Sol-gel synthesis of fluoride glasses and thin films: The effects of processing on the chemical, physical, optical, and rare earth fluorescence properties of sol-gel ZBLA glasses.

摘要

Fluoride glasses have the potential to be ultra-low loss optical fiber and active optical devices due to their intrinsic clarity, wide transmission window, and low phonon energy. Unfortunately, conventional processing methods have failed to produce defect free glasses, fibers, or thin films. However, sol-gel techniques offer high purity, low temperature processing routes conducive to high quality optics. Thus, a modified sol-gel technique was investigated as an alternative approach for fluoride glass production.; Hydrous oxide gels and thin films were prepared by hydrolyzing an alcoholic solution of alkoxides and hydroxides. Subsequent fluorination of the gels in gaseous hydrogen fluoride led to the successful formation of ZBLA ({dollar}rm 57ZrFsb4{dollar}-36BaF{dollar}sb2{dollar}-4LaF{dollar}sb3{dollar}-3AlF{dollar}sb3,{dollar} in mol%) fluoride glasses. However, the resulting glasses had inferior optical properties. The thermal processing and analysis of these materials was then studied to determine the cause of the poor transparency and to find a remedy.; The poor transparency of the sol-gel fluoride glasses was due to residual organics that led to carbon and reduced zirconium species that were strongly absorbing. However, optical quality glasses could be produced by removing these contaminants via treatment with a high temperature oxidizing atmosphere such as NF{dollar}sb3{dollar} or SF{dollar}sb6{dollar} without introducing other contaminants such as oxygen. The resulting glasses had chemical, electrical, mechanical, and optical properties commensurate with conventionally prepared glasses. It was also found that hydrocarbon contamination could be avoided altogether by using an inorganic sol-gel process involving the polymerization of zirconium hydroxychloride salts.; To study the gel structure and local environment of rare earth dopants during thermal processing and conversion of the gel, Eu{dollar}sp{lcub}3+{rcub}{dollar} fluorescence spectroscopy was employed. The Eu{dollar}sp{lcub}3+{rcub}{dollar} fluorescence revealed a change in site symmetry and decrease in host phonon energy upon fluorination. In addition to the well known red Eu{dollar}sp{lcub}3+{rcub}{dollar} luminescence, ultraviolet, blue, and green emissions were also observed in fluoride glasses and discovered to be concentration dependent. The Eu{dollar}sp{lcub}3+{rcub}{dollar} fluorescence was concluded to be a good probe for evaluating sol-gel fluoride materials and that the concentration dependence of the high energy emissions of Eu{dollar}sp{lcub}3+{rcub}{dollar} was due to electric dipole-dipole and dipole-quadrupole cross relaxations.