Generation and rate constant of phosphorescence

Phosphorescence is another important type of excited state radiation transition, which is the radiation released when excited state molecules lose their lives to low energy states with different multiplicity. Usually observed phosphorescence is the radiation released when the first excited triplet state (Ti) transits to the ground state (S) (Kasha rule).
Generally, phosphorescence is much weaker than fluorescence, because the T-state emitting phosphorescence is usually not easy to directly absorb photons from the S-state, and the T-state is mainly formed by crossing from the S-state through the system. Due to the competition between fluorescence and internal conversion process, the quantum yield of crossing from S state to T state system is greatly reduced.
On the other hand, unlike the fluorescence process, the phosphorescence emission process is a spin-forbidden process. The mesh ash is forbidden to block Neidingtong crane 10-5~10-8. Therefore, the phosphorescence emission rate constant k. Far more than the fluorescence rate constant k; Small. k。 Generally 10-1~103s-1。 The phosphorescence rate constant k is defined as the lifetime of natural phosphorescence radiation (assuming that only phosphorescence is inactivated and nothing else the lifetime of excited triplets during inactivation)
Zp is the lifetime of triplet, that is, the time it takes for triplet to live to 1/e. That is, the reciprocal of the sum of inactivation rate constants. Kp will be increased due to the heavy atom effect or paramagnetic molecules.