A theoretical investigation of the role of the chemical bond in the Raman and fluorescence response of molecule-semiconductor nanoparticle hybrids – FRAMOLSENT

We will undertake a unified treatment of both fluorescence emission and Raman scattering in a nanosystem consisting of a molecule chemically bound to a nanoparticle or cluster of a metal oxide that behaves as a semiconductor in bulk phase, interacting with a laser field. These processes must be jointly considered, as the excitation and decay pathways become interdependent due to the appearance of midgap states, induced by the formation of the chemical bond, that play a fundamental role in both photoexcitation and electron injection into the nanoparticle. We will be mostly interested in resonant processes, which are present in the hybrid but not in the separate components due to the reduction of the energy gap for electron excitation, where the laser simultaneously provokes the creation of an electron-hole exciton and probes the Raman and fluorescence responses. Our approach involves the calculation of the cross section for both processes based on the properties of the time-correlation function of the effective dipole moment of the system whose time evolution is described by Liouville-von Neumann equation. To solve this equation we separate the hybrid into a primary quantum region and a secondary region responsible for environmental effects. The calculation of the relaxation parameters involved in this equation will be accomplished through the use of Density Functional Theory for both the ground and excited states. We will consider both model systems to test our approach and realistic systems consisting of oxide clusters and nanoparticles, e.g., TiO2 and an organic molecule. The calculated cross section using our approach will also be compared with the corresponding magnitudes considering each process separately.