Spectroscopic characterization of Eu3+-doped inorganic and alkoxide sol-gel derived fluorozirconate glass and zirconium fluoride gels

A new process for making fluoride glasses via the sol-gel route was investigated using Eu3+ fluorescence spectroscopy as a probe of the process. Both Eu3+ doped alkoxide ZBLA and zirconium fluoride gels and inorganic zirconium fluoride gels were synthesized and fluorinated with HF gas between 100 and 800 degrees C. All gels showed changes in Eu3+ site symmetry upon drying and fluorination. The alkoxide gels darkened due to the incomplete combustion of alkoxy ligands and quenched fluorescence and decreased lifetimes. The inorganic gels were free of this problem and exhibited increasing lifetimes with increasing fluorination temperature and upper level Eu3+ D-5(J) fluorescence never before seen in sol-gel derived materials. Thus, fluorination of inorganic gels can produce low phonon energy hosts, while transparent sol-gel fluoride glasses equivalent to conventionally prepared glasses can only be prepared by melting the fluorinated alkoxide derived gel in an oxidizing atmosphere.