Energy transfer and energy level decay processes in Tm ³-doped tellurite glass

The primary excited state decay and energy transfer processes in singly Tm ³-doped TeO ₂:ZnO:Bi ₂O ₃:GeO ₂ (TZBG) glass relating to the ³F ₄ → ³H ₆ ∼1.85 m laser transition have been investigated in detail using time-resolved fluorescence spectroscopy. Selective laser excitation of the ³H ₄ manifold at 794 nm, the ³H ₅ manifold at 1220 nm, and ³F ₄ manifold at 1760 nm has established that the ³H ₅ manifold is entirely quenched by multiphonon relaxation in tellurite glass. The luminescence from the ³H ₄ manifold with an emission peak at 1465 nm suffers strong suppression due to cross relaxation that populates the ³F ₄ level with a near quadratic dependence on the Tm ³ concentration. The ³F ₄ lifetime becomes longer as the Tm ³ concentration increases due to energy migration and decreases to 2.92 ms when Tm ³ 4 mol. as a result of quasi-resonant energy transfer to free OH ^- radicals present in the glass at concentrations between 1 10 ¹⁸ cm ^-3 and 2 10 ¹⁸ 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 Tm ³( ³F ₄) → OH ^- energy transfer rates were used in a numerical model for laser transitions emitting at 2335 nm and 1865 nm.