High Accuracy Relative Luminescence Quantum Yield Measurements of Upconverting Nanoparticles

Abstract: The name Upconverting nanoparticles refers to a novel category of luminescence emitters that are capable of generating visible luminescence upon excitation with noncoherent and longer wavelength monochromatic near-infrared light, at excitation fluence rates as low as 1-103 W/cm2. This unique optical behaviour is of great interest to researchers as it could potentially allow for virtually autofluorescence free luminescence imaging of living tissue. With them also exhibiting other advantageous properties such as a low toxicity to living cells, a high resistance to photobleaching and a small size, these nanocrystals show great potential for replacing or complementing conventional fluorophores in a wide selection of imaging applications. For this thesis, a system based on a conventional fluorometer concept, is designed and assembled which allows for the full characterization of the quantum yield of dilute samples of Upconverting nanoparticles as a function of the excitation radiation fluence rate. In addition to this, a proof-of-concept experiment is carried out with the aim to demonstrate how this dependence of the upconversion process on the excitation power density can be utilized to extract additional spatial information with a nanoparticle tomography measurement that would not be obtainable if conventional fluorophores instead had been probed.