Luminescent Erbium-Based Nanoparticles Synthesized by Pulsed Laser Ablation in Liquid

Erbium and erbium oxide nanoparticles (Er-NPs) have been synthesized in deionized (DI) water using the green and environmentally friendly technique of pulsed laser ablation in liquid (PLAL), with laser fluence ranging from 2.5 to 20.9 J/cm2. Owing to the careful examination of the nanoparticle morphology, crystal structure, and chemical composition, the occurrence of various growth regimes is evidenced. The size of the Er-NPs is found to increase with the laser fluence, and the formed nanoparticles are surrounded by a thin hydroxide layer of a few nanometers thickness, originating from water and chemical residues. The activation of 4f–4f optical transitions associated with trivalent Er3+ ions is promoted by the formation of erbium oxide. The Er-NPs having diameters lower than 100 nm are made of Er2O3, whereas Er-NPs of larger dimensions are made of an oxidized erbium oxide matrix containing a large amount of excess Er, the concentration of which increases gradually inside the Er-NPs. The formation of this graded Er/Er2O3 core–shell structure gives rise to a decrease in the Er visible photoluminescence emission. These findings shed light on the influence of the PLAL laser fluence on both the geometry and the composition of Er-NPs, as well as its consequence on their photoemission capacity, making them relevant for easy implementation with tunable properties in advanced photonics devices.