Tuning Electron-Phonon Coupling in Se-Doped Fe₂O₃ for Efficient Photocatalysis: Experimental and First-Principles Calculations

Reducing the electron-phonon (el-ph) coupling in Fe2O3 can significantly boost carrier mobility by overcoming the customary trapping effects caused by polaron formation. Despite various efforts to understand the polaron formation and their transport properties, any direct measurement of el-ph coupling strength is still lacking. Hence, we prepared Fe2O3 and Se-doped Fe2O3 through a solid-state reaction and measured the el-ph coupling strength through the Fano-resonance approach. The reduced coupling strength in Se-modified Fe2O3 indicates that the self-trapped carriers can easily hop the lattice and consequently have a larger lifetime, as confirmed in time-resolved photoluminescence measurements. Further, to determine the Se doping site and to reveal the underlying mechanism for the changes in carrier lifetime, we performed first-principles density functional theory calculations by considering all the possible substitutional doping models. Our calculations show that Se will substitute the O atoms (Se@O) under ambient conditions rather than Fe atoms (Se@Fe), and Se@O doping produces two major occupied gap states within the band gap above the valence band maximum about 0.3 and 1.0 eV, respectively. Besides, the Se:Fe2O3 exhibits better photocatalytic degradation toward rhodamine dye due to the decreased el-ph coupling strength. In essence, the report provides both experimental and theoretical insight into understanding the polaron hopping mechanism in Fe2O3.