Nd(3+), Yb(3+):YF(3) Optical Temperature Nanosensors Operating in the Biological Windows

This work is devoted to the study of thermometric performances of Nd(3+) (0.1 or 0.5 mol.%), Yb(3+) (X%):YF(3) nanoparticles. Temperature sensitivity of spectral shape is related to the phonon-assisted nature of energy transfer (PAET) between Nd(3+) and Yb(3+)). However, in the case of single-doped Nd(3+) (0.1 or 0.5 mol.%):YF(3) nanoparticles, luminescence decay time (LDT) of (4)F(3/2) level of Nd(3+) in Nd(3+) (0.5 mol.%):YF(3) decreases with the temperature decrease. In turn, luminescence decay time in Nd(3+) (0.1 mol.%):YF(3) sample remains constant. It was proposed, that at 0.5 mol.% the cross-relaxation (CR) between Nd(3+) ions takes place in contradistinction from 0.1 mol.% Nd(3+) concentration. The decrease of LDT with temperature is explained by the decrease of distances between Nd(3+) 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(3+) (0.5 mol.%), Yb(3+) (X%):YF(3)) nanoparticles provides higher temperature sensitivity compared to the systems having one process (Nd(3+) (0.1 mol.%), Yb(3+) (X%):YF(3)). The experimental results confirmed this suggestion. The maximum relative temperature sensitivity was 0.9%·K(−1) at 80 K.