Analysis of defects dominating carrier recombination in CeO₂ single crystal for photocatalytic applications

In photocatalytic water splitting and CO 2 reduction, recently, cerium oxide (CeO 2 ) has been widely investigated. Defects that can directly dominate carrier recombination are essential for the photocatalytic performance of CeO 2 . In this study, several photoluminescence (PL) peaks are observed on the (100) face of an undoped CeO 2 single crystal, indicating the presence of defects. Moreover, we characterize carrier recombination using time-resolved photoluminescence (TR-PL) and microwave photoconductivity decay ( μ -PCD) measurements. The temperature dependence of decay curves is the result of carrier trapping and emission at deep levels. These decay curves are observed separately using a 565 nm band-pass filter (BPF) based on the PL spectra. The trap energy level ( E T ) and majority carrier capture cross-section ( σ T ) of each defect are also analyzed using rate equations to fit the experimental results. The temperature-dependent time constants are well reproduced by a recombination model using hole traps HT infrared and HT visible at E T of 0.76 and 0.55 eV from the conduction or valence band, with estimated σ T of the order of 10 −21 and 10 −22 cm 2 for without and with the BPF, respectively. These findings regarding the presence of multiple defects in a single crystal indicate the necessity to focus on defect control.