Hole Trapping Process and Highly Sensitive Ratiometric Thermometry over a Wide Temperature Range in Pr-Doped NaLaTiO Layered Perovskite Microcrystals.

We demonstrate a potential optical thermometric material, Pr-doped triple-layered perovskite NaLaTiO microcrystals, which promises a remarkable performance in temperature sensing over a wide temperature range (125-533 K), with a maximum relative sensitivity of 2.43% K at 423 K. Both temperature and high-pressure dependent photoluminescence measurements were performed for this compound. It turns out that the Pr-Ti intervalence charge transfer state is the primary cause for the very efficient thermometric characteristics in the 296-533 K range. In the 125-300 K range, P and P levels of Pr can be exploited as thermally coupled energy levels for temperature sensing with high sensitivity at and below room temperature. A significant enhancement of the Pr ions' luminescence observed in the 4.5-300 K range is ascribed to an efficient, thermally activated energy transfer process from the host to Pr ions. Carrier recombination on Pr related hole traps was proposed in the studied system. The thermoluminescence properties are investigated, and possible mechanisms for the interpretation of the experimental results are discussed as well. This work may provide a perspective approach to design a high-performance, self-calibrated optical thermometer operating over a wide temperature range.