Fig. 3.

a Fluorescence images, average luminous intensities, and PL patterns of Fe₂O₃–XFe₂O₄ by the excitation of 488 nm. b reflects the surface photovoltages and KPFM phase images. The work function values of Fe₂O₃ and FeFe₂O₄ are 5.35 eV [26] and 5.52 eV [27], respectively, and the charges transfer between the different work functions of two materials for their Fermi levels to equilibrate. The corresponding theoretical surface potential images are shown in (c). d means the calculated effective masses of electron-hole pairs and surface potential illustration