Excited state relaxation dynamics and non-radiative energy transfer in fluoroindate glass singly doped with thulium and doubly doped with thulium and terbium

Effect of activator concentration on luminescence spectra and luminescence decay of excited states of Tm³⁺ in indium-based fluoride glass has been investigated. Self-quenching of luminescence originating in the ¹D₂, ¹G₄ and the ³H₄ levels is found to be significant at doping levels as low as 0.5%. Luminescence decay curves are consistent with the Inokuti-Hirayama model for the non-radiative energy transfer involving an electric dipole-electric dipole interaction. Critical distance R₀ = 12.3 Å, derived from an analysis of the ¹G₄ decay, is relatively high and indicates that the glass matrix favours the ion-ion interaction. Relaxation dynamics for glass samples doubly doped with thulium and terbium provides evidence that terbium ions are able to shorten the ³F₄ lifetime with extremely high efficiency. However, the Tm³⁺→Tb³⁺ energy transfer contributes adversely to relaxation of the ³H₄ level. Critical distance for this interaction is nearly the same as that for the self-quenching of Tm³⁺ luminescence.