Blue ($^{5}D_{4}\ensuremath{\rightarrow}^{7}F_{6}$) as well as uv anti-Stokes ($^{5}D_{3}\ensuremath{\rightarrow}^{7}F_{6}$) fluorescences are observed in Tb
F3 at low temperature when the
5D4 Stark components of the
Tb3+ active ions are excited. In addition, when the
5D4 exciton density is high enough, holes appear in the center of each excitation line of the visible emission, and in the corresponding absorption spectrum as well. Fluorescence dynamics and intensities are then studied for increasing pump powers. These properties are expressed as combinations of exciton-exciton annihilation and cross-relaxation processes. Saturation effects on both intrinsic and perturbed
Tb3+ ions are discussed.
The propagation of a laser pulse through a GaAs-GaAlAs MQW is investigated in the frame of classical optics. Optical spectra are calculated in the vicinity of the 1 s -exciton resonance of GaAs taking into account interference effects and nonlinear absorption caused by many-exciton effects at high excitation. The density of excited e-h pairs and intensities of transmitted and reflected beam are determined in dependence on the intensity of stationary incident laser beam by simultaneous solution of the problem of exciton diffusion and propagation of the electromagnetic wave. The observed strong nonlinearities refer to an optical bistable behaviour.