Photoluminescence
Introduction :
If a Light falls on a semiconductor material, the charge carriers (Electron Holes Pair are generated).They are produced either by band to band transitions(intrinsic) or by transmission involving forbidden energy levels(extrinsic )as shown in figure .
Emission is of two types:
Fluorescence (Direct or fast process): :
In direct or fast emission, the emission of photons stop within approximately 10-8 s after the excitation is turned off. Such a fast process is referred as fluorescence. As we know 10-8 s is the lofe time of an atom in excited state it means after this time excited atom returns to ground state.
Phosphorescence (Slow Process) :
if the emission occurs even after the excitation has ceased, the process is known as Phosphorescence.
