Effects of Ho3+ concentration on the microstructure, photoluminescence and temperature sensing properties of ZrO2: Er3+/Yb3+/Ho3+ nanocrystals

Abstract

Optical thermometry in the second near-infrared (NIR-II) window with high tissue penetration depth has great value in biological and medical sciences. Herein, we reported the synthesis of ZrO2: Er3+/Yb3+/Ho3+ nanocrystals for temperature sensing in both NIR-II and visible regions. The effects of Ho3+ co-doping concentration on the structure, morphology, photoluminescence properties and temperature sensing behaviors of ZrO2: Er3+/Yb3+/Ho3+ were investigated in detail. X-ray diffraction and scanning electron microscopy measurements validated that the introduction of Ho3+ ions could induce the phase transition of ZrO2 from monoclinic to tetragonal phase and increase the crystalline grain size of the samples. Upon 980 nm excitation, the enhancements in both visible and near-infrared emissions were achieved via the addition of 0.05 mol%Ho3+. Meanwhile, the optical thermometry performances of the samples were found to depend on the Ho3+ concentration, when the luminescence intensity ratio of I525/I541 (LIR-1) and also that of I1463/I1224 (LIR-2) were selected for temperature sensing. For LIR-2, the maximal relative sensing sensitivity (Sr) of 2.08%K−1 was obtained for the 1%Ho3+ co-doped sample at 303 K, which was higher than many other phosphors operating in the NIR-II window. The present work may provide an effective route to develop efficient visible and NIR luminescence materials for high-performance temperature sensing.