PbSe-Based Colloidal Core/Shell Heterostructures for Optoelectronic Applications

Lead-based (IV–VI) colloidal quantum dots (QDs) are of widespread scientific and technological interest owing to their size-tunable band-gap energy in the near-infrared optical region. This article reviews the synthesis of PbSe-based heterostructures and their structural and optical investigations at various temperatures. The review focuses on the structures consisting of a PbSe core coated with a PbSexS1–x (0 ≤ x ≤ 1) or CdSe shell. The former-type shells were epitaxially grown on the PbSe core, while the latter-type shells were synthesized using partial cation-exchange. The influence of the QD composition and the ambient conditions, i.e., exposure to oxygen, on the QD optical properties, such as radiative lifetime, Stokes shift, and other temperature-dependent characteristics, was investigated. The study revealed unique properties of core/shell heterostructures of various compositions, which offer the opportunity of fine-tuning the QD electronic structure by changing their architecture. A theoretical model of the QD electronic band structure was developed and correlated with the results of the optical studies. The review also outlines the challenges related to potential applications of colloidal PbSe-based heterostructures

Quantum Confinement Regimes in CdTe Nanocrystals Probed by Single Dot Spectroscopy : From Strong Confinement to the Bulk Limit

Sufficiently large semiconductor nanocrystals are a useful model system to characterize bulk-like excitons, with the electron and hole bound predominantly by Coulomb interaction. We present optical characterization of excitons in individual giant CdTe nanocrystals with diameters up to 25.5 nm at 4.2 K under varying excitation power and magnetic field strength. We determine values for the biexciton binding energy, diamagnetic shift constant, and Landé g-factor, which approach the bulk values with increasing nanocrystal size. (Figure Presented)

Impact of anisotropy in spin-orbit coupling on the magneto-optical properties of bulk lead halide perovskites

The renaissance of interest in halide perovskites, triggered by their unprecedented performance in optoelectronic applications, elicited worldwide efforts to uncover a variety of intriguing physical properties, with a particular interest in spin-orbit effects. The current work presents the first magneto-optical experimental evidence for anisotropic electron-hole interactions arising from bulk orthorhombic MAPbBr3. Magneto-photoluminescence spectra, monitored along with several different crystallographic directions, were dominated by dual exciton emission peaks, while each exhibited a highly nonlinear response to a magnetic field. Moreover, these plots depicted asymmetry from -B0 to +B0, with a strong dependence on the axis of observations. A theoretical model implementing anisotropy in the electron-hole interaction, Rashba effect, Landé g factors, and a lesser contribution from an Overhauser effect, corroborated the experimental results. These research discoveries expand the possible applications of excitons in halide perovskites toward optoelectronic and information devices.ISSN:1098-0121ISSN:0163-1829ISSN:1550-235XISSN:0556-2805ISSN:2469-9969ISSN:1095-3795ISSN:2469-995

Hydrogen-like Wannier–Mott Excitons in Single Crystal of Methylammonium Lead Bromide Perovskite

A thorough investigation of exciton properties in bulk CH₃NH₃PbBr₃ perovskite single crystals was carried out by recording the reflectance, steady-state and transient photoluminescence spectra of submicron volumes across the crystal. The study included an examination of the spectra profiles at various temperatures and laser excitation fluencies. The results resolved the first and second hydrogen-like Wannier–Mott exciton transitions at low temperatures, from which the ground-state exciton’s binding energy of 15.33 meV and Bohr radius of ∼4.38 nm were derived. Furthermore, the photoluminescence temperature dependence suggested dominance of delayed exciton emission at elevated temperatures, originating from detrapping of carriers from shallow traps or/and from retrapping of electron–hole pairs into exciton states. The study revealed knowledge about several currently controversial issues that have an impact on functionality of perovskite materials in optoelectronic devices

Influence of Alloying on the Optical Properties of IV–VI Nanorods

The synthesis and structural and optical characterization of PbSe_<i>x</i>S_1–<i>x</i> and PbSe/PbSe_<i>x</i>S_1–<i>x</i> nanorods with a diameter between 2 and 4.5 nm and a length of 10 to 38 nm is reported. The energy band gap of the nanorods exhibits a pronounced variation upon the change in diameter and composition, with a minor influence on lengths beyond 10 nm. The photoluminescence spectrum of the nanorods is composed of a dominant band, accompanied by a satellite band at elevated temperatures. The dominant band shows an exceptionally small band gap temperature coefficient and negligible extension of the radiative lifetime at cryogenic temperatures compared with the photoluminescence processes in PbSe nanorods and in PbSe_<i>x</i>S_1–<i>x</i> quantum dots with similar band gap energy. A theoretical model suggests the occurrence of independent transitions from a pair of band-edge valleys, located at the L points of Brillouin zone, related to the dominant and satellite emission processes. Each valley is four-fold degenerate and possesses a relatively small electron–hole exchange interaction

Polarized emission in II–VI and perovskite colloidal quantum dots

The polarized emission of colloidal quantum dots from II–VI and perovskite semiconductors were investigated thoroughly, revealing information about the optical transitions in these materials and their potential use in various opto-electronic or spintronic applications. The studies included recording of the micro-photoluminescence of individual nanostructures at cryogenic temperatures, with or without the influence of an external magnetic field. The experimental conditions enabled detection of circular and/or linear polarized emission to elucidate the exciton manifolds, angular momentum of the emitting states, Landé g-factors, single exciton and bi-exciton binding energies, the excitons’ effective Bohr radii, and the unique influence of the Rashba effect. The study advances the understanding of other phenomena such as electron–hole dissociation, long diffusion lengths, and spin coherence, facilitating appropriate design of optical and spin-based devices

Polarized emission in II-VI and perovskite colloidal quantum dots

ISSN:1361-6455ISSN:0368-3508ISSN:0953-4075ISSN:0022-370

Polarized emission in II–VI and perovskite colloidal quantum dots

The polarized emission of colloidal quantum dots from II–VI and perovskite semiconductors were investigated thoroughly, revealing information about the optical transitions in these materials and their potential use in various opto-electronic or spintronic applications. The studies included recording of the micro-photoluminescence of individual nanostructures at cryogenic temperatures, with or without the influence of an external magnetic field. The experimental conditions enabled detection of circular and/or linear polarized emission to elucidate the exciton manifolds, angular momentum of the emitting states, Landé g-factors, single exciton and bi-exciton binding energies, the excitons’ effective Bohr radii, and the unique influence of the Rashba effect. The study advances the understanding of other phenomena such as electron–hole dissociation, long diffusion lengths, and spin coherence, facilitating appropriate design of optical and spin-based devices