One-step surfactant-free controllable synthesis and tunable up-conversion/down-shifting white light emissions of Sr2YF7 crystals doped with Ln3+ ions

Abstract

In this work, uniform and monodisperse Sr₂YF₇ spheres were successfully synthesized via a facile one-step hydrothermal route without employing any surfactant. Particularly, a well-defined morphology of Sr₂YF₇ crystals ranging from spherical to octahedral shape was first achieved by adjusting the pH values. In addition, the spherical products doped with 6% Ln³⁺ (Ln = La, Ce, Pr, Sm, Gd, and Dy) show different sizes ranging from 300 to 600 nm. The Sr₂YF₇ crystals also exhibit excellent multicolor DS/UC luminescence properties after doping with different Ln³⁺ ions. Energy transfer from Tb³⁺ to Eu³⁺ was observed in Sr₂YF₇ crystals; the Sr₂YF₇:Dy³⁺ crystals showed nearly white light emission under UV excitation; Sr₂YF₇:Yb³⁺/Er³⁺/Tm³⁺ crystals could produce pure white light with a CIE color coordinate of (0.3123, 0.3005) by controlling the doping concentrations of Er³⁺ and Tm³⁺ ions under 980 nm excitation. The as-prepared phosphors may potentially serve as light, color displays and markers in biological imaging.