Why QDs have broad excitation spectrum
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Shalin Mehta |
Why QDs have broad excitation spectrum
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Hi All,
Just curious why QDs don't have narrow absorption spectra like their emission spectra. For QDs, the energy levels in valence and conduction band of semiconductor atoms are discrete and tunable with size(which lead to emission of photons with certain energy leading to narrow emission spectrum). During excitation process why photons with any energy (> energy of photons emitted ) can move electrons from valence to conduction band? Doesn't quantization of energy levels play role during excitation? Cheers Shalin -- My co-ordinates: Shalin Mehta, Graduate student Graduate Programme in Bioengineering, NUS, Singapore Email: shalin {dot} mehta {at} gmail {dot} com Blog: electricsbm.blogspot.com Mobile: +65 90694182 |
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Shalin Mehta |
Re: Why QDs have broad excitation spectrum
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I should mention that I think energy levels within valence and conduction bands are also discrete. So as in case of fluorescent dyes, I would expect that photons with only certain energy range can excite electrons in QDs. Instead we see that any sufficiently high energy photon can move electron in QD from valence band to conduction band.
On 9/26/07, Shalin Mehta <[hidden email]> wrote: Hi All, -- My co-ordinates: Shalin Mehta, Graduate student Graduate Programme in Bioengineering, NUS, Singapore Email: shalin {dot} mehta {at} gmail {dot} com Blog: electricsbm.blogspot.com Mobile: +65 90694182 |
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Matt Bootman |
Re: Why QDs have broad excitation spectrum
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Hi Shalin,
When QDs absorb a photon, an electron transfers from the valence band to the conduction band in the semiconductor alloy of the QD core. This creates an exciton (electron-hole pair) that recombines to emit a photon. This happens whenever the energy of the absorbed photon is above the bandgap energy between the two elements (usually Cd and Se) in the core. Excitons can be created over a wide range of energies within the core that correspond to the energy of the absorbed photon. However, the higher-energy excitons always “relax” to the lowest bandgap energy before they recombine and emit a photon. That is why absorbance is broad but emission is narrow.
Regards,
Matt Matt Bootman -----Original Message-----
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the CONFOCAL archive at http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal
I should mention that I think energy levels within valence and conduction bands
are also discrete. So as in case of fluorescent dyes, I would expect that
photons with only certain energy range can excite electrons in QDs. Instead we
see that any sufficiently high energy photon can move electron in QD from
valence band to conduction band. On 9/26/07, Shalin Mehta <[hidden email]> wrote: Hi All,
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John Oreopoulos |
Labview virtual instrument for Roper cascade 512B EMCCD camera?
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In reply to this post by Shalin Mehta
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Hello listserver,
Does anyone by chance have a Labview VI program that can run a Roper Cascade 512B EMCCD camera? For example, I'm looking for a Labview Vi that would allow me to setup experimental conditions for the camera (ROIs, exposure, temperature, etc.), collect data from the camera, perform online math and display and store the data, etc. Thank you. John Oreopoulos, BSc, PhD Candidate University of Toronto Institute For Biomaterials and Biomedical Engineering Centre For Studies in Molecular Imaging Tel: W:416-946-5022 |
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