Luminescence of defect centres in Hg2Cl2

Luminescence in Hg 2 Cl 2 crystals excited with UV light is investigated in the spectral region 0.8-2.25 eV. Measurements are performed on as-grown samples and on samples previously exposed to UV light at RT. Six emission bands are found which depend on the concentration of the photochemical entities produced by irradiation of the crystals at RT. It is concluded that infra-red OR) luminescence of Hg 2 Cl 2 originates from crystal defects. The observed emission bands are tentatively attributed to the emission of (HgCl x Br 3-x ) - and (HgCl x Br 4-x ) 2- complexes formed with residual Br impurities. Centres responsible for IR Hg 2 Cl 2 emissions are excited : (i) via excitons of Hg 2 Cl 2 , (ii) via excited states of isolated Hg 2 Br 2 molecules, and (iii) resonantly through the excitation bands of defect centres.