Weakly coupled metal-semiconductor plasmonic nanoparticles in solution

The optical properties of binary metal-semiconductor (gold-copper sulphide, both of which are plasmonic in nature) nanoparticle system has been investigated in solution, demonstrating a clear plasmonic coupling between them, due to proximity effect. Monodisperse nanoparticles of gold and copper sulphide were first synthesized using reported methods and then characterized using advanced instrumental techniques. Upon gradual addition of copper sulphide nanoparticle dispersion to that of gold nanoparticles, the intensity of the characteristic localized surface plasmon resonance (LSPR) peak of gold nanoparticles gets reduced, while that of the copper sulphide increases and an ‘isosbestic point’ could be observed. However, the reduction and the increase in the intensities do not follow the trends as expected from simple dilution/increase in the concentrations indicating a plasmonic coupling between them. The same coupling in the mixed state could be seen with respect to the shift in binding energies of the core-level orbitals of the both the materials, from the XPS spectra. Thus, the present study exemplifies a facile solution method to tune the LSPR bands in plasmonic nanomaterials for any potential device application.