Growth and Decay of Delayed Luminescence

Abstract

We have investigated the rise lifetimes and decay lifetimes of the long‐lived luminescences of the following systems: a naphthalene‐d_s, a phenanthrene, and a triphenylene solution in a rigid‐glass matrix; a phenanthrene‐d₁₀, a phenanthrene, a naphthalene‐d_s, and a chrysene solution in a biphenyl crystal; and chrysene in solution in a phenanthrene crystal. It has been found that the luminescence rise time is invariably shorter than the luminescence decay time. This phenomenon is satisfactorily explicable on the basis of the following attitudes: In rigid glasses, triplet‐triplet absorption events contribute to depopulation of the triplet state and decrease the rise time; in mixed crystals, on the other hand, triplet‐triplet annihilation events are dominantly responsible for abbreviating the rise time. The effects of excitation intensity and excitation wavelength on the delayed luminescence rise times of rigid‐glass solutions, and the effects of excitation intensity, concentration of guest species, and temperature on the delayed luminescence rise times of mixed‐crystal systems are discussed. The activation energies for the annihilation process were obtained from a first‐order analysis of the luminescence decay and rise times. The agreement between calculated activation energies and $T_{\text{1H}}{\mathrm{\hspace{0.17em}-\hspace{0.17em}T}}_{\text{1G}}$ spectroscopic energy gaps is satisfactory and validates the postulated kinetic processes.