The thermo-optic relevance of Ho3+ in fluoride microcrystals embedded in electrospun fibers

Abstract

Na(Y_1−x−yHo_xYb_y)F₄/PAN (NYF-HY/PAN) composite fibers were synthesized using an electrospinning method, and the sub-micron crystals embedded in the fibers had complete hexagonal crystal structures. Under 977 nm laser excitation, strong green and red up-conversion (UC) emission that originated from flexible fibers were due to the radiative transitions (⁵F₄, ⁵S₂) → ⁵I₈ and ⁵F₅ → ⁵I₈ of Ho³⁺, respectively. The effective green fluorescence emission (539 and 548 nm) can be applied to micro-domain non-contact temperature measurements, realizing rapid and dynamic temperature acquisition in a complex environment without destroying the temperature field. In the temperature range of 313–393 K, the absolute and relative sensitivity of the fibers are 0.00373 K⁻¹ and 0.723% K⁻¹, respectively, which indicates that the NYF-HY/PAN composite fibers have good thermal sensitivity. Composite fibers in which crystallites are embedded have superior properties, with great stability, high sensitivity, and excellent flexibility, providing a reliable reference for developing temperature-sensing materials for the biomedical field.