Enhancing upconversion emissions and temperature sensing properties by incorporating Mn 2+ for KLu 2 F 7 :Yb 3+ /Er 3+ nanocrystals based on thermally and non-thermally coupled levels

Pure phase KLu 2 F 7 :Yb 3+ /Er 3+ /Mn 2+ nanocrystals were obtained for which the temperature sensitivity reached up to 45.11 × 10 −3 K −1 employing non-thermally coupled levels.