Synthesis and luminescence properties of green-to-red color-tunable upconverting K2Gd(PO4)(WO4):Yb3+,Tb3+,Eu3+ phosphors

Scientists are increasingly interested in new inorganic luminescence materials that could be excited with near-infrared (NIR) radiation. These materials can be used as luminescent thermometers, bio-imaging agents, anti-counterfeiting pigments, etc. In this manuscript, we report the synthesis and investigation of optical properties of two series of K2Gd(PO4)(WO4):20%Tb3+ (KGPW): the first, KGPW:20%Tb3+ doped with 1–20% Eu3+, and the second, KGPW:10%Yb3+,20%Tb3+ doped with 1–20% Eu3+. The phase-pure specimens were prepared using a solid-state synthesis method. Down-shifting and upconversion luminescence studies have been performed using 340 and 980 nm excitation, respectively. For upconversion emission luminescence, Yb3+ ions were used as sensitizers in the KGPW phosphors. In these phosphors, Yb3+ ions absorb the 980 nm radiation and transfer the energy to Tb3+ ions. At his point, Tb3+ ions either emit themselves or transfer part or all of their energy to Eu3+ ions. It was observed that the emission color of the synthesized phosphors could be successfully tuned from the green to red by varying the Tb/Eu concentration ratio regardless of the 340 or 980 nm excitation. Such color change proves that one luminescent material (KGPW) can provide three colors (i.e., green, orange, and red). Herein, the optical properties, such as reflection, down-shifting excitation and emission spectra, upconversion emission spectra, fluorescence lifetime, thermal quenching, color coordinates, and quantum efficiency, were studied using steady-state and kinetic spectroscopy