Evaluation of energy transfer coefficients in Tm-doped fibers for fiber lasers

In this work we report on the determination of the cross-relaxation energy-transfer coefficients from the measurements of the fluorescence lifetimes of the ³F₄ and ³H₄ energy levels of Tm³⁺ ions in the experimentally prepared optical fibers. Optical fiber preforms were prepared by solution-doping of Tm³⁺ ions with either Al³⁺ ions or dispersed alumina nanoparticles. Optical fibers were characterized by means of Tm, Al and Ge concentrations, refractive index profiles, optical spectral attenuations, luminescence spectra and fluorescence lifetimes. Highly aluminium-codoped optical fibers exhibited fluorescence lifetimes of up to 756 μs.