Temperature dependent upconversion properties of Yb3+:Ho3+ co-doped Gd2O3 nanoparticles prepared by pulsed laser ablation in water

Yb3+:Ho3+ co-doped Gd2O3 nanoparticles were successfully synthesized by pulsed laser ablation in water under different laser energy. The phase structure, morphology, crystallization and upconversion photoluminescence properties of obtained samples were investigated using X-Ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and photoluminescence spectra. The mechanism of the upconversion process was discussed based on the energy level diagram and power dependent upconversion emission. Upconversion mechanisms and thermal effects caused by absorption of excitation laser were discussed. Temperature dependent green and red emissions of Yb3+:Ho3+ co-doped Gd2O3 nanoparticles under the excitation of 980 nm were investigated in the low temperature range of 130 K-280 K. Non-radiative decay rate theory was used to explain the difference of quenching rates of green and red emissions. A further study on temperature sensing properties based on fluorescence intensity ratio (FIR) of green and red emissions was carried out. The FIR as a function of temperature can be well fitted by the model based on the thermal quenching theory. The relative sensitivity reaches its maximum value of 0.804% K-1 at 216 K.