Host Materials for Laser-Excited Fluorescence of Lanthanide Probe Ions

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Abstract
An extensive study has been made of a wide range of materials to evaluate their suitability as hosts for laser-excited site selective fluorescence methods using rare earth probe ions. They are evaluated for their suitability in both direct measurements of fluorescent ions incorporated into their lattices and indirect measurements where a nonfluorescent ion is associated with a fluorescent probe ion. The association can occur because the two ions are charge compensating each other or because the nonfluorescent ion enters a lattice of fluorescent probes. These experiments have shown that probe ion methods reveal a great deal more complexity that is present at the microscopic level and cannot be measured by conventional methods. This complexity can be associated with phase heterogeneity, solid state defect equilibria, or nonstoichiometry of individual phases. Probe ion methods promise to provide a new tool to characterize such materials. This complexity prevents most of the materials from being applicable for trace ion analysis because of the sensitivity to environmental interferences. Some of the materials, however, do not exhibit this sensitivity and are consequently suitable for direct measurements. In particular, it is shown that CaO and ThO2 are good matrices which have little interference for lanthanide analyses.