Hi,
I wanted to clarify a few points about PEF phenomenon.
1. To observe the enhancement in PL setup, how important is the excitation wavelength of source? for instance if I am using AU NP around 580 nm and my fluorophore emission is ~620nm, can i get intensity enhancement with 350 nm laser source?
2. is it important for plasmonic peak to be red or blue shifted with respect to the fluorophores?
3. Do those NPs provide photonic states only when LSPR is excited or there would be such states even off-resonance too?
Interesting questions. I'll try to answer some of those.
1. In your example there is 40 nm offset between the plasmon peak and the fluorescence emission. Although the largest enhancement occurs when both emission and LSPR are in resonance, most plasmon peaks are relatively broad so you could still enhance the emission. About the excitation wavelength, if the fluorophore has an absorption closer to green, then the same LSPR tail (not the peak) could enhance both, the excitation and the emission.
2. I am not sure about this. Considering the last scenario in my reply above, a broad LSPR peak could enhance both, the fluorophore emission and the laser excitation.
3. I'm not sure what exactly you mean by "photonic states" in this case.
I look forward to reading more helpful answers.
I would like to try to discuss some points here with best of my understanding,
1. I think wavelength source is quite important as system shows maximum fluorescence at wavelength it can absorb. if you will change the source (from 580 to 350, is huge difference), than i think fluorescence intensity may decrease unless fluorophore you have used for stabilizing or coating AuNPs has high absorption at 350 nm. As you mentioned it is AuNPs, than i dont think SPR band of AuNPs will absorb in the UV region (350 nm) but it may support fluorescence if your fluorophore has absorption at 350 nm. Hence absorption behaviour of your fluorophore ( you have used for stabilizing or coating AuNPs) will decide the increase or decrease in fluorescent intensity by changing the laser source to 350 nm.
2. I think red or blue shift of the plasmonic peak depends on the molecular layers at metal surface and molecular binding events.
3. I am not sure about this. I would also like to know the explanation of this.
I am also eager to hear good discussion on this topic.
Raul D. Rodriguez , sorry for the delayed response, can you please explain your following point again: ' if the fluorophore has an absorption closer to green, then the same LSPR tail (not the peak) could enhance both, the excitation and the emission.'
In our fluorophores (QDs, there is very little stoke shift).
2. Also, In my setup, since I added dielectric spacer, so some of my samples' plasmonic shifts beyond 620 nm, this is why i asked question 2.
3. What tool do you recommend to observe this enhancement at resonance? is SNOM the only option?
Gaurav Vyas , when you say, ' it may support fluorescence if your fluorophore has absorption at 350 nm '. Do you mean the fluorophore will induce LSPR, in such a scenario?
Thanks
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