Sub-millielectronvolt\nLine Widths in Polarized Low-Temperature\nPhotoluminescence of 2D PbS Nanoplatelets

Colloidal semiconductor nanocrystals are promising materials\nfor\nclassical and quantum light sources due to their efficient photoluminescence\n(PL) and versatile chemistry. While visible emitters are well-established,\nexcellent (near-infrared) sources are still being pursued. We present\nthe first comprehensive analysis of low-temperature PL from two-dimensional\n(2D) PbS nanoplatelets (NPLs). Ultrathin 2D PbS NPLs exhibit high\ncrystallinity confirmed by scanning transmission electron microscopy,\nrevealing Moiré patterns in overlapping NPLs. At 4 K, unique\nPL features are observed in single PbS NPLs, including narrow zero-phonon\nlines with line widths down to 0.6 meV and a linear degree of polarization\nup to 90%. Time-resolved measurements identify trions as the dominant\nemission source with a 2.3 ns decay time. Sub-meV spectral diffusion\nand no inherent blinking over minutes are observed, as well as discrete\nspectral jumps without memory effects. These findings advance the\nunderstanding and underscore the potential of colloidal PbS NPLs for\noptical and quantum technologies.