Up-conversion luminescence, temperature sensing properties and laser-induced heating effect of Er3+/Yb3+ co-doped YNbO4 phosphors under 1550 nm excitation

YNbO4 phosphors with various Er3+ and Yb3+ concentrations were synthesized via a traditional high-temperature solid-state reaction method. Their crystal structure was investigated by means of X-ray diffraction (XRD) and Rietveld refinements, and it was confirmed that the obtained samples exist in monoclinic phase. The Er3+ and Yb3+ concentration-dependent up-conversion (UC) luminescence was studied under 1550 nm excitation. By inspecting the dependence of UC intensity on the laser working current, it was found that four-photon and three-photon population processes were co-existent for generating the green UC emissions in the samples with higher Yb3+ concentrations. In addition, it was observed that the temperature sensing properties of YNbO4:Er3+/Yb3+ phosphors were sensitive to both Er3+ and Yb3+ doping concentrations. Furthermore, based on the obtained temperature response of the UC luminescence phosphors, 1550 nm laser-irradiation-induced thermal effect was studied, and it was discovered that the sample temperature was very sensitive to the doping concentrations of Er3+ and Yb3+ and the excitation power.