Phase Transition‐Driven Highly Sensitive, NIR–NIR Band‐Shape Luminescent Thermometer Based on LiYO2:Nd3+

Abstract Almost all existing luminescent thermometers rely on the temperature‐dependent processes such as multi‐phonon relaxation and phonon‐assisted energy transfers, thermal population, or coupling between energy levels of ground and excited states of luminescent species (lanthanides, transition metals, quantum dots, fluorescent molecules, etc.). Although such phenomena are in principle suitable for straightforward calibration, aiming to offer high temperature sensitivity, high temperature resolution and the widest possible temperature sensitivity range, their performance is often dependent on the excitation intensity or sample dispersive properties and often suffers from insufficient brightness, which further becomes dimmer at increased temperatures. Exploiting temperature‐dependent continuous phase transitions that modify the same near‐infrared (NIR) emission band under the same NIR excitation wavelength may provide an alternative reading method for temperature sensing. Here, such a new principle of luminescent nano‐thermometry (LNT) using a Nd 3+ doped nanocrystalline LiYO 2 matrix is studied, significant sensitivities of up to 6%/K are achieved, and other issues found in conventional LNT are circumvented. Due to the hysteresis found in this class of LNT, they may find applications in studies of temperature gradients and can be integrated with modern nanophotonic devices.