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

Abstract Population dynamics of the 3 F 4 and 3 H 4 levels in Tm 3+ doped ZB(L)AN glasses was studied for Tm 3+ concentrations from 0.5 to 12 mol%. Fluorescence waveforms from these levels were measured at 1.8 μm ( 3 F 4 ) and 800 nm ( 3 H 4 ) with both direct and indirect pumping. Decay from the 3 F 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 Tm 3+ ions followed by quenching at sites to which the ions could migrate. The decay of the directly pumped 3 H 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 3 H 4 , 3 H 6 → 3 F 4 , 3 F 4 was obtained. When the 3 F 4 level is pumped at 1660 nm, the decay of the 3 H 4 level confirmed the influence of the up-conversion energy transfer process 3 F 4 , 3 F 4 → 3 H 4 , 3 H 6 .