Explain the term phosphorescence.

Explanation

Electron from Second Singlet State `S_2)` may return to next higher energy level `(S_1)` by losing some of its extra energy in the form of heat. From first single state `S_1)` electron further drops to first triplet state `T_1)`. Triplet State is unstable having half life time of `10^-3` seconds and electrons returns to ground state with emission of light in red region called as phosphorescence. Phosphorescence is the delayed emission of absorbed radiations. Pathway of electron during Phosphorescence: `S_2rightarrowS_1rightarrowT_1rightarrowS_0`