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 (⁴I_11/2 + ²F_5/2 → ⁴I_13/2 + ²F_7/2), 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 Ho^{3+ 5}I₆ and Er^{3+ 4}I_13/2. 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.