Europium-doped mesoporous titania thin films: rare-earth locations and emission fluctuations under illumination
Résumé
Herein, EuIII-doped 3D mesoscopically ordered arrays of mesoporous and nanocrystalline titania are prepared and studied. The rare-earth-doped titania thin films - synthesized via evaporation-induced self-assembly (EISA) - are characterized by using environmental ellipsoporosimetry, electronic microscopy (i.e. high-resolution scanning electron microscopy, HR-SEM, and transmission electron microscopy, HR-TEM), X-ray diffraction, and luminescence spectroscopy. Structural characterizations show that high europium-ion loadings can be incorporated into the titanium-dioxide walls without destroying the mesoporous arrangement. The luminescence properties of EuIII are investigated by using steady-state and time-resolved spectroscopy via excitation of the EuIII ions through the titania host. Using EuIII luminescence as a probe, the europium-ion sites can be addressed with at least two different environments within the mesoporous framework, namely, a nanocrystalline environment and a glasslike one. Emission fluctuations (5D07F2) are observed upon continuous UV excitation in the host matrix. These fluctuations are attributed to charge trapping and appear to be strongly dependent on the amount of europium and the level of crystallinity.