Mixed valence Ce-doped TiO2 with multiple energy levels and efficient charge transfer for boosted SERS performance

Considering the variable valence characteristics of rare earth elements, they can be in a variety of valence forms coexistence. Doping of rare earth element with different valence states may produce different energy levels to tune the semiconductor energy band structure. We utilize rare earth element Ce doping TiO2 for the development of high-performance semiconductor surface-enhanced Raman scattering (SERS) substrates based on an energylevel tuning strategy. Ce doping not only forms multiple energy levels including Ce3+ and Ce4+ metal doping energy levels in the bandgap of TiO2, but also enriches the surface state level of TiO2 itself, which together promote the separation of photogenerated carriers and improve charge transfer efficiency between substrates and absorbed molecules. This endows TiO2 semiconductor substrate with a higher SERS enhancement factor, which can reach 2.2 x 106. The detectable concentration of methylene blue can be as low as 10-10 mol/L. Moreover, the semiconductor substrate exhibits excellent uniformity and stability. This study not only provides a new strategy to develop excellent semiconductor SERS substrate with multiple energy levels, but also lays the foundation for promising practical application of semiconductor substrate.