Excitation mechanisms and excited states of the I 1 bound exciton in CdS

For the neutral‐acceptor‐bound exciton emission (I 1 ) of CdS three new excitation lines with light E ⟂ c are found at 1.2, 2.5, and 3.7 meV on the high energy side of the I 1 line. The nearest one is interpreted as due to the simultaneous excitation of the bound exciton and a transverse‐acoustic phonon. The other two are understood as the direct creation of the I 1 bound exciton in excited states with one of the equal holes belonging to a higher configuration. With light E ‖ c the excitation mechanisms via the free exciton states A L and A F and the bound exciton states I 1B and I 1B are discussed. An excitation intensity dependent energy shift of the long wavelength tail of the band edge is reported for the first time.