Coupled ESRF-EuXFEL proposal: Excited states of Co3O4 studied by static and time-resolved RIXS

The interest in charge transfer excitations in Transition Metal Oxides (TMOs) is due to the photocatalytic and photovoltaic applications of these materials. Co3O4 is especially intriguing for showing different relaxation pathways when exciting at two different wavelengths, faster at 400 nm than at 800 nm. Static and time-resolved RIXS experiments, jointly made, can provide insight on these different time scales and on the microscopic mechanisms underlying. We propose to measure at ID32 medium and high resolution static RIXS spectra of a Co3O4 single crystal, to obtain a definitive assignment of the excitations in the 0.5-3.0 eV range and to study electron-phonon coupling for the dominant A1g. Together with future trRIXS measurements to be proposed at SCS@EuXFEL, those results will clarify the role of Co3+ sites, in defining the electronic properties of this intriguing material and the microscopic origin of different photoexcited states lifetimes.

过渡金属氧化物（Transition Metal Oxides, TMOs）中的电荷转移激发之所以受到广泛关注，源于这类材料在光催化与光伏领域的应用前景。四氧化三钴（Co₃O₄）尤为引人瞩目：其在两种不同波长激发下呈现出截然不同的弛豫路径，400 nm激发时的弛豫速率快于800 nm。联合开展静态与时间分辨共振非弹性X射线散射（Resonant Inelastic X-ray Scattering, RIXS）实验，能够揭示这些差异对应的时间尺度及其背后的微观机制。我们提议在ID32光束线测量四氧化三钴单晶的中、高分辨率静态RIXS光谱，以明确归属0.5~3.0 eV能区内的激发态，并针对主导性A₁g模研究电子-声子耦合效应。结合未来拟在SCS@EuXFEL开展的trRIXS测量，上述研究结果将阐明Co³⁺位点在定义该特殊材料电子性质，以及不同光激发态寿命的微观起源中所扮演的关键角色。