Optical temperature sensing behavior of Er3+/Yb3+/Tm3+:Y2O3 nanoparticles based on thermally and non-thermally coupled levels

Er3+/Yb3+/Tm3+ triply doped Y2O3 nanoparticles have been synthesized by solute combustion method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) demonstrate that the prepared particles are cubic Y2O3 phase with the average size of ∼49 nm. The blue (Tm3+: 1G4→3H6), green (Er3+: 2H11∕2, 4S3∕2→4I15∕2) and red (Er3+: 4F9∕2→4I15∕2) upconversion (UC) emissions are observed upon a 980 nm excitation. Applying the fluorescence intensity ratio (FIR) technique, the optical temperature sensing behaviors are studied based on thermally coupled levels (2H11∕2 and 4S3∕2 of Er3+) and non-thermally coupled levels (1G4(b) (Tm3+) and 2H11∕2 (Er3+)), respectively. The results show that the absolute sensing sensitivity is much higher in the entire experimental temperature range, when the non-thermally coupled levels with different temperature dependences (1G4(b) (Tm3+) and 2H11∕2 (Er3+)) are selected as the thermometric index. The maximum absolute sensitivity is found to be as high as ∼1640×10−4 K−1 at 573 K. This demonstrates that an optical temperature sensor with high performance can be designed based on the Er3+/Yb3+/Tm3+:Y2O3 nanoparticles.