Anomalous quantum confinement of the longitudinal optical phonon mode in PbSe quantum dots

Abstract

We have investigated the diameter dependence of the Raman spectra of lead selenide nanocrystals. The first-order Raman peak at about 136 cm −1 and its second-order overtone at twice this wavenumber move up in energy with decreasing nanocrystal diameter. This anomalous behavior is interpreted in terms of quantum confinement of the longitudinal optical (LO) phonon whose frequency displays a minimum at in the dispersion of bulk PbSe. We perform ab initio calculations of the phonons of PbSe slabs with up to 15 layers. The LO mode perpendicular to the slab shifts indeed upwards with decreasing layer thickness, thus validating the interpretation of the anomalous radius dependence of the Raman spectra in terms of quantum confinement.

Large-scale and facile fabrication of PbSe nanostructures by selenization of a Pb sheet

“…In addition, the Raman spectra show a SP mode that is stronger for the sample that was grown at 400 ○ C. This mode belongs to the Pb-O-Pb stretching mode at the surface of the nanocrystals. 27 Therefore, the Raman results also confirm that the obtained nanostructures are PbSe.…”

Emission Kinetics from PbSe Quantum Dots in Glass Matrix at High Excitation Levels

“…These data allow deriving standard characteristics of the QDs by employing semi‐empirical expressions . We find a temperature coefficient d E g ′/d T = (120 ± 9) μeV K −1 , and Debye temperature of (101 ± 19) K. The longitudinal optical (LO) phonon energy (18.6 ± 2.6) meV is consistent with reports, but falls below the value of (29.6 ± 0.8) meV obtained from the FWHM(T) evolution. The Arrhenius plot of the PL line points to an activation energy of 16.5 meV, see inset in Figure b, which matches the LO phonon energy obtained from the E g ′(T) evolution.…”

Temperature-Dependent Photoluminescent Properties of PbSe Nanoplatelets

“…However, Raman spectra obtained for the PbSe QDs of the same size, synthesized by cation-exchange and direct hot-injection methods, demonstrate similar behavior. The positions of phonon peaks were determined and compared to the known literature data [ 73 , 74 , 75 , 76 ]. The positions of the typical phonon peaks (LA(X), 2TA(X), LO(X) and/or LA(X)/TA(X), 2TO(X), and LO(Γ)) are close for both types of QDs and PbSe NPLs (see Table S1 , Supplementary Materials ).…”