Effect of the crystal structure of small precursor particles on the growth of β-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 β-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 α-NaREF₄ (cubic phase) or β-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 α-phase as well as β-phase particles grow by Ostwald-ripening but narrow particle size distributions of the β-NaREF₄ product particles are only obtained when α-phase precursor particles are employed. Since the small particles are also formed as intermediate products in the standard synthesis of β-NaSmF₄, β-NaEuF₄, β-NaGdF₄ and β-NaTbF₄ particles, their crystal phase is an important parameter to obtain a narrow size distribution in these systems.