Hydrothermal synthesis of SrF2:Yb3+/Er3+ micro-/nanocrystals with multiform morphologies and upconversion properties

Micro- and nanocrystals cubic-phase SrF2:Yb3+/Er3+ upconversion luminescence phosphors were synthesized via a facile hydrothermal route in the presence of different surfactants. The samples were characterized with X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and upconversion emission spectra. As-prepared products showed a variety of morphologies, such as cubic-shaped microcrystal, hierarchical structure microspheres, spherical-shaped nanocrystals and nanosheets. The intrinsic structural feature of cubic-phase SrF2 and two important external factors, namely, the surfactants in the reaction solution and fluoride sources, were responsible for shape determination of SrF2:Yb3+/Er3+. The possible formation mechanisms for products with various architectures were presented. A systematic study on the photoluminescence of Yb3+/Er3+-doped SrF2 samples with cubic shape, microspheres, spherical and nanosheets shapes showed that the optical properties of these products were strongly dependent on their morphologies and size.