Singlet exciton, charge-carrier production

Here, n is the concentration of the charge carriers, [S] is the concenhation of singlet excitons, I the intensity of the UV radiation, Uj the constant for photoionisation of the singlet excitons, and k2 is the rate constant for charge-carrier production by two-photon absorption. AU three processes are proportional to 1. For the separation into individual processes, the spectral dependence of the quadratic photogeneration of charge-carrier pairs was determined and analysed [31]. 

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