Delayed fluorescence ODMR in isotopically mixed naphthalene crystals: Effect of critical concentration transport on signal polarity

Delayed fluorescence ODMR as a probe of triplet-triplet fusion probability

“…Delayed fluorescence (0:티 ODMR has been obseπed in sever외 mixed and "neat" molecular crystal systems in both hi방1 and zero magnetic fi리d [11][12][13][14][15][16]. In our work [9] we found an intri맹ing dependence of the sign of the zero-field DF-ODMR signal on naphthalene-h 8 (N-h) concentration. At a concentration of 2.7 mole percent N-h in naphthalene-ds (N-d), well below the critic외 concentration, all three DF-ODMR signals corresponding to the three zero field transitions in N-h triplet species were negative, i.e.…”

“…To record ODMR, the monochromator was set to either the (0,512) vibronic band in the delayed fluorescence (DF-ODMR) at 32 1.9 nm, or the (0,0) phosphorescence peak at 47 were used, and typi때ly a hundred sweeps needed to be signal averaged for acceptable signal to noise. Additional experimental details are given 피 our earlier report [9].…”

“…In very recent work [9], we have briefly reported a study of the delayed fluorescence in this system using optical detection of magn려c resonance (ODMR). Application of microwaves can modulate the delayed fluorescence because the probability of triplet-triplet fusion to form a fluorescent singlet st없 depends on the spin states of the interacting excitons [1 이 .…”

“…In the earlier work [9] we rationalized the change in the sign of the DF-ODMR in terms of the kinetic scheme for σiplet exciton 없m피피ation first introduced by Johnson and Meπifield [1 이 ， in which the migrating triplet excitons first react to form 때 encounter pair, which can then either dissociate due to exciton motion or can react to produce one naphthalene molecule in its excited singlet state plus a ground state naphthalene: k, 1? T+T 낀l π T] 파 SO+S1 πIe triplet p밍rs may couple to form q띠ntet， σiplet and sin밍et p머r states, but only pair states with singlet amplitude may lead to delayed fluorescence. In zero field, only exciton p없rs xζ yy and zz have nonzero sin밍et 따npli tude; thus k 2 is nonzero only for these pair states.…”

“…In what follows we first briefly describe our experiment외 observations of DF-ODMR in the N-hlN-d system [9]. Then the kinetic model is presented and its application to our results is discussed.…”