Synchronous realization of green upconversion emission enhancement and optical temperature sensitivity improvement in phosphors NaYF4: Yb, Ho via Mn doping

In this paper, highly fluorescent, structurally homogeneous, and small-sized NaYF 4 upconversion nanoparticles were synthesized via the hydrothermal method, Yb/Ho/Mn co-doping altered the local symmetry of the crystals, slightly deforming their structure and enhancing the fluorescence intensity of the nanocrystals. The strong green light emission from the synthesized samples was mechanistically explained by energy transfer upconversion combined with excited state absorption process involving Yb-Mn dimers. The highest fluorescence intensity was observed with 15 mol% Mn 2+ , which increased the fluorescence intensity by a factor of approximately 10.88 compared to the undoped sample. Furthermore, this work explored the optical temperature-sensing properties of these upconversion fluorescent nanocrystals for non-contact temperature measurement, leveraging thermal and non-thermal coupling mechanisms. It provided a promising strategy for developing high-performance optical temperature sensors using other transition metal-doped lanthanide materials.