Bistable light emission was induced by exciting a thin (5.5 mu m) CdS film with the 514.5-nm line of an argon laser, The infrared bistable emission of thr thin CdS film was investigated by using n-type GaAs wafers as cut-off filters. The loop contrast of the bistable luminescence defends on Joule heating and variation of the n-type carrier concentration of the wafers. The dependence on the latter is considerably more sensitive than on the thermal red shift of the GaAs gap. The reason underlies the enhanced absorption of heavily doped n-type GaAs at energies below 1.36 eV.