Mn2+-doped ZnSe nanocrystals (Mn:ZnSe d-dots) with high optical qualityhigh dopant emission quantum yield with monoexponential dopant-emission decay dynamicsenable systematic and quantitative studies of temperature- and Mn2+ concentration-dependent optical properties of the dopant emission, especially its relationship with magnetic coupling. While temperature-dependent steady-state and transient dopant emission of d-dots with dilute Mn2+ concentrations originated from isolated Mn2+ ions, and can be quantitatively treated as a result of exciton–phonon coupling of isolated paramagnetic emission centers. Dopant emission of d-dots with high Mn2+ concentrations (up to 50% of Zn2+ ions being replaced by Mn2+ ions in the core nanocrystals) are found solely related to magnetically coupled Mn2+ emission. Magnetic coupling effects on steady-state dopant emission of d-dots with high Mn2+ concentrations are much stronger than those observed for doped bulk semiconductors, which is found to follow a strong and universe shell-thickness dependence for the epitaxial ZnSe and/or ZnS shells of the d-dots. By exciting the magnetically coupled Mn2+ ions directly, dopant-emission of d-dots with high Mn2+ concentrations exhibit monoexponential decay dynamics. In addition to this emission channel, a minor channel with slightly longer decay lifetime appears when the host nanocrystals with high Mn2+ concentrations are excited, which is barely visible at room temperature and increases its fraction by decreasing temperature.

By taking advantage of well-defined spectroscopic signatures of high-quality CdSe/CdS core/shell QDs, the effects of oxygen on photoluminescence (PL) of QDs were studied systematically and quantitatively at both single-dot and ensemble (on substrate and in solution) levels, which reveals a unified yet simple picture. With a sufficient amount of oxygen in the system during photoexcitation, the core/shell QDs in all forms would be deionized timely from the photogenerated and inefficient trion state back to the efficient single-exciton state, with superoxide radicals as the reduction product of oxygen. Under a given excitation power, rates of both spontaneous deionization and photodeionization channels increased by increasing the oxygen pressure, but photoionization of the QDs was barely affected by the oxygen pressure. While stabilizing PL by oxygen was identified for both CdSe plain core and CdSe/CdS core/shell QDs, irreversible photocorrosion was only observed for CdSe plain core QDs, suggesting the importance of high-quality epitaxial shells for QDs in various applications.

Zinc-blende CdSe, CdS, and CdSe/CdS core/shell nanocrystals with a structure-matched shape (cube-shaped, edge length ≤30 nm) are synthesized via a universal scheme. With the edge length up to five times larger than exciton diameter of the bulk semiconductors, the nanocrystals exhibit novel properties in the weakly confined size regime, such as near-unity single exciton and biexciton photoluminescence (PL) quantum yields, singlenanocrystal PL nonblinking, mixed PL decay dynamics of exciton and free carriers with sub-microsecond monoexponential decay lifetime, and stable yet extremely narrow PL full width at half maximum (FWHM < 0.1 meV) at 1.8 K. Their monodisperse edge length, shape, and facet structure enable demonstration of unexpected yet size-dependent PL properties at room temperature, including unusually broad and abnormally size-dependent PL FWHM (∼100 meV), nonmonotonic size dependence of PL peak energy, and dual-peak single-exciton PL. Calculations suggest that these unusual properties should be originated from the band-edge electron/hole states of the dynamic-exciton, whose exciton binding energy is too small to hold the photogenerated electron−hole pair as a bonded Wannier exciton in a weakly confined nanocrystal.

Wurtzite CdSe@CdS dot@platelet nanocrystals with (001) and (00–1) polar facets as the basal planes and (100) family of nonpolar facets as the side planes are applied for studying surface defects on semiconductor nanocrystals. When they are terminated with cadmium ions coordinated with carboxylate ligands, a single set of absorption features and band-edge photoluminescence (PL) with near unity PL quantum yield and monoexponential PL decay dynamics (lifetime ∼28 ns) are observed. In addition to these spectral signatures, when the surface is converted to sulfur-terminated, a second set of sharp absorption features with decent extinction coefficients and a secondary band-edge PL with low PL quantum yield and long-lifetime (>78 ns) PL decay dynamics are reproducibly recorded. Photochemical analysis confirms that the secondary UV–vis and PL spectral features are quantitatively correlated with each other. Chemical analysis and X-ray photoelectron spectroscopy measurements confirm that such secondary spectral features are well correlated with the sulfide (such as −SH) and disulfide (such as −S–S−) surface sites of a basal plane, which likely form surface hole electronic states delocalized on the entire basal plane. Results suggest that, for studying surface defects on semiconductor nanocrystals, it is essential to prepare a nearly monodisperse surface structure in terms of facets and surface chemical bonding.

Emission of amino benzothiadiazoles is controllable and might be used for white solution emission, fluorescent chemosensors, and emitting materials in OLEDs.