NIR Luminescence lifetime nanothermometry based on phonon assisted Yb3+-Nd3+ energy transfer

Luminescence thermometry in biomedical sciences is highly desirable, but also highly challenging and demanding technology. Numerous artifacts have been found during steady-state spectroscopy temperature quantification, such as ratiometric spectroscopy. Oppositely, luminescence lifetime is considered as most reliable indicator of temperature thermometry because this luminescent feature is not susceptible to sample properties or luminescence reabsorption by the nanothermometers themselves. Unfortunately, this type of thermometers is much less studied and known. Here, thermometric properties of the Yb3+ ions in Nd0.5RE0.4Yb0.1PO4 luminescent temperature probes were evaluated aiming to design and optimize luminescence lifetime based nanothermometers. Temperature dependency of the luminescent lifetimes is induced by thermally activated phonon assisted energy transfer from 2F5/2 state of Yb3+ ions to the 4F3/2 state of Nd3+ ions, which in turn is responsible the significant quenching of the Yb3+:2F5/2 lifetime. It was also found, that the thermal quenching and thus relative sensitivity of luminescent thermometer can be intentionally altered by the RE ions used (RE= Y, Lu, La, Gd). The highest relative sensitivity was found for Nd0.5Y0.4Yb0.1PO4 SR=1.22%/K at 355K at it remains above 1%/K up to 500K. The high sensitivity and reliable thermometric performance of the Nd0.5La0.4Yb0.1PO4 was confirmed by the high reproducibility of the temperature readout and the temperature uncertainty being as low as δT=0.05 K at 383K.