Analysis of Optical Properties and Structures of Nitrogen Doped Gallium Oxide

To promote photocatalytic activity of gallium oxides (Ga2O3) on CO2 reduction with water under visible light irradiation, we have tried nitrogen doping into Ga2O3 with different crystalline structures. In diffuse reflectance UV-vis spectra, absorption bands appeared in the visible light region after the nitrogen doping and the absorption edge shifted to a longer wavelength region with increasing nitrogen doping temperature. N K-edge XANES analysis clearly showed two kinds of nitrogen species doped in the samples; gallium nitride (GaN) species and molecular like nitrogen. In XRD patterns, nitrogen doping at temperatures above 823 K, gallium nitride phases appeared while the original crystal structures of gallium oxide samples maintained when nitrogen doping temperature was less than 823 K. However, photocatalytic CO2 reduction under visible light irradiation was insignificant for all the nitrogen doped samples, because nitrogen doped in Ga2O3 samples was unstable in water under the visible light irradiation.