A latest-generation fluoride with excellent structural stiffness for ultra-efficient photoluminescence and specific four-peak emission temperature sensing†
Abstract
Fluorides have garnered tremendous attention in rare-earth-doped fluorescent probes owing to their low phonon energy and excellent optical transparency. However, the latest generation of fluorides, LiYF4, is plagued by extremely complex and uncontrollable synthesis methods, which greatly restricts its further exploration and application. Herein, a straightforward one-step method for the synthesis LiYF4:Ln3+ with micron-sized cones and nano-spheres is reported. Astonishingly, self-sensitized luminescence was achieved under multi-wavelength excitation when Er3+ was singly doped. LiYF4:Yb3+,Er3+ demonstrated superior luminescence intensity to those of commercial green phosphors (NaYF4:Yb3+,Er3+); this ultra-efficient photoluminescence was confirmed from the crystal structure, electronic band properties, morphological analysis and Debye temperature calculations. Further, by constructing cross-relaxation between the Ce3+ and Er3+ ions (4I11/2 + 2F5/2 → 4I13/2 + 2F7/2), the specific four-peak emission (SFPE) intensity of Er3+ in NIR-IIb was significantly increased, further enhancing the relative sensitivity of thermally coupled temperature sensing based on SFPE. Subsequently, non-thermally coupled temperature sensing based on SFPE was also achieved through the construction of phonon-assisted energy transfer between Ho3+ 5I6 and Er3+ 4I13/2. In summary, this paper not only puts forward theoretical and experimental arguments for the use of LiYF4 to replace the conventional NaYF4, but also substantiates the extraordinary prospects of LiYF4 as a temperature-sensitive fluorescent probe in nanomedicine.