Resonant electronic Raman scattering from Ir4+ ions in β-Ga2O3

We report the observation of resonant electronic Raman scattering (ERS) originating from Ir4+ ions in bulk β-Ga2O3 crystals grown by the Czochralski method. The observed ERS peak at 5150 cm−1 at room temperature is attributed to an internal transition within the split 2T2g ground state of Ir4+ ions under strong octahedral crystal field conditions and combined action of spin–orbit coupling and low-symmetry field components. The ERS efficiency is found to strongly depend on the photon energy used for optical excitation and exhibits a maximum at about 2.9 eV. In accordance with the linear dependence of the ERS peak intensity on the optical excitation power, the enhancement around 2.9 eV is explained by Raman scattering in resonance with electronic transitions from the Ir4+ ground state 2T2g to the first excited state 4T1g. The optically induced Ir3+/4+ charge transfer is discussed as an alternative, but less likely the origin of the observed enhancement of the ERS efficiency.