Question

What is fluorescence and how is it generated? explain absorption and emission

Answer 1

Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. In most of the cases, the emitted light has longer wavelength and therefore lower energy than the absorbed radiation.

The fluorescence process is governed by three three events all of which occur on timescales that are separated by several orders of magnitude. The first, excitation of a susceptible molecule by an incoming photon happens in phemtoseconds, while the second vibrational relaxation of excited state electrons to the lowest energy level is much slower and can be measured in picoseconds. The final process, emission of a longer wavelength photon and return of the molecule to the ground state, occure in relatively long time period of nanoseconds.

Absorption of energy by flurochromes occurs between the closely spaced vibrational and rotational energy levels of the excited states in different molecular orbits.

Emission is opposite to that of absorption. When the substance interacts with light, some of its molecules absorb the heat from the light and get excited. This causes them to become unstable and they try to emit the excess energy to get back to normal. The excited molecules release the excess energy in the form of photons, which is also known as light particles.