Electronic and vibronic states of the acceptor—bound-exciton complex (A0,X) in CdS

High-density excitation spectroscopy of the acceptor—bound-exciton emission $I_1$ in CdS results in series of new resonance states, situated on the high-energy side of the $I_1$. For polarized laser light $\overrightarrow{\mathrm{E}}\perp c$ the series $I_1^1$ to $I_1^5$ appears, and is superimposed by another series of resonance maxima $V_1$ to $V_7$ at highest excitation intensities. For $\overrightarrow{\mathrm{E}}\parallel c$, excitation of the $I_1$ via a couple of doublets in the spectral region of the known absorption lines $I_{1B}$ and $I_{1B^{\prime }}$ is observed for the first time. They are interpreted as electronic ground-state levels of the ($A^0$,$X_B$) complex with one of its holes originating from the $B$ valence band. The splitting off of the ground state by electron-hole and hole-hole exchange interactions is discussed in a simple fine-structure model of the ($A^0$,$X$) complex. The series $I_1^1$ to $I_1^5$ is thus attributed to ground- and excited-electronic-state levels of ($A^0$,$X_A$). Molecular analogous rotation or vibration modes of the ($A^0$,$X$) complex are discussed as origins of the series $V_1$ to $V_7$.