SCALING ANALYSIS OF EXCITON ANNIHILATIONS IN HIGHLY ANISOTROPIC CRYSTALS

A scaling analysis is presented for incoherent exciton migration in hi ghly anisotropic crystals at high exciton densities. At these densitie s, exciton-exciton annihilation is an important mechanism for the deca y of the exciton population. The direct computer simulation of these s ystems is often not feasible due to the large number of exciton hops t hat occur on the relevant experimental time scale. The scaling analysi s allows for the physical exciton migration and annihilation problem t o be mapped into an equivalent problem with approximately the same pop ulation decay profile, but with a much smaller number of exciton hops in the time scale of interest. In this scaling analysis, the efficienc y of annihilation when two excitons occupy the same lattice site depen ds on the degree of scaling of the lattice. A procedure is presented f or the calculation of this probability of annihilation as the degree o f scaling is varied. This procedure is tested, and it is found to prod uce population decay curves that are insensitive to the scaling of the lattice. Comparison is made to experimental data for (CH3)4NMnCl3 (TM MC), and the simulation procedure provides an excellent fit to the exp erimental results.