What is it about?

The paper explores the effects that the shell of organic ligands has on the fluorescence properties of CdSe nanocrystal QDs. We used Nuclear Magnetic Resonance, a resolution spectroscopic tool (like MRI) to determine the coverage of the ligand on the QD surface and showed coverage to be consistent with models of the fluorescence, which indicate that the ligand-shell has a dominant role in governing the ubiquitous, intermittent, on-off blinking in the fluorescence observed in these QDs.

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Why is it important?

The Quantum Dot (QD) is a new bit of nanotech that gives new QLED TVs near-perfect colour reproduction, gives solar cells more oomph in power and shines a "stronger" light on biological and medical imaging! These nanocrystal materials absorb light and fluoresce with superior efficiency, but can suffer from blinking in the light they emit, switching on and off like a flashlight and this reduces the overall efficiency of emission from a bulk ensemble of QDs, in a QLED pixel for example. The QD is not isolated but normally wrapped in a shell of organic ligand molecules that stabilise the QD. The paper explores this "sphere of influence" on the fluorescence properties of CdSe nanocrystal QDs. We used Nuclear Magnetic Resonance, a resolution spectroscopic tool (like MRI) to determine the coverage of the ligand on the QD surface and showed this to be consistent with our models of the fluorescence blinking observed in these QD, which indicate that the ligand-shell has a dominant role in governing the on and off switching times of the nano-flashlight. Understanding and ultimately controlling the "flashlight" is important for different applications. For displays, for example, the more QDs made to fluoresce for longer and not blink, make for brighter displays at a lower energy cost.

Perspectives

Quantum Dots provide a great example of nanotechnology now in use, in a basic household appliance, with genuine added value, making the tech widely accessible. The QD provides an excellent vehicle for understanding basic quantum mechanics from the simple "particle-in-a-box" description of size tunable colour of light emission, to more abstract concepts of "quantum tunnelling" that describes the blinking of fluorescence observed in these nanocrystals. The paper presents new collaborative work between our laser spectroscopy lab and the NMR lab at Sussex Uni, inspired by the excellent work undertaken by the PhD students involved and aimed at exploiting new tools for a more comprehensive characterisation of the our QDs. We hope the paper, or at least this reflection, inspires readers to think about the science behind the technologies and products they encounter everyday!

Mark Osborne
University of Sussex

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This page is a summary of: Measurement of ligand coverage on cadmium selenide nanocrystals and its influence on dielectric dependent photoluminescence intermittency, Communications Chemistry, June 2019, Springer Science + Business Media,
DOI: 10.1038/s42004-019-0164-x.
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