Atomically dispersed metal catalysts (ADCs), as an emerging class of heterogeneous catalysts, have been widely investigated during the past two decades. The atomic dispersion nature of the catalyti...

Surface Coordination Chemistry of Atomically Dispersed Metal Catalysts.

Ultraviolet optical absorption, emission, and excitation spectra are presented for 14-MeV neutron-irradiated high-purity crystalline ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$. Low-temperature polarized excitation spectra for the 3.8-eV luminescence correlated well with polarized absorption at 4.8 eV (both polarizations) and 5.4 eV ($\stackrel{\ensuremath{\rightarrow}}{\mathrm{E}}\ensuremath{\perp}\stackrel{\ensuremath{\rightarrow}}{\mathrm{c}}$). These optical properties compare favorably with those predicted using wave functions from an earlier pointion calculation for the ${\mathrm{F}}^{+}$ center by La, Bartram, and Cox. The 4.8- and 5.4-eV absorption bands are assigned to the $1A\ensuremath{\rightarrow}1B$ and $1A\ensuremath{\rightarrow}2A$ transitions, respectively, of the ${F}^{+}$ center and the 3.8-eV luminescence is assigned to the $1B\ensuremath{\rightarrow}1A$ transition. The $1A\ensuremath{\rightarrow}2B$ transition could not be conclusively identified, but preliminary evidence suggests it occurs near 6.3 eV. Similar absorption and emission bands are observed following energetic-proton and ${\mathrm{Al}}^{+}$ bombardment. Other uv optical properties are presented, including the quantum efficiency, lifetime, and temperature dependence of the emission.

Optical properties of the F + center in crystalline Al 2 O 3

Strategies for Stabilizing Atomically Dispersed Metal Catalysts

Electron transfer at oxide surfaces. The MgO paradigm: from defects to ultrathin films.

Some observations on the photoluminescence of doped β-galliumsesquioxide

Single crystals of MgO have been additively colored by heating them in Mg vapor at temperatures from 1600 to 1800\ifmmode^\circ\else\textdegree\fi{}C and pressures up to 4000 Torr. The ${F}^{+}$ and ${F}^{\ensuremath{'}}$ optical absorption bands (due to anion vacancies containing one and two electrons, respectively) were observed to be extremely similar but distinguishable, and were observed at liquid-nitrogen temperature to peak at 4.96 and 5.03 eV, respectively. The oscillator strength for the ${F}^{\ensuremath{'}}$ center is estimated to be 0.70\ifmmode\pm\else\textpm\fi{}0.05. A photoconversion process ${F}^{+}\ensuremath{\leftrightarrow}{F}^{\ensuremath{'}}$ was studied. The luminescence bands for these centers were observed at 3.1 and 2.4 eV, respectively. The density of ${F}^{\ensuremath{'}}$ centers ${N}_{{F}^{\ensuremath{'}}}$ produced by the additive coloring process was observed to be related to the density of atoms in the vapor ${N}_{\mathrm{Mg}}$ by the equation ${N}_{{F}^{\ensuremath{'}}}=1270{N}_{\mathrm{Mg}}{e}^{\ensuremath{-}\frac{Q}{\mathrm{kT}}}$, where $Q=1.53$ eV. The temperature dependence of these two bands was measured and is discussed.

F + and F ′ Centers in Magnesium Oxide

F + F Center Conversions in Magnesium Oxide

Electron-spin resonance of uv-irradiated sodium azide

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F + and F ′ Centers in Magnesium Oxide

F + F Center Conversions in Magnesium Oxide

Electron-spin resonance of uv-irradiated sodium azide