Study of the Evolution of Nanoparticle Crystallization and Optical Properties in Glass Ceramics

该项目的目标是确定掺Eu的氟锆酸盐玻璃的光学性质的微观结构和化学来源，以及掺入氯纳米复合材料。该微晶玻璃具有作为X射线成像板的潜在应用，例如在数字乳房X光照相系统中。这项研究的另一个目标是提供对材料如何为这一应用进行优化的见解。掺Eu的氟锆酸盐玻璃，再加上氯的掺杂，可以进行热处理，形成一种新型的纳米复合材料，其中含有氯化钡纳米晶体，能够将电离辐射(通常是x射线)转化为稳定的电子空穴对。之后可以用扫描激光束在所谓的“光激励发光”(PSL)过程中读出这些光。光学研究表明，这种纳米复合玻璃发出的光比同等体积的单晶多五倍。光输出增加的原因尚不清楚，但答案在于纳米粒子与其宿主玻璃基质之间的界面，这是由于形成了氯化钡纳米粒子。分析纳米尺度界面的结构和组成的理想技术是通过透射电子显微镜(TEM)。以前已经对在不同温度下退火的样品进行了非原位透射电子显微镜分析，但这只提供了现有科学的快照。计划中的透射电子显微镜研究包括对纳米晶体及其与玻璃基质的界面的原子级结构进行高分辨率成像，以及对纳米晶体内部和周围的化学分布进行能量过滤透射电子显微镜(EFTEM)成分测绘。此外，为了诱导纳米晶体成核，将对先前在炉中进行热处理或用不同能量和脉冲长度的激光照射的样品进行检查，并将三种成核技术--非原位热法、激光和原位热法进行比较。田纳西大学太空研究所定期为K-12举办夏季科学夏令营，并雇用暑期实习生。UTSI的全体工作人员都参与了外展工作。约翰逊博士为高中生和本科生制定了一个详细的为期七周的暑期研究体验计划。学生们收到一个微晶玻璃样品，并经历了一系列的表征、口头陈述、报告准备、职业生涯日和模拟拨款写作研讨会。这项计划的最终结果是准备一篇期刊文章。PI经常担任阿贡为中学女生举办的工程介绍日活动的导师。

The goal of this project is to determine the microstructural and chemical origins of the optical properties of Europium-doped fluorozirconate glasses, additionally doped with chlorine nanocomposite materials. The glass ceramics have potential applications as an x-ray imaging plate, for example in a digital mammography system. A further goal of the research is to provide insights into ways in which the material could be optimized for this application. Europium-doped fluorozirconate glasses, additionally doped with chlorine, can be heat-treated in such a way that it forms a novel nanocomposite material containing barium chloride nanocrystals, with the ability to convert ionizing radiation (usually x-rays) into stable electronhole pairs. These can be read out afterwards with a scanning laser beam in a so-called "photostimulated luminescence" (PSL) process. Optical studies have shown that the nanocomposite glasses gives out five times more light than the equivalent volume of the single crystal. The reason for this increased light output is not understood but the answer lies in the interface between the nanoparticles and its host glass matrix, as a result of the formation of the barium chloride nanoparticles. The ideal technique to analyze the structure and composition across nanoscale interfaces is by transmission electron microscopy (TEM). Ex situ TEM analysis has previously been carried out on samples that were annealed at various temperatures but this only provides a snapshot of the available science. The planned TEM studies include high resolution imaging of the atomic-scale structure of the nanocrystals and their interfaces with the glass matrix, in conjunction with energy-filtered TEM (EFTEM) composition mapping of the chemical distribution in and around the nanocrystals. Further, samples, which have previously been heat-treated in a furnace or irradiated by a laser with different energies and pulse length, in order to induce nanocrystal nucleation, will be examined and the three nucleation techniques, ex situ thermal, laser, and in situ thermal will be compared.The University of Tennessee Space Institute regularly runs summer science camps for K-12 and employs summer interns. The entire UTSI staff participates in the outreach efforts. Dr. Johnson has developed a detailed seven week summer research experience program for a combination of high-school and undergraduate students. The students receive a glass-ceramic sample and go through a program of characterization, oral presentation, report preparation, career day and mock grant writing workshop. The program culminates in the preparation of a journal article. The PI regularly acts as a mentor for the Introduce a Girl to Engineering day, which is a program at Argonne for Middle School female students.