Nd3+, Yb3+:YF3 Optical Temperature Nanosensors Operating in the Biological Windows

Abstract

This work is devoted to the study of thermometric performances of Nd3+ (0.1 or 0.5 mol.%), Yb3+ (X%):YF3 nanoparticles. Temperature sensitivity of spectral shape is related to the phonon-assisted nature of energy transfer (PAET) between Nd3+ and Yb3+). However, in the case of single-doped Nd3+ (0.1 or 0.5 mol.%):YF3 nanoparticles, luminescence decay time (LDT) of 4F3/2 level of Nd3+ in Nd3+ (0.5 mol.%):YF3 decreases with the temperature decrease. In turn, luminescence decay time in Nd3+ (0.1 mol.%):YF3 sample remains constant. It was proposed, that at 0.5 mol.% the cross-relaxation (CR) between Nd3+ ions takes place in contradistinction from 0.1 mol.% Nd3+ concentration. The decrease of LDT with temperature is explained by the decrease of distances between Nd3+ 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 (Nd3+ (0.5 mol.%), Yb3+ (X%):YF3) nanoparticles provides higher temperature sensitivity compared to the systems having one process (Nd3+ (0.1 mol.%), Yb3+ (X%):YF3). The experimental results confirmed this suggestion. The maximum relative temperature sensitivity was 0.9%·K−1 at 80 K.

Spectral-Kinetic Characterization of YF3: Eu3+ and YF3: (Eu3+, Nd3+) Nanoparticles for Optical Temperature Sensing

“…The nanoparticles were synthesized via the co-precipitation method in distilled water with subsequent hydrothermal treatment [4,16]. The detailed synthesis procedure is described in our previous work devoted to rare-earth-doped YF3 nanoparticles [8]. According to the work [17], the annealing of the obtained YF3 nanoparticles at 400 °C in air does not lead to the formation of impurity phases hence we choice the annealing at 400 °C in air for 3 hours.…”

“…In its turn, down-conversion optical temperature sensors based on Nd 3+ /Yb 3+ [12,13], Pr 3+ /Yb 3+ , Er 3+ /Yb 3+ [14] ion pair (where the first ion serves as a donor of energy) are also based on the same mechanism. In our previous work, we suggested, that for Nd 3+ /Yb 3+ :YF3 nanoparticles the thermal expansion and, as a consequence, the decrease of distance between interacting ions also contribute in the temperature sensitivity of the spectral-kinetic characteristics [8,13]. After literature analysis, we concluded, that the Eu 3+ /Nd 3+ system in capable of demonstrating notable temperature sensitivity under Eu 3+ excitation [15].…”

“…The YF3 matrix provides substitution of Y 3+ ions by RE 3+ ones without valence change or charge compensation. Finally, in our previous work [8], we developed a hypothesis, that thermal expansion of YF3 also contributes in the temperature sensitivity of the RE spectral-kinetic characteristics. Thus, it is interesting to study another ion pair in this promising matrix.…”

“…Indeed, it depends on the application [4]. For medical applications including hyperthermia, the phosphors should operate in the so-called biological window, where the biological tissues are partially transparent [8,9]. In the case of in vitro studies, the excitation in this spectral range is also desirable because the operation in the biological window provides the lack of autofluorescence from cells.…”

Spectral-Kinetic Characterization of YF3: Eu3+ and YF3: (Eu3+, Nd3+) Nanoparticles for Optical Temperature Sensing

“…The YF 3 matrix provides a substitution of Y 3+ ions by RE 3+ ones without valence change or charge compensation. Finally, in our previous work [11], we developed a hypothesis that the thermal expansion of YF 3 also contributes to the temperature sensitivity of the RE spectral-kinetic characteristics. Thus, it is interesting to study another ion pair in this promising matrix.…”