Synthesis and Spectroscopic Characterization of Manganese Doped Zinc Sulfide Quantum Dot Nanocrystals
Date of Award
Doctor of Philosophy
Zinc sulphide quantum dots were synthesized in aqueous media using sodium polyphosphate as the stabilizer. The nanoparticles were 2.5 ± 0.5 nm and 5.0 ± 0.5 nm diameter depending on the synthetic procedure employed and the amount of Mn doped varied from 0.003 to 0.32% (w/w). The nanoparticles were characterized by UV-Vis absorption, luminescence, EPR, near edge x-ray absorption fine structure (NEXAFS), and x-ray photoelectron spectroscopy (XPS), and x-ray diffraction (XRD), and transmission electron microscopy (TEM). These quantum dots show a strong emission at 590 nm due to the 4T1 -6A1 transition characteristic of Mn occupying Zn positions in the lattice in a slightly distorted Td site. The intensity of the emission at 590 nm increases asymptotically with the concentration of Mn(II) while the lifetime of this emission decreases. The EPR data reveal that Mn2+ exists in at least three different types of environments: a slightly distorted Td site, a highly distorted site near the surface of the nanoparticle and surface sites where Mn2+ is adsorbed. The sites responsible for the luminescence of ZnS:Mn are the Td sites inside the nanoparticle. The 590 nm emission is enhanced when the nanoparticles photo-react with cysteine. This change in intensity could be employed for the design of nanosensors.
Gonzalez Beerman, Pedro A., "Synthesis and Spectroscopic Characterization of Manganese Doped Zinc Sulfide Quantum Dot Nanocrystals" (2005). Dissertations. 1016.