INFRARED LUMINESCENCE OF MERCUROUS CHLORIDE CRYSTALS

In Hg2Cl2 crystals broad luminescence bands excited with UV light have been studied in the spectral range 0.8-2.25 eV. The measurements have been performed on as-grown crystals and on crystals previously expose d to UV light at RT. The emission spectra consist of six bands peaking at 0.82, 1.06, 1.23, 1.39, 1.51, and 1.72 eV with FWHM of 0.21-0.33 e V. Their intensities depend conspicuously on the concentration of the photochemical products induced by irradiation of the crystals at RT. I t is concluded that the infra-red luminescence of Hg2Cl2 originates fr om crystal defects, especially that complexes (HgClxBr3-x)(-) and (HgC lxBr4-x)(2-) are responsible for these emissions. Excitation of the lu minescence can occur: (i) via excitons in the Hg2Cl2 matrix, (ii) via excited states of Hg2Br2 molecules, and (iii) resonantly through the e xcitation bands of defect centres. A configurational coordinate diagra m for the emission observed at 1.51 eV is proposed. A model for the te mperature quenching of luminescence and energy transfer between two di fferent kinds of centres is used to explain the more complicated tempe rature dependence of this luminescence.