Simultaneous enhancement of phonons modes with molecular vibrations due to Mg doping of a TiO2 substrate

The Raman behavior of Mg-doped TiO2 (0%, 1%, 3% and 5%) nanoparticles (NPs) prepared by a sol-gel method was investigated. It was found that the Mg2+ ions were in situ doped into the TiO2 NPs. Normal Raman and surface enhanced Raman scattering (SERS) spectra have been measured. We observe the enhanced Raman intensity of both the adsorbed molecules and the phonon modes of the Mg-TiO2 NPs when 4-mercaptobenzoic acid (4-MBA) is the probing molecule adsorbed on the Mg-TiO2 NPs. The results showed that the Mg doping concentration and the contents of the surface defects play an important role in the synergistic enhanced phenomenon. The performances of these substrates strongly depend on the charge-transfer resonance mechanism, which originates from the electron and energy transfer between the semiconductor's and the molecule's interfaces.