  Fast emitting polymeric scintillators are requested in advanced applications
where high-speed detectors with large signal-to-noise ratio are needed.
However, their low density implies a weak stopping power of high energy
radiations, thus a limited light output and sensitivity. To enhance their
performances, polymeric scintillators can be loaded with dense nanoparticles
(NPs). We investigate the properties of a series of polymeric scintillators by
means of photoluminescence and scintillation spectroscopy, comparing standard
scintillators with a composite system loaded with dense hafnium dioxide (HfO2)
NPs. The nanocomposite shows a scintillation yield enhancement of +100% with
unchanged time response. We provide for the first time an interpretation of
this effect, pointing out the local effect of NPs in the generation of emissive
states upon interaction with the ionizing radiation. The obtained results
indicate that coupling of fast conjugated emitters with optically inert dense
NPs could allow to surpass the actual limits of pure polymeric scintillators.
