Upconversion luminescence and temperature sensing of Dy3+ and Yb3+ codoped Bi2WO6 powder in aqueous environments

Abstract

x%Dy3+, y%Yb3+: Bi2WO6 (x=0.5, 1, 3, 5; y=1, 6, 10, 15) upconversion luminescent powders were prepared using a high-temperature solid-phase method. X-ray diffraction experiments revealed that moderate amounts of Dy3+ and Yb3+ doping essentially did not affect the orthorhombic crystal system structure of the Bi2WO6 matrix materials. SEM photos and EDS granularity analysis showed that the particles size of the synthesized 0.5% Dy3+, 10% Yb3+: Bi2WO6 powder was between 0.5-6 μm, and SEM mapping and EDS energy spectra revealed that all the elements were better distributed in the sample. Under 980 nm excitation, the upconversion luminescence of Dy3+ in the powder was the strongest when the molar fractions of Dy3+ and Yb3+ were 0.5% and 10%, respectively. From 10 mW to 100 mW, the emission light intensity I and the excitation power Pn of Dy3+ in this sample were linear. The absorbed photon numbers n were 2.63 and 2.65, as calculated from the 546 nm and 660 nm emission peaks of Dy3+ in this excitation power range, which indicated that the above two emissions originated from three-photon absorption. Under 980 nm excitation (100 mW), the 660 nm/546 nm fluorescence intensity ratio of the 0.5% Dy3+, 10% Yb3+: Bi2WO6 powder was used to characterize the temperature, the relative thermometry sensitivity Sr was obtained with a maximum of 0.0151 K-1 (423 K), and the minimum temperature resolution was 0.58 K. Chromaticity coordinates revealed that the luminescence of this powder shifted from the green to the yellow region first and then gradually to the red region as the temperature increased. This result indicated that the powder sample synthesized in this work has potential applications in thermochromic optical anticounterfeiting. Under 980 nm excitation (380 mW), for the 60.7 NTU sample in an aqueous environment, from 331 K to 298 K, the temperature was characterized by the fluorescence intensity ratio of 660 nm /546 nm. The obtained maximum Sr was 0.0868 K-1 (323 K), and the minimum temperature resolution was 3.03 K.