  Several fields of applications require a reliable characterization of the
photothermal response and heat dissipation of nanoscopic systems, which remains
a challenging task both for modeling and experimental measurements. Here, we
present a new implementation of anti-Stokes thermometry that enables the in
situ photothermal characterization of individual nanoparticles (NPs) from a
single hyperspectral photoluminescence confocal image. The method is
label-free, applicable to any NP with detectable anti-Stokes emission, and does
not require any prior information about the NP itself or the surrounding media.
With it, we first studied the photothermal response of spherical gold NPs of
different sizes on glass substrates, immersed in water, and found that heat
dissipation is mainly dominated by the water for NPs larger than 50 nm. Then,
the role of the substrate was studied by comparing the photothermal response of
80 nm gold NPs on glass with sapphire and graphene, two materials with high
thermal conductivity. For a given irradiance level, the NPs reach temperatures
18% lower on sapphire and 24% higher on graphene than on bare glass. The fact
that the presence of a highly conductive material such as graphene leads to a
poorer thermal dissipation demonstrates that interfacial thermal resistances
play a very significant role in nanoscopic systems, and emphasize the need for
in situ experimental thermometry techniques. The developed method will allow
addressing several open questions about the role of temperature in
plasmon-assisted applications, especially ones where NPs of arbitrary shapes
are present in complex matrixes and environments.
