In this article, we present a theoretical study on the sub-bandgap refractive indexes and optical properties of Si-doped β-Ga₂O₃ thin films based on newly developed models. The measured sub-bandgap refractive indexes of β-Ga₂O₃ thin film are explained well with the new model, leading to the determination of an explicit analytical dispersion of refractive indexes for photon energy below an effective optical bandgap energy of 4.952 eV for the β-Ga₂O₃ thin film. Then, the oscillatory structures in long wavelength regions in experimental transmission spectra of Si-doped β-Ga₂O₃ thin films with different Si doping concentrations are quantitively interpreted utilizing the determined sub-bandgap refractive index dispersion. Meanwhile, effective optical bandgap values of Si-doped β-Ga₂O₃ thin films are further determined and are found to decrease with increasing the Si doping concentration as expectedly. In addition, the sub-bandgap absorption coefficients of Si-doped β-Ga₂O₃ thin film are calculated under the frame of the Franz–Keldysh mechanism due to the electric field effect of ionized Si impurities. The theoretical absorption coefficients agree with the available experimental data. These key parameters obtained in the present study may enrich the present understanding of the sub-bandgap refractive indexes and optical properties of impurity-doped β-Ga₂O₃ thin films.

Native point defects in ZnO are so complicated that most of them are still debating issues, although they have been studied for decades. In this paper, we experimentally reveal two sub-components usually hidden in the low energy tail of the main broad green luminescence band peaking at 547 nm (~2.267 eV) in intentionally undoped ZnO single crystal by selecting the below-band-gap (BBG) optical excitations (e.g. light wavelengths of 385 nm and 450 nm). Moreover, both sub-components are manifested as long persistent phosphorescence once the BBG excitations are removed. With the aid of a newly developed model, the energy depths of two electron traps involved within the long lived orange luminescence are determined to be 44 meV and 300 meV, respectively. The candidates of these two electron traps are argued to be most likely hydrogen and zinc interstitials in ZnO.