Low‐temperature photoluminescence spectroscopy was used to study AlxGa1−xAs intrinsic epitaxial layers in the range of aluminum content between 0.45<x<0.9 in the region where the band gap minimum is indirect. Nonintentionally doped samples were grown by liquid phase epitaxy very near the saturation temperature (∼800 °C). The heterostructures consisted of an AlxGa1−xAs layer grown on top of a GaAs Si‐doped (n∼2×1018cm−3) substrate with orientation (100) 2° toward the (110). There is little information on the zero phonon excitonic lines for Al compositionsx≳0.6, because the appearance of these lines depends on several factors such as internal strength, crystalline defects, and impurities. In our samples the excitonic lines were observable up tox=0.9. Transitions related to bound‐to‐free carrier as well as their phonon replicas were observable too. The data obtained from the spectra fitted with multigaussian lines allowed us to estimate the dependencies on the Al composition,x, of the bound exciton peak, the bound exciton binding energy, and the exciton localization energy. The acceptor ionization energy attributed to carbon residual impurities in As sites and its dependence onxwas also obtained. Fitting by Gaussian lines the phonon region, the PL spectra fitted better with the TO(X) AlAs‐type branch rather than the LO(X) AlAs‐type, with a linear dependence withxin the studied range. The phonon energies of the GaAs type seem to behave almost constant and it was difficult to assign them to the LO(X) GaAs type or to TO(X) GaAs type due to the scatter of the data for high values ofx. Other phonon replicas from the bound exciton and the electron‐to‐acceptor carbon transition (e‐A°) coincide with the LO(X) AlAs type and TA(X), TA(X)+LA(X) and two LA(X) phonon energies. All the dependencies we present here are valid for aluminum compositions in the range 0.48<x<0.90. ©1995 American Institute of Physics.