Excitation spectroscopy on the M-band of red HgI2

The luminescence of red HgI₂ is investigated as a function of excitation intensity and -wavelength. At low excitation, emission is due to free and bound exciton recombination, at high levels a “M-band” is dominating. This M-band is partially ascribed to biexciton decay, this assumption being supported by resonances found in the excitation spectra. The biexciton binding energy is determined to be 6±1 meV.