Photo-luminescence (PL) Spectroscopy

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3 жыл бұрын

Photoluminescence (PL) is basically light emission from any matter after the photon's absorption (UV-Vis).
Two types of PL
Fluorescence and Phosphorescence

Пікірлер: 37

@annoon-i1l Ай бұрын

thanks,,,,,,,,,,,what type of instrument that can detect

@robertomartins8582 4 ай бұрын

hello!! i’d like to say that is a very good video!! i have a question: in the case of phosphorescence PL type, how the relaxation can occurs? the material has to be stimulated again or simply decay lower than the fluorescence? i mean this because of “optically stimulated luminescence“ which is caused by previous irradiation, but i’m this case leads to a anti stokes emission! thanks for the content !!!

@qamarwali 4 ай бұрын

In fluorescence, the molecule quickly re-emits within a very short (nanoseconds), while phosphorescence involves a longer timescale for light emission. No extra stimulation is required. These both can occurs simultaneously BUT one has to use sophisticated machine to measure these two process at the same time. In Raman spectroscopy, when light absorbed by molecules, the following phenomenon occurs. *Rayleigh Scattering:* When the emit light has exactly the same frequency, energy, wavelength or color. This is due to the coherent scattering (Elastic scattering). For instance, > 99% scattered photons demonstrate the "Rayleigh effect" *Raman Scattering (Stokes & Anti-Stokes)* Raman scattering is based on the inelastic scattering and overall, < 1% of scattered photons demonstrate the "Raman effect" *Stokes Scattering:* When the emit light has lower energy than the incident photons and most of the Raman scattering composed of the Stokes scattering. *Anti- Stokes Scattering:* When the emit light has higher energy than the absorbed photons and this is very rarely occurring phenomena as the molecule are required to be higher vibrational state which is very rare. According to Boltzmann distribution. To sum up, the Rayleigh scattering >>>> Stokes scattering > Anti-Stokes scattering ....

@qamarwali 4 ай бұрын

Many thanks for the nice words. I am sorry if I could not answer exactly. Wish you good luck!

@kuljitsihra17 7 ай бұрын

How can we take photoluminescence spectra of semiconductor solid material? Should we take it for its suspension in water? And how to take excitation wavelength for starting?

@qamarwali 7 ай бұрын

1. Yes, we can take PL for solid material too, as the setup has a sample holder for solid material or powder also. 2. If you have a pure compound, then take the UV- vis absorption test. The lambda max is the excitation wavelength . Then, put your solution or powder in spectrometry and set this wavelength as the excitation wavelength

@kuljitsihra17 7 ай бұрын

@@qamarwali got it. Thank you so much.

@kuljitsihra17 7 ай бұрын

Sir, If I want to take uv-vis spectra of composite material which is not completely soluble in any solvent e.g., some biochar based materials, how to take the uv- vis spectra to find the bandgap?

@qamarwali 7 ай бұрын

@kuljitsihra17 mostly the UV absorption works for liquid sample and there are Cuvette which filled from. We take the base line for that liquid first. I think there is also possibllility to design your own cavette type sample holder of any quartz materials , preparing your materials as a thin sample, and then taking the UV. But you have to take the baseline of that quart first. The band gap calculation is then easy, just like for pure sample using Tauc plot.

@sam._.buswell8181 2 жыл бұрын

fantastic explination sir. very well done indeed. this topic is much clearer now

@qamarwali 8 ай бұрын

My pleasure. Many thanks 😊

@shahzadahmed5012 3 жыл бұрын

Nice video sir. I really liked it. I have a question, how can we distinguish in spectrum whether it is Fluorescence or phosphorescence peak? Which peak will tell us the bandgap (Fluorescence or phosphorescence)?

@qamarwali 3 жыл бұрын

One answers is Fluorescence has shorter wavelength than the Phosphorescence. It's is due to the fact that the relaxation is between singlet and triplet states, respectively. Which peak will tell us the band gap is difficult for me to answer. I will search and revert asap. Or I will make another video.

@qamarwali 3 жыл бұрын

@Shehzad Ahmed to the best of knowledge Fluorescent and Phosphorecent have different materials.

@shahzadahmed5012 3 жыл бұрын

@@qamarwali thanks for the explanation. I got my nearest answer but how do we decide which material will show fluorescence and phosphorescence, I mean which method will tell us this because if we do unknown sample how would I know this peak is due to phosphorescence Or fluorescence?

@qamarwali 3 жыл бұрын

Good question. When we cease for source of light, the Fluorescence will nearly immidiatly stop. While in the case of Phosphorescence the emmission will last for quite sometime after cease the source light.

@shahzadahmed5012 3 жыл бұрын

@@qamarwali Wow thanks a lot. So before doing PL we first need to do UV and visible lamp to check whether the material is fluorescence active or phosphorescence and then we can go for PL. Thanks

@Zaman-t6o 5 ай бұрын

Sir can PL spectroscopy detect crystal deffect in nanoparticles. If so how

@qamarwali 5 ай бұрын

Of course, PL spectroscopy detect defects in materials. Defects in a material can influence the electronic and optical properties because of the additional energy levels introduced within the materials leading to a significantly changes in the PL spectrum. When you see *PL peak shifts* or *changes in PL intensity* in your PL spectrum of the pristine (pure) sample. Then it shows that the material contains defects. If you don't have the PL spectrum for comparison then just take help from the Literature!

@Zaman-t6o 5 ай бұрын

@@qamarwali Thank you so much Sir.... I am learning a lot from your Videos .