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

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 1x10¹⁸ cm⁻³ and 2x10¹⁸ 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.8 page(s