Upconversion luminescence of Ca2Gd8(SiO4)6O2:Yb3+-Tm3+-Tb3+/Eu3+ phosphors for optical temperature sensing

Abstract

In order to develop new upconversion (UC) phosphors for optical temperature sensors, a series of Yb3+-Tm3+-Tb3+/Eu3+ doped Ca2Gd8(SiO4)6O2 (CGS) samples were designed by solid-state reaction method. The phase purity was examined by XRD patterns, which revealed that the obtained samples are all single-phase in spite of the rare earth (RE) ions doping. Upon 980 nm excitation, the emission peaks of all the doped luminescent ions (Tm3+, Tb3+ and Eu3+) have been observed, and the energy transfer processes among the RE ions in the UC luminescence were discussed with the help of the energy level diagram and decay curves. The competitive absorption between Tm3+ and Tb3+/Eu3+ from Yb3+ was proposed to interpret the sharp decrease of Tm3+ emission intensity. The temperature sensing behavior was evaluated by measuring the temperature-dependent UC luminescence of the typical CGS:10%Yb3+,0.2%Tm3+,10%Tb3+,1.25%Eu3+ phosphor. It has been found that the fluorescence intensity ratio (FIR) technique by employing ITb/IEu and ITb/ITm can generate high absolute sensitivity, but the relative sensitivity still needs further improvement compared with some other phosphors doped with Er3+/Ho3+/Tm3+.