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.