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Applying a technique to determine the k=0 components in the exciton densities of sates (DOS) we found: (1) The DOS in anthracene microcrystallites appears as sharp bands followed by broad tails extended towards higher energies. (2) The exciton bandwidth which depends linearly on the size of microcrystallites where the diameter is smaller than 60 Å. (3) The bandwidth takes its maximum value 340 cm-1 for microcrystallite of 65 Å. (4) For larger microcrystallites, the bandwidth decreases asymptotically to 300 cm-1. (5) This width 300 cm-1 is equivalent to the bandwidth for bulk crystal. (6) Exciton scattering at the surface of microcrystallites is extremely effective.

Indirect free-exciton luminescence in AgC1 single crystal accompanied by TO(L) phonon emission is found for the first time at 382.9 nm (3.238 eV) at 2 K for picosecond pulse laser excitation at 351 nm (3.53 eV).The luminescence decay curve monitored at 382.9 nm has a fast decay component, 20 ps, which is interpreted as the selftrapping time of holes generated at the L point. A luminescence band peaking at 385 nm(3.221 eV) is found, which is assigned as due to the optical transition from a point around the exit of the quantum mechanical tunneling process through the self-trapping potential barrier. The rise time 70 ps is interpreted as the time required for tunneling. A luminescence band peaking at 386.5 nm (3.208 eV) is found and assigned to be due to excitons bound by shallow impurity.