I want to take Life time of my metal complex. From emission and excitation spectrum, How do I differentiate the Fluorescence and phosphorescence properties?
Emission spectra will be more red shifted in the case of phosphorescence (i.e., low energy). As a result Stokes' shift is less for fluorescence and larger for phosphorescence.
From the excitation spectrum one cannot differentiate between fluorescence and phosphorescence.
One can differentiate fluorescence from phosphorescence based on their lifetimes. In case of fluorescence the lifetimes are lower than in the case of phosphorescence. (Delayed fluorescence - be careful!!!).
Emission spectra will be more red shifted in the case of phosphorescence (i.e., low energy). As a result Stokes' shift is less for fluorescence and larger for phosphorescence.
From the excitation spectrum one cannot differentiate between fluorescence and phosphorescence.
One can differentiate fluorescence from phosphorescence based on their lifetimes. In case of fluorescence the lifetimes are lower than in the case of phosphorescence. (Delayed fluorescence - be careful!!!).
If the source of phosphorescence is long-living (> ns) triplet you could also compare the aerated and degassed sample. Oxygen is a good triplet quencher and because its triplet energy is very low, it should quench almost all other triplets. Measurement of the lifetimes of each luminiscence should also help you to distinguish the fluorescence and phosphorescence. If you would be able to construct a 3D plot of change of the luminiscence in time (using time-resolved spectroscopy) you should get a good idea about luminiscence of your system in general (but be aware, this is not done very routinely and may be time consuming despite the output should be very educational and helpful). However I am more familiar with metal-free fluorophores, so these are just very general things, sorry.
1. You cannot get fluorescence lifetimes out of intensity-based steady-state spectra. You can either extract it from fluorescence decays using TCSPC (time domain) or out of modulation curves (frequency domain).
2. The singlet-state lifetime is usually much shorter (ns) than the triplet-state lifetime (microseconds or above).
a. You can differentiate between them according to these time separations.
b. In that light, quenching the Triplet-state (by oxygen or by redox compounds such as MEA, TROLOX, etc.) will just shorten its lifetime, therefore the time separation between singlet and triplet state lifetimes will be reduced and the separability that allows one to get the singlet state lifetime will be reduced.
3. The intersystem-crossing (ISC) is a low probability process, therefore the amount of triplet state occupancy will usually be very low in comparison to the overall excited-state occupancy, so in most cases, even if you have a mixture of fluorescence and phosphorescence, the phosphorescence will most likely be negligible in comparison with the fluorescence
4. As is mentioned above, the ground-excited states' energy gaps for singlet and triplet states are different, therefore, you have, also, spectral separation between the two.
5. The triplet-state occupancy depends on the ISC, which is, in turn, depending strongly on saturation levels, hence on excitation power. Try working with excitation power as low as possible in order to diminish the probability for ISC.
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Chem Rev. Author manuscript; available in PMC May 12, 2011.
Published in final edited form as:
Chem Rev. May 12, 2010; 110(5): 2641–2684.
doi: 10.1021/cr900343z
PMCID: PMC2924670
NIHMSID: NIHMS220622
Fluorescence Lifetime Measurements and Biological Imaging
Mikhail Y. Berezincorresponding author and Samuel Achilefucorresponding author
I think the main difference between Florescence and phosphorescence is their dynamic as stated before by colleagues. So, one has to observe the radiation intensity as a function of time after pulsed excitation. This can be accomplished by high speed photodetectors such as pin diodes or avalanche photodiode.
Best wishes
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