Optical properties of crystalline and ion-beam amorphized Bi12GeO20: Relevance for waveguide applications

•Crystalline Bi12GeO20 samples were irradiated with F ions at 30 MeV.•Optical properties were determined using spectroscopic ellipsometry.•Tauc plots were used to determine the energy gap.•Energy gap values were 2.82 ± 0.02 eV and 2.37 ± 0.04 eV for pristine and damaged BGO.

Crystalline Bi12GeO20 samples were irradiated with F ions at 30 MeV. Spectroscopic ellipsometry measurements were used to determine the optical constants of the pristine and irradiated material. The critical points model was used to represent the material’s dielectric function. Excellent fits of the experimental ellipsometry measurements were obtained in both, the pristine and irradiated samples. Moreover, a very good agreement was also found between the ellipsometric determination of thickness and that predicted by SRIM calculations. Tauc plots revealed an energy gap of 2.82 ± 0.02 eV for the crystalline phase that is red-shifted to 2.37 ± 0.04 eV in the irradiated material.