Realizing chemical codoping in TiO₂

We demonstrate experimentally a chemical codoping approach that would simultaneously narrow the band gap and control the band edge positions of TiO₂ semiconductors. It is shown that a sequential doping scheme with nitrogen (N) leading the way, followed by phosphorus (P), is crucial for the incorporation of both N and P into the anion sites. Various characterization techniques confirm the formation of the N-P bonds, and as a consequence of chemical codoping, the band gap of TiO₂ is reduced from 3.2 eV to 1.8 eV. The realization of chemical codoping could be an important step forward in improving the general performance of electronic and optoelectronic materials and devices.