In recent years, optical thermometry based on inorganic nanomaterials has demonstrated significant application potential in biomedical temperature sensing due to its high sensitivity, non-contact measurement capability, and excellent biocompatibility. Compared with a single temperature sensing mode, the development of a multi-mode optical temperature sensing strategy is expected to significantly improve the accuracy and reliability of temperature detection, which has become an important research direction in this field. In this work, a series of CaF₂:Mn²⁺ nanoparticles with particle size of about 10~20 nm have been successfully prepared through a solvothermal approach. In order to further reveal the structure-activity relationship of CaF₂:Mn²⁺, its structural composition and microscopic morphology were systematically characterized by X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy. The luminescence properties and temperature-dependent response behavior of CaF₂:Mn²⁺ were explored in detail by spectroscopic analysis. On this basis, the potential application prospects of the material in the field of optical temperature sensing are further discussed. The experimental results demonstrate that the nanoparticles exhibit significant temperature-dependent characteristics in luminescence intensity, emission peak position, and fluorescence lifetime. Further investigation revealed that the CaF₂:Mn²⁺ nanoparticles exhibited characteristic emission from Mn²⁺-Mn²⁺ dimers (680~950 nm) within the first near-infrared biological window (650~950 nm), and showed stronger thermal quenching effects compared to Mn²⁺ ions. Based on these experimental results, we have established a multimodal optical temperature sensing strategy utilizing CaF₂:Mn²⁺ nanoparticles. Among these, the temperature sensing models based on luminescence intensity of the Mn²⁺-Mn²⁺ dimer, the luminescence intensity ratio (Mn²⁺ ions / Mn²⁺-Mn²⁺ dimer), and the lifetime of the Mn²⁺-Mn²⁺ dimer demonstrate optimal temperature sensing performance within the physiological temperature range (300~330 K). Corresponding relative sensitivities are 2.82%•K⁻¹ (330 K), 0.79%•K⁻¹ (305 K), and 0.65%•K⁻¹ (330 K), respectively, providing a reliable multi-mode measurement scheme for biological thermometry. This study not only confirms the application potential of CaF₂:Mn²⁺ nanoparticles in the field of biological temperature sensing, but also provides important theoretical references and experimental basis for the development of novel high-sensitivity biothermometry probes.

Key words: CaF₂:Mn²⁺ nanoparticles, Mn²⁺-Mn²⁺ dimers, luminescence intensity ratio, biothermometry, multimodal thermometry