Abstract
The hot-injection approach has been intensively studied for the synthesis of nanocrystals formed in one-stage nucleation and growth. In the present study, we evaluated the application of hot injection in the preparation of hexagonal-phase NaYF4:Yb,Er nanocrystals, which is different in that it contains two stages: formation of cubic phase and consequent hexagonal phase. We found that when oleylamine was used as both solvent and ligand, the injecting temperature dictates the nucleation rate of cubic phase. Comparing with the classical heating-up approach, the phase transformation was accelerated. Following the same mechanism, in the mixed solvent of oleic acid (OA), trioctylphosphine (TOP), and octadecene, the size and shape of nanocrystals can be simultaneously adjusted. Especially, continuous change of aspect ratio of rodlike hexagonal-phase NaYF4:Yb,Er nanocrystals was observed and was ascribed to the kinetic balance between OA-TOP coupling and the phase transformation. Our results showed that kinetically adjusting the cubic-to-hexagonal phase transformation of NaYF4:Yb,Er nanocrystals is of great importance for size and shape optimization, and the hot-injection approach provides more synthetic possibilities for the nanocrystals formed with a phase transformation process.
Published Version
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