Pulsed laser ablation in liquid (PLAL) is nowadays gaining popularity as innovative, reliable and efficient technique to produce high-purity nanoparticles (NPs) of many inorganic and organic materials. In this context, attention has been recently focused on luminescent up-conversion NPs (UCNPs) which, being characterized by sharp emission bands in ultraviolet (UV)-to-near-infrared (NIR) range upon NIR irradiation, are in fact of great interest in many biological and biomedical applications. Moreover, with respect to organic dyes NPs and quantum dots, UCNPs show less toxicity, increased chemical stability, long-lifetime decays and lack of photo-bleaching. Our research focuses on generation of UCNPs of rare earth lanthanide-doped crystalline material, namely 18%Yb:1%Er:NAYF4, by PLAL in water. It is well known that optical properties of NPs strongly depend on their features, as for instance size and shape, which in turn may be controlled by laser ablation parameters. Therefore, two different laser sources are used for the ablation processes in order to find the set of laser parameter, i.e. pulse duration, laser fluence and repetition rate, for which the luminescence of UPNPs is optimized: (i) Amplitude Satsuma HP3 system: 330 fs pulse duration, 1030 wavelength and (ii) Eolite Hegoa system: 50 ps pulse duration, 1030 nm wavelength. UCNPs are finally characterized by spectrophotometer analyses to define emission range and intensity under NIR light and by transmission electron microscopy (TEM) to determine their size and shape.