Luminescence properties and energy transfer mechanism of Er3+/Tm3+ co-doped tellurite glasses

► Er3+/Tm3+ co-doped tellurite glasses were prepared by melt-quenching method. ► Luminescence properties of samples with varied Tm3+ concentration were investigated. ► 1.85μm fluorescence intensity improved evidently with an enhanced PAET. ► ET mechanism was investigated by evaluating micro-coefficient and phonon contribution. ► The prepared glass possesses a large amplification quality factor of Tm3+ at 1.85μm. Er3+ single doped and Er3+/Tm3+ co-doped tellurite glasses with composition of TeO2–ZnO–Na2O were prepared by the melt-quenching method, and the absorption and fluorescence spectra were measured. The intensity parameters Ωt (t=2, 4, 6), spontaneous radiative transition rates A, fluorescence branching ratios β and radiative lifetimes τrad of Tm3+ ions were calculated from the measured absorption spectra based on the Judd–Ofelt theory, and the luminescence properties of samples with different doped concentration of Er3+–Tm3+ ions were investigated from the measured fluorescence emission spectra under the 800nm LD excitation. It was shown that the 1.53μm fluorescence emission intensity of Er3+ ions decreases with the increasing of Tm3+ ion doped concentration, while the 1.85μm fluorescence emission intensity of Tm3+ ions increases accordingly. The energy transfer mechanisms between Er3+ and Tm3+ ions were investigated to explain the fluorescence varying behavior, and it indicates that phonon-assisted non-resonant energy transfers from Er3+ to Tm3+ ions play a very important role in the 1.85μm fluorescence emission of Tm3+ ions. The energy transfer coefficient and phonon contribution for the existed energy transfer process between Er3+ and Tm3+ ions were calculated and analyzed. Meanwhile, the 1.85μm band stimulated absorption, emission cross-sections and gain coefficient of Tm3+:3F4→3H6 transitions were also obtained and analyzed. The research shows that Er3+/Tm3+ co-doped TeO2–ZnO–Na2O glass is a promising host material applied for 1.85μm band solid lasers and amplifiers.