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Physics of Fluorescence – the Jablonski Diagram
So what is really happening when something fluoresces? Electromagnetic radiation at one wavelength is absorbed and is then re-emitted at a longer wavelength. Wavelengths of light correspond to perceived colors (if they fall in the visible range), and this means that shorter wavelength light like ultraviolet or blue is converted to longer wavelength light, like green, yellow, orange, red.
Before we get too much into the physics, a ‘Quick Start’ summary:
- Photon #1 hits molecule
- Photon #1 absorbed, electron at ground level gains energy and jumps to higher level
- Electron loses some of that energy
- Electron jumps back down to ground level and emits photon #2
- Photon #2 has less energy, corresponding to a different color (wavelength of light)
A Jablonski diagram (below) is typically used to illustrate the physics of fluorescence. In the diagram electronic (energy) states are indicated by bold horizontal lines. The thin horizontal lines above them represent vibrational/rotational sublevels. Electrons are normally at the lowest energy state, indicated by S0. When a photon (indicated by the blue line entering from the left) with appropriate energy interacts with a molecule the photon may be absorbed, causing an electron to jump to one of the levels of an excited state (S1 or S2 in the diagram). By ‘appropriate energy’ we mean an amount corresponding to the energy difference between the ground and excited states. Thus not all incident photons are equally likely to be absorbed. This transition process is very fast, on the order of 10-15 seconds (a millionth of a billionth of a second).
An excited-state electron rapidly (on the order of 10-12 seconds) loses its energy to vibration (heat), a process called , and falls to the lowest level of the first (S1) excited state. From there the electron may fall to one of the sub-levels of the ground (S0) state, emitting a photon with energy equivalent to the energy difference of the transition. This happens on a time scale of nanoseconds (10-9 – 10-8 seconds) after the initial photon was absorbed. Since the emitted photon has less energy than the absorbed photon it is at a longer wavelength. This explains the magical process of fluorescence that converts light of one wavelength (color) to another, and leads to the phenomenal display of highly saturated colors in corals and so many other marine organisms.
The probability that a photon will be absorbed varies with wavelength (energy). Even for those photons that are absorbed there are other processes that compete with fluorescence for de-excitation of the excited-state electrons. In chlorophyll, for example, the energy of excited-state electrons is used to power the chemical engine of photosynthesis, and only a small fraction comes out as the deep red fluorescence we see in plants and algae. The number of photons fluoresced relative to the number absorbed is the . The higher the absorption and quantum efficiency, the brighter the fluorescence.
Another way to think about this is with the old model of electrons orbiting around the nucleus. In the ground (S0) state the electrons are in the orbital closest to the nucleus. When they absorb the energy of an incoming photon they jump to a higher orbital (S1, S2, etc.) or its sublevels. They can’t jump to the spaces between orbitals, and that is why not all wavelengths of light will make something fluoresce.
The best way to document the fluorescence properties of a particular specimen is to measure and spectra. The excitation spectrum is a plot of the relative efficiency of different wavelengths of light to excite fluorescence in the subject, while the emission spectrum is a plot of the relative distribution of energy released in the form of fluorescence.
KEZAKO: What is the difference between phosphorescence and fluorescence?
Kezako is the serie that addresses issues of science in a few minutes. The episode \”What is the difference between fluorescence and phosphorescence?\” addresses the two apparently different phenomena found with fluorescent markers, stickers, glowworms or fireflies.
This episode is one of the six released in Lille 3000.
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Jablonski diagram of Fluorescence and phosphorescence.By Dr.Sindhu Tayade
Singlet vs triplet states
We begin by sketching out a Jablonski diagram containing singlet (S) and triplet (T) states.
■ We discuss the \”approximate\” meaning of singlet and triplet, and then delve into the quantum mechanics of spin to examine more closely the triplet state.
Basics and principle of Raman Spectroscopy | Learn under 5 min | Stokes and Anti-Stokes | AI 09
Analytical Instrumentation Raman Spectroscopy
One may have heard about Raman effect quite a lot of times. In this video we are going to discuss the concept of Raman scattering first. But we also need to understand Rayleigh scattering first. Once the phenomenon of Raman scattering is explained, this video will discuss why and how the Raman effect takes place and how Raman scattering is generated. The viewer will also learn about the stokes lines and antistokes lines and how Raman scattering is a two photon process. Finally, the use of Raman effect in spectroscopy is discussed. This will help to perform qualitative and quantitative analysis on the sample under test.
The Raman scattering takes place due to inelastic collision between photons and electrons. The difference in energy between incident photon and emitted photon generates Raman lines. Depending on the emitted frequency, the lines generated are called as Stokes lines if their frequency is less than incident frequency of photons, if the frequency of emitted photons is greater than incident frequency, it is called as Antistokes lines. From the Raman spectra, one can determine the molecule in the sample by studying the stokes and antistokes lines. Similarly, from their intensity one can calculate the concentration of a particular sample.
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Photochemistry : Introduction \u0026 Jablonski Diagram
General introduction of photochemistry , singlet and , triplet excited states ,fate of excited species , jablonski diagram , fluorescence and phosphorescence
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