What is the difference between Raman scattering and fluorescence

[Emmangel]

What is the difference between Raman scattering and fluorescence emission?

 

[davenn]

Hi Emmangel
Welcome to PF :)

there is a difference... this clip from wiki should hopefully clear it up ...

The Raman effect occurs when light impinges upon a molecule and interacts with the electron cloud and the bonds of that molecule. For the spontaneous Raman effect, which is a form of light scattering, a photon excites the molecule from the ground state to a virtual energy state. When the molecule relaxes it emits a photon and it returns to a different rotational or vibrational state. The difference in energy between the original state and this new state leads to a shift in the emitted photon's frequency away from the excitation wavelength. The Raman effect, which is a light scattering phenomenon, should not be confused with absorption (as with fluorescence) where the molecule is excited to a discrete (not virtual) energy level.

so really simply Raman scattering is more akin to reflection, fluorescence isnt, rather it is an absorption effect

cheers
Dave

 

[krd]

fluorescence isnt, rather its absorption

I'm not sure about this. But I think fluorescences is due to certain kinds of chiral molecules getting twisted tighter by different light, and then releasing the light as they uncoil. And I think this is why you can see a perceptible time delay in the drop off fluorescence when you switch off your UV source or whatever.

And there are certain sweets - mints - that if you crack them in the dark, you'll see them fluores for a few seconds.

 

[davenn]

I'm not sure about this. But I think fluorescences is due to certain kinds of chiral molecules getting twisted tighter by different light, and then releasing the light as they uncoil. And I think this is why you can see a perceptible time delay in the drop off fluorescence when you switch off your UV source or whatever.

And there are certain sweets - mints - that if you crack them in the dark, you'll see them fluores for a few seconds.

dunno if that would be fluorescence or luminescence

On the other hand to align with the earlier statement, my fluorescing rocks and minerals
absorb the light of one wavelength and re-emit it at a different wavelength
Under plain "white light" they are nothing outstanding to look at, under UV light they fluoresce amazing bright and vivid colours, that bear no relation to their white light colours

Dave

 

[sardar]

Raman scattering and fluorescence are both types of light scattering phenomena, but they differ in the way they interact with the molecules in a sample.

Raman scattering is a type of inelastic scattering, where the incident light interacts with the vibrational modes of the molecules in the sample. This results in a shift in the energy of the scattered light, which can be measured to determine the molecular vibrations present in the sample.

On the other hand, fluorescence is a type of photoluminescence, where the incident light is absorbed by the molecules in the sample and then re-emitted at a longer wavelength. This process is known as fluorescence emission. The emitted light has a lower energy than the incident light, and the difference in energy is known as the Stokes shift.

One of the main differences between Raman scattering and fluorescence is the type of information they provide about the sample. Raman scattering is sensitive to the molecular vibrations, which can provide information about the chemical bonds and structures present in the sample. On the other hand, fluorescence emission is sensitive to the electronic structure of the molecules, which can provide information about the electronic states and energy levels in the sample.

Additionally, Raman scattering is a relatively weak effect compared to fluorescence, which means that it requires higher intensity light sources and longer measurement times to obtain a signal. This also means that Raman scattering is less prone to photobleaching or photodamage of the sample, making it a useful technique for studying delicate or light-sensitive samples.

In summary, the main difference between Raman scattering and fluorescence lies in the type of information they provide about the sample and the underlying physical processes involved. Raman scattering is sensitive to molecular vibrations, while fluorescence is sensitive to electronic structure.