We report photoluminescence investigations of heavily doped AlxGa1-xN:Si films grown by molecular beam epitaxy on sapphire substrates. The wide intensive defect-related band dominates in the photoluminescence spectra of AlxGa1-xN:Si films with the Al content higher than 0.38 covering the whole visible spectral range. This band is attributed to donor-acceptor and free electron-acceptor transitions involving the same acceptor. The acceptor ionization energy of about 1.87 eV for heavily doped AlN:Si was obtained, decrease of Al content leads to decrease of the acceptor ionization energy. The donor was assigned to the Si atom on the Ga/Al site; the acceptor might be (0/-) transition level of the CN or (2-/3-) transition level of the VAl.