超快成像用BaF2闪烁陶瓷的制备及光学性能研究

Fabrication and optical properties of BaF2 scintillation ceramics for ultrafast imaging applications

  • 摘要: 为应对高重复频率及事例堆积挑战,未来超快成像探测器对闪烁体提出了更高要求,即具备超快时间响应、短X射线衰减长度及低慢发光特性。BaF2闪烁陶瓷兼具快速响应、第一纳秒内高光产额及短X射线衰减长度等核心优势,在超快成像领域展现出巨大应用潜力。本研究以硝酸钡(Ba(NO3)2)和二水合氟化钾(KF·2H2O)为原料,采用化学共沉淀法合成BaF2粉体,并通过热压烧结技术制备BaF2闪烁陶瓷。探究不同热压烧结温度(550~650 ℃)对BaF2闪烁陶瓷微观结构、光学透过率及X射线激发发光(XEL)强度的影响规律。研究结果表明,随着热压温度升高,陶瓷内部气孔数量呈先减少后增加的趋势,BaF2陶瓷的直线透过率及XEL强度呈先增加后下降的趋势。经热压烧结(600 ℃×2 h,50 MPa)制备的BaF2闪烁陶瓷(厚度1 mm)在800 nm处的直线透过率为48.2%,其快发光XEL强度最高且慢分量抑制效果显著。与BaF2单晶相比,陶瓷样品中的慢衰减分量得到有效抑制,快衰减分量占比达10.6%(单晶为6.2%),光产额为4021 ph·MeV−1。进一步通过表征测试探究慢衰减分量的抑制机理,研究证实BaF2闪烁陶瓷内部存在较快的自陷激子猝灭中心,且其在109 K处的热释光峰强度低于单晶样品,从而导致陶瓷中慢衰减分量占比降低。本工作系统阐明了热压温度对陶瓷综合性能的调控规律,并结合单晶对照实验,揭示了BaF2陶瓷慢发光的抑制机制。

     

    Abstract: To address the high repetition rates and pileup effects in the development of future ultrafast imagers, stringent requirements have been proposed for scintillators. Novel ultrafast scintillators featuring short X-ray attenuation lengths and low levels of slow components are required. BaF2 scintillation ceramics combine core advantages, such as fast response characteristics, high light yield within the first nanosecond, and short X-ray attenuation length, demonstrating significant potential for ultrafast imaging applications. In this study, BaF2 powder was synthesized via a chemical co-precipitation method using barium nitrate (Ba(NO3)2) and potassium fluoride dihydrate (KF·2H2O) as raw materials2, and BaF2 scintillation ceramics were prepared using hot-pressing technology. The effects of hot-pressing temperature (550-650 ℃) on the microstructure, optical transmittance, and X-ray excited luminescence (XEL) intensity of BaF2 scintillation ceramics were investigated. The results indicate that as the hot-pressing temperature increases, the pore density in the ceramics initially decreases and then increases. Similarly, the in-line transmittance and XEL intensity of the BaF2 ceramics first increase and then decrease with rising hot-pressing temperature. BaF2 scintillation ceramics prepared by hot-pressing (1 mm thickness) at 600 ℃ for 2 h under 50 MPa exhibited an in-line transmittance of 48.2% at 800 nm, the highest fast luminescence XEL intensity, and significant suppression of the slow component. Compared with BaF2 single crystals, the slow decay component in the ceramic samples was effectively suppressed; the fast decay component accounted for 10.6% (compared to 6.2% in single crystals), and the light yield was 4021 ph/MeV. Furthermore, the mechanism underlying the suppression of the slow decay component in the ceramics was investigated. The study confirmed the presence of fast self-trapped exciton quenching centers within the BaF2 scintillation ceramics, evidenced by a lower intensity of the 109 K thermoluminescence peak compared to that of the single crystal sample. This phenomenon leads to a reduced proportion of the slow decay component in the ceramics. This work elucidates how hot-pressing temperature affects the overall performance of the ceramics and, through comparison with single crystals, reveals the mechanism suppressing the slow luminescence of BaF2 ceramics.

     

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