Crystal-growth and spectroscopy of Er3+ ions in calcium gallogermanate

This paper reports on the Czochralski growth of large single crystals of Er3+ doped Ca3Ga2Ge4O14 (CGGO) in radio frequency heated induction furnaces operating at 18 kHz. Crystals were successfully grown at concentrations of 0.005, 0.05, 0.5 and 5 mol% of the ErF3 dopant, and were of exceptionally good optical quality. Spectroscopic studies of the intra-4f shell absorption and fluorescence transitions of the Er3+ ions in this material were performed at 10 K, Measurements of the optical linewidths show no signs of concentration broadening up to 5 mol%, a feature attributable to the intrinsic compositional disorder of the crystal. We have identified 67 crystal-field levels of the C-2 symmetry site available for occupation by a trivalent rare-earth ion and observe strong up-conversion fluorescence for excitation (both resonant and non-resonant) of the absorption transitions from the ground state to the F-4(9/2) multiplet. Prominent self-absorption dips observed in excitation spectra recorded whilst monitoring up-converted fluorescence, demonstrate the importance of radiative energy transfer at high concentrations. (C) 2000 Elsevier Science B.V. All rights reserved.