On the electronic transitions of α-Fe2O3 hematite nanoparticles with different size and morphology: Analysis by simultaneous deconvolution of UV-vis absorption and MCD spectra

Nanostructures of the naturally-existing most stable iron oxide, hematite (alpha-Fe2O3), gain significant research interest in various recent applications. In this study, we put the main focus on magneto-optical (MO) properties of hematite nanoparticles synthesized by a solvothermal approach, and the effects of size, morphology, and particle aggregation on the magnetic circular dichroism (MCD) and conventional absorption spectra are investigated. Simultaneous deconvolution of UV-vis absorption and MCD spectra allows us to discuss the nature of electronic transitions of various hematite nanoarchitectures on the basis of possible transitions in the 3d(5) system, giving enhanced spectral resolution and detailed assignments. Consequently, we find (i) characteristic sizeand shape-dependent MCD responses at 450-470 nm; and (ii) the presence of both spin-allowed pair excitation and Laporte-forbidden d-d transition with opposite MCD signs in close energy at around 550 nm.