Self-Assembled Three-Dimensional Architectures of Y2-(WO4)3:Eu: Controlled Synthesis, Growth Mechanism, and Shape-Dependent Luminescence Properties

Monoclinic Y-2(WO4)(3):Eu with three-dimensional hierarchical architectures were successfully synthesized by a hydrothermal method in ligand-free and chelating ligand-mediated processes, respectively. Microflowers assembled from two-dimensional nanoflakes were obtained in a surfactant- and template-free process, whereas microspheres with dandelion-like appearance assembled from one-dimensional nanoplates were observed upon the introduction of the appropriate amount of ethylenediamine tetraacetic acid (EDTA) to the precursor. X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED), energy-dispersive spectra (EDS), and photoluminescence (PL) spectroscopy were employed to characterize the as-obtained products. It was found that the amount of ligand agent, reaction temperature and time, and type of organic additive have crucial influences on the morphology of the resulting microstructures. The possible formation mechanisms for different microstructures were put forward. The addition of EDTA significantly changed the reaction pathway due to the excellent chelating and capping ability of EDTA. A detailed investigation on the photoluminescence of Y-2(WO4)(3):Eu samples with flower-like, dandelion-like, and spindle microstructures indicates that the optical properties of these phosphors are strongly dependent on the morphology and size. The dandelion-like structure exhibits the strongest red emission with high color purity,