Constructing multiform morphologies of YF: Er3+/Yb3+ up-conversion nano/micro-crystals towards sub-tissue thermometry

Er3+/Yb3+ co-doped YF3 samples with uniform rice-like, two-dimension (2D) hexagonal nano-architectures and truncated octahedral micro-crystals were synthesized through a one-step hydrothermal method, and their possible growth mechanisms were also proposed. Upon 980 nm excitation, the up-conversion (UC) emitting color of samples was finely modulated from yellow to pure green with increasing the particle size, which was interpreted in terms of non-radiative process and surface effect. Thermometric capabilities of samples with different morphologies were evaluated based on the fluorescence intensity ratio (FIR) of 2H11/2 and 4S3/2 levels through temperature-dependent UC spectra, and the optimal absolute sensitivities of samples were all approached to about 0.0026 K-1 at 490 K. The potentiality of rice-like nano-crystals for temperature detection in sub-tissue was demonstrated by ex vivo experiments. Results display that the sensitivity of YF3: Er3+/Yb3+ nano/micro-crystals is independent of morphologies and sizes, which exploit an effective avenue for developing UC-based thermometers in sub-tissue with stable sensitivity.