Plasmonic nanoparticles
are renowned as efficient heaters due to
their capability to resonantly absorb and concentrate electromagnetic
radiation, trigger excitation of highly energetic (hot) carriers,
and locally convert their excess energy into heat via ultrafast nonradiative
relaxation processes. Furthermore, in assembly configurations (i.e.,
suprastructures), collective effects can even enhance the heating
performance. Here, we report on the dynamics of photothermal conversion
and the related nonlinear optical response from water-soluble nanoeggs
consisting of a Au nanocrystal assembly trapped in a water-soluble
shell of ferrite nanocrystals (also called colloidosome) of ∼250–300
nm in size. This nanoegg configuration of the plasmonic assembly enables
control of the size of the gold suprastructure core by changing the
Au concentration in the chemical synthesis. Different metal concentrations
are analyzed by means of ultrafast pump–probe spectroscopy
and semiclassical modeling of photothermal dynamics from the onset
of hot-carrier photogeneration (few picosecond time scale) to the
heating of the matrix ligands in the suprastructure core (hundreds
of nanoseconds). Results show the possibility to design and tailor
the photothermal properties of the nanoeggs by acting on the core
size and indicate superior performances (both in terms of peak temperatures
and thermalization speed) compared to conventional (unstructured)
nanoheaters of comparable size and chemical composition.