Site-selective fluorescence and spectroscopic properties of Yb-doped lanthanum titanate glasses

Ytterbium-doped lanthanum titanate glasses were prepared by levitation melting for the detailed characterization of the Yb3+${\rm Yb}<^>{3+}$ spectroscopic properties in the rare-earth titanate glass host. Low-temperature fluorescence spectroscopy reveals distinct site-selectivity in both static and lifetime fluorescence measurements suggesting an absence of clustering as well as significant variation of local ytterbium environments. Typical site-selectivity behavior of a shrinking Stark manifold with lower excitation energy is observed. At 77 K, both the mean emission frequency and the fluorescence lifetime initially increase as the excitation energy decreases from about 11100 to 10750 cm-1${\rm cm}<^>{-1}$ and then slightly decrease at lower excitation energy. Temperature-dependent lifetime measurements between 77 and 420 K show a decreasing lifetime with increasing temperature and are well described by a two-level thermal activation model. The temperature-dependent fluorescence spectroscopy coupled with a room temperature white light absorption measurement allow the determination of the Stark energy levels of Yb3+${\rm Yb}<^>{3+}$ in lanthanum titanate glass as well as the calculation of the laser cross-sections.