Hydrothermal synthesis of BaYF5:Yb3+/Er3+ upconversion luminescence submicrospheres by a surfactant-free aqueous solution route

► BaYF5:Yb3+/Er3+ upconversion luminescence submicrospheres have been first prepared in this paper. ► The size and shape of BaYF5:Yb3+/Er3+ were controlled by adjusting the fluoride sources, temperature and reaction time. ► A systematic study on the photoluminescence of Yb3+/Er3+-doped BaYF5 samples with different size and shapes has shown that the optical properties of products are strongly dependent on their size.