translate English to French: In particular, two bands previously unobserved under extrinsic excitation were detected at 1.35 and 1.68 eV, and have been attributed to donor–acceptor pairs and free-electron to acceptor transitions respectively.
Sous excitation extrinsèque, deux bandes additionnelles observées à 1,35 et 1,68 eV sont attribuées respectivement à des transitions donneurs–accepteurs et électrons libres – accepteurs.