One-dimensional hexagonal-phase NaYF4: Controlled synthesis, self-assembly, and morphology-dependent up-conversion luminescence properties

One-dimensional (1D) hexagonal-phase NaYF4 with various morphologies including nanowires, nanowire bundles, submicrorods, and hexagonal microprisms have been selectively synthesized via a facile complexing reagent-surfactant-assisted hydrothermal route. The effects of reaction temperature, the amount of SDBS (sodium dodecylbenzenesulfonate) and citric acid, and the sorts of surfactants and complexing reagents on the morphology, size, and crystal phase purity of the as-synthesized products have been investigated in detail. By choosing NaYF4 nanowire as a candidate, its formation mechanism was proposed on the basis of XRD analysis and SEM observation of the products at the different reaction time periods. The studies on the up-conversion emission of hexagonal-phase Yb3+, Er3+ ions-codoped NaYF4 including nanowires, submicrorods, and hexagonal microprisms showed that the optical properties of the as-synthesized materials are morphology-dependent. It was found that NaYF4 : Yb, Er nanowires had the highest ratios between the intensities of green and red band emission whereas hexagonal NaYF4 : Yb, Er microprisms had the lowest ones. The synthesis of hexagonal-phase NaYF4 with controllable size and morphology, optical properties, together with the realization of self-assembly of NaYF4 nanowires reported in this work will be useful for further applications in the fabrication of optoelectronic nanodevices.