Charge neutral crystal field transitions: A measure of electron–phonon interaction

We report a study on the charge neutral crystal field (d–d) transitions and their possible correlation with coupling between continuum states above the optical band gap in pure and irradiated PrFeO₃. For this purpose, room temperature optical absorption spectroscopy and Raman spectroscopy measurements were carried out. It was observed that width (W_d–d) and relative intensity (I_D) of d–d transition scaled with the extent of disorder created by laser irradiation. The consistent broadening of the d–d transition with irradiation indicates enhanced coupling between crystal field excitations and continuum states above the gap. These results are consistent with observed asymmetry in Raman modes and the Gaussian-like nature of excitonic spectral line shapes of optical absorption spectra with laser irradiation. Thus, we demonstrated a new way to probe the electron–exciton interactions in terms of crystal field transitions and excitonic line shapes in highly correlated systems. Additionally, the present work provides crucial information regarding lattice disordering in polycrystalline PrFeO₃ with irradiation and may have significant implications for caution in using this material in extremely high radiation environments at room temperature. The results are further supported with a first-principle calculation carried out using density functional theory.