Size Control of Nearly Monodisperse β‑NaGdF₄ Particles Prepared from Small α‑NaGdF₄ Nanocrystals

NaGdF₄ nanocrystals of the hexagonal β-phase can be prepared with very narrow size distribution from small particles of the cubic α-phase of NaGdF₄, but until now, this method does not allow to control the final particle size. Here we show that the size of β-NaGdF₄ particles can be varied between 4 nm and more than 60 nm by using small α-phase particles with different sodium content as precursor. Heating of the 3–4 nm α-phase particles dispersed in oleic acid/octadecene solvent leads to Ostwald-ripening and the formation of β-NaGdF₄ particles with narrow size distribution in all cases. The size of the β-NaGdF₄ particles increases with increasing sodium deficiency of the α-phase particles indicating that the number of β-phase seeds nucleating in the system depends on the ratio of sodium to gadolinium used in the synthesis of the α-phase material