Exciton absorption of light in a smooth random field

A study is made of interband absorption of light in a smooth random field that varies slowly in space. When the exciton energy in the random field is much less than the exciton binding energy, the influence of the random field on the discrete spectrum of the exciton is expressed through the appearance of an exponential “tail” to every exciton line. But if the exciton energy in the random field is much greater than the exciton binding energy, the exciton effects are unimportant because the random field breaks up the excitons.