Wide-range ratiometric upconversion luminescence thermometry based on non-thermally coupled levels of Er in high-temperature cubic phase NaYF4: Yb, Er.

Abstract

Wide-range optical thermal sensing is achieved here based on the two-photon upconversion luminescence of the high-temperature (HT) cubic phase NaYF4:Yb, Er. In the range of room temperature to 973K, the single-phase sample exhibits two bands of green and red emission with different dependences on the temperature. The CIE chromaticity diagram shows that the color point moves from deep red (0.6357, 0.3501) at room temperature to the yellow region (0.4379, 0.475) at 600K and then to the green region (0.318, 0.669) at 973K. It reveals that HT cubic phase NaYF4:Yb, Er is the promising ratiometric and colorimetric luminescent thermometer. The relative sensitivity decreases slightly up to 673K and then increases with the increasing temperature. The lattice expansion of the HT cubic phase alters the crystal symmetry around the activator ion and further increases the green-to-red emission ratio.