Direct and indirect transitions in the luminescence of SnS2

Abstract

The luminescence properties of SnS₂ single crystals were studied in the absorption edge region at room temperature and at low temperature (10 K). The band structure near the band gap minimum was clarified by studying the luminescence of SnS₂ crystals. The band gap minimum is determined by indirect transitions from the L to Γ points of the Brillouin zone (E₉ = 2.324 eV at 300 K). At an energy of 2.400 eV, indirect transitions from the M to Γ points occur. Direct electron transitions in the Brillouin zone - C₁–V₁ in E∥b polarization (2.690 eV) and C₁–V₂ in E⊥b polarization (2.846 eV) - also appear in the luminescence spectra. The most intense luminescence maximum was detected at 3.263 eV (300 K) and is associated with the C₁–V₃ transitions. At low temperatures (10 K), the maximum E₆ at 3.362 eV, due to C₁–V₄ transitions, appears with weaker intensity. A colloidal solution of SnS₂ quantum dots luminesces at 300 K over a wide energy range. By changing the size of the quantum dots, the luminescence region can be shifted. The main contribution to the luminescence of quantum dots of layered SnS₂ is due to direct transitions at the center of the Brillouin zone.