Cs+-Assisted Synthesis of NaLaF4 Nanoparticles

NaLaF4 has been proposed as an efficient host for luminescent materials due to its low phonon energy. However, chemical synthesis of pure NaLaF4 nanoparticles with high crystallinity and uniform size has not been fully addressed. Herein, we demonstrate a strategy for controlled synthesis of NaLaF4 nanoparticles through Cs+-assisted co-precipitation in a binary solvent mixture of oleic acid and 1-octadecene. Mechanistic investigation reveals that the presence of Cs+ promotes deprotonation of oleic acid, which contributes to stabilization of NaLaF4 nanoparticles against decomposition into LaF3, Na-oleate, and HF in an acidic environment. Compared to a typical NaYF4 host, NaLaF4 nanoparticles provide stronger near-infrared (NIR) emissions for Nd3+ dopants in aqueous solution under 808 nm excitation, which substantiates the promise of NaLaF4 for constructing efficient luminescent materials for bioimaging and sensing applications.