The influence of the Er 3+ dopant concentration in LaPO 4 :Nd 3+ , Er 3+ on thermometric properties of ratiometric and kinetic-based luminescent thermometers operating in NIR II and NIR III optical windows

In this work, properties of the near infrared absorbing and near infrared emitting Er 3+ and Nd 3+ co-doped LaPO 4 nanocrystals luminescent thermometer were investigated by exploiting luminescence spectra ratiometric and luminescence lifetime. The unique configuration of the energy levels of Nd 3+ and Er 3+ ions and the energy transfer between them requires temperature dependent phonon assistance. Since, the probability of this process is dependent on the distance between interacting ions, the thermometric parameters of luminescent thermometers were investigated as a function of Er 3+ dopant concentration. Strong susceptibility of its probability to temperature changes enables to quantify temperature with relative sensitivity as high as S R  = 1.15%/K for LaPO 4 :1%Nd 3+, 20%Er 3+ nanocrystals in the ratiometric approach and S R  = 2.3%/K at 600 K for LaPO 4 :1%Nd 3+, 5%Er 3+ in the luminescence lifetime based mode. The obtained results confirm the high applicative potential of this phosphor for remote temperature measurements.