Ln3+ doped nanoparticles: new optical and magnetic properties

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The lanthanides, elements La-Lu, are fascinating because of their optical and magnetic properties and their practical use permeates our society (e.g. strong magnets, MRI contrast agents). My inter- and multidisciplinary research programme will explore new directions, all based on colloidally stable (doped) nanoparticles (NPs):1) singly doped NPs: stable single-photon sources that operate in the telecommunication window are much sought after for optical quantum computing and cryptography. Methods will be developed to dope a NP with one Er3+, which emits at 1.55 micron. Such singly doped NPs also allow to determine the photophysics of one Er3+ ion;2) photoluminescence through two-photon excitation of doped NPs: preliminary data show that this is possible with Eu3+, Tb3+, Dy3+, and Sm3+. This is a hardly explored field and promises some new and exciting photophysics, e.g. there is theoretical work that concludes that the two-photon intra-4f transition of the Ln3+ ions is allowed, unlike the one-photon process. It may pave the way for optical correlation spectroscopy with non-overlapping emissions;3) upconversion (core-shell) NPs that convert two or more low-energy photons into one of higher energy (usually near-infrared irradiation to red, green, and blue light) are much studied. However, the quantum yields are still much lower than their bulk counterparts, for which the reasons remain elusive. I hypothesize that the low-temperature synthesis, i.e. around 300 degrees C, of the NPs leads to internal defects that are main quenching sites. UVic's scanning transmission electron holography microscope (STEHM) will be used.4) MRI correlation: contrast in MRI is often enhanced by adding a T1 or T2 contrast agent. It seems possible to perform magnetic resonance correlation imaging if “T1-only” and “T2-only” contrast agents can be developed. We have some data to support this hypothesis;5) magnetic NPs as “single molecule magnets”: the field of single molecule magnets, SMMs, has made huge progress over the last two decades, but getting stable SMMs at temperatures above liquid nitrogen remains a formidable unresolved issue. I propose to make SmCo2, NdFeB, and the-like NPs. It should be possible to make these NPs large enough and still a single magnetic domain such that the blocking temperature is above liquid nitrogen;6) the X-ray radiation dose quantification during in-vivo studies (e.g. cancer diagnosis and treatment) is an unresolved issue. I propose to make NPs that have a T2 contrast that is not susceptible to a change in its oxidation state by X-ray induced processes, e.g. Dy3+, and a T1 contrast that is and turns on by X-ray induced photo-electrons (e.g. Eu3+, which is impotent as contrast agent, to Eu2+ which is a potent T1 contrast agent). The T2 contrast then serves as an internal standard. An internal standard is necessary for one never knows how much NPs localize in a tumour because of heterogeneity.