Radiation decolorization of corundum

Photoelectrochemical Characterization of the Anodic Film on Zinc in KOH Solution

“…Pourbaix diagrams indicate that Zn(OH)2 is stable over a range of pH near 7, but no other solid species are thermodynamically favored over the range of potential and pH in our investigations. Ex situ x-ray diffraction measurements of anodic zinc films demonstrate the presence of ZnO (5-7), but in situ measurements to support the assumption that the film is composed of ZnO are less clear (8)(9)(10)(11)(12)(13)(14).ZnO is an n-type extrinsic semiconductor with a bandgap of 3.2 eV (388 nm) exhibiting direct electron transitions and nonstoiehiometry. Extrinsic conductivity is attributed to reactive interstitial zinc (Zni) (15) Zn, = Zni § + e…”

“…Pourbaix diagrams indicate that Zn(OH)2 is stable over a range of pH near 7, but no other solid species are thermodynamically favored over the range of potential and pH in our investigations. Ex situ x-ray diffraction measurements of anodic zinc films demonstrate the presence of ZnO (5)(6)(7), but in situ measurements to support the assumption that the film is composed of ZnO are less clear (8)(9)(10)(11)(12)(13)(14).…”

“…Extrinsic conductivity is attributed to reactive interstitial zinc (Zni) (15) Zn, = Zni § + e [8] Upon illumination with super-bandgap energy photons, ZnO undergoes photoanodic dissolution (16) ZnO + 2 holes* = Zn 2 § + 1/2 O2 [9] Reviews of photoelectrochemical methods are given by Stimming (17), Chazalviel (18), and Peter (19). Photocurrent studies in the zinc system indicate the presence of a ZnO film on passive zinc in borate solutions (20), and data *Electrochemical Society Student Member.…”

Intrinsic luminescence centers in γ - and θ -alumina nanoparticles

“…[28,29] 3.56 eV and 5.28 eV excitation bands were caused by ICTs in the F + 2 centers and photo-conversions of F 2+ 2 to F + 2 centers, respectively. [11,[30][31][32][33][34] It has been demonstrated that a quantum photo excitation energy higher than 5 eV (∼ hν ≥ 5 eV) can dissociate an electron from an F 2 center to release into the conduction band. [11,30] 5.28 eV excitation energy was supposed to release an electron of F 2 center to the conduction band and then this electron would be trapped by an F 2+ 2 center and a photon at 3.32 eV would be emitted in the following reactions: [20,29]…”

“…[50,51] It has been established that the aluminum vacancies related to hole traps, i.e., V centers (a hole trapped on an oxygen ion forming an O − , and two O − were adjacent to an aluminum vacancy forming a V − center), V 2− centers (a center comprised of an O − adjacent to an aluminum vacancy) and V − OH centers (an OH − ion adjacent to a V 2− center) act as trapping centers and have an absorption band near 3 eV. Also, such centers can absorb light in the UV region [32,34,[52][53][54] (i.e. 3.1-4.1 eV).…”