Intrinsic gap emission and its geometry dependence of thin-film CdS excited by two-photon absorption

The emission of thin-film CdS on glass is investigated by ultra-fast pulsed excitation at room temperature. It is demonstrated that. in contrast to single-photon excitation, two-photon excitation causes intrinsic gap emission in extrinsic samples without transitions below the gap. The spectra are perfectly fitted by the van Roosbroeck-Shockley relation, which describes the detailed balance between absorption and emission. The spectrum measured through the glass is shifted 40 meV to lower energies with respect to the front emission due to increased absorption at the glass/CdS interface.