Nd3+-Doped Lanthanum Oxychloride Nanocrystals as Nanothermometers

The development of optical nanothermometers operating in the near-infrared (NIR) is of high relevance toward temperature measurements in biological systems. We propose herein the use of Nd3+-doped lanthanum oxychloride nanocrystals as an efficient system with intense photoluminescence under NIR irradiation in the first biological transparency window and emission in the second biological window with excellent emission stability over time under 808 nm excitation, regardless of Nd3+ concentration, which can be considered as a particular strength of our system. Additionally, surface passivation through over-growth of an inert LaOCl shell around optically active LaOCl/Nd3+ cores was found to further enhance the photoluminescence intensity and also the lifetime of the 1066 nm, F-4(3/2) to I-4(11/2) transition, without affecting its (ratiometric) sensitivity toward temperature changes. As required for biological applications, we show that the obtained (initially hydrophobic) nanocrystals can be readily transferred into aqueous solvents with high, long-term stability, through either ligand exchange or encapsulation with an amphiphilic polymer.

Automated summary

The study introduces Nd3+-doped lanthanum oxychloride nanocrystals as an efficient optical nanothermometer system, showing strong photoluminescence under NIR excitation. The over-growth of an inert shell around the optically active cores enhances the photoluminescence intensity and lifetime.