Techniques for characterisation and applications of long-lifetime luminescence in the microsecond region

High-resolution characterisation of lanthanide-based luminescence complexes and nanomaterials provides in-depth insights to understand the details of energy-transfer process and photon luminescence mechanisms, guiding new designs for probes and methods for advanced sensing applications. Comparing many recent developments of lanthanide luminescent materials, current spectrometer-based instruments are insufficient in characterising the optical properties of nanoscale and micro-scale luminescence samples. This PhD program of optoelectronics engineering explores time-resolved approaches through demonstrations of two purpose-built devices for comprehensive characterisation and advanced applications of long-lived luminescent materials. The first part of this thesis describes a design of a multi-colour time-gated luminescence (TGL) microscope. Implementing a high-speed Xenon flash lamp and synchronised time-gated detection unit, we suggest a practical approach to upgrade a commercial microscope for low-background time-gated luminescence imaging at low cost, with high stability and simplicity. We applied this system for simultaneous inspection of pathogenic micro-organisms and evaluated its detection sensitivity by imaging single luminescent nanoparticles. The second part of this thesis presents an imaging-spectroscopy platform for high-resolution simultaneous characterisation of lifetimes and spectra of long-lived luminescence materials. Incorporating a multi-channel photomultiplier tube as a linear array detector behind a spectrometer, we realised a three-dimensional time-resolved spectrometer; coupling the 3-D spectrometer to a purpose-built laser scanning confocal microscope; we demonstrated a microscope-based device for characterisation of nanoscale and micro-scale luminescent samples. The third part of this thesis showcases new functionalities of the imaging-spectroscopy system by nanophotonic characterisation of the new generation of colour-coded upconversion micro-rods and single upconversion nanoparticles. In addition to the main result chapters, I have obtained some preliminary results on the exploration of the relationship between the excitation power and luminescence lifetime using our time-resolved spectroscopy system. Moreover, I have also succeeded in demonstrating two other optical characterisation systems for measurement of luminescence quantum yield of upconversion activators, and characterisation of upconversion polarisation properties. These results are also included in this thesis as three appendices. The advances brought to the characterisation systems in this thesis provide a set of new tools for exploring the rich optical properties of long-lived luminescence materials at the nanoscale and promoting novel luminescence materials for ultrasensitive and rapid sensing applications. The three key result chapters of this thesis are presented by publication of four peer-reviewed journal papers. The introduction chapter is presented as a manuscript of a review article and the conclusion chapter is followed by three appendices containing the results of my work in parallel during the last three and half years of PhD research.