Pulsed laser deposition of transparent fluoride glass

The presence of reduced zirconium in fluorozirconate (FZ) glasses is highly unfavorable due to its detrimental effect on glass quality. Previous researchers have relied upon the use of a fluorine-containing processing gas to prevent the reduction of zirconium in FZ glasses deposited as thin films by pulsed laser deposition (PLD). However, the use of a fluorine-containing processing gas as an oxidizing agent is disadvantageous, due to its toxicity. Eliminating the need for the processing gas would lead to a significantly safer and simpler process. Our approach is to incorporate indium, which is multivalent, into the PLD ablation target in order to stabilize the zirconium and remove the need for a processing gas. A ZLANI glass, based on the composition 60.24ZrF4-4.13LaF3-3.54AlF3-31.49NaF-0.59InF3 (values are in mol%), was synthesized for use as an ablation target. Using the ZLANI target, FZ glass films were successfully deposited on fused silica substrates by PLD, without the need for any processing gas. Multiple depositions were performed to observe the effects of deposition duration on growth rate and on film roughness. The deposited films are transparent with a brownish coloration. The source of this coloration is postulated to be color centers that are created during synthesis. Thermal annealing increases light transmission through the films up to 400%, depending upon wavelength, in the UV and visible spectrum (350–600 nm), after a series of heat treatments culminating at 300 °C. The fact that the transparency of the films can be correlated to annealing temperature suggests that the films may be of use as passive temperature sensors.