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-ds, a phenanthrene, and a triphenylene solution in a rigid-glass matrix; a phenanthrene-d10, a phenanthrene, a naphthalene-ds, 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 T1H − T1G spectroscopic energy gaps is satisfactory and validates the postulated kinetic processes.

Effects of impurity traps on exciton-guest, triplet-triplet annihilation in pyrene-d10 doped single crystal of fluorene

“…The overall features of delayed fluorescence decaying at various temperatures are similar to those already observed [1,4] in other mixed crystals. Delayed fluorescence decays, are nearly exponential at temperatures, T > 180 K, and deviations from exponentiality are observed at short times after excitation cut-off.…”

“…Trap (impurity)-guest and trap (impurity)-trap (impurity) triplet annihilation play a dominant role in producing phosphorescence and delayed fluorescence in such crystals [1]. It has been known for some time that delayed fluorescence is generally observed in many organic mixed-crystal systems [2,3,4], where the lowest excited singlet states ($1) and lowest excited triplet states (T~) of the guest are energetically lower than $1 and Tx of the host. It is well-known that in aromatic crystals the mutual annihilation of triplet excitons can lead to singlet excitons which decay with emission of delayed fluorescence.…”

“…shows that pyrene-d 10 phosphorescence is independent of temperature in almost all regions except near 77 K, in such a situation equation(4) can be used to obtain the impurity thermal energy levels. The plots of log (Id~/lpi) vs T-1 should give straight lines with slopes AEi/k , provided Ipp is independent of temperature.…”

Rise time-based phosphor thermometry using Mg4FGeO6:Mn4+

“…That is, the excitation light-induced heating only contributed a small part to the excitation energy effect. As reported by previous studiy [32], the decrease of rise time caused by the increase of excitation energy may main due to the photo-physical nature. According to the previous studies on the rise time [32], energy transfer occurs from molecule to molecule and the excitation energy is delocalized.…”

“…As reported by previous studiy [32], the decrease of rise time caused by the increase of excitation energy may main due to the photo-physical nature. According to the previous studies on the rise time [32], energy transfer occurs from molecule to molecule and the excitation energy is delocalized. Triplettriplet absorption of both the exciting light and the emitted phosphorescent light contributes significantly to the depopulation of triplet states.…”