Explain the principle of Fluorescence and Phosphorescence. | Analytical Chemistry

Many compounds absorb ultraviolet or visible light and undergo an electronic transition from low electronic energy levels to high electronic, energy levels. This Absorption of light requires 10-15 sec.

The instant re-emission of the absorbed energy is called Fluorescence.

While delayed re-emission of the absorbed energy is called Phosphorescence.

For most molecules, the electrons are paired in the ground state i.e. pair of electrons have opposite spins this is called singlet state. As the spin is paired up, they do not show any magnetic moment.
But if the electrons have the same spin the magnetic moment of both the electrons gets combined and they behave like a tiny magnet. This state where the electron pair is having the same spin is called as triplet state.
In a molecule, there are several electronic energy levels and electrons are present at the ground state in the singlet state i.e. with opposite spins. When a molecule absorbs U.V. or Visible light, one electron from ground state undergoes to an excited state. Now the excited state is also having several vibrational levels, so the excited electron loses its energy by intermolecular collision and it comes to the lowest vibrational level of the excited state. Finally, the electron from the lowest vibrational level of excited state returns to the ground state by emitting the radiation or light of lower energy or higher wavelength.
This overall process of absorption, intermolecular collision, and emission take 10-4 to 10-8 sec which is very small thus it looks like instant re-emission of light. But the energy of radiation emitted is always less than the energy of radiation absorbed. Or in other words, the wavelength of emitted radiation will be always higher than the wavelength of radiation absorbed. This is Fluorescence phenomenon.

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[RyukoChan]

Wow, very good video, congratulations :)
(I am a colleague from "The Cube", Rizzi ;-) )

[btn]

Just amazing 👍
Bestest brief or compact explanation...

[smilingflower]

The explanation is good, but what's the music for? It's distracting. Would have been much better without any background noise.

[jasdevtuteja]

Well explained in less amount of time!!

[krishnendudas]

Very good explanation of the trickiest part in short time

[xIbrax]

You forgot to reinverse de spin of the electron when it comes back to the ground (singulet) state

[abhishekkaushik]

Nice video to quickly brush up on the concept thank you

[ishikapapneja]

What happens when we transfer slightly higher energy that causes both electrons from the singlet state to move to an excited state?

[davefoc]

I read the Wikipedia article on this first. I did not understand it. The graphics in this video did a great job of explaining the top levle ideas, but now I have more questions. One obvious one is why does the spin flip in some situation and not in others?

[Keato]

It was an excellent video. What was the last sentence in the video ? It was something about the “virulent of the energy absorbed is less that the energy emitted...” I might be wrong

[pvm]

Thanks, It's Well explained and easy to understand

[landau]

Hello, how can two electrons be in the same quantum state at the end of the phosphorescence process? Shouldn't one of the electrons change its spin state according to the Pauli principle?

[ishfaqwani]

Then what is the role of doublet in fluorescence

[pharmactutorials]

Really very much inspired by you sir... I had been watch your videos from my 3rd Yr bpharm.... Thankyou for your easiest explanation... #PharmaCtutorial

[mdborhanuddin]

Thank you so much sir. Can you share me an XPS old data, I want to practice it.

[kamraniyat]

make videos on electrode processes and kinetics

[nitin]

Then how does it describe, transition from Singlet1 to Triplet1 state ie S1 to T1 and S2 to T2 ?

[sonaliraj]

What kind of substance undergoes phosphorescence

[mohamadhanan]

what does intermolecular collision means?

[vishalmanvatkar]

Very well explain sir please aur analaytical chemistry ke videos daliye MSC sem fourth ke