Exploring New Host Materials for Lanthanide-Based Luminescence Thermometry

用於鑭系發光測温的新型基質材料的探索

Student thesis: Doctoral Thesis

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Award date26 Mar 2021

Abstract

Temperature is a critical parameter measuring the internal thermal energy state of a substrate. The temperature measurement is a ubiquitous requirement for micrometric and nanometric systems whose dynamics and performance strongly depend on temperature. With the development of nanomaterials nowadays, the temperature inside the nanosized items is required to be measured precisely. While the conventional thermometer is ineffective for micro- and nano-scale systems measurements, lanthanide-doped nanothermometer has been developed and utilized in biological temperature sensing, temperature mapping of microcircuits, and microfluidics. The commonly used lanthanide-doped nanothermometer was constrained by either immature synthesis approaches, or poor emission properties, limited temperature range as well as low sensitivity. Therefore, exploring non-contact, non-invasive, and self-referencing nanothermometers in new host materials is an important strategy for expanding the toolbox of lanthanide-doped nanoparticles.

The thesis begins with an introduction to the mechanisms and important parameters of a thermometer, along with a review of recent advances in the development of luminescence materials used as optical thermometers for applications in different fields. The use of trivalent lanthanide ions (Ln3+) that present temperature-dependent luminescence properties would open up new opportunities for technological applications.

In Chapter 4, we establish a Cs+-assisted strategy for the controlled synthesis of uniform NaLaF4 nanoparticles as a new host material for nanothermometry in the second biological window (II-BW). The presence of Cs+ promotes deprotonation of oleic acid, which contributes to the stabilization of NaLaF4 nanoparticles against decomposing into LaF3, Na-oleate, and HF in an acidic environment. By doping Nd3+ and Yb3+ into core–shell NaLaF4 nanoparticles, strong NIR emissions at 982 nm (Yb3+, 2F5/22F7/2 transition) and 1057 nm (Nd3+, 4F3/24I11/2 transition) are obtained under excitation of 808 nm, which permits ratiometric luminescence thermometry at II-BW with a relative sensitivity of 0.50 %·K-1 at 298 K.

In Chapter 5, we present an investigation of temperature-dependent upconversion luminescence in core–shell ScF3 nanoparticles that feature negative thermal expansion (NTE) characteristic. A hot-injection method is developed to synthesize the ScF3 nanoparticles with uniform size and morphology by controlling the reaction temperature and injection rate. The core–shell ScF3 nanoparticles render thermal enhancement of upconversion luminescence in various lanthanide ions including Er3+, Tm3+, and Ho3+ over a temperature range from 168–248 K. Besides, temperature-dependent emission spectra are measured in the ScF3:Yb/Er core–shell nanoparticles, registering a maximum thermal sensitivity of 1.73 %·K-1 at 168 K.

In Chapter 6, we describe a synthesis of orthorhombic KSc2F7:Yb/Er (18/2 mol%)@KSc2F7 core–shell nanorods using a thermal-decomposition method. The upconversion spectra are examined in the temperature range of 298–473 K, illustrating a maximum relative thermal sensitivity of 1.62 %·K-1 at 298 K.

    Research areas

  • Lanthanide doping, Nanothermometer, Host materials, Core–shell, Nanoparticles, Thermal sensitivity