Novel Fluorescence Techniques for Real-Time Mineral Identification

Abstract

Fluorescence is the rapid emission of light after photon absorption. The absorption and emission characteristics of a sample depend on both the fluorescent species and the surrounding lattice. Fluorescence can thus be used to identify particular materials, even in a complicated environment. Upconversion fluorescence is a process wherein the sample absorbs one or more photons of a lower energy than the photons of fluorescence emission. Upconversion fluorescence wavelengths are much less likely to excite upconversion from multiple samples at once, which can provide greater sample specificity for sample identification. There is great need for real-time mineral sensors to enable real-time ore sorting and mineral processing controls, which are required for the application of mining optimisation techniques such as grade engineering. Fluorescence is real-time, non-contact and non-destructive by nature, and does not require pre-treatment of samples. This makes it interesting for sensor development. An advantage for deployment over other sensor techniques include the comparative safety of even high-energy excitation sources over radiation-based techniques. Another is the fact that fluorescence is a material-dependent phenomenon, and so has the ability to enable the creation of mineral-specific rather than element-specific sensors. Light-based excitation sources can also be much cheaper than other excitation sources currently used. Before prototypes can be made, mineral fluorescence signals must be discovered, identified and tested for use in mineral identification. This thesis describes the development of a new, state-of-the-art system designed for dual-wave excitation, providing the capability to find and characterise novel conventional and upconversion signals. This Dual-Wavelength System is characterised and tested on multiple mineral specimens, then applied to the search for previously unknown signals for further study. Quantitative upconversion fluorescence measurements using rare earth dopants found in minerals are conducted in synthetic ZBLAN glass, providing both context for natural mineral upconversion signals and direct experimental measurements of a fibre-based upconversion kinetic parameter for the first time. Upconversion signals are described and characterised in natural mineral samples for the first time. An additional lattice defect-based conventional fluorescence signal is discovered and characterised, highlighting the flexibility and broad capabilities of the Dual-Wavelength System and the great potential for such "novel" fluorescences to open new possibilities for real-time, non-contact material sensing. These new signals are assessed for their potential for mineral discrimination and abundance measurements.