In this paper, we report distinct enhancement of surface-state emissions (SSEs) of colloidal CdSe quantum dots (QDs) via coupling to localized plasmons (LPs) in Ag nanostructures. The roles of oleic acid (OA) ligand on QDs in the formation of Ag nanostructures and in the intense enhancement of SSEs of CdSe QDs are explored. We find that OA ligand on CdSe QDs plays a critical role in modifying the morphology of the contacted Ag, which consequently impacts the coupling of QD emitters with LPs in Ag. A systematic study of size effect of QDs on coupling of SSEs with LPs shows that as-deposited small Ag particles favorably enhance the SSEs of small-size CdSe QDs. The OA ligand on QDs yields better Ag crystallinity and clear corners during the annealing process; therefore, it promotes reshaping of small Ag particles into larger ones, favorable to enhance the SSEs of large-size CdSe QDs. The annealed QDs/Ag hybrid structures are more stable than the unannealed ones due to the loss of the OA ligand in the heating process. The selective coupling of QD emitters with LPs in Ag nanostructures allows feasible realization of microscale fluorescent color patterns. The approach of OA-assisted modification of plasmonic properties of Ag nanostructures provides a new route to synthesizing bright luminescence materials and devices that use colloidal QDs.

The lattice-structure-mismatched CdTe/PbTe heterostructures are emerging materials with unique properties and promising applications in midinfrared optoelectronics and spintronics. High-density two-dimensional electron gas at the metastable twisted interfaces of CdTe/PbTe (111) is investigated experimentally and theoretically. CdTe thin films grown on PbTe(111) using molecular-beam epitaxy are found to have high electron mobilities and carrier concentrations from Hall-effect measurements: 2.02 × 10 4 cm 2 /V s and 4.5 × 10 18 cm −3 at 2 K, and 6.70 × 10 3 cm 2 /V s and 6.0 × 10 19 cm −3 at 77 K. Our density-functional theory modeling reveals that the epitaxially grown CdTe/PbTe (111) heterostructures form metastable twisted interfaces that exhibit unusual structural and electronic properties: (1) The PbTe epilayer on CdTe(111) substrates is structurally highly distorted from the rocksalt structure within the first ∼4.5 nm from the interface, which is caused by the stereochemical activity of the Pb s 2 lone pair. (2) The CdTe eplilayer on the PbTe(111) forms spontaneously a high density two-dimensional electron gas (2DEG) over 10 13 cm −2 near the interface, without the need for doping, which explains the experimentally observed high carrier density and mobility. It is a much simpler heterostructure yet able to offer high electron mobility comparable to and one or two order magnitude higher sheet carrier density than the best achieved values for those of Si and II-VI based quantum well structures relying on modulation doping.

We propose by exploring CdTe/PbTe single heterojunctions (SHs) that the abnormal enhancement of mid-infrared light emission from CdTe/PbTe heterostructures is due to coupling with surface plasmons. It is discovered that the observed intense mid-infrared luminescence in the SHs comes from the inherent polar interface character and coupling of surface plasmons localized at the metallic CdTe/PbTe interface to light emitted from the narrow gap PbTe. The finding offers an approach to manipulate mid-infrared light and to fabricate improved mid-infrared optoelectronic devices.

Magnetic semiconductors based on two-dimensional (2D) crystals have attracted attention owing to their intrinsic ferromagnetism and have potential for spintronic devices. Here, full-potential linearized augmented plane wave plus local orbitals method is used to explore the structural, electronic, magnetic, and magneto-optical properties of CrI monolayer. Our first-principles calculations show that CrI monolayer is a ferromagnetic indirect semiconductor with spin-up and spin-down band gaps of 1.23 and 1.90 eV, respectively, and a magnetic moment of 2.93 [Formula: see text] per Cr atom. Based on the macroscopic linear response theory, we systematically study the influences of external magnetic field and out-of-plane strain on the magneto-optical Kerr effect spectra in CrI monolayer. The Kerr rotation of CrI monolayer at 1.96 eV photon energy is [Formula: see text], which is consistent with the recent experiments. We find that the Kerr rotation reaches its maximum when the external magnetic field is perpendicular to CrI plane, while it is almost zero on turning the magnetic field in the plane. This result as well as the sizable magnetocrystalline anisotropy energy (MAE) of 0.79 meV verifies that CrI monolayer has a strong magnetic anisotropy with an out-of-plane easy axis. Further, applying out-of-plane compressive and tensile strain upon CrI monolayer, we observe a redshift of the Kerr rotation spectra with the increase of the strain and the peak values of the Kerr rotation increase correspondingly. The rich electronic and magnetic properties, especially the magneto-optical spectra, render CrI monolayer a promising 2D magnetic material for applications from sensing to data storage.

Localized surface plasmon resonance (LSPR) and photoactivation (PA) effects are combined for the tuning of fluorescent colors of colloidal CdSe quantum dots (QDs). It is found that LSPR with QD emitters intensely enhances surface state emission, accompanied by a remarkable red-shift of fluorescent colors, while PA treatment with colloidal QDs leads to a distinct enhancement of band-edge emission, accompanied by a peak blue-shift. Furthermore, the LSPR effect on QD emitters can be continuously tuned by the PA process. The combination of the post-synthetic approaches allows feasible realization of multi-color patterns from one batch of QDs and the approaches can also be compatible with other micro-fabrication technologies of QD embossed fluorescent patterns, which undoubtedly provides a way of precisely tuning the colors of light-emitting materials and devices that use colloidal QDs.