Tungsten trioxide (WO3 − x) nanoparticles prepared by pulsed laser ablation in water

► First time prepared, by laser ablation in water, WOx nanoparticles (NPs). ► Nearly 60% of almost stoichiometric (x = 2.9), small size (2-6 nm) NPs plus 80-100 nm aggregates. ► A plasma shielding effect occurs at high laser fluence. ► Modulation of optical gap with the NPs size. ► Potential scalability of the production technique.