Ultraviolet Absorption of Hg₂Cl₂‐and Hg₂Br₂ Single Crystals

Abstract

The optical unpolarized absorption spectra of Hg,CI, and Hg,Br, single crystals were measured in the spectral range 230-400 nm. A sharp exciton peak and other absorption bands of both halides were observed near the fundamental absorption edge. The absorption peaks due to the splitting of the halogen doublet were also observed. Positions of the exciton peaks are characteristic for the Frenkel (localized) type of excitons. Possible interpretations of the other observed bands are discussed.

Near infra‐red luminescence of Hg2Cl2

“…From a comparison of the excitation spectra of Hg,Cl, at RT and at 82 K, we find that the excitation spectra reflect the temperature behaviour of the absorption spectra [8]. The lowest energy absorption peak of Hg,Cl, crystals, an exciton peak, is centred close to 309 nm at 5 K [8]. Therefore, it is supposed that UV light of the observed excitation band with maximum at 300 nm excites the NIR luminescence mainly via excitons and not by a resonance process within the luminescence centres.…”

“…From a comparison of the excitation spectra of Hg,Cl, at RT and at 82 K, we find that the excitation spectra reflect the temperature behaviour of the absorption spectra [8]. The lowest energy absorption peak of Hg,Cl, crystals, an exciton peak, is centred close to 309 nm at 5 K [8].…”

“…The lowest energy absorption peak of Hg,Cl, crystals, an exciton peak, is centred close to 309 nm at 5 K [8]. Therefore, it is supposed that UV light of the observed excitation band with maximum at 300 nm excites the NIR luminescence mainly via excitons and not by a resonance process within the luminescence centres.…”

“…In contrast to the observations on thin films, absorption measurements performed on single crystals reveal no structure typical of delocalized excitons. In the case of the crystals, the experimental results are discussed in the frame of localized excitons [8]. However, as far as we know, calculations on the electronic band structure of the Hg,Cl, crystal have not been performed up to now, a fact that strongly limits an interpretation of the nature of the observed absorption bands near 3.9eV.…”