Population dynamics of the 3F4 and 3H4 levels in highly-doped Tm3+:ZB(L)AN glasses

Population dynamics of the F-3(4) and H-3(4) levels in Tm3+ doped ZB(L)AN glasses was studied for Tm3+ concentrations from 0.5 to 12 mol%. Fluorescence waveforms from these levels were measured at 1.8 mu m (F-3(4)) and 800 nm (H-3(4)) with both direct and indirect pumping. Decay from the F-3(4) level was found to be exponential with non-radiative decay rates proportional to the square of the Tm concentration. This indicated a process of energy migration by diffusion within the excited Tm3+ ions followed by quenching at sites to which the ions could migrate. The decay of the directly pumped H-3(4) level exhibited both exponential and non-exponential behavior depending on the concentration. For the lowest concentration (0.5 mol%) the decay was exponential, but at concentrations of 1, 2, 4 and 6 mol% the decay waveforms were distinctly non-exponential. The non-exponential waveforms could be fitted by the Yokota-Tanimoto model for diffusion of excited donors and dipole-dipole interactions with acceptors. This model produced values for C-DD and C-DA, the donor-donor and donor-acceptor energy transfer parameters, respectively. At the higher concentrations (8, 10, 12 mol%) the waveforms were exponential with decay rates from which the cross-relaxation parameter for the process H-3(4), H-3(6) F-3(4), F-3(4) was obtained. When the F-3(4) level is pumped at 1660 nm, the decay of the H-3(4) level confirmed the influence of the up-conversion energy transfer process F-3(4), F-3(4) -> H-3(4), H-3(6.) (c) 2006 Elsevier B.V. All rights reserved.