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

Population dynamics of the 3F4 and 3H4 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 μm (3F4) and 800 nm (3H4) with both direct and indirect pumping. Decay from the 3F4 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 3H4 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 CDD and CDA, 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 3H4, 3H6 → 3F4, 3F4 was obtained. When the 3F4 level is pumped at 1660 nm, the decay of the 3H4 level confirmed the influence of the up-conversion energy transfer process 3F4, 3F4 → 3H4, 3H6.