Question

how do fluorescent dyes emit light? explain the fluorescence emission process?

Answer 1

Fluorescent dyes generally have pi-electron systems that can absorb energy from the light radiation. These electrons are capable of being excited, via absorbing the light energy, to a higher energy state, known as an excited state. The energy of the excited state cannot be sustained for the longer duration so it “decays” or decreases, resulted in the form of emission of light energy. This process is called fluorescence. The energy is released in the form of a photon.

the fluorescence emission process can be summarized as:

Step 1. Excitation of a fluorophore through the absorption of light energy.

Step 2. A transient excited lifetime with some loss of energy.

Step 3. Return of the fluorophore to its ground state, accompanied by the emission of light.

The light energy emitted is always of a longer wavelength than the light energy absorbed, due to the energy lost during the transient excited lifetime, as shown in Step 2. In general, emitted fluorescence light has a longer wavelength and lower energy than the absorbed light. This phenomenon, called as Stokes shift, is due to energy loss between the time a photon is absorbed and when a new one photon is emitted.