铈掺杂硅酸镥多晶闪烁陶瓷的设计、制备及发光性能研究
发布时间：2018-10-21 09:53
【摘要】：铈掺杂硅酸镥(Lu_2SiO_5:Ce,LSO:Ce)是一种综合性能优良的闪烁材料,具有高密度(7.4 g/cm3)、高光产额(27,300 photons/MeV)、快衰减时间(40 ns)、化学性质稳定等一系列优良的特性,在核医学成像方面具有良好的应用前景。由于Ce在LSO中的分凝系数非常低(~0.22),使其在LSO:Ce单晶中的分布严重不均,导致闪烁性能波动。此外,LSO的熔点高达2100℃,已接近铱坩埚和保温材料的极限使用温度,导致最终的生长成本增加。本论文选择LSO:Ce为研究对象,对其多晶陶瓷的制备科学进行了系统研究,阐明了制备过程中关键物理、化学条件与LSO:Ce闪烁陶瓷性能与显微结构、组分之间的关联。以LuCl_3?6H_2O、CeCl_3?7H_2O和正硅酸四乙酯(TEOS)为原料,环氧丙烷(PPO)为反应助剂,异丙醇为液相介质,采用溶胶-凝胶法制备了LSO:Ce前驱体,经过130℃真空干燥后,再在1000℃的空气下煅烧后得到了一次晶粒尺寸为70 nm的单相LSO纳米晶粉体。经过高能行星球磨处理后粉体的平均粒径由1μm减小至200 nm,比表面积达13.74 m2/g。球磨后的LSO:Ce粉体压制而成的素坯与球磨之前的粉体压制的素坯相比较,其起始烧结温度由1500℃降低到1200℃,在1650℃下的线收缩也由4.75%提高至6.92%。将前驱体通过喷雾干燥后获得了球形LSO:Ce前驱粉体。该前驱粉体在1000℃和1100℃的空气下煅烧2 h后分别得到两种不同晶体结构的LSO:Ce粉体。该粉体颗粒是由约50 nm的LSO:Ce纳米晶粒堆积而成的实心球形颗粒,其粒径约为2μm。采用放电等离子体烧结(SPS)技术将所合成的微米级球形LSO:Ce粉体在1200℃/80 MPa下烧结5 min后得到了平均晶粒尺寸为1.3μm的LSO:Ce陶瓷,其相对密度为99.8%。而亚微米LSO:Ce粉体,在同样的烧结条件下得到的LSO:Ce陶瓷的平均晶粒尺寸仅为0.6μm,其相对密度可达99.9%。采用球磨后的LSO:Ce粉体压制的素坯,在流动氢气下经1700℃/2 h无压烧结后获得了半透明的LSO:Ce陶瓷,其相对密度为99.7%,平均晶粒尺寸约为5μm。该LSO:Ce闪烁陶瓷的相对光产额达到LSO:Ce单晶的91%,衰减时间仅为20 ns。而将以上素坯在1650℃的空气气氛下烧结4 h后获得了相对密度为99.72%,平均晶粒尺寸为1.4μm的LSO:Ce陶瓷。该陶瓷在1600℃/150 MPa的氩气氛下经热等静压(HIP)处理1 h后,获得了相对密度高达99.9%的LSO:Ce光学陶瓷,其晶粒尺寸约为1.7μm,晶界干净。在420 nm处的光学直线透过率可达1.4%,这是由于LSO晶体结构高达0.028的双折射引起的,在4.4μm的中红外波长处的直线透过率接近50%(样品厚度为1 mm),这一透过率数据符合Rayleigh Gans Debye模型计算得到的结果。X-射线吸收近边结构(XANES)谱的分析表明:经HIP处理后的多晶LSO:Ce陶瓷在1300℃的空气氛下退火4 h后,其Ce离子仍保持+3价态。LSO:Ce陶瓷中的氧空位缺陷深度由0.95 eV降低至0.66 eV,缺陷的浓度也降低至退火之前的6.7%,光产额提高至退火前的1.81倍。LSO:Ce陶瓷中Ce1(CeLu1)发射强度较Ce2(CeLu2)高9倍,二者发射的发光衰减时间分别为22 ns和40 ns,均比单晶中Ce1和Ce2发射的衰减时间短。在50至150 K范围内LSO:Ce陶瓷总发射强度随温度上升呈现略微的降低,这主要是由于Ce2发射的热淬灭引起的;而在150至300 K范围内总发射强度随温度上升呈现出显著的提高,这是由于载流子的传输速率随温度上升而增大,从而使得Ce1的发射强度显著提高。研究了Y~（3+）离子掺杂对于LYSO:Ce陶瓷发光特性的影响。扩展X-射线吸收精细结构(EXAFS)谱表征结果显示Y~（3+）在LSO晶格中占据Lu~（3+）格位。其紫外激发发射强度随Y~（3+）含量的增加呈现出下降的趋势,主要是由于随Y~（3+）含量增大,Ce2的发射比例增加。Ce1和Ce2的发光衰减时间在Y~（3+）含量40%的条件下都随着Y~（3+）含量增大而增加,Y~（3+）含量40%的条件下,Ce1的衰减时间稳定在30 ns左右,Ce2的衰减时间稳定在47 ns左右。LYSO:Ce陶瓷的X-射线激发发光(XEL)谱和137Cs能谱都表明其光产额在Y~（3+）含量40%的条件下都随着Y~（3+）含量增大而提高,其原因在于,Ce~（3+）周围的氧空位趋向于富集在Y~（3+）周围,从而提高Ce~（3+）荧光发射;在Y~（3+）含量40%的条件下会随着Y~（3+）含量的增大而下降,这是由于晶格中过多的氧空位影响了载流子的传输,使Ce~（3+）荧光发射减弱。
[Abstract]:The rare earth doped silicic acid (Lu _ 2SiO _ 5: Ce, LSO: Ce) is a kind of scintillating material with excellent comprehensive performance. It has a series of excellent properties such as high density (7. 4g/ cm3), high light transmittance (27, 300 photoons/ MeV), fast decay time (40 ns), chemical stability and so on. and has good application prospect in nuclear medicine imaging. Because the fractional condensation coefficient of Ce in LSO is very low (~ 0. 22), the distribution of Ce in LSO: Ce single crystal is seriously uneven, which leads to the fluctuation of scintillation performance. In addition, the melting point of the LSO is high to 2100 DEG C, and the limit use temperature of the crucible and the thermal insulation material has been approached, resulting in an increase in the final growth cost. In this paper, LSO: Ce is chosen as the research object, the preparation science of its polycrystalline ceramics is systematically studied, and the key physical, chemical conditions and LSO: Ce scintillation ceramic properties and the correlation between the components are expounded. The LSO: Ce precursor was prepared by using LuCl _ 3? 6H _ 2O, CeCl _ 3? 7H _ 2O and tetraethyl silicate (TEOS) as raw material and propylene oxide (PPO) as reaction assistant and isopropanol as liquid medium, and after vacuum drying at 130 鈩，
本文编号：2284750
[Abstract]:The rare earth doped silicic acid (Lu _ 2SiO _ 5: Ce, LSO: Ce) is a kind of scintillating material with excellent comprehensive performance. It has a series of excellent properties such as high density (7. 4g/ cm3), high light transmittance (27, 300 photoons/ MeV), fast decay time (40 ns), chemical stability and so on. and has good application prospect in nuclear medicine imaging. Because the fractional condensation coefficient of Ce in LSO is very low (~ 0. 22), the distribution of Ce in LSO: Ce single crystal is seriously uneven, which leads to the fluctuation of scintillation performance. In addition, the melting point of the LSO is high to 2100 DEG C, and the limit use temperature of the crucible and the thermal insulation material has been approached, resulting in an increase in the final growth cost. In this paper, LSO: Ce is chosen as the research object, the preparation science of its polycrystalline ceramics is systematically studied, and the key physical, chemical conditions and LSO: Ce scintillation ceramic properties and the correlation between the components are expounded. The LSO: Ce precursor was prepared by using LuCl _ 3? 6H _ 2O, CeCl _ 3? 7H _ 2O and tetraethyl silicate (TEOS) as raw material and propylene oxide (PPO) as reaction assistant and isopropanol as liquid medium, and after vacuum drying at 130 鈩，
本文编号：2284750
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