Ostwald Ripening, Particle Size Focusing, and Decomposition of Sub-10 nm NaREF4 (RE = La, Ce, Pr, Nd) Nanocrystals

Abstract

NaREF4 nanocrystals of the lighter rare earth elements RE = La, Ce, Pr, Nd are more difficult to prepare than those of the heavier lanthanides because the materials are sensitive to decomposition. Here, we present a procedure for the synthesis of sub-10 nm particles of β-NaLaF4, β-NaCeF4, β-NaPrF4, and β-NaNdF4, as well as of α-NaCeF4, α-NaPrF4, and α-NaNdF4. These particles were used to study the decomposition reaction taking place in the standard oleic acid/octadecene solvent. Ostwald ripening of the β-phase particles in this solvent leads to the expected particle growth and broadening of the particle size distribution only in the case of RE = Ce, Pr, Nd, whereas particles of NaLaF4 decompose to LaF3. Ostwald ripening of the α-phase particles in oleic acid/octadecene yields two products: larger particles of the hexagonal β-phase with a very narrow size distribution and smaller particles of the rare earth trifluoride REF3. The yield of the nearly monodisperse β-NaREF4 particles decreases from Nd to Ce an...