Colloidal semiconductor nanocrystals are promising materials for classical and quantum light sources due to their efficient photoluminescence (PL) and versatile chemistry. While visible emitters are well-established, excellent (near-infrared) sources are still being pursued. We present the first comprehensive analysis of low-temperature PL from two-dimensional (2D) PbS nanoplatelets (NPLs). Ultrathin 2D PbS NPLs exhibit high crystallinity confirmed by scanning transmission electron microscopy, revealing Moiré patterns in overlapping NPLs. At 4 K, unique PL features are observed in single PbS NPLs, including narrow zero-phonon lines with line widths down to 0.6 meV and a linear degree of polarization up to 90%. Time-resolved measurements identify trions as the dominant emission source with a 2.3 ns decay time. Sub-meV spectral diffusion and no inherent blinking over minutes are observed, as well as discrete spectral jumps without memory effects. These findings advance the understanding and underscore the potential of colloidal PbS NPLs for optical and quantum technologies.
Keywords: PbS nanoplatelets; cryogenic temperatures; polarized photoluminescence; sub-meV line widths; trions.