Photoluminescence-based temperature sensing using TTFA sensitized NaMgF3 nanoparticles doped with europium

The temperature-dependent luminescence of crystalline nanocomposites has shown to have promising applications for temperature sensing in systems requiring a high resolu- tion and fast response time over a wide range of temperatures. Through the utilization of novel synthesis methods, highly luminescence nanocomposites present an exciting possibility for capturing spatial temperature distribution details with sub-micrometre precision, surpassing the capabilities of traditional temperature sensing methods. This thesis focuses on developing the foundation for a wireless, luminescent-based temper- ature sensor for the monitoring of power grid assets in New Zealand, by examining the compound NaMgF3 doped with trivalent europium (Eu3+) and sensitized with 2-thenoyltrifluoroacetone (TTFA). The structural and luminescence properties of this compound were studied to determine an optimal europium concentration that produces reproducible and high-resolution temperature-dependent luminescence over a temper- ature range attractive for such electronic devices.The examination of X-ray diffraction patterns yielded an anisotropic expansion of the unit cell volume with Eu3+ concentration, along with the formation of impurity compounds indicating the incomplete incorporation of Eu3+ into the nanoparticles.The luminescence characterization observed a decrease in the 5D0 → 7F2 relative to the 5D0 → 7F1 Eu3+ transitions, and a decrease in the luminescence lifetimes, with increasing Eu3+ concentration. Furthermore, systematic changes in the Judd-Ofelt parameters, quantum efficiencies, and stimulated emission cross-section were explained using a model of surface and core europium sites, whereby high Eu3+ concentrations result in greater core site emission.Strong temperature-dependent Eu3+ emission was found over the 300 - 460 K tem- perature range, with sample degradation occurring at temperatures above 460 K. A simple kinetic model is evaluated whereby excitation occurs directly into the TTFA ligand and subsequent energy transfer to the 5DJ states of Eu3+. From this model, thermal quenching is shown to be a result of greater back transfer between the 5D0 state of Eu3+ and the T1 state of TTFA, placing the T1 and S1 states of TTFA at 2.62 eV and 3.54 eV respectively. Furthermore, it was found that the relative sensor sensitivity ranges from 0.2 to 2.8% K−1, and is amongst the highest of any inorganic nano-thermometers. The resolution was found to be higher than 1 K over the 300 - 460 K range, with the finest resolution being 0.1 K, indicating that this compound is an excellent candidate for temperature sensing.</p