Optical characterization of Tm3+ in a high barium-tellurite glass in absence and presence of Yb3+: Evidence of strong crystal-field effect and efficient Yb3+→Tm3+ energy transfer

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Abstract Optical properties of Tm3+ are studied in a (high Ba2+, La3+)-tellurite glass in absence and the presence of co-dopant Yb3+. The Tm3+ ion in this host exhibits strong vis–NIR absorption and intense ~1.83 μm NIR-emission along with another weak emission at ~1.48 μm upon excitation of its 794 nm 3H6→3F4 absorption. In the case of the Yb3+-codoped glass, when the glass is excited through the 978 nm (2F7/2→2F5/2) absorption transition of Yb3+, its Tm3+ ion shows strong ~1.83 μm NIR-emission but no ~1.48 μm emission. The same glass, on the other hand, when is excited with a 980 nm laser, its Tm3+ ion exhibits a strong 804 nm and a relatively weak ~474 nm upconversion emissions. Both the results indicate that an efficient phonon assisted energy transfer takes place from Yb3+ to Tm3+ in the case of the co-doped glass. Co-relation of the optical properties of the Tm3+ ion with its calculated optical parameters shows that the ion in this host experiences a strong crystal field. Strong ~1.83 μm NIR-emission of the Tm3+ doped glass and its calculated high values of gain cross-section suggest that the glass is prospective for use as 1.75–1.90 μm tunable 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 a bio-marker.