Synthesis of Nanocrystal Quantum Dots with Enhanced Photoluminescence for Luminescent Optoelectronics

This thesis examines different approaches towards achieving greater luminescence efficiencies in colloidal nanocrystal quantum dots with primary focus towards application within singlet fission photon-multiplier down-conversion systems. Specific challenges to characterising their luminescent properties have been explored in detail, also applicable to other luminescent materials. Additionally, alternative applications for luminescent quantum dots have been investigated, and finally, the gap between small-scale synthesis and industrial production was explored for the material system of most interest. PbS quantum dots were synthesised and their luminescence efficiencies were enhanced through cation exchange with cadmium. It was found that the luminescence improvement was sensitive to a multitude of factors, particularly reaction duration at hitherto unexplored short timescales. Time-resolved optical and structural characterisation was performed indicating a two-step mechanism consisting of cation adsorption followed by subsequent exchange. Halting the reaction to the adsorption stage resulted in the highest luminescence efficiencies. The lead-free quantum dot systems InAs and CuInSe2 were investigated as alternative near-infrared emitters for photon-multiplication. Core-shell approaches with a variety of materials and complex structures were employed to improve their otherwise poor luminescence. The measurement of photoluminescence quantum efficiency is widely used for luminescent material characterisation. As a figure of merit for colloidal quantum dots, the method was examined in great detail. The sources of systematic error were identified and random measurement error quantified for a recognised measurement methodology in order to obtain accurate measurements with meaningful uncertainty bounds, applied for a photon-multiplier demonstrator system. CdSe and InP core-shell quantum dots were synthesised for a novel voltage probe. Their stability under electrolytic environments and strong response to applied electric fields was demonstrated for a biological voltage sensor. PbS quantum dots were synthesised using a commercially-available microfluidic flow reactor. The challenges to product quality and reproducibility upon scale-up were examined. Mitigation strategies against the problems encountered were proposed.