Strong crystal-field effect and efficient phonon assisted Yb3+ → Tm3+ energy transfer in a (Yb3+/Tm3+) co-doped high barium-tellurite glass

Optical properties of Tm3+ are studied in a (high Ba2+, La3+)-tellurite glass in the absence and the presence of co-dopant Yb3+. The Tm3+ ion in this host exhibits strong Vis-NIR absorption and intense NIR-emission at similar to 1.83 mu m along with a weak NIR emission at similar to 1.48 mu m upon excitation through its 794 nm H-3(6) -> F-3(4) absorption. Co-relation of the optical properties of the ion with its calculated optical parameters shows that the Tm3+ ion in this host, experiences a strong crystal field. In the case of the Yb3+-co-doped glass, when it is excited through the 978 nm F-2(7/2) -> F-2(5/2) absorption transition of Yb3+, its Tm3+ ion shows strong similar to 1.83 mu m NIR-emission but no similar to 1.48 mu m emission. Under 980 nm laser excitation, however, the Tm3+ ion of the co-doped glass, shows a strong 804 nm and a relatively weak similar to 474 nm upconversion emissions along with two other very weak components at similar to 648 and similar to 694 nm. All these results indicate that an efficient phonon assisted energy transfer occurs from Yb3+ to Tm3+ in the case of the co-doped glass. The results are interpreted in terms of effect of high Ba2+ in the glass-structure and coupling of some phonons of its nonbridging oxygens with the electronic states of the incorporated Tm3+ and Yb3+. Strong similar to 1.83 mu m NIR-emission of the Tm3+-glass and its calculated high values of gain cross-section suggest that the glass is prospective for use as 1.75-1.90 mu m solid state laser medium; while the observed intense 804 nm upconversion emission of the co-doped glass indicates that the material should be useful as bio-marker. (C) 2014 Elsevier B.V. All rights reserved.