Energy transfer and energy level decay processes in Tm3+-doped tellurite glass

Abstract

The primary excited state decay and energy transfer processes in singly Tm3+-doped TeO2:ZnO:Bi2O3:GeO2 (TZBG) glass relating to the 3F4 → 3H6 ∼1.85 μm laser transition have been investigated in detail using time-resolved fluorescence spectroscopy. Selective laser excitation of the 3H4 manifold at 794 nm, the 3H5 manifold at 1220 nm, and 3F4 manifold at 1760 nm has established that the 3H5 manifold is entirely quenched by multiphonon relaxation in tellurite glass. The luminescence from the 3H4 manifold with an emission peak at 1465 nm suffers strong suppression due to cross relaxation that populates the 3F4 level with a near quadratic dependence on the Tm3+ concentration. The 3F4 lifetime becomes longer as the Tm3+ concentration increases due to energy migration and decreases to 2.92 ms when [Tm3+] = 4 mol. % as a result of quasi-resonant energy transfer to free OH− radicals present in the glass at concentrations between 1 × 1018 cm−3 and 2 × 1018 cm−3. Judd-Ofelt theory in conjunction with absorption measurements were used to obtain the radiative lifetimes and branching ratios of the energy levels located below 25 000 cm−1. The spectroscopic parameters, the cross relaxation and Tm3+(3F4) → OH− energy transfer rates were used in a numerical model for laser transitions emitting at 2335 nm and 1865 nm.