| This dissertation is a study of energy transfer and dephasing of optical excitations in amorphous materials as exemplified by Yb('3+) ions in inorganic glasses. This rare earth ion has a number of properties which make it ideal for such studies. The Stark splitting within the ground and excited state manifolds is large enough to overcome the inhomogeneous broadening of the optical transitions, so that narrowband optical pumping results in a well defined set of excited ions. The simple spectrum of energy levels, consisting of a single excited state manifold, precludes processes such as cross relaxation and multiphonon decay, which compete with the fundamental energy transfer and dephasing interactions.;We have used this laser system together with a Fabry-Perot etalon spectrometer to measure the homogeneous linewidth of the ('2)F(,5/2)(1)-('2)F(,7/2)(1) transition of Yb('3+) from 70 to 6K in silicate and phosphate glasses. In contrast to the behavior observed in other rare earth doped glass systems, the temperature dependence of the homogeneous width of this transition changes from T('1.8) at high temperatures to T('1.4) below 40K. The low temperature behavior is consistent with an interaction between the dipole moment of the Yb('3+) ions and elastic perturbations of the amorphous lattice caused by phonon induced tunneling of two level systems. At higher temperatures a Raman process dominates the dephasing, as observed in other rare earth ions.;Energy transfer measurements were made using single channel photon counting techniques and a computer controlled data acquisition system. The results of these measurements indicate a one phonon assisted transfer process is responsible for the energy transfer, with the distance dependence of the coupling between ions roughly consistent with a quadrupole-quadrupole interaction.;Ytterbium systems has not been widely studied in the past due to the location of the excited state manifold at (TURN)10,000 (ANGSTROM), which is beyond the range of stable and efficient laser dyes and detectors. We have developed a unique narrowband high power pulsed color center laser to carry out high resolution time resolved fluorescence line narrowing (FLN) in Yb('3+) doped silicate and phosphate glasses. |
