The formation of quasi-two-dimensional multiparticle excitations − biexcitons, electron-hole liquid (EHL) and plasma in tunnel-transparent for electrons SiGe layers of Si/Si0.91Ge0.09/Si heterostructures has been investigated by methods of photoluminescence (PL) in the near-infrared (NIR) and visible spectral ranges. When the PL line form in the visible region was compared with the numerical convolution of the spectrum in the NIR region, corresponding to one-electron transitions in EHL, it was apparent that the radiation in the visible region at low temperatures and high levels of excitation were caused by the two-electron transitions in quasi-two-dimensional EHL.