Enhancing upconversion emissions and temperature sensing properties by incorporating Mn2+ for KLu2F7:Yb3+/Er3+ nanocrystals based on thermally and non-thermally coupled levels†
Abstract
Upconversion (UC) nanocrystal phosphors have received increasing attention for designing optical temperature sensors. Developing an efficient UC phosphor with superior temperature sensing properties remains a challenging task. Herein, we report dual-emitting and thermochromic Mn2+ co-doped KLu2F7:Yb3+/Er3+ nanocrystals, synthesized by a modified hydrothermal method. The marked influence of Mn2+ on the UC luminescence and thermal sensing performances of the KLu2F7:Yb3+/Er3+ nanocrystals was shown. The introduction of Mn2+ into the KLu2F7:Yb3+/Er3+ nanocrystals resulted in a slight change in crystal structure and morphology. The Mn2+ ions were shown to improve the UC emission, which might be attributed to the distortion of the local symmetry. Moreover, the optical temperature sensing properties of the nanocrystals were investigated. Based on the fluorescence intensity ratio of the thermally coupled levels and non-thermally coupled levels corresponding to the Arrhenius equation, the thermal sensing behavior of KLu2F7:Yb3+/Er3+ and KLu2F7:Yb3+/Er3+/Mn2+ was studied in the range of 303–543 K. Compared with the previous study, the KLu2F7:Yb3+/Er3+/Mn2+ nanocrystals exhibited outstanding temperature sensing properties based on non-thermally coupled levels. This study not only discussed the influence of Mn2+ doping on KLu2F7:Yb3+/Er3+ nanocrystals working as nanothermometers, but also provided a general approach to enhance the properties of optical temperature sensors by introducing non-thermally coupled levels.