Enhanced Photovoltage Response of Hematite-X-Ferrite Interfaces (X = Cr, Mn, Co, or Ni)

High-fluorescent p-X-ferrites (XFe₂O₄; XFO; X = Fe, Cr, Mn, Co, or Ni) embedded in n-hematite (Fe₂O₃) surfaces were successfully fabricated via a facile bio-approach using Shewanella oneidensis MR-1. The results revealed that the X ions with high/low work functions modify the unpaired spin Fe²⁺-O^2- orbitals in the XFe₂O₄ lattices to become localized paired spin orbitals at the bottom of conduction band, separating the photovoltage response signals (73.36~455.16/-72.63~-32.43 meV). These (Fe₂O₃)-O-O-(XFe₂O₄) interfacial coupling behaviors at two fluorescence emission peaks (785/795 nm) are explained via calculating electron-hole effective masses (Fe₂O₃-FeFe₂O₄ 17.23 × 10^-31 kg; Fe₂O₃-CoFe₂O₄ 3.93 × 10^-31 kg; Fe₂O₃-NiFe₂O₄ 11.59 × 10^-31 kg; Fe₂O₃-CrFe₂O₄ -4.2 × 10^-31 kg; Fe₂O₃-MnFe₂O₄ -11.73 × 10^-31 kg). Such a system could open up a new idea in the design of photovoltage response biosensors.