Time-dependent Emission Stokes Shift in Au, Ag and Au/Ag Fluorescent Nanoclusters : Evidence of Multiple Emissive States
Au, Ag and bimetallic Au/Ag nanoclusters were prepared under similar microwave-irradiated synthesis conditions in aqueous solutions, using BSA as stabilizer. The nanoclusters exhibited strong fluoresence with characteristic emission spectral peaks features that suggested the presence of multiple emissive states in each case. Time-resolved emission studies revealed the very rare incidence of time-dependent emission Stokes shift in metal nanoclusters over a time-scale of ~10 ns. The shifts were of varying degrees: ~200 cm-1 for Ag, ~750 cm-1 for Au and ~1400 cm-1 for Au/Ag nanoclusters,. Application of the Time-resolved Area Normalized Emission Spectra (TRANES) method confirmed the existence of multiple emissive species in each of the nanoclusters, which also helped explain the time-dependent emission Stokes shift.