Upconversion luminescence properties and thermal quenching mechanisms in the layered perovskite La1.9Er0.1Ti2O7 towards an application as optical temperature sensor

The structural evolution between the monoclinic (layered-perovskite) and cubic (pyrochlore) structures is studied for the complete series of La2-xErxTi2O7 synthetized by solid-state reaction. A partial solid solution with layered perovskite structure is achieved until x = 0.10. The luminescence properties of these oxides show a low quantum efficiency and the concentration quenching is observed for x = 0.10. However, La1.9Er0.1Ti2O7 oxide exhibits interesting UpConversion (UC) properties at multiple excitation wavelengths (784, 808 and 980 nm). Laser power studies have demonstrated a two-photon upconversion process for 808 and 980 nm excitations. Moreover, the measurement of the lifetimes on the F-4(9/2) -> I-4(15/2) and S-4(3/2) -> I-4(15/2) transitions makes it possible to identify an Energy Transfer (ET) mechanism. The thermal effect on upconversion properties is also studied under 808 nm excitation. The UC intensity shows atypical evolutions: F-4(9/2) -> I-4(15/2) transition follows a continuous decrease as a function of temperature, while S-4(3/2) -> I-4(15/2) and H-2(11/2) -> I-4(15/2) transitions reach maxima at 150 and 450 K, respectively. The calculation of temperature dependent Fluorescence Intensity Ratio and CIE 1931 color coordinates indicated that La1.9Er0.1Ti2O7 oxide could serve as a temperature sensor. (C) 2018 Elsevier B.V. All rights reserved.