SIZE-DEPENDENT EXCITON DENSITIES OF STATES AND EXCITON BANDWIDTHS IN ANTHRACENE MICROCRYSTALLITES

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