Continuous preparation of dual-mode luminescent LaPO₄:Tb³⁺,Yb³⁺ nanoparticles by reactive flash nanoprecipitation

The efficient and scalable synthesis of lanthanide-doped NPs, which exhibit down- and upconversion luminescent properties simultaneously, is still a main challenge that are hindering their adoption. Herein, we employed a facile method, i.e. reactive flash nanoprecipitation, to fabricate dual-mode luminescent lanthanide phosphate (LnPO₄) NPs: lanthanum phosphate (LaPO₄) co-doped with Tb³⁺ and Yb³⁺. The lanthanide source streams and phosphate ion source streams were efficiently mixed in a multi-inlet vortex mixer reactor, and the use of a stabilizer was found to facilitate the formation of uniformly-dispersed LnPO₄ nanocrystals. It is demonstrated that the annealed LnPO₄ NPs exhibited intense down- and upconversion emission under UV and NIR irradiation, respectively. Notably, through adjusting the LnPO₄ to stabilizer mass ratio, the NP diameter could be tuned in a range between 50 and 200 nm, and the composition of LaPO₄:Tb³⁺,Yb³⁺ NPs could be easily tuned by adjusting the flow rate ratio of the feed streams.