摘要：Hexagonal upconversion microcrystals of β-NaYF4were prepared through a simple, one-step, rapid, template-free and mild solvothermal synthesis method. Addition of Na2HPO4influenced crystal transition from the cubic phase to the hexagonal phase. Results showed that the phase (cubic or hexagonal) and upconversion emission intensity of NaYF4can be rationally tuned by introducing inorganic dopant ions to achieve a precisely defined molar ratio of Na2HPO4to Ln3+. SEM observations and XRD analyses helped identify fundamental considerations for crystal transition control during upconversion of NaYF4particles. Results also showed that Na2HPO4shortened the reaction time (3h) of cubic-to-hexagonal crystal transition and significantly reduced the reaction temperature (200°C) during the preparation of hexagonal phase upconversion microcrystals. © 2015 Elsevier Ltd.

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