Unraveling the Role of F-Type Color Centers on the Optical and Electrical Properties of Al2W3O12 Nanoparticles with Different Content of Oxygen Vacancies

Identification and tuning of defects in nanomaterials are critical to the advancement of emerging technologies. In this work, F-type color centers in Al₂W₃O₁₂ nanopowders, formed via extrinsic oxygen vacancies, were comprehensively studied for the first time. By correlating photoluminescence (PL), electron paramagnetic resonance (EPR), and diffuse reflectance spectroscopy (DRS), the types of F color centers were identified, unraveling their influence on the optical and electrical properties of Al₂W₃O₁₂ nanopowders. EPR coupled with X-ray photoelectron spectroscopy (XPS) demonstrated that the formation of F-type color centers in Al₂W₃O₁₂ nanopowders is mainly generated by an electronic charge compensation process. Our experimental findings highlighted that the increased concentration of F and F⁺ color centers, present in the heat-treated Al₂W₃O₁₂ nanopowders under inert and reducing atmospheres, contributed to enhanced visible light sensitivity and higher electrical conductivity due to the introduction of intermediate energy levels within the band gap by the F-type color centers, the contribution of free electrons from the formation of F⁺ color centers, and the excitation of trapped electrons in the F⁺ and F color centers to the conduction band. These findings provide new insights into the creation and tuning of F-type color centers in nanomaterials, potentially enabling applications in advanced technological devices.