Intrinsic polaronic photocarrier dynamics in hematite

Barrierless Self-Trapping of Photocarriers in Co3O4

“…The fast decay of the PIA may reflect the decrease in the absorption coefficient due to hot carrier cooling, ,, which however is ruled out because such a phenomenon is also observed by pumping the sample at the absorption-edge so that hot carriers are absent (Figure S3). As demonstrated previously, the free carriers have a greater absorption coefficient than the localized carriers, especially in the NIR and IR regions, ,, and thus, we attribute the rapid PIA decline to the free-carrier localization. The residual PIA signals at long delays then correspond to the optical transitions from localized states to higher energy states. , Further evidence will be presented later to validate this attribution.…”

“…As demonstrated previously, the free carriers have a greater absorption coefficient than the localized carriers, especially in the NIR and IR regions, ,, and thus, we attribute the rapid PIA decline to the free-carrier localization. The residual PIA signals at long delays then correspond to the optical transitions from localized states to higher energy states. , Further evidence will be presented later to validate this attribution.…”

“…The residual PIA signals at long delays then correspond to the optical transitions from localized states to higher energy states. 14,25 Further evidence will be presented later to validate this attribution.…”

“…Given the narrow bandwidth and the ionic nature of TMOs, the stabilization energy arising from delocalization is usually smaller than that arising from the lattice polarization, and thus, the formation of severely localized polarons via self-trapping is energetically more favorable in these materials. Time-resolved spectroscopic studies have confirmed that the self-trapping occurs on a subpicosecond time scale in a wide variety of TMOs. − Both theoretical and experimental results have suggested that the polarons in these TMOs are confined within a dimension of lattice unit and thus belong to the small polaron category. − …”

“…Limited by the range of the probe wavelength, only part of the PIB LMCT band is captured, and the cause of this TA feature needs to be explored in the future. The flat PIA band usually results from the intraband absorption of carriers ,,, or absorption redshift due to the thermal effect . The thermal effect is not considered to account for the PIA before 3 ps because the lattice heating appears on a much longer time scale .…”