Investigation of Energy Transfer in Samarium Doped Calcium-Tungstate Crystals Using Time-Resolved Site Selection Spectroscopy.

Scope and Method of Study. This study employs the technique of time resolved spectroscopy using narrow line pulsed exitation from a tunable dye laser. The purpose of the investigation is to explore the process of transfer of exitation energy among trivalent samarium impurities in calcium tungstate crystals. The specific process involves direct electronic exitation of samarium ions and subsequent non-radiative energy transfer to samarium ions in other types of sites. Findings and Conclusions. Previous results have indicated the existence of two major samarium sites in calcium tungstate which differ in energy by 54 cm('-1). It was found that energy transfer at low temperature (about 10(DEGREES)K) occurs by a single step exchange interaction. At temperatures above 50(DEGREES)K a phonon assisted multistep migration of exitation energy among the higher energy sites is evident. This multistep process is a two phonon assisted resonant process involving the participation of a higher lying level in the excited state manifold. Quenching of the fluorescence intensity, as a function of concentration at low temperature, was found to involve the exchange interaction also.The quenching is attributed to a cross relaxation process involving a ground state-excited state samarium pair.