A concept of a field-dependent photoinjection process has been developed and applied to the low-energy light data from photodischarge measurements reported by Pai and Ing, and by Tabak and Warter. The model involves a field-dependent photogeneration of free carriers based on a Poole-Frenkel-type effect. Comparison with data tends to support the idea that the intermediate states are excitons. It is shown that the derived expression for the photoinjection efficiency fits the available experimental data on holes rather well for the entire range of field at room temperature. Indications are that the expression is valid down to about 250°K. The low-field data is shown to be highly dependent upon the mobility and the recombination velocity. Based on the reported experimental data, the recombination velocity and the effective band gap are found to be 200 cm/sec and 2.65 eV, respectively. © 1970 The American Physical Society.