The photophysical and photochemical properties of rose bengal (RB) in degassed aqueous and acetonitrile solutions were studied using steady-state and transient absorption spectroscopies. This comprehensive investigation provides detailed information about the kinetics and the optical properties of all intermediates involved: the triplet excited state and the oxidized and reduced forms of RB. A full kinetic description is used to control the concentrations of these intermediates by changing the initial experimental conditions.

We have investigated the optical properties of thin films of topological insulators Bi2Te3, Bi2Se3 and their alloys Bi2(Te1−xSex)3 on BaF2 substrates by a combination of infrared ellipsometry and reflectivity in the energy range from 0.06 to 6.5 eV. For the onset of interband absorption in Bi2Se3, after the correction for the Burstein-Moss effect, we find the value of direct bandgap of 215±10 meV at 10 K. Our data supports the picture that Bi2Se3 has a direct band gap located at the Γ point in the Brillouin zone and that the valence band reaches up to the Dirac point and has the shape of a downward oriented paraboloid, i.e. without a camel-back structure. In Bi2Te3, the onset of strong direct interband absorption at 10 K is at a similar energy of about 200 meV, with a weaker additional feature at about 170 meV. Our data support the recent GW band structure calculations suggesting that the direct interband transition does not occur at the Γ point but near the Z-F line of the Brillouin zone. In the Bi2(Te1−xSex)3 alloy, the energy of the onset of direct interband transitions exhibits a maximum near x = 0.3 (i.e. the composition of Bi2Te2Se), suggesting that the crossover of the direct interband transitions between the two points in the Brillouin zone occurs close to this composition.

We present results of our broadband ellipsometry measurements of the optical response of ferromagnetic La0.7Sr0.3CoO3. Our data show that the ferromagnetic transition is accompanied by a transfer of optical spectral weight from an absorption band centered at 1.5 eV to a narrow component of the Drude-like peak. The associated reduction of the intraband kinetic energy is significantly larger than kBTc, confirming that the double exchange plays a major role in the ferromagnetism of doped cobaltites. In conjunction with results of recent theoretical studies, the temperature dependence of the Drude-like peak suggests that the double exchange is mediated by t2g orbitals.