ABSTRACT
Co-doped TiO2 nanoparticles were synthesized via non hydrous complex-polymer sol-gel method. A series of Co(x):Ti1-x O2 samples with x = 0.01, 0.03, 0.05, 0.08 and 0.10, were prepared and subsequently annealed at 400 degrees, 600 degrees and 800 degrees C. Structural and magnetic properties of Co(x):Ti1-x O2 have been studied by means of X-ray diffraction and DC magnetometry. All samples annealed at 400 degrees C show a paramagnetic behavior with an average grain size of 11 nm. With increasing annealing temperatures a complete crystallization is seen with growth of the cluster size up to 31 nm with clear evidence of a presence of CoTiO3. For all concentrations and annealing conditions no sign of a metallic phase, even at x = 0.10, is seen.
ABSTRACT
A molecular exciton signature is established and investigated under different ambient conditions in rubrene single crystals. An oxygen-related band gap state is found to form in the ambient atmosphere. This state acts as an acceptor center and assists in the fast dissociation of excitons, resulting in a higher dark and photoconductivity of oxidized rubrene. The band gap state produces a well-defined photoluminescence band at an energy 0.25 eV below the energy of the 0-0 molecular exciton transition. Two-photon excitation spectroscopy shows that the states are concentrated near the surface of naturally oxidized rubrene.
