Nd, Yb:YF Optical Temperature Nanosensors Operating in the Biological Windows

This work is devoted to the study of thermometric performances of Nd (0.1 or 0.5 mol.%), Yb (X%):YF nanoparticles. Temperature sensitivity of spectral shape is related to the phonon-assisted nature of energy transfer (PAET) between Nd and Yb). However, in the case of single-doped Nd (0.1 or 0.5 mol.%):YF nanoparticles, luminescence decay time (LDT) of F level of Nd in Nd (0.5 mol.%):YF decreases with the temperature decrease. In turn, luminescence decay time in Nd (0.1 mol.%):YF sample remains constant. It was proposed, that at 0.5 mol.% the cross-relaxation (CR) between Nd ions takes place in contradistinction from 0.1 mol.% Nd concentration. The decrease of LDT with temperature is explained by the decrease of distances between Nd with temperature that leads to the increase of cross-relaxation efficiency. It was suggested, that the presence of both CR and PAET processes in the studied system (Nd (0.5 mol.%), Yb (X%):YF) nanoparticles provides higher temperature sensitivity compared to the systems having one process (Nd (0.1 mol.%), Yb (X%):YF). The experimental results confirmed this suggestion. The maximum relative temperature sensitivity was 0.9%·K at 80 K.