2, Vanderbilt University, Nashville, Tennessee, United States
Lead sulfide nanocrystal quantum dots (QDs) possess size-dependent tunable photoluminescence (PL) from the near-infrared to the mid-infrared owing to the strong quantum confinement effect. Despite great interest in PbS QDs for both fundamental research and practical applications, single nanocrystal spectroscopy of PbS QDs with emission in the telecom wavelength range still remains challenging. Here, we report PL spectral and polarization studies for single PbS/CdS core/shell QDs that emit in the telecom O-band window (1260 nm - 1360 nm, i.e., 0.99 eV - 0.91 eV). Room-temperature PL spectral data reveal that there is a broad distribution of emission peak energy of single QDs spanning from 0.95 eV to 1.2 eV. A correlated TEM-PL analysis reveals that the inhomogeneous energetic broadening is related to PbS core size variation. Single PbS/CdS QDs demonstrate broad homogeneous linewidths with a mean value of 87.8 meV at room-temperature and 27.0 meV at 6 K, indicative of a much faster dephasing time compared to conventional CdSe QDs. Spectral diffusion of 10-20 meV detected for single PbS/CdS QDs at 6 K constitutes a significant contribution to the homogeneous linewidth broadening. We also report emission polarization for single PbS/CdS QDs, which has been corroborated by a theoretical calculation involving a consideration of shape asymmetry.