Reviewer comment was "fluorescence lifetime is defined as the average time a nanoparticle/molecule spends in its excited singlet state S1 before spontaneous emission occurs. It differs with the calculated mean/average fluorescence lifetime. Although authors also cited, here using the different concept, the equation in P3, L13 is incorrect. " I have calculated average life time from TRPL data.
I don't know if it can help u, but as far as i known, fluorescence lifetime includes the radiative emission and the nonradiative emission, while the calculated mean/average fluorescence lifetime just include the radiative emission.
@Peter Kapusta: I have prepared a luminescent nanocrystal. Then I have calculated the average fluorescence life time in toluene from time-resolved PL measurements. I have fiited the spectrum triexponentially. Using average fluorescence lifetime and quantum yield, I have determined the radiative and non-radiative rate.
@Harry ten Brink: The PL decay spectrum has been collected using a time-correlated single photon counting (TCSPC) technique, and the numerical fit is formatted with the F900 software in which the Marquardt-Levenberg algorithm is used. Then I have calculated the average lifetime using the data obtained after fitting. Previously, I have attached a document where you will find all the equations.
My question is why the reviewer made the remark
"It differs with the CALCULATED mean/average fluorescence lifetime."
What did you write on this in your manuscript: an equation from the manual of your instrument?
@Harry ten Brink: In my manuscript, I have mentioned only the average fluorescence lifetime which has been calculated from TRPL data. Reviewer thought that the equation i have used is not the right one.Attached please find the document. He tried to differentiate between fluorescence lifetime and the calculated average fluorescence lifetime. You will also find those equations in "Principles of
Fluorescence Spectroscopy" (Joseph R. Lakowicz).
When you cite you give the page number FCS!! and FYI do you think I do not have this book?
As pointed out by Peter, I believe that you can calculate average lifetimes using equation mentioned in the attached document. However, yo have to be careful if you want to deduce radiative and non-radiative decay rates (kr and knr) from these average values using the PLQY equation . The PLQY equation is only valid for mono-exponential decay and might not provide a true picture of excited state decay pathways for multi-exponential decay behaviour. There are two possible ways that you can address this issue:
(1) If you know the origin of the multi-exponential behaviour, then you have 3 populations decaying mono-exponentially, each with its own kr and knr. In this case, yo can't use average lifetime values to deduce kr and knr. You would have to deal with each component separately.
(2) If you don't know the origin of the multi-exponential behaviour, which is often observed with quantum dots/ luminescent nanocrystals, then you can prepare highly luminescent fluorophores (QY as close to one as possible) and fit them with mono-exponential fits. Even with relatively poor fits, you can use the lifetime value to approximate your kr and knr values. Alivisatos and coworkers recently did similar treatment of quatum dots to calculate kr even with poor mono-exponential fits.
If the quantum yield is really low, then non-radiative decay pathways are dominating and I am not sure if there is a way to accurately measure radiative and non-radiative rates using time-resolved emission data.I hope this helps.
Note: Link to Alivisatos article:
http://pubs.acs.org/doi/abs/10.1021/ja512278a
- Saurabh
Dear Atanu,
welcome,
I know my answer is late but the page is open for answers. I hope that my answer adds some clarification to the subject.
The photo luminescence decay process is normally a relaxation process following an exponential decay curve having the formulation
phi(t)= phi0 exp -t/Tau,
the excited sates emitting the photons do not elapse the same time but but theoretically statistically some of them emit after excited and some of them may last very long times.
One defines an average lifetime for them which all would last if they emit simultaneously. This is the average lifetime and its quantitatively equal the time constant of the relaxation process Tau.
This is the precise definition of Tau. It is measured as it is defined.
Best wishes
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