Effect of dopant contents on upconversion luminescence and temperature sensing behavior in Ca3La6Si6O24:Yb3+-Er3+/Ho3+ phosphors

At present, improving the sensitivity is one main object for optical temperature sensing. In this work, a series of Yb3+-Er3+ and Yb3+-Ho3+ doped Ca3La6Si6O24 (CLS) phosphors were designed by solid-state reaction method to develop new rare earth (RE) ions activated upconversion luminescence materials based on thermally coupled and non-thermally coupled levels of Er3+/Ho3+. For the CLS:0.6Yb3+,xEr3+ (0.03 ≤ x ≤ 0.18) and CLS:yYb3+,0.03Er3+ (0.3 ≤ y ≤ 1.2) samples, the relative intensities of Er3+ different emission peaks change with the RE ions concentrations, which was interpreted by the proposed cross-relaxation (CR) processes. For the CLS:0.6Yb3+,mHo3+ (0.03 ≤ m ≤ 0.18) and CLS:nYb3+,0.03Ho3+ (0.3 ≤ n ≤ 1.2) samples, the 5F5-5I8 transition intensity of Ho3+ shows a continuous decrease with increasing Yb3+ or Ho3+ concentrations by normalizing the (5F4,5S2)-5I8 transition of Ho3+, which was explained by the CR between Yb3+ and Ho3+. The temperature dependence of the fluorescence intensity ratio for Er3+ and Ho3+ emissions was discussed in detail. The relative and absolute sensitivities were compared by using thermally coupled and non-thermally coupled levels of Er3+ and Ho3+. The present investigation could be instructive to develop new luminescent materials with high sensitivity.