Evidence for emission and transfer of energy from excited edge sites of MgO smokes by photoluminescence experiments

Properties of oxide thin films and their adsorption behavior studied by scanning tunneling microscopy and conductance spectroscopy

“…UV-VIS spectroscopy, are widely used to gain insights into the oxide electronic structure, for instance into the gap size, the presence of localized defect states and the energy of electron-hole pair excitations. 130,133,449 Also here, a spatially-resolving technique would be highly desirable, as optical properties of oxide materials are almost exclusively defect-mediated and hence sensitive to the local environment in which the optical transition takes place. 23,55 Photon emission spectroscopy with the STM, where local optical modes are excited by electron/hole injection from the tip, offers the required spatial resolution.…”

“…131,132,133 Spatially-resolved optical experiments with an STM are therefore a powerful means to probe the defect structure of oxide surfaces. This is especially true, because structural parameters of the emission centre and its specific optical behavior can be explored simultaneously at the local scale.…”

“…As a result, surface steps, corners and kinks are the preferred trapping and recombination centers for coupled electron-hole pairs (excitons), being the fundamental electronic excitation in a gap material. 23,55,243 The decay of excitonic modes is the main source for the emission of photons 131,132,133 and hot-electrons from the oxide surface. 244,245,246 Not surprisingly, the properties and abundance of lowcoordinated surface sites is therefore tightly connected with the optical and photochemical activity of oxide materials.…”

“…Hereby, optical spectroscopy 131,132,133 , XPS and EELS 247,248 are ideally suited to detect defect-induced electronic states in the band gap, while electronparamagnetic resonance spectroscopy (EPR) is sensitive to oxide defects carrying an unpaired electron. 249 Thermal desorption and infrared-absorption spectroscopy, on the other hand, enable an investigation of defect-mediated adsorption processes.…”

Photon mapping of MgO thin films with an STM

“…Wide band-gap insulators, such as simple oxides or alkali-halogenides, exhibit a rich optical behavior, characterized by various excitation and deexcitation channels with sub band-gap energy [1][2][3][4]. The diversity of optical modes is related to structural imperfections in the crystal lattice, such as point defects, step or corner atoms.…”