Phys.org  May 30, 2022 Nanocrystalline TiO2, a semiconductor, darkens when irradiated with ultraviolet (UV) light due to charge separation and reduction of titanium atoms. The color change is not permanent because oxygen in the air re-oxidizes the titanium and causes a return to transparency. To sustain the color change for a longer period researchers at UC Riverside used nitrogen as a dopant and decorated the crystals with a common non-toxic substance diethylene glycol which played a crucial role in the color change. Using light-writing methods they produced patterns or printed text by illuminating the paper or glass substrate through a […]