Abstract

Luminescence and Raman spectroscopy using high-density tunable laser sources in the bound exciton region of CdS yield new informations about excitation channels and excited states of the four-particle (A°,X) complex. Excitation spectroscopy of the I₁ luminescence due to the recombination of the (A°,X) complex with two A-valence-band holes in its electronic ground state led to the identification of four fine structure levels of the (A°,X_B) complex with one hole from the second B valence band. Excitation with light of polarization $\stackrel{\rightharpoonup }{\text{E}}\Vert \stackrel{\rightharpoonup }{\text{c}}$ and of an energy which coincides with one of these four levels, split off by hole-hole and electron-hole exchange interaction, is followed by a B-A hole conversion and subsequent I₁ recombination of the complex. The sharp and strong excitation resonances due to the (A°,X_B) levels allow measurements in a magnetic field giving detailed informations about the nature of these states and the interaction mechanisms involved. Investigations of a resonant electronic Raman effect due to hole scattering from the B to the A valence band within the (A°,X) complex supported these results. Four Raman lines showing resonance behaviour successively at the four (A°,X_B) levels with distinctly different properties from known low-density Raman spectroscopy¹ could be observed. Polarization and magnetic field dependent measurements were used to identify the Raman mechanism to be a one-photon resonant electronic scattering process within the (A°,X) levels while gain measurements and the observation of a mode structure in the high-density excitation spectra supported the excistance of stimulated Raman transitions. High-density excitation spectra of the I₁ bound exciton with polarization ${\stackrel{\rightharpoonup }{\text{E}}}_{\perp }\stackrel{\rightharpoonup }{\text{c}}$ showed resonances due to first order forbidden electronic excited states² of the (A°,X_A) complex. Extremely high excitation intensities led to the observation of vibration like resonances of the I₁ luminescence. Intensity, temperature and magnetic field dependent measurements enabled us to develop a theoretical model to explain these resonances to be vibrations of the particles within the (A°,X) complex analogous to the case of a diatomic molecule.

© 1984 Optical Society of America