Comparison of transient state and steady state exciton–exciton annihilation rates based on Förster-type energy transfer

Abstract

A new concept of an effective mass in the slowing down of fast neutrons is introduced. This concept, by accounting for absorption in an increased effective mass, places scattering in the presence of absorption on a formally equivalent basis with pure scattering. Thus absorption in slowing-down theory need not be considered as a separate phenomenon, but only as a generalized form of pure scattering.For a mixture, the effective mass includes the effect of absorption in an effective single element. A model of the moderation process is considered which allows a description of the mixture by the simpler single-element equations.

Analysis of the phosphorescent dye concentration dependence of triplet-triplet annihilation in organic host-guest systems

“…The interaction leading to TTA can be a Förster-type dipole-dipole process, which is quantum-mechanically allowed due to the small mixed-in singlet-character in the predominantly triplet-type states. In contrast, at low dye concentrations, where the role of exciton diffusion is limited, the TTA process is predominantly a single-step process, with a rate determined almost entirely by the rate of the direct interaction process [22][23][24]. We note that also a Dexter-type interaction could contribute to the annihilation process.…”

“…25 for deducing the TTA mechanism from transient PL measurements can be applied successfully for any dye concentration, (ii) to establish an accurate description using a single set of microscopic parameters to quantify the TTA and diffusion rates in the full guest concentration range, and (iii) whether it is then possible to deduce the type of diffusion process (Förster or Dexter-type) from the analysis. In the literature, both types of processes have been argued to be relevant [21][22][23][24][25][26][27][28][29][30]. For this purpose, we extend the study carried out in ref.…”

Clarifying the mechanism of triplet–triplet annihilation in phosphorescent organic host–guest systems: A combined experimental and simulation study

“…2(a)), because of the different effective weights of the data points. The result is also sensitive to the time-range included in the fit [13]. The ambiguities in the conventional fit process, mentioned above, and the sensitivity to noise at longer delay times have led in Ref.…”

“…In recent studies, the effective TTA rate in host-guest systems as used in phosphorescent OLEDs is described as being controlled either by the rate of direct long-range Förster-type triplet-triplet interactions [11][12][13], or by the rate of a more indirect process of exciton diffusion followed by a relatively shortrange capture step [14][15][16]. The relative role of both processes is a subject of current debate [11][12][13][14][15][16][17][18]. The diffusion-controlled picture is consistent with the conventional phenomenological description of TTA as a bimolecular process which modifies the time dependence of the triplet volume density, T (t), in a manner as described by the last term in the expression…”

Triplet exciton diffusion in metalorganic phosphorescent host-guest systems from first principles

“…This effect, known as concentration quenching, is attributed to increased triplet exciton diffusion at high guest concentrations, when transfer between the guests is favored due to shorter distances [5,6]. Furthermore, at high luminance levels, triplet exciton diffusion enhances the IQE loss ("rolloff") that occurs due to triplet-triplet annihilation (TTA) and triplet-polaron quenching (TPQ) [7][8][9][10][11][12][13][14][15][16][17][18][19].…”