Photoluminescence (PL) Spectroscopy: Fluorescence Vs. Phosphorescence

hotoluminescence (PL) spectroscopy.

PL spectroscopy is used to study the electronic and optical properties of materials. In this technique, simply photons excite electrons to higher energy levels, and the subsequent relaxation of electrons to the lower energy levels results in the emission of photons (light). The techniques provide information about the band structure of the materials, defects states, and the composition, etc.

In PL spectroscopy, there are two phenomena occurring, i.e., radiative and non-radiative recombination. The radiative recombination of charges produces photons, whereas the non-radiative recombination does not produce photons but instead, it generates heat and phonons or thermal energy.

In the radiative emission, PL can then be separated into two main types, i.e., fluorescence and phosphorescence.

Fluorescence means immediate emission of light, while the phosphorescence means delayed emission, and it is also called delayed fluorescence.
Fluorescent material: When the emission is immediate and thereby only visible only and only if the light source is continuously on (such as UV lights and we will get visible light)

Phosphorescent material: It can store the absorbed light energy for some time and then release light after some time, resulting in an afterglow that lasts after the light has been switched off.

In both cases the wavelength is longer than the absorbed photons' wavelength and this is called Stokes Shifts.