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.

Tuning of electronic properties in IV-VI colloidal nanostructures by alloy composition and architecture.

Colloidal lead chalcogenide (IV-VI) quantum dots and rods are of widespread scientific and technological interest, owing to their size tunable energy band gap at the near-infrared optical regime. This article reviews the development and investigation of IV-VI derivatives, consisting of a core (dot or rod) coated with an epitaxial shell, when either the core or the shell (or both) has an alloy composition, so the entire structure has the chemical formula PbSexS1-x/PbSeyS1-y (0 ≤ x(y) ≤ 1). The article describes synthesis procedures and an examination of the structures' chemical and temperature stability.

Anomalous independence of multiple exciton generation on different group IV-VI quantum dot architectures.

Multiple exciton generation (MEG) in PbSe quantum dots (QDs), PbSe(x)S(1-x) alloy QDs, PbSe/PbS core/shell QDs, and PbSe/PbSe(y)S(1-y) core/alloy-shell QDs was studied with time-resolved optical pump and probe spectroscopy. The optical absorption exhibits a red-shift upon the introduction of a shell around a PbSe core, which increases with the thickness of the shell. According to electronic structure calculations this can be attributed to charge delocalization into the shell.

Composition-tunable optical properties of colloidal IV-VI quantum dots, composed of core/shell heterostructures with alloy components.

Colloidal quantum dots (CQDs) attract worldwide scientific and technological attention due to the ability to engineer their optical properties by the variation of their size. However, several important applications, such as biological tagging and photovoltaic cells, impose a limit on their size yet demand tunability and thermal stability of the optical band edge. This work introduces a new class of heterostructures, composed of PbSe or PbSe(y)S(1-y) cores, coated by PbS or PbSe(x)S(1-x) shells, with different core-radius/shell-width division, with a radial gradient composition (with 0 < y < 1, 0 < x < 1), which offer a control of the band edge properties by varying the CQDs' composition.

Thermally activated photoluminescence in lead selenide colloidal quantum dots.

The thermal activation processes in PbSe colloidal quantum dots and their influence on the ground-state exciton emission are discussed. Activation of a dark exciton occurs at 1.4-7 K, assisted by an acoustic phonon coupling.