Luminescence by exciton‐exciton collision in GaSe

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Abstract
The photoluminescence of GaSe at 80 °K at high excitation with one‐ and two‐photon pumping is reported. The investigated energy range includes the emission localized between the indirect and the direct edges. Only the free exciton emission is observed at low pumping intensities. As the pumping increases, an extra band (L band) is observed, 20 meV below the free exciton. This band shows stimulation effects and may be ascribed to an exciton‐exciton collision process. Photocurrent measurements, resonantly excited at the excitonic wavelength, are in agreement with this conclusion.