Upconversion luminescence and temperature sensing properties in LiGd(WO4)2: Er3+, Yb3+, Nd3+ microparticles under 785 nm excitation

Abstract Upconverting materials excited by near-infrared light are getting attention due to their biological applications in cancer treatment. Er3+, Yb3+ and Nd3+ tri-doped LiLn(WO4)2 (Ln = Y/La/Gd) phosphors were synthesized via the typical solid-state method. LiGd(WO4)2: Er3+, Yb3+, Nd3+ (LGW) phosphors exhibit the most intense green emission under 785 nm excitation among the three doped host materials, which is ascribed to their lowest phonon density and the strong absorption properties. Nd3+ and Yb3+ concentration effect on its luminescent properties and the energy transfer of Nd3+→Yb3+→Er3+ under 785 nm excitation are discussed. The ratio of integrated intensity from the 4S3/2/2H11/2 → 4I15/2 transition of Er3+ is characteristic of the optical temperature sensing based on fluorescence intensity ratio (FIR). LGW shows high absolute sensitivity about 0.0070 K−1 at 439 K and broad temperature sensing ranging from 200 K to 600 K under the excitation of 785 nm compared with systems doped with Er3+. Our significant results predicate the potential applications of this lanthanum-doped tungstate in optical thermometers.