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Successive redox-mediated visible-light ferrophotovoltaics
摘要： Titanium oxide materials have multiple functions such as photocatalytic and photovoltaic effects. Ferroelectrics provide access to light energy conversion that delivers above-bandgap voltages arising from spatial inversion symmetry breaking, whereas their wide bandgap leads to poor absorption of visible light. Bandgap narrowing offers a potential solution, but this material modification suppresses spontaneous polarization and, hence, sacrifices photo-voltages. Here, we report successive-redox mediated ferrophotovoltaics that exhibit a robust visible-light response. Our single-crystal experiments and ab initio calculations, along with photo-luminescence analysis, demonstrate that divalent Fe2+ and trivalent Fe3+ coexisted in a prototypical ferroelectric barium titanate BaTiO3 introduce donor and acceptor levels, respectively, and that two sequential Fe3+/Fe2+ redox reactions enhance the photogenerated power not only under visible light but also at photon energies greater than the bandgap. Our approach opens a promising route to the visible-light activation of photovoltaics and, potentially, of photocatalysts.
关键词： ferrophotovoltaics,redox reactions,barium titanate,photovoltaic effect,visible-light response
更新于2025-09-23 15:19:57
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Раrаdохical Sесоndаrу Emissiоn Mаss Sресtrum оf thе Lеuсо Fоrm оf Mеthуlеnе Bluе
摘要： A paradoxical relation between the secondary emission mass spectra of Methylene Blue and its leuco form is revealed: in the mass spectrum of the dye cation Cat+ (oxidized form with the molecular weight 284), an intense product of its reduction with m/z 285 is recorded, while the mass spectrum of the leuco dye (reduced form with the molecular weight 285) corresponds to an oxidized form with a dominating peak at m/z 284. An explanation of this empirical fact is proposed: the redox reactions induced by ionizing factors under the conditions of secondary emission experiments pass in the direction permitted for the particular initial form of the redox-active compound. Namely, an oxidized form undergoes reduction, whereas the reduced form is oxidized. This effect should be taken into account for the correct identification of redox-active compounds by their secondary emission mass spectra and for simulating redox reactions in the systems containing redox-active dyes under mass spectrometric conditions.
关键词： leuco form,Methylene Blue cationic dye,secondary emission mass spectrometry,redox reactions
更新于2025-09-19 17:15:36
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Photoluminescence and phosphorescence of Mn2+ ion activated green phosphor Na2ZnSiO4:Mn2+ synthesized by self-reduction
摘要： Mn2+ activated phosphors are vital for lighting and displays, whereas the multivalent states characteristics of Mn made that reducing atmosphere (such as H2, CO, H2/N2) is generally required in the synthesis processes. Herein, a Mn2+ doped silicate green phosphor Na2ZnSiO4:Mn2+ was synthesized by an unconventional self-reduction of Mn7+/Mn4+/Mn3+ to Mn2+ under air atmosphere. Upon 260 nm excitation, an intense green photoluminescence band centered at 515 nm and the phosphorescence after stoppage of the excitation source can be observed in this phosphor. The photoluminescence and phosphorescence properties, self-reduction processes and mechanism in Na2ZnSiO4:Mn, as well as the phase transformations of the different Mn sources (MnCO3, Mn2O3, MnO2) at various temperatures were investigated systematically. Based on these investigations, together with the density functional theory (DFT) calculations, a self-reduction mechanism of Mn7+/Mn4+/Mn3+ to Mn2+ based on zinc vacancies VZn'' has been proposed. This work provides not only a new luminescent material, but also new insights into the Mn valence states controlling and luminescence tuning.
关键词： Mn2+,redox reactions,self-reduction,defects
更新于2025-09-19 17:15:36
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Nanoscale oxygen ion dynamics in SrFeO <sub/>2.5+δ</sub> epitaxial thin films
摘要： A variety of functional properties in transition metal oxides are often underpinned by oxygen vacancies. While the oxygen vacancy concentration and arrangements are well-known to have strong influence on the physical properties of oxides, the oxygen dynamics in oxides—including oxygen ion incorporation and movements during redox reactions—remain elusive. Performing conductive AFM studies of epitaxial thin films of oxygen-deficient SrFeO2.5 treated by air-annealing at various temperatures, we observe oxidation-induced enhancement of local electronic conduction on the higher terraces near the outer step edges at which oxygen ions are preferably incorporated and diffuse into the films. We also show that the local conduction can be reversibly controlled by electric-field-induced redox reactions at room temperature. These results highlight the importance of the nanoscale oxygen dynamics in redox reactions in SrFeO2.5 films.
关键词： SrFeO2.5,transition metal oxides,redox reactions,conductive AFM,oxygen vacancies
更新于2025-09-09 09:28:46