SAMPLE-DEPENDENT OPTICAL DEPHASING IN BULK CRYSTALLINE SAMPLES OF Y2O3EU3+

Two-pulse photon-echo measurements were made on the F-7(0) <-> 5D0 optical transition in a number of crystalline samples Of Y2O3:Eu3+ prepared by three different crystal-growth techniques. For crystals prepared by a laser-heated pedestal growth or arc-imaging furnace process, we report the observation of an additional sample-dependent contribution to the optical dephasing in comparison with a crystal grown by flame fusion. The dephasing rate 1/T(m) at 1.4 K is up to two orders of magnitude faster than that previously reported for the flame-fusion-grown crystal, and is uncorrelated with concentration. Measurements up to 14 K show that 1/T(m) increases linearly with temperature, in contrast to the expected T7 behavior due to a two-phonon Raman process. The linear temperature dependence is similar to that seen in glasses and disordered crystalline systems, suggesting the presence of disorder in the samples with more rapid dephasing. The crystals were examined by x-ray diffraction, excitation spectroscopy, and near-field optical microscopy to provide information on the nature of the disorder. The effect of annealing on the crystal dynamics is also investigated.