Neodymium(III) doped fluoride nanoparticles as non-contact optical temperature sensors

D. Wawrzynczyk,   A. Bednarkiewicz,   M. Nyk,   W. Strek, M. Samoc

Nanoscale, 2012,4, 6959-6961

Today we would like to present to you one of the first report concerning Nd3+ doped luminescent thermometer. The importance of this kind of thermometer is related with its full NIR operating mode- both absorption and emission bands are localized in so called optical window of biological tissue (750-1000 nm) for which light absorption and scattering is the lowest leading to meaningful increase of the depth of the temperature sensing. This is the main advantage of using Nd3+ based luminescent thermometers in biomedical applications comparing to the thermometers based on up-conversion (Yb3+, Er3+; Yb3+ Tm3+ etc). In up-conversion only absorption (Yb3+ absorption) covers the optical window while emission is strongly reduced. Moreover Nd3+ emission is simply linear Stokes process hence its quantum efficiency is much higher comparing to up-conversion. In this paper 830 nm line (4I9/2->4F5/2 transition) was used as an excitation and changes of the 4F3/2->4I9/2 was used as a luminescent temperature probe. 4F3/2 state of Nd3+ ions is splited into 2 Stark component (R1 and R2) and population of R2 increases with temperature in respect to R1. Therefore emission intensities associated with transition from these sates to Z1 component of ground 4I9/2 state changes with temperature. Emission intensities at 863 nm and 870 nm were analyzed in a temperature range (0-150oC) for 10%Nd:NaYF4 and 15%Nd:NaYF4. It was found that sensitivity of such thermometer decreases according to relation determined from Boltzmann distribution from 0.1%K-1 at 0 to 0.05%K-1 at 420K for 10%Nd3+. In case of higher dopant concentration sensitivity was even lower. The fact of low sensitivity of this kind of thermometer is associated with low energy separation between R1 and R2 is very small (~60 cm-1). Despite the fact of its low sensitivity the higher depth on which temperature can be determined and higher efficiency of the emission process make this kind of thermometer at least interesting from application point of view…