Effect of Aluminum Co-dopoing in Rare Earth Doped Sol-gel Glasses

Thao Nguyen T. Nguyen, '08, and A. Silversmith

Physics Department

Hamilton College

 

The sol-gel process provides a pathway to make glasses at low temperature. Glasses made by this method and annealed at temperatures close to the transition temperature of glass display similar properties to traditionally prepared melt glass. Sol-gel glass doped with rare earth (RE) ions have many potential applications as optical materials, but poor fluorescence yield is a serious problem. It has been shown that RE-doped sol-gels show significantly enhanced fluorescence when co-doped with aluminum. The generally understanding is that aluminum ions spread out uniformly in the gel matrix and attract RE ions to them, thus reducing fluorescence quenching caused by cross-relaxation between RE ions in clusters. Recently, a computational model by Monteil et al., suggests that aluminum ions form Al-rich regions in which RE ions are found.

Our current work uses terbium (Tb3+) ions as a probe to study the effect of aluminum on fluorescence of RE-doped sol-gels. Our experimental results suggest that Al ions do form Al-rich regions and that RE ions cluster in those regions. Pulsed laser experiments allow us to measure the local effective concentration near Tb3+ ions that emit blue light. The local concentration is much lower than the actual doping level, except when the Al:RE ratio is greater than 10. We interpret this to mean that only a small fraction of Tb dopants that are isolated emit; most ions reside in clusters and their 5D3-7FJ emission is fully quenched.

You can learn more about laser spectroscopy at Hamilton here.