Effect of the crystal structure of small precursor particles on the growth of beta-NaREF4 (RE = Sm, Eu, Gd, Tb) nanocrystals

Abstract

The origin of the narrow particle size distributions obtained in the oleic acid-based synthesis of hexagonal phase beta-NaREF4 nanocrystals (RE = Sm, Eu, Gd, Tb) has been investigated. Compared to the standard synthesis, the growth conditions were simplified by using small purified particles of either alpha-NaREF4 (cubic phase) or beta-NaREF4 (hexagonal phase) as single-source precursors, thereby avoiding the complications arising from the simultaneous presence of molecular educts and intermediately formed small particles. The study shows that alpha-phase as well as beta-phase particles grow by Ostwald-ripening but narrow particle size distributions of the beta-NaREF4 product particles are only obtained when alpha-phase precursor particles are employed. Since the small particles are also formed as intermediate products in the standard synthesis of beta-NaSmF4, beta-NaEuF4, beta-NaGdF4 and beta-NaTbF4 particles, their crystal phase is an important parameter to obtain a narrow size distribution in these systems.