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

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 Omega(t) (t = 2, 4, 6), spontaneous radiative transition rates A, fluorescence branching ratios beta and radiative lifetimes tau(rad) 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 800 nm LD excitation. It was shown that the 1.53 mu m fluorescence emission intensity of Er3+ ions decreases with the increasing of Tm3+ ion doped concentration, while the 1.85 mu m 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 1.85 mu m 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 1.85 mu m band stimulated absorption, emission cross-sections and gain coefficient of Tm3+: F-3(4)-> H-3(6) 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 1.85 mu m band solid lasers and amplifiers. (C) 2012 Published by Elsevier B.V.