Yb3+-concentration-dependent upconversion luminescence of Ho3+-Yb3+ codoped La9.31(Si1.04O4)6O2 for optical thermometer

A series of La9.31(1-x)(Si1.04O4)(6)O-2:1%Ho3+,xYb(3+) (LS:1%Ho3+,xYb(3+), 0 <= x <= 20%) phosphors were synthesized by a solid-state reaction process. The structure and morphology of the samples were investigated by XRD, SEM, TEM, etc. Under the excitation of 980 nm, the LS:Ho3+,Yb3+ exhibited strong red emission and weak green emission. The intensities of the two UC emissions varied differently with the increase of Yb3+ concentration, which was interpreted by possible cross-relaxations. And, the cross-relaxation processes were verified from the decreasing decay lifetimes of Ho3+ with the increase of Yb3+ concentration. Importantly, based on the fluorescence intensity ratio (FIR) technique, the temperature sensing properties in the system were characterized in the temperature range of 283-523 K. The different change rates of the green and red emission intensities with temperature were explained by using the decay lifetimes at various temperature. The S-A value of LS:1% Ho3+,10%Yb3+ reached 0.0551 K--(1) in the wide temperature range from 298 to 548 K. The above investigation results indicated that the LS:Ho3+,Yb3+ phosphors may be potential candidates for optical temperature sensor.