Photoluminescence of mercurous halides

Mercurous halides show strong orange luminescence at 77°K when excited at energies above the fundamental absorption edge. At room temperature this luminescence is strong only in the chloride and bromide. Spectral features, including band maxima and half widths of both excitation and emission spectra are also temperature dependent. At 77°K a strong green luminescence was observed from the Hg₂Cl₂. Both Hg₂F₂ and Hg₂I₂ exhibited weak green emission, while no luminescence was observed from Hg₂Br₂ in this spectral region. The common orange luminescence is tentatively attributed to structural defects unique to mercurous salts, while the green emission is ascribed to an unspecified impurity center.