Exciton dynamics: direct observation of K → K' scattering in a one-dimensional triplet exciton system by electron spin echo spectroscopy

Excition dynamics: intraband scattering and trapping in s-tetrachlorobenzene between 0·35 K and 1·25 K

“…In this system, optical emission originates from the exciton, 26 680 cm -1 above the ground state, and from traps lying 8 cm -1, 18 cm -1, and 50 cm -1 below the origin, designated as XI, X~, and Y respectively. Shortly after laser excitation, there exists an appreciable overpopulation of the k--0 band state, which can be (Reproduced by permission from [5]). explained by the optical selection rule [19].…”

“…The time-resolved ESE spectrum obtained by van Strien et al at 1.13 K [5] is reproduced in figure 2 to provide a convenient reference for the scattering measurements that follow. The crystal used in this study was not annealed below its melting point after growth; in addition, it contained one principal chemical impurity, 1-bromo,2,4,5-trichlorobenzene, at a level of 0.1 per cent.…”

“…For example, relying on optical methods alone, Leong and Hanson have concluded that thermalization over the band in DBN is complete within 50 ns at 21 K [4]. Earlier, in a series of experiments on TCB, van Strien et al used electron spin echoes in zero magnetic field to measure the band populations as a function of time [5,6]. A clear correspondence between electron spin echoes and k states exists because the height of the echo is related directly to the number of spins contributing to the signal, and the frequency of the microwave transition between a pair of triplet sublevels varies with k in the same way as does the electronic energy [7].…”