(a) Spectroscopic characterization of hybrid nanoparticles. The blue curve represents the absorption spectrum of the nanoparticles in water solution; the green curve is the corresponding emission spectrum at 488 nm excitation. The red curve is the emission spectrum of a dried drop of the same solution on a glass plate, at the same excitation wavelength (sample 1). Inset: hybrid nanoparticle configuration. The outer surface consists of a polysiloxane shell (green) covered with a luminescent coating that can be either Rhodamine or Fluorescein (yellow). The core is composed of a lanthanide oxide and gadolinium oxide (pink). (b) Comparison between near-field (dashed) and far-field (plain) emission spectra of hybrid nanoparticles, with corresponding blue and red curve fittings. The first has been obtained by using transmission mode SNOM. Intensity values have been normalized.