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

Abstract

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 4F9/2 → 4I15/2 and 4S3/2 → 4I15/2 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: 4F9/2 → 4I15/2 transition follows a continuous decrease as a function of temperature, while 4S3/2 → 4I15/2 and 2H11/2 → 4I15/2 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.