How does phosphorescence occur?
• 1. Absorption of light promotes an electron from the ground electronic and usually ground vibrational states to an excited vibrational state of the excited electronic state. • 2. A series of intermolecular vibrational relaxations (IVR) occur releasing energy in the form of heat. • 3. During IVR an intersystem crossing takes place. • Moving of electrons to a different excited state for which transitions back to the ground state is forbidden • 4. When a transition is forbidden the rate of emission slows down. • This emission is called phosphorescence instead of florescence.
