From structural phase transition to highly sensitive lifetime based luminescent thermometer: multifaceted modification of thermometric performance in Y0.9xNdxYb0.1PO4 nanocrystals

The development of a highly sensitive luminescent thermometer requires a deep understanding of the correlation between the structural properties of the host material and the temperature-dependent luminescence properties of lanthanide emitters embedded in these matrices. In some cases, the presence or increased concentration of the co-dopant ions can alter not only the spectral features, but may additionally cause far-ranging structural changes that further, even more tremendously, modify the luminescence properties of the phosphor. In this work, the temperature dependent luminescence kinetics in response to structural changes induced by increasing Nd³⁺ ion doping in Y_0.9−xNd_xYb_0.1PO₄ nanocrystals are investigated, which correspondingly demonstrated phase transitions from xenotime to monazite structures. Consequently, the low temperature lifetime of the ²F_5/2 state of Yb³⁺ elongates. Moreover, by increasing the Nd³⁺ amount, the relative sensitivity of the Yb³⁺ luminescence lifetime-based luminescent thermometer was enhanced and, simultaneously, the temperature at which high sensitivity is achieved was reduced. The maximal relative sensitivity was found to be 2%/K at 273 K for Nd_0.9Yb_0.1PO₄ nanocrystals.