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Yes:
"When a system (be it a molecule or atom) absorbs a photon, it gains  
energy and enters an excited state. One way for the system to relax is  
to emit a photon, thus losing its energy (another method would be the  
loss of heat energy). When the emitted photon has less energy than the  
absorbed photon, this energy difference is the Stokes shift. If the  
emitted photon has more energy, the energy difference is called an  
anti-Stokes shift;[3] this extra energy comes from dissipation of  
thermal phonons in a crystal lattice, cooling the crystal in the  
process. Yttrium oxysulfidedoped with gadolinium oxysulfide is a  
common industrial anti-Stokes pigment, absorbing in the near-infrared  
and emitting in the visible portion of the spectrum."
http://en.wikipedia.org/wiki/Stokes_shift

Hope this helps, Mark


On 29/04/2011, at 2:10 AM, Coutu, Cathy wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> *****
>
> Sorry, but I'm not familiar with an "antistokes shift".  Would that  
> be an emission with a shorter wavelength than the excitation???
>
> Cathy
>
> Cathy Coutu, M. Sc.
> Technician / Technicienne
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> -----Original Message-----
> From: Confocal Microscopy List [mailto:[log in to unmask] 
> ] On Behalf Of Mark Cannell
> Sent: April-28-11 4:43 AM
> To: [log in to unmask]
> Subject: Re: same excitation and emission peaks
>
> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> *****
>
> Quite so. But in this case he's not looking for an antistokes shift
> just re-emission of the same apparent energy. It's the lower
> probability of re-emission at this wavelength that prevents violation
> of the second law.
>
> Cheers
>
> On 28/04/2011, at 10:30 PM, Andreas Bruckbauer wrote:
>
>> *****
>> To join, leave or search the confocal microscopy listserv, go to:
>> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
>> *****
>>
>>
>>
>> To distinguish between Rayleigh or Mie scattering ('reflection') and
>> photoluminescence you would need to measure time resolved, see e.g.
>> G. Plesson et al. PHYSICAL REVIEW B 70, 205424 (2004). What you
>> measure is most likely the excitation light, but you could try to
>> vary the with of the excitation line if this is possible in your
>> instrument and see if the peak varies accordingly.
>>
>> I think what Mark meant was the interaction of the excited electron
>> with phonons, usually the energy is dissipated as phonons but you
>> could also have phonons transferring energy to the electron in which
>> case it would gain energy from the phonon. If it does not relax
>> further and goes back into the ground state by emitting a photon,
>> you will get anti stokes fluorescence. At room temperature the
>> energy of a single phonon would be around kT (25 meV compared to 3
>> eV for a blue photon), so you need a lot of electron-phonon
>> interaction to make a noticable shift.
>>
>> In case of the metal particle you will also have plasmon excitation.
>>
>> best wishes
>>
>> Andreas
>>
>>
>>
>>
>>
>>
>> -----Original Message-----
>> From: Johannes-P. Koch <[log in to unmask]>
>> To: [log in to unmask]
>> Sent: Thu, 28 Apr 2011 8:27
>> Subject: Re: same excitation and emission peaks
>>
>>
>> *****
>> To join, leave or search the confocal microscopy listserv, go to:
>> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
>> *****
>>
>> Think so too; if you measure something in a fluorimeter, you always
>> get a scattering "line" or peak (if looking at your spectra in 2D)!
>>
>>
>> Mark, could you comment on your phonon stuff?
>>
>> To my knowledge, phonons as such do not fluoresce; they do interact
>> with photons, i.e. you can generate a fluorescing photon by
>> annihilating a phonon or vice versa; still wherever you go, their is
>> some loss of energy, meaning that you cannot have exactly the same
>> peaks. - probabilistic or not!
>>
>> Johannes
>>
>> Am 28.04.2011 08:57, schrieb Sudipta Maiti:
>>> *****
>>> To join, leave or search the confocal microscopy listserv, go to:
>>> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
>>> *****
>>>
>>> are you not just looking at Rayleigh scattering?
>>> Sudipta
>>> On Thu, 28 Apr 2011 12:24:29 +0530, charu tanwar wrote
>>>> *****
>>>> To join, leave or search the confocal microscopy listserv, go to:
>>>> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
>>>> *****
>>>>
>>>> yes...that is what i also thought of. But this is the data we are
>>>> getting after repeatedly doing the experiment. Thanks
>>>>
>>>> CHARU TANWAR
>>>> Imaging Specialist
>>>> Advanced Instrumentation Research Facility
>>>> Jawaharlal Nehru University
>>>> New Delhi 110067
>>>> India.
>>>>
>>>> --- On Wed, 27/4/11, Jeffrey L. Travis<[log in to unmask]>  wrote:
>>>>
>>>> From: Jeffrey L. Travis<[log in to unmask]>
>>>> Subject: Re: same excitation and emission peaks
>>>> To: [log in to unmask]
>>>> Date: Wednesday, 27 April, 2011, 7:33 PM
>>>>
>>>> *****
>>>> To join, leave or search the confocal microscopy listserv, go to:
>>>> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
>>>> *****
>>>>
>>>> Wouldn't that violate the Second Law?
>>>>
>>>> On 4/27/2011 9:59 AM, Charu Tanwar wrote:
>>>>> *****
>>>>> To join, leave or search the confocal microscopy listserv, go to:
>>>>> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
>>>>> *****
>>>>>
>>>>> Dear List
>>>>>
>>>>> Not a direct confocal related query.
>>>>> Anyone please let me know whether any metallic nanoparticle with a
>>> definite size
>>>>> can have the same emission peak as its excitation peak???
>>>>>
>>>>> Thanks in advance
>>>>>
>>>>> Charu Tanwar
>>>>> Imaging Specialist
>>>>> Advanced Instrumentation Research Facility
>>>>> Jawaharlal Nehru University
>>>>> New Delhi
>>>>> India.
>>>>>
>>>>>
>>>
>>>
>>> Dr. Sudipta Maiti
>>> Associate Professor
>>> Dept. of Chemical Sciences
>>> Tata Institute of Fundamental Research
>>> Homi Bhabha Raod, Colaba, Mumbai 400005
>>> Ph. 91-22-2278-2716 / 2539
>>> Fax: 91-22-2280-4610
>>> alternate e-mail: [log in to unmask]
>>> url: biophotonics.wetpaint.com
>>>
>>
>> -- Mag. Johannes-P. KOCH 
>> Department of Biochemistry and Cell Biology
>> MFPL, University of Vienna
>> Dr. Bohrgasse 9/5
>> A-1030 Vienna
>> Austria
>>
>> phone: 0043 1 4277 52809
>> fax: 0043 1 4277 9528
>>
>> mail to: [log in to unmask]
>>
>>
>>