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

NaGdF4 nanocrystals of the hexagonal beta-phase can be prepared with very narrow size distribution from small particles of the cubic alpha-phase of NaGdF4, but until now, this method does not allow to control the final particle size. Here we show that the size of beta-NaGdF4 particles can be varied between 4 nm and more than 60 nm by using small alpha-phase particles with different sodium content as precursor. Heating of the 34 nm alpha-phase particles dispersed in oleic acid/octadecene solvent leads to Ostwald-ripening and the formation of beta-NaGdF4 particles with narrow size distribution in all cases. The size of the beta-NaGdF4 particles increases with increasing sodium deficiency of the alpha-phase particles indicating that the number of beta-phase seeds nucleating in the system depends on the ratio of sodium to gadolinium used in the synthesis of the alpha-phase material.