Tuning the spectral and temporal response in PtAu core–shell nanoparticles

Ultrafast laser spectroscopy has been used to measure the electron–phonon coupling constant in PtAu core–shell bimetallic nanoparticles. A chemical reduction method was used to prepare Pt cores of 12.5 nm diameter and a γ-radiolytic deposition technique was then used to grow Au shells of variable thickness. The resulting nanoparticles have a spectrum that is characteristic of Au. It is found that the electron–phonon coupling time for these hybrid nanoparticles (τe–ph∼200 fs) is over a factor of 3 shorter than that for plain Au nanoparticles (τe–ph∼650 fs). The faster dynamical response is due to the large electron–phonon coupling constant for Pt, which provides efficient scattering of the excited electrons. Platinum dominates the temporal response, even for a 1:6 molar ratio of Pt to Au, because it has a much larger density of states near the Fermi level compared to Au.