Optical thermometry through infrared excited green upconversion emissions of Er3+ -Yb3+ co-doped LaAlO3 phosphors
Er3+/Yb3+ single- and co-doped LaAlO3 ceramic phosphors have been synthesized by the conventional solid-state reaction method. The structural, morphological, and optical properties of (z at. %) Er: LaAlO3, (1 at.% Er), (y at.% Yb): LaAlO3, and (7 at.% Yb), (x at.% Er): LaAlO3 samples were investigated. The upconversion (UC) luminescence spectra of (Er3+, Yb3+): LaAlO3 phosphors exhibit strong green and weak red emissions under 973 nm excitation. By measuring the power dependence of the UC emission intensity, it was shown that the 4S3/2, 2H11/2, and 4F9/2 levels responsible for the green and red emissions, respectively, are populated by two-photon processes. The luminescence decay of the 4S3/2 (Er3+) level was analyzed. The luminescence intensity ratio (LIR) temperature dependence for the thermally coupled levels (2H11/2 and 4S3/2) of Er3+ ions in (1 at. % Er, 7 at. % Yb): LaAlO3 sample was calculated and the variations of absolute thermal sensitivity (Sa) and relative thermal sensitivity (Sr) with temperature were determined. The maximum values obtained for the Sr and Sa parameters were Sr = 2.44% K−1 at 175 K and Sa = 0.0048 K−1 at 400 K. The results show that (Er3+, Yb3+): LaAlO3 ceramic phosphors are suitable upconverting materials for green display devices and present great potential as non-contact optical temperature sensors.