Hydrothermal synthesis of NaGdF₄:Yb³⁺, Er³⁺ and Na(Y, Gd)F₄:Yb³⁺, Er³⁺: size control and luminescent properties

NaGdF₄:Yb³⁺, Er³⁺ and Na(Y, Gd)F₄:Yb³⁺, Er³⁺ crystals were synthesized by hydrothermal methods. The size and luminous intensity of the particles can be adjusted by changing the temperature, time, pH value, the molar ratios of trisodium citrate to Ln³⁺ ions, F^- to Ln³⁺ ions and Gd³⁺ to Y³⁺ ions. Diffraction (XRD), photoluminescence (PL) spectra, and field emission-scanning electron microscopy (FE-SEM) were used to characterize and analysis the samples. The low pH value is found to promote the formation of GdF₃, while NaGdF₄ benefits from high pH value. The increasing of trisodium citrate content can restrain the growth of the particle to reduce the luminous intensity. The addition to the fluorine content accelerates the growth along (001) crystal orientation relative to (101) crystal orientation and further enhances luminous intensity. With the increasing of doped Y³⁺ content, particle size increases, while the luminous intensity show a trend of rising after decline first.