To understand the plasmonic heating mechanism and the discrepancy between the temperature obtained from the Raman thermometry and the melting of the TiO2, the temperature of the Au nanoparticles was calculated using plasmonic heating models. It has been established that when illuminating an ensemble of plasmonic NPs, the heating was not necessarily localized around each NP. The temperature increase experienced at the center of the illuminated areas results from two contributions, self-heating and collective heating. Self-heating is due to the absorption of energy from light by a single particle and the increase in its temperature can be calculated. Under CW laser irradiation, the increase of steady-state temperature of a single spherical nanoparticle of radius R from absorption of light depends on the nanoparticle's absorption cross section (σabs), the light intensity I, and the average thermal conductivity (𝜅̅ ) of the air and the support matrix according to