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

University Of Tennessee Space Institute, Tullahoma TN

Investigators

Abstract

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.