ And Al 3+ Co-doping reduces light yield (>10) 4 (ph. / MeV), while the decay time is significantly accelerated (approaching 30ns); as long as Ca 2+ And Al 3+ Co-doping all exhibited extremely low fluorescence response.

[0035] The ultrafast, high-brightness, extremely low-fluorescence rare-earth orthosilicate scintillator material according to this application has a scintillator yield >10 4 The scintillation light decay time is within 35 ns, and the fluorescence response is within 5% of that of LYSO:Ce scintillation materials.

[0036] In addition, the optical absorption spectrum at 358 nm (Ce 3+ The absorption coefficient at the absorption peak is <2.5 cm⁻¹. -1 This can significantly reduce crystal self-absorption and increase the output of scintillation photons from inside the crystal (equivalent to higher light yield), especially for large-sized crystals.

[0037] In addition, it significantly reduces afterglow levels and eliminates photo-induced afterglow. Its extremely low fluorescence response characteristics mean that it does not require light protection during use and transportation, and it is completely resistant to ultraviolet interference in application scenarios, thus improving the detection signal-to-noise ratio.

[0038] Ultrafast, high-brightness, and extremely low-fluorescence rare-earth orthosilicate scintillation materials, due to their combination of high light yield, rapid scintillation decay, extremely low fluorescence response, and extremely low afterglow level without photoinduced afterglow, can be better applied to mixed-field radiation detection, high-energy physics detection and particle identification, and nuclear medicine imaging (TOF-PET, PET-CT, PET-MRI). Attached Figure Description

[0039] Figure 1 For Lu 1.7994-2y Y 0.2 Ce 0.0006 Ca 2y Si (1-z) Al z X-ray diffraction pattern of O5 (y=z=0.001,0.003) single crystal;

[0040] Figure 2 For Lu 1.7994-2y Y 0.2 Ce 0.0006 Ca 2y Si (1-z) Al z Multichannel energy spectrum of O5 (y=z=0.001,0.003,0.005) single crystal;

[0041] Figure 3 For Lu 1.7994-2y Y 0.2 Ce 0.0006 Ca 2y Si (1-z) Al z Scintillation decay time spectrum of O5 (y=z=0.001,0.003,0.005) single crystal;

[0042] Figure 4 For Lu 1.7994-2y Y 0.2 Ce 0.0006 Ca 2y Si (1-z) Al z Photoluminescence spectrum of O5 (y=z=0.001,0.003) single crystal;

[0043] Figure 5 For Lu 1.7994-2y Y 0.2 Ce 0.0006 Ca 2y Si (1-z) Al z Optical absorption spectrum of O5 (y=z=0.001,0.003) single crystal;

[0044] Figure 6 For Lu 1.7994-2y Y0.2 Ce 0.0006 Ca 2y Si (1-z) Al z Afterglow decay spectra of O5 (y = z = 0.001) single crystals;

[0045] Figure 7 is Lu 1.7994-2y Y 0.2 Ce 0.0006 Ca 2y Si (1-z) Al z X-ray excitation spectra of O5 (y = z = 0.001, 0.003) single crystals. Detailed implementation manners

[0046] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present invention fall within the scope of protection of the present invention.

[0047] First, the ultrafast high-brightness and extremely low fluorescence rare-earth orthosilicate scintillation material according to the embodiments of the present application will be described below.

[0048] The ultrafast high-brightness and extremely low fluorescence rare-earth orthosilicate scintillation material according to the embodiments of the present application has the chemical formula RE 2(1-x-y-a) Ce 2x Ca 2y A 2a Si (1-z) Al z O5, where 0 < x ≤ 0.05, 0 < y ≤ 0.02, 0 < z ≤ 0.05, 0 ≤ a ≤ 0.01, the RE represents a rare-earth element, the rare-earth element is selected from at least one of lanthanum, lutetium, yttrium, and gadolinium, the A represents other doping elements, and the other doping elements are selected from at least one of lithium Li, sodium Na, potassium K, rubidium Rb, cesium Cs, magnesium Mg, strontium Sr, scandium Sc, and copper Cu.

[0049] Among them, if the y value and the z value are excessive, it will cause the single crystal to be difficult to prepare due to too high impurity content, and at the same time cause a significant deterioration in the scintillation light output.

[0050] The ultrafast high-brightness and extremely low fluorescence rare-earth orthosilicate scintillation material according to the embodiments of the present invention performs co-doping of Ca 2+ and Al 3+ in the rare-earth orthosilicate scintillation material. Ca 2+ Due to its relatively large ionic radius and strong electron-withdrawing characteristics, it mainly occupies the RE1 lattice site, and Al3+ Due to Si 4+ With similar ionic radii and Al-O bonds being very similar to Si-O bonds, it mainly occupies Si lattice sites.

[0051] also, Figure 1 Ca is shown 2+ With Al 3+ X-ray diffraction patterns for doping concentrations of 0.1% and 0.3% are shown, with LYSO:Ce material (i.e., undoped Ca) also shown for reference. 2+ With Al 3+ ), and Al-doped only 3+ Furthermore, its X-ray diffraction pattern shows a doping concentration of 0.6% (equivalent to the atomic percentage of Si). (From...) Figure 1 It can be seen that all the diffraction peaks recorded in the figure can pass through (Lu 1.81 Y 0.19 The SiO5 structure was indexed (PDF#97-015-9308), and no impurity peaks were found. Furthermore, compared to LYSO:Ce materials, Al... 3+ The shift of doped X-ray diffraction peaks to lower angles indicates that doping increases the unit cell volume. Al 3+ Radius 56pm, rare earth RE 3+ Ionic radius >100 pm, Si 4+ Radius 40pm, if Al 3+ Replace rare earth RE 3+ Lattice sites inevitably lead to a reduction in unit cell volume; in other words, an increase in unit cell volume indicates that the Al... 3+ It occupies Si lattice sites. Furthermore, the diffraction peaks after Ca and Al co-doping shift further towards smaller angles. This contrasts with the larger radius Al... 3+ Ca 2+ Replacing Lu respectively 3+ Si 4+ Their synergistic effect further increases the cell volume.

[0052] In other words, according to the ultrafast high-brightness, extremely low-fluorescence rare-earth orthosilicate scintillation material of this application, Ca is carried out in the rare-earth orthosilicate scintillation material. 2+ With Al 3+ Simultaneous doping enables the simultaneous doping of rare-earth and silicon lattice sites, which can be formed separately. and These composite defects reduce the number of oxygen vacancies during scintillation. The carrier trapping capability optimizes scintillation output and afterglow performance.

[0053] also, Figure 2The multichannel energy dispersive spectra of single crystals of LYSO:Ce, LYSO:Ce, 0.1at%Ca, 0.1at%Al, and LYSO:Ce, 0.3at%Ca, 0.3at%Al are shown. Figure 2 It can be seen that with a small amount of Ca doping 2+ With Al 3+ Under the condition of LYSO:Ce, 0.1at%Ca, 0.1at%Al, its light yield can be further improved relative to LYSO:Ce.

[0054] Figure 3 The scintillation decay time spectra of LYSO:Ce, LYSO:Ce,0.1at%Ca,0.1at%Al, LYSO:Ce,0.3at%Ca,0.3at%Al, and LYSO:Ce,0.5at%Ca,0.5at%Al single crystals are shown, with fitted decay times of 40.6 ns, 34.5 ns, 31.6 ns, and 28.7 ns, respectively. Figure 3 It can be seen that the decay time is further improved with increasing doping concentration. Combined with... Figure 2 and Figure 3 It can be seen that the Ca content is low (<0.3%). 2+ And Al 3+ Co-doping significantly increases light yield while accelerating decay time (~35 ns). At higher (≥0.3%) Ca... 2+ And Al 3+ Co-doping reduces light yield (>10) 4 (ph. / MeV), while the decay time is significantly accelerated (approaching 30ns).

[0055] Figure 4 The photoluminescence spectra of LYSO:Ce, LYSO:Ce, 0.1at%Ca, 0.1at%Al, and LYSO:Ce, 0.3at%Ca, 0.3at%Al single crystals are shown. As can be seen from the figure, according to the ultrafast high-brightness, extremely low-fluorescence rare-earth orthosilicate scintillation material of this application, Ca... 2+ With Al 3+ Simultaneous doping of LYSO:Ce,0.1at%Ca,0.1at%Al and LYSO:Ce,0.3at%Ca single crystals results in relative fluorescence intensity (i.e. fluorescence intensity relative to LYSO:Ce) of less than 5%. In other words, the ultrafast high-brightness, extremely low fluorescence rare earth orthosilicate scintillation material of this application achieves extremely low fluorescence response, solving the problem of photoinduced afterglow caused by environmental ultraviolet radiation.

[0056] Figure 5The optical absorption spectra of LYSO:Ce, LYSO:Ce, 0.6at%Al, LYSO:Ce, 0.1at%Ca, 0.1at%Al, and LYSO:Ce, 0.3at%Ca, 0.3at%Al single crystals are shown. From... Figure 5 Furthermore, it can be seen from this that Al 3+ The optical absorption spectrum of the doped LYSO:Ce, 0.6 at% Al crystal clearly shows the presence of Ce. 4+ -O 2- Charge transfer band (CT), attributed to Al 3+ Replace Si 4+ Subsequently, a negatively charged point defect Al' is formed. Si Under the influence of charge balance, Al' Si Induced Ce 3+ Transformation into stable Ce 4 + Furthermore, as can be seen from the figures, the LYSO:Ce,0.1at%Ca,0.1at%Al and LYSO:Ce,0.3at%Ca,0.3at%Al single crystals according to the two embodiments of this application not only exhibit obvious Ce... 4+ -O 2- Charge transfer band (CT), and Ce 3+ The absorption coefficients of all absorption peaks (358 nm) are <2.5 cm⁻¹. -1 And the corresponding Ce 4+ The absorption peak is significantly enhanced. At 358 nm in the optical absorption spectrum (Ce... 3+ The absorption coefficient of the absorption peak was significantly reduced (<2.5 cm⁻¹). -1 This significantly reduces crystal self-absorption, increasing the output of scintillation photons from within the crystal (equivalent to higher light yield), especially for large-size crystals. Furthermore, due to point defects in Al... Si 'and Ca Lu The simultaneous formation of ' led to a large amount of Ce 3+ Transformation into stable Ce 4+ To maintain charge balance, thereby bypassing Ce 3+ The initial hole-capturing process of the emission further shortens the scintillation decay time; simultaneously, due to Ce 4+ With an empty 4f ground state, this material exhibits extremely low fluorescence response and complete resistance to ultraviolet interference.

[0057] Figure 6 The afterglow decay spectra of LYSO:Ce, LYSO:Ce, 0.3at%Ca, LYSO:Ce, 0.6at%Al, and LYSO:Ce, 0.1at%Ca, 0.1at%Al single crystals are shown. Figure 7The X-ray excitation spectra of single crystals of LYSO:Ce, LYSO:Ce, 0.6%Al, LYSO:Ce, 0.3%Ca, LYSO:Ce, 0.1at%Ca, 0.1at%Al, and LYSO:Ce, 0.3at%Ca, 0.3at%Al are shown. Figure 6 It can be seen that the afterglow performance of Ca and Al co-doped LYSO:Ce is significantly improved compared with that of Ca or Al single-doped LYSO:Ce. Figure 7 It can be known that Ca 2+ And Al 3+ The dual-lattice co-doping of Ce makes Ce 3+ The emission peak is blue-shifted and broadened, and the Ce1 content is significantly increased, thereby significantly shortening the emission decay time and achieving improved scintillation yield and afterglow performance.

[0058] In summary, the ultrafast, high-brightness, extremely low-fluorescence rare-earth orthosilicate scintillation material according to embodiments of the present invention can simultaneously achieve high light yield, rapid scintillation decay, and extremely low fluorescence response. Furthermore, it significantly reduces afterglow levels and eliminates photo-induced afterglow. The extremely low fluorescence response characteristic eliminates the need for light-shielding treatment during use and transportation, and provides complete resistance to ultraviolet interference in application scenarios, thus improving the detection signal-to-noise ratio. The ultrafast, high-brightness, extremely low-fluorescence rare-earth orthosilicate scintillation material according to this application, due to its combination of high light yield, rapid scintillation decay, extremely low fluorescence response, and extremely low afterglow levels without photo-induced afterglow, can be better applied in mixed-field radiation detection, high-energy physics detection and particle discrimination, and nuclear medicine imaging (TOF-PET, PET-CT, PET-MRI).

[0059] Furthermore, the ultrafast, high-brightness, extremely low-fluorescence rare-earth orthosilicate scintillation material of this application may or may not be doped with other doping elements. In other words, when a is 0, i.e., without the other doping elements mentioned, its chemical formula is RE. 2(1-x-y) Ce 2x Ca 2y Si (1-z) Al z O5, when a is greater than 0, indicates doping with other doping elements mentioned above. Whether or not to dope with these elements can be appropriately selected based on the actual application scenario and performance requirements. For example, Li + Na + They tend to occupy six-coordinate interstitial spaces or rare earth sites, inhibiting V O The formation or space-related Ce and V O The dissociation of Cu can improve the scintillation yield; 2+ Mg 2+This will cause a combined effect of enhanced thermal ionization of cerium ions in the 5d1 state and reduced emission contribution from Ce2 centers (i.e., sites adjacent to the six oxygen atoms), further shortening the decay time. Those skilled in the art can appropriately choose to add or not add other corresponding doping elements based on specific application scenarios and performance requirements.

[0060] Furthermore, as a rare earth element, lutetium or yttrium, or a solid solution of both, is preferred; more preferably, a solid solution of both lutetium and yttrium, wherein the molar ratio of lutetium to yttrium is 9:1. By introducing Y, which is cheaper, has a lower melting point, and a larger ionic radius, into LSO:Ce crystals and combining it with lutetium-Lu in the aforementioned molar ratio to prepare a solid solution of LYSO:Ce, it is possible to achieve a reduction in melting point, a reduction in cost (raw materials, electricity costs for single crystal growth), a reduction in defect levels, and an optimization of crystal performance.

[0061] The following describes the ultrafast, high-brightness, extremely low-fluorescence rare-earth orthosilicate scintillation material and its preparation method in further detail with reference to specific embodiments.

[0062] Example 1 (Growth of Y using the Czochralski method) 2(1-x-y) Ce 2x Ca 2y Si (1-z) Al z O5 single crystal)

[0063] Single crystals were grown using the Czochralski method. The ingredients were prepared in the following molar ratios: Y₂O₃:CeO₂:CaCO₃:SiO₂:Al₂O₃ = 1 - xy:2x:2y:1 - z:z / 2 (x = 0.0001, 0.0003, 0.001, 0.003, 0.006, 0.01, 0.03, 0.05; y = 0.0005, 0.001, 0.002, 0.004, 0.008, 0.01, 0.02; z = 0.0005, 0.001, 0.002, 0.004, 0.008, 0.01, 0.02, 0.04, 0.05). After thorough mixing, the mixture was pressed using cold isostatic pressing (pressure 3 GPa). The pressed bulk material is placed in an iridium crucible, and under a nitrogen protective atmosphere, it is induction heated until fully melted. After seeding, a single crystal of the predetermined size is slowly pulled from the melt to grow, thus obtaining Y... 2(1-x-y) Ce 2x Ca 2y Si (1-z) Al z O5 single crystal. The parameters of the Czochralski method include: pulling speed of 0.7-3 mm / h and rotation speed of 3-15 r / min.

[0064] Example 2 (Growth of Y using the Czochralski method) 1.99 Ce 0.002 Ca 0.008Si (1-z) Al z O5 single crystal)

[0065] Single crystals were grown using the Czochralski method. The materials were prepared by mass ratio of Y₂O₃:CeO₂:CaCO₃:SiO₂:Al₂O₃ = 0.995:0.002:0.002:1-z:z / 2 (where z = 0.0005, 0.001, 0.002, 0.004, 0.008, 0.01, 0.02, 0.04, 0.05). After thorough mixing, the mixture was pressed using cold isostatic pressing (3 GPa). The pressed bulk was placed in an iridium crucible, and under a nitrogen protective atmosphere, it was induction heated until fully melted. A seed crystal was then used to slowly pull single crystals of the predetermined size from the melt, yielding Y₂O₃. 1.99 Ce 0.002 Ca 0.002 Si (1-z) Al z O5 single crystal. The parameters of the Czochralski method include: pulling speed of 2-4 mm / h and rotation speed of 10-20 r / min.

[0066] Example 3 (Growth of Lu by Czochralski method) 2(1-x-y) Ce 2x Ca 2y Si (1-z) Al z O5 single crystal)

[0067] Single crystals were grown using the Czochralski method. The ingredients were prepared in the following molar ratios: Lu₂O₃:CeO₂:CaCO₃:SiO₂:Al₂O₃ = 1 - xy:2x:2y:1 - z:z / 2 (x = 0.0001, 0.0003, 0.001, 0.003, 0.006, 0.01, 0.03, 0.05; y = 0.0005, 0.001, 0.002, 0.004, 0.008, 0.01, 0.02; z = 0.0005, 0.001, 0.002, 0.004, 0.008, 0.01, 0.02, 0.04, 0.05). After thorough mixing, the mixture was pressed using cold isostatic pressing (at a pressure of 3 GPa). The pressed bulk material is placed in an iridium crucible, and under a nitrogen protective atmosphere, it is induction heated until fully melted. After seeding, a single crystal of the predetermined size is slowly pulled from the melt to grow, yielding Lu. 2(1-x-y) Ce 2x Ca 2y Si (1-z) Al z O5 single crystal. The parameters for the Czochralski method include: design of required dimensional parameters, temperature field design, PID quality control temperature, pulling speed of 1-5 mm / h, and rotation speed of 8-10 r / min.

[0068] Example 4 (Growth of Lu using the micro-pull-down method) 1.8-2x-2y Y 0.2 Ce 2x Ca 2y Si (1-z) Al z O5)

[0069] Single crystals were grown using the micro-pull-down method (μ-PD). The molar ratio of Lu₂O₃:Y₂O₃:CeO₂:CaCO₃:SiO₂:Al₂O₃ was 0.9 - xy:0.1:2x:2y:1 - z:z / 2 (where x = 0.0001, 0.0003, 0.001, 0.003, 0.006, 0.01, 0.03, 0.05; y = 0.0005, 0.001, 0.002, 0.0...). 0.04, 0.008, 0.01, 0.02; z = 0.0005, 0.001, 0.002, 0.004, 0.008, 0.01, 0.02, 0.04, 0.05), after thorough and uniform mixing, the mixed powder was pre-sintered in a muffle furnace at 1600℃ for 20 hours. The sintered polycrystalline material was then placed in an iridium crucible and, under a nitrogen protective atmosphere, induction heated until fully melted. After the seed crystal came into contact with the melt, it was slowly pulled downwards to obtain Lu. 1.8-2x-2y Y 0.2 Ce 2x Ca 2y Si (1-z) Al z O5 single crystal. The parameters for the micro-pull-down method include a micro-pull-down speed of 3–20 mm / h.

[0070] Example 5 (Growth of Lu using the micro-pull-down method) 1.7994-2y Y 0.2 Ce 0.0006 Ca 2y Si (1-z) Al z O5 single crystal)

[0071] Single crystals were grown using the micro-pulling method (μ-PD). The following formula was used: Lu₂O₃:Y₂O₃:CeO₂:CaCO₃:SiO₂:Al₂O₃ = 0.8997 - y:0.1:0.0006:2y:1 - z:z / 2 (where y = 0.0005, 0.001, 0.002, 0.003, 0.004, 0.008, 0.01, 0.02; z = 0.0005, 0.001, 0.002, 0.003, 0.004, 0.008, 0.01, 0.02, 0.04, 0.05). After thorough mixing, the powder mixture was pre-sintered at 1600℃ for 20 hours in a muffle furnace. The sintered polycrystalline material was then placed in an iridium crucible and melted completely by induction heating under a nitrogen protective atmosphere. After the seed crystal comes into contact with the melt, it is slowly pulled downwards to obtain Lu. 1.7994-2y Y 0.2 Ce 0.0006 Ca 2y Si (1-z) Al z For O5 single crystal, the parameters of the micro-pull-down method include: design of required size parameters, design of temperature field, and micro-pull-down speed of 10-15 mm / h.

[0072] Among them, crystal sample Lu 1.7994-2y Y 0.2 Ce 0.0006 Ca 2y Si (1-z) Al z O5 (y = z = 0.0005, 0.001, 0.003, 0.005) are labeled as LYSO:Ce,0.05at%Ca,0.05at%Al, LYSO:Ce,0.1at%Ca,0.1at%Al, LYSO:Ce,0.3at%Ca,0.3at%Al and LYSO:Ce,0.5at%Ca,0.5at%Al, respectively.

[0073] To compare the unique and beneficial effects of Ca and Al co-doping, undoped (Lu) alloys were grown using the same process parameters. 1.7994 Y 0.2 Ce 0.0006 SiO5), with 0.3% Ca (Lu) as a single doping agent. 1.7934 Y 0.2 Ce 0.0006 Ca 0.006 SiO5), with 0.3% Al (Lu) as a single dopant. 1.7994 Y 0.2 Ce 0.0006 Si 0.997 Al 0.003 O5) and 0.6% Al(Lu) 1.7994 Y 0.2 Ce0.0006 Si 0.994 Al 0.006 O5) single crystals, labeled as LYSO:Ce, LYSO:Ce, 0.3%Ca, LYSO:Ce, 0.3%Al, and LYSO:Ce, 0.6%Al, respectively.

[0074] The relative Ce1 / Ce2 content, relative fluorescence intensity, scintillation decay time, and relative light yield of each crystal sample in Example 5 are shown in Table 1. For comparison, the properties of undoped LYSO:Ce and Ca or Al single-doped LYSO:Ce single crystals are also shown.

[0075] The XEL spectrum was fitted using three Gaussian peaks (peak positions: 3.13, 2.95, and 2.69 eV, respectively), and the Ce1 / Ce2 ratio was obtained by calculating the ratio of the Gaussian peak areas of Ce1 and Ce2.

[0076] Fluorescence spectra were measured using a fluorescence spectrometer; a 450W continuous xenon lamp was used as the excitation source. Relative fluorescence intensity was the percentage ratio of the sample fluorescence intensity to the strongest peak of the LYSO:Ce fluorescence spectrum.

[0077] The optical absorption spectrum of 200-800 nm was obtained using a UV-IR spectrophotometer, and the absorption coefficient at 358 nm was read.

[0078] flicker decay to in 137 Scintillation decay curves were recorded under Cs illumination using a photomultiplier tube (Hamamatsu R6233 PMT) and an oscilloscope (Agilent DSO 9404A). Single-shot exponential fitting was performed to obtain the decay time of the pulse spectrum; recording was performed using a PMT and channel analyzer. 137 The pulse height spectrum of the sample was obtained under 662 keV γ-ray irradiation from a Cs radiation source. The number of channels was read from the pulse height spectrum, and the relative light yield was obtained by comparing it with the absolute light yield of the standard LYSO:Ce sample calibrated by single photons.

[0079] Table 1. Fluorescence and scintillation properties of each crystal sample in Example 5.

[0080]

[0081] As shown in Table 1, compared with undoped LYSO:Ce and Ca or Al single-doped LYSO:Ce, Ca and Al co-doped LYSO has a significantly increased fast emission Ce1 ratio, extremely low fluorescence response (<5%), extremely low Ce3+ optical absorption spectrum intensity, and maintains a high light yield of over 104 ph. / MeV while significantly accelerating scintillation decay.

[0082] Example 6 (Gd growth by Czochralski method)1.998-2y Ce 0.002 Ca 2y Si 0.994 Al 0.006 O5)

[0083] Single crystals were grown using the Czochralski method. The materials were prepared by mass ratio of Gd₂O₃:CeO₂:CaCO₃:SiO₂:Al₂O₃ = 0.999 - y:0.002:2y:0.994:0.003 (where y = 0.0005, 0.001, 0.002, 0.003, 0.004, 0.008, 0.01, 0.02). After thorough mixing, the mixture was pressed using cold isostatic pressing (3 GPa). The pressed bulk was placed in an iridium crucible, and under a nitrogen protective atmosphere, it was induction heated until fully melted. A seed crystal was then used for seeding, and single crystals of the predetermined size were slowly pulled from the melt to obtain Gd₂O₃. 1.998-2y Ce 0.002 Ca 2y Si 0.994 Al 0.006 O5 single crystal. The parameters of the Czochralski method include: pulling speed of 0.7-6 mm / h and rotation speed of 6-20 r / min.

[0084] Example 7 (Growth of Lu using the micro-pull-down method) 1.6 Y 0.2 Gd 0.2 Ce 2x Ca 2y Si 1-z Al z O5)

[0085] Single crystals were grown using the micro-pull-down method (μ-PD). The molar ratio of Lu₂O₃:Y₂O₃:Gd₂O₃:CeO₂:CaCO₃:SiO₂:Al₂O₃ was 0.8:0.1:0.1:2x:2y:1-z:z / 2 (where x = 0.0001, 0.0003, 0.001, 0.003, 0.006, 0.01, 0.03, 0.05; y = 0.0005, 0.001, 0.002). The following parameters were used: z = 0.004, 0.008, 0.01, 0.02; z = 0.0005, 0.001, 0.002, 0.004, 0.008, 0.01, 0.02, 0.04, 0.05. After thorough mixing, the mixed powder was pre-sintered in a muffle furnace at 1600℃ for 30 hours. The sintered polycrystalline material was then placed in an iridium crucible and fully melted by induction heating under a nitrogen protective atmosphere. After the seed crystal came into contact with the melt, it was slowly pulled downwards to obtain Lu. 1.6 Y 0.2 Gd 0.2 Ce 2x Ca2y Si 1-z Al z O5 single crystal. The parameters for the micro-pull-down method include a micro-pull-down speed of 10–20 mm / h.

[0086] Example 8 (Growth of Lu using the micro-pull-down method) 1.9-2x-2y La 0.1 Ce 2x Ca 2y Si 1-z Al z O5)

[0087] Single crystals were grown using the micro-pull-down method (μ-PD). The molar ratio of Lu₂O₃:La₂O₃:CeO₂:CaCO₃:SiO₂:Al₂O₃ was 0.95 - xy:0.05:2x:2y:1 - z:z / 2 (where x = 0.0001, 0.0003, 0.001, 0.003, 0.006, 0.01, 0.03, 0.05; y = 0.0005, 0.001, 0.002, 0.003, 0.005). 0.005, 0.008, 0.01, 0.02; z = 0.0005, 0.001, 0.002, 0.003, 0.004, 0.008, 0.01, 0.02, 0.04, 0.05), after thorough and uniform mixing, the mixed powder was pre-sintered in a muffle furnace at 1600℃ for 20 hours. The sintered polycrystalline material was then placed in an iridium crucible and, under a nitrogen protective atmosphere, induction heated until fully melted. After the seed crystal came into contact with the melt, it was slowly pulled downwards to obtain Lu. 1.9-2x-2y La 0.1 Ce 2x Ca 2y Si 1- z Al z O5 single crystal. The parameters for the micro-pull-down method include a micro-pull-down speed of 5–20 mm / h.

[0088] Example 9 (Growth of Lu by Czochralski method) 1.798-2y-2a Y 0.2 Ce 0.002 Ca 2y Li 2a Si (1-z) Al z O5)

[0089] Single crystals were grown using the Czochralski method. The ingredients were prepared in the following molar ratios: Lu₂O₃:Y₂O₃:CeO₂:CaCO₃:Li₂CO₃:SiO₂:Al₂O₃ = 0.899 - ya:0.1:0.001:2y:a:1 -z:z / 2 (y = 0.0005, 0.001, 0.002, 0.004, 0.008, 0.01, 0.02; a = 0.001, 0.003, 0.005, 0.01; z = 0.0005, 0.001, 0.002, 0.004, 0.008, 0.01, 0.02, 0.04, 0.05). After thorough mixing, the mixture was pressed using cold isostatic pressing (pressure 3 GPa). The pressed bulk material is placed in an iridium crucible, and under a nitrogen protective atmosphere, it is induction heated until fully melted. After seeding, a single crystal of the predetermined size is slowly pulled from the melt to grow, yielding Lu. 1.798-2y-2a Y 0.2 Ce 0.002 Ca 2y Li 2a Si (1-z) Al z O5 single crystal. The parameters for the Czochralski method include: pulling speed of 1-5 mm / h and rotation speed of 3-10 r / min.

[0090] Example 10 (Growth of Lu by Czochralski method) 1.798-2y-2a Gd 0.2 Ce 0.002 Ca 2y Cu 2a Si (1-z) Al z O5)

[0091] Single crystals were grown using the Czochralski method. The ingredients were prepared in the following molar ratios: Lu₂O₃:Gd₂O₃:CeO₂:CaCO₃:CuO:SiO₂:Al₂O₃ = 0.899 - ya:0.1:0.001:2y:2a:1-z:z / 2 (y = 0.0005, 0.001, 0.002, 0.004, 0.008, 0.01, 0.02; a = 0.001, 0.003, 0.005, 0.01; z = 0.0005, 0.001, 0.002, 0.004, 0.008, 0.01, 0.02, 0.04, 0.05). After thorough mixing, the mixture was pressed using cold isostatic pressing (pressure 3 GPa). The pressed bulk material is placed in an iridium crucible, and under a nitrogen protective atmosphere, it is induction heated until fully melted. After seeding, a single crystal of the predetermined size is slowly pulled from the melt to grow, yielding Lu. 1.798-2y-2a Gd 0.2 Ce 0.002 Ca 2y Cu2a Si (1-z) Al z O5 single crystal. The parameters of the Czochralski method include: pulling speed of 3-10 mm / h and rotation speed of 2-10 r / min.

[0092] Example 11 (Growth of Lu by Czochralski method) 1.598-2y-2a Y 0.2 La 0.2 Ce 0.002 Ca 2y Sc 2a Si (1-z) Al z O5)

[0093] Single crystals were grown using the Czochralski method. The ingredients were prepared in the following molar ratios: Lu₂O₃:Y₂O₃:La₂O₃:CeO₂:CaCO₃:Sc₂O₃:SiO₂:Al₂O₃ = 0.799 - ya:0.1:0.1:0.001:2y:a:1-z:z / 2 (y = 0.0005, 0.001, 0.002, 0.004, 0.008, 0.01, 0.02; a = 0.001, 0.003, 0.005, 0.01; z = 0.0005, 0.001, 0.002, 0.004, 0.008, 0.01, 0.02, 0.04, 0.05). After thorough mixing, the mixture was pressed using cold isostatic pressing (at a pressure of 3 GPa). The pressed bulk material is placed in an iridium crucible, and under a nitrogen protective atmosphere, it is induction heated until fully melted. After seeding, a single crystal of the predetermined size is slowly pulled from the melt to grow, yielding Lu. 1.598-2y- 2a Y 0.2 La 0.2 Ce 0.002 Ca 2y Sc 2a Si (1-z) Al z O5 single crystal. The parameters of the Czochralski method include: pulling speed of 4-10 mm / h and rotation speed of 5-12 r / min.

[0094] Through the above embodiments, combined with different compositions and different processes, the ultrafast high-brightness, extremely low-fluorescence rare-earth orthosilicate scintillation material of this application was prepared.

[0095] It should be noted that the performance of the single crystal with a portion of the composition of Example 5 was described in the above embodiments. In fact, the single crystals obtained by other components and other processes have the same results as those in Example 5. However, the details are omitted here.

[0096] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An ultrafast, high-brightness, extremely low-fluorescence rare-earth orthosilicate scintillation material, characterized in that, The chemical formula of the ultrafast, high-brightness, ultra-low fluorescence rare-earth orthosilicate scintillation material is RE. 2(1-x-y-a) Ce 2x Ca 2y A 2a Si (1-z) Al z O5, where 0.0001≤x≤0.003, 0.003≤y≤0.005, y=z, 0≤a≤0.01, RE represents a rare earth element, which is selected from at least one of lanthanum, lutetium, yttrium, and gadolinium. The A represents other doping elements, which are selected from at least one of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), magnesium (Mg), strontium (Sr), scandium (Sc), and copper (Cu).

2. The ultrafast, high-brightness, extremely low-fluorescence rare-earth orthosilicate scintillation material according to claim 1, characterized in that, The rare earth element is lutetium or yttrium or a solid solution of both.

3. The ultrafast, high-brightness, extremely low-fluorescence rare-earth orthosilicate scintillation material according to claim 2, characterized in that, The rare earth element is a solid solution of lutetium and yttrium, wherein the molar ratio of lutetium to yttrium is 9:

1.

4. The ultrafast, high-brightness, extremely low-fluorescence rare-earth orthosilicate scintillation material according to any one of claims 1 to 3, characterized in that, The scintillation yield of the ultrafast, high-brightness, ultra-low-fluorescence rare-earth orthosilicate scintillation material is >10. 4 The scintillation light decay time is within 35 ns, and the fluorescence response is within 5% of that of LYSO:Ce scintillation materials.

5. The ultrafast, high-brightness, extremely low-fluorescence rare-earth orthosilicate scintillation material according to claim 4, characterized in that, The absorption coefficient at 358 nm in the optical absorption spectrum is <2.5 cm⁻¹. -1 .

6. A method for preparing an ultrafast, high-brightness, extremely low-fluorescence rare-earth orthosilicate scintillation material, characterized in that, The chemical formula of the ultrafast, high-brightness, ultra-low fluorescence rare-earth orthosilicate scintillation material is RE. 2(1-x-y-a) Ce 2x Ca 2y A 2a Si (1-z) Al z O5, where 0.0001≤x≤0.003, 0.003≤y≤0.005, y=z, 0≤a≤0.01, RE represents a rare earth element, which is selected from at least one of lanthanum, lutetium, yttrium, and gadolinium. The A represents other doping elements, which are selected from at least one of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), magnesium (Mg), strontium (Sr), scandium (Sc), and copper (Cu). The ultrafast, high-brightness, extremely low-fluorescence rare-earth orthosilicate scintillation material is a single crystal, and the preparation method includes the following steps: S1, as raw material, weigh rare earth oxides, CeO2, SiO2, Al2O3, oxides of other doped elements, CaCO3 or CaO according to the chemical formula of the ultrafast high brightness ultra-low fluorescence rare earth orthosilicate scintillation material, and mix them thoroughly to obtain a mixed powder. S2, after the mixed powder is pressed into shape, it is subjected to solid-phase reaction at 1000-2000 °C for 5-200 hours to obtain a polycrystalline material with a single phase composition; S3, the polycrystalline material is placed in a container and heated to melt it, and the melt is controlled to cool and crystallize slowly to obtain a single crystal crude product; S4. Anneal the single crystal crude product at 1000-1400 °C for 10-200 hours to obtain the ultrafast high-brightness ultra-low fluorescence rare earth orthosilicate scintillation material.

7. The preparation method according to claim 6, characterized in that, Step S4 specifically includes: The crude single crystal is placed in a muffle furnace, and air or a mixture of inert gas and oxygen is introduced into it. Next, the muffle furnace is heated to 1000-1400℃ at a heating rate of less than 300℃ / hour and held at that temperature for 10-200 hours. Subsequently, the temperature was reduced to room temperature at a rate of less than 150 °C / hour to obtain the ultrafast high-brightness, extremely low-fluorescence rare-earth orthosilicate scintillation material.

8. The application of the ultrafast high-brightness, extremely low-fluorescence rare-earth orthosilicate scintillation material according to any one of claims 1 to 5 in any field including mixed field radiation detection, high-energy physics detection and particle discrimination, and nuclear medicine imaging.

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