Development of an Upconverting Nanoparticles Quantum Yield Measurement System

Abstract: Fluorescence imaging is a growing biomedical technique; it can be used to localize the luminescent biomarkers inside the tissue. Lanthanide-doped upconverting nanoparticles (UCNPs) are promising luminescent probes for multiple applications in biophotonics. They allow acquiring autofluorescence-free recordings with high spatial resolution. How- ever, upconverting nanoparticles have a low quantum yield, especially at low excitation power densities. In this thesis, an upconverting nanoparticles quantum yield measure- ment system is developed, the upconverting nanoparticles used are the sodium yttrium tetra fluoride doped with thulium and ytterbium ions, NaYF4: Yb3+,Tm3+. The quantum yield for UCNPs is dependent on the excitation power density. A well-characterized dye, DY-781, with a known quantum yield of 11.9%, is used as the reference dye in these measurements. Upconverting nanoparticles quantum yield is then obtained by using a comparative method. At the balance point, half way to completely saturating the excitation, the power density equals 3214 mW/cm^2 yield of approximately 0.33%. The quantum yield of upconverting nanoparticles can be presented as a function of the excitation power density, and the values for maximum attainable quantum yield is estimated to be 0.69%. The setup is successful for obtaining the saturation of thulium-doped upconverting nanoparticles as they saturate at low power densities.