Probing Shallow and Deep Oxygen Traps in Binary Transition Metal Oxide, α-CoV₂O₆, Using Ultrafast Pump–Probe Spectroscopy

In this study, we have investigated the ultrafast carrier dynamics in the binary transition metal oxide, α- CoV2O6, using nondegenerate pump (3.14 eV)–probe (1.57 eV) transmission spectroscopy at room temperature. A detailed look at the time-resolved differential transmission data taken at various pump fluence excitations reveals the presence of two types of traps in the journey of photoexcited electrons: the shallow trap states and deep trap states. This finding is corroborated by steady-state absorption and photoluminescence spectra. First-principles density functional theory calculations reveal that these trap states originate from oxygen vacancies in α- CoV2O6. The empirical kinetic model consisting of these two trap states further indicates that the photoexcited electrons become trapped in these states on ultrafast timeframes: the trapping time in shallower traps is about 2 ps, whereas the capture time in deeper midgap traps takes about 30 ps. It further indicates that approximately 44% and 40% of the excited electrons are trapped in the shallow and midgap trap states, respectively, highlighting their crucial role in the optical properties of α- CoV2O6.