A HIGHLY REPRODUCIBLE AND SCALABLE APPROACH TO THE SYNTHESIS OF MULTISHELL SODIUM-HEAVY RARE EARTH FLUORIDE NANOPARTICLES WITH AN OPTIMIZED CATIONIC COMPOSITION

The mass synthesis of heavy REE-based β-NaY0.5F4:Gd0.5@β-NaLnF4:Yb/X @β-Na(Y, Lu)F4 (Ln = Y, Yb, Lu; X = Er, Tm) nanoparticles via nanoseed-mediated heterogeneous crystallization, ensuring the fabrication of objects with a required morphology, crystal structure and photoluminescent properties, is presented. The optimal experimental parameters (x(Gd3+) = 0.5 and t = 15 min) for the synthesis of ultrafine (3–4 nm) hexagonal β-NaYF4:Gd (x = 0 ÷ 0.5) nanoseeds by high-temperature co-precipitation of acetate precursors in organic solvents were determined. The heterogeneous crystallization method was successfully applied to produce monodisperse β-NaY0.5F4:Gd0.5@β-NaLnF4:Yb/X@β-Na(Y, Lu)F4 (Ln = Y, Yb, Lu; X = Er, Tm) nanoparticles with the “nanoseed @ active core @ inert shell” structure in the size range from 10 to 60 nm, which was confirmed by XRD and TEM analysis. Nanoparticles with the active β-NaYbF4:Tm core demonstrate the best photoluminescence performance in the UV (λ = 364 nm) and visible (λ = 452 nm) spectral regions, exceeding the values of lutetium (by 3.4 and 3.9 times) and yttrium (by 7.6 and 9.3 times) counterparts. The heavy REE-based β-NaY0.5F4:Gd0.5@β-Na(Yb, Lu)F4:Yb/Er@β-NaLuF4 nanoparticles exhibit the most efficient up- and down-conversion photoluminescence in the visible and NIR ranges upon excitation at λ = 978 nm. The proposed method was utilized for large-scale synthesis of heavy REE-based β-NaY0.5F4:Gd0.5@β-NaYbF4:Tm@β-NaLuF4 nanoparticles with optimized cationic composition up to 80 g per production cycle which will facilitate their practical implementation in photonics and biotechnology.