Effect of Li+ ion concentration on upconversion emission and temperature sensing behavior of La2O3:Er3+ phosphors

The effects of Li+ co-doping concentration on the structure, upconversion luminescence and temperature sensing behavior of Er3+:La2O3 phosphors were investigated. X-ray diffraction and scanning electron microscopy observations reveal that Li+ ion co-doping can change the lattice parameter of La2O3 host and increase the particle size of the samples. The optical investigation shows that co-doping of Li+ ions can enhance the upconversion emission of Er3+ ions in La2O3 matrix effectively. Most importantly, the temperature sensing sensitivity of the samples is found to be dependent on Li+ co-doping concentration, when the emission intensity ratio of the (2H11/2 → 4I15/2) and (4S3/2 → 4I15/2) transitions of Er3+ is chosen as the thermometric index. Both of the optimum upconversion luminescence and temperature sensing sensitivity are obtained for 7 mol% Li+ co-doped sample. When the Li+ concentration is beyond 7 mol%, both the quenching in upconversion intensity and the degradation of temperature sensitivity are observed, which may be due to the serious distortion in local crystal field around Er3+ ions caused by the excess Li+ ions.