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

Upconverting materials excited by near-infrared light are getting attention due to their biological applications in cancer treatment. Er 3+ , Yb 3+ and Nd 3+ tri-doped LiLn(WO 4 ) 2 (Ln = Y/La/Gd) phosphors were synthesized via the typical solid-state method. LiGd(WO 4 ) 2 : Er 3+ , Yb 3+ , Nd 3+ (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. Nd 3+ and Yb 3+ concentration effect on its luminescent properties and the energy transfer of Nd 3+ →Yb 3+ →Er 3+ under 785 nm excitation are discussed. The ratio of integrated intensity from the 4 S 3/2 / 2 H 11/2  →  4 I 15/2 transition of Er 3+ 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 Er 3+ . Our significant results predicate the potential applications of this lanthanum-doped tungstate in optical thermometers.