Knowledge Bank

The rise-time characteristics of $T1\to S0$ phosphorescence in glassy solutions and in mixed crystals will be discussed. It is generally observed that the phosphorescence growth rate constant $kPR$ is larger than the decay rate constant $kPD$. This difference is attributed to (i) ground state depletion; (ii) triplet-triplet absorption $(T1\leftarrow T1)$; and (iii) triplet-triplet annihilation $(S1,T1,Q1\leftarrow T1+T1)$. In glassy solution (i) and (ii) are predominant, while in mixed crystals, (iii) is dominant.