Nanoparticles have attracted much attention due to their unique properties, not only for fundamental research but also for industrial applications.
A significant number of methods have been proposed for the synthesis of nanoparticles, including co-precipitation methods, sol-gel methods, solvothermal processes. Most of these methods rely on chemical synthesis, the so-called bottom-up, whereby ionic molecules are reduced to form nuclei that will grow until they reach the desired nanometric size. Such bottom-up methods typically allow narrow size distributions and can, in some cases, be scaled up to industrial volumes. However, one of their drawbacks lies in the fact that they are material-dependent as the synthesis protocol will change completely depending on whether metallic, organic or inorganic NPs are to be produced. These methods most often rely on the use of surfactants to stabilize the produced NPs, which can act as contaminants for the ultimate use of the NP solutions or even cause toxicity issues when the NPs are used for biological or medical applications.
Another synthesis method that is gaining ground for NP production is pulsed laser ablation in liquids (PLAL). This method relies on a top-down process whereby the laser is used to fragment a solid substrate of macroscopic size down to nano-sized objects.This method has been reported to produce stable NPs in various solutions without the need for additional chemicals, making them more compatible with biomedical applications. Another advantage of PLAL lies in its simplicity. Furthermore, PLAL can be implemented to produce NPs of different nature and from different materials with more or less the same protocol. There have been a number of reports where PLAL was used to generate NPs in different categories of materials, predominantly metals, mainly gold and silver, as well as polymers, semiconductors, oxides, etc.
ALPhANOV created for the first time to our knowledge upconverting phosphor nanoparticules via PLAL. As opposed to more conventional downconversion luminescent materials, up-converting nanophosphors absorb two or more low-energy photons to emit a higher-energy photon. In particular, infrared-to-visible upconversion materials hold strong potential for fluorescent labeling and bio-marking.