[en] In this work, highly luminescent quaternary CuNiInS nanocrystals (NCs) are put forward as a good prototype for investigating defect-induced room temperature ferromagnetism. A ferromagnetic Ni cation can preserve the strong luminescence of NCs without introducing intermediate energy levels in the center of the forbidden band. The strong luminescence of NCs is used as an indicator for monitoring the concentration of vacancy defects inside them, facilitating the investigation of the origin of room temperature ferromagnetism in CuNiInS NCs. Our results reveal that the patching of Cu vacancies $({{\mathrm{V}}_{\mathrm{C}\mathrm{u}}}^{-<!--\; ???\; -->})$ with Ni will result in bound magnetic polarons composed of both ${{\mathrm{V}}_{\mathrm{C}\mathrm{u}}}^{-<!--\; ???\; -->}$ and a substitution of Cu by Ni $({{\mathrm{N}\mathrm{i}}_{\mathrm{C}\mathrm{u}}}^{+}),$ giving rise to the room temperature ferromagnetism of CuNiInS NCs. Either the ferromagnetic Ni or the non-ferromagnetic Cu cation can tune the magnetism of CuNiInS NCs because of the change of bound magnetic polaron concentration at the altered concentration ratio of ${{\mathrm{V}}_{\mathrm{C}\mathrm{u}}}^{-<!--\; ???\; -->}$ and ${{\mathrm{N}\mathrm{i}}_{\mathrm{C}\mathrm{u}}}^{+}$. (paper)

[en] Colloidal CdSe/ZnS core/shell nanocrystals (NCs), which were dispersed in SiO₂ sol, were utilized to fabricate a SiO₂:NCs/TiO₂ all-dielectric photonic band gap (PBG) structure. The third-order nonlinear refractive index (n₂) of the PBG structure was nearly triple of that of the SiO₂:NCs film due to the local field enhancement in the PBG structure. The photoinduced change in refractive index (Δn) could shift the PBG band edge, so the PBG structure would show significant transmission modification, whose transmission change was ∼17 folds of that of the SiO₂:NCs film. Under excitation of a 30 GW/cm² femtosecond laser beam, a transmission decrease of 80% was realized

[en] At present, the CH₃NH₃PbBr₃ quantum dots (QDs) reported in the literature usually contain two synthesis steps: the initial preparation of CH₃NH₃Br via the reaction of flammable CH₃NH₂ and HBr, together with the subsequent formation of CH₃NH₃PbBr₃ QDs. To avoid the use of dangerous CH₃NH₂, this work develops a novel one-pot method for synthesizing CH₃NH₃PbBr₃ QDs using safe and commercially available reactants (CH₃NH₃Cl, KBr and PbCl₂). It is found that ultrasonic treatment plays a key role during the synthesis of CH₃NH₃PbBr₃ QDs. Without ultrasonic irradiation, it is not possible to synthesize CH₃NH₃PbBr₃ QDs under heating or vigorous stirring. Aliquots of samples taken at different ultrasonic irradiation time intervals show a time-dependent redshift in the emission wavelength. This suggests the formation of CH₃NH₃PbCl₃ QDs first, followed by the formation of CH₃NH₃PbBr₃ QDs through ultrasonically promoted halide exchange. Moreover, mixed CH₃NH₃PbCl _x Br_{3− x} QDs with a tunable emission wavelength can also be prepared through this one-pot method by controlling the ultrasonic irradiation time. In comparison to the previous two-step method, the current one-pot method is simpler, less time-consuming and does not use flammable CH₃NH₂. The as-prepared CH₃NH₃PbBr₃ QDs show a comparable photoluminescence (PL) quantum yield (QY) to that of the literature. What is more, the ultrasonic time-controlled emission wavelength of CH₃NH₃PbCl _x Br_{3− x} QDs also provides an alternative way of tuning QD emission to the traditional way of controlling the halide ratios. (paper)

[en] Preparing quantum dots (QDs) with strong stability against salts is extremely important in some environments with ultrahigh salts concentration, such as the oil exploitation, wastewater treatment and biological markers. In this paper, we reported a simple new method to prepared highly stable QDs by using multi-branched ligands. Our results suggested that multi-branched ligands-capped QDs have extremely good dynamic stability even in salt-saturated solution. Unlike to traditional dynamic stability theory, which considers the electrostatic repulsion of QDs dominant QD stability, the current work found a new determined factor: the steric hindrance of ligand structure. The high steric hindrance effect of multi-branched ligands can maintain the single dispersity of QDs even at extremely low electrostatic repulsion. As a result, QDs with ultrahigh stability against salts can be realized. (paper)

[en] Ag@ZnO core–shell nanostructures, ZnO nanoparticles (NPs), and Ag NPs were synthesized by laser ablation in water using 8 ns, 1064 nm, and 50 mJ/pulse. The structural, morphological, componential, and optical properties of as-synthesized NPs were examined by X-ray diffraction, transmission electron microscopy, electron diffraction spectrum, and ultraviolet–visible absorption, respectively. The third-order nonlinear optical properties of aqueous dispersions of three NPs were characterized by performing Z-scan experiments with femtosecond laser pulses at 800 nm. It is shown that three NPs exhibit the positive refractive nonlinearity in the absence of nonlinear absorption and the third-order nonlinear refraction index increases in the order of NPs ZnO < Ag < Ag@ZnO. The results indicate that the Ag@ZnO core–shell nanostructure is a promising candidate for applications in ultrafast all-optical switching.

[en] A novel red light-emitting material, Ca₃Al₂O₆:Eu³⁺, which is the first example found in the Ca₃Al₂O₆ host, was prepared by calcination of a layered double hydroxide precursor at 1350 deg. C. The precursor, [Ca_2.9-xAl₂Eu_x(OH)_9.8](NO₃)_2+x.2.5H₂O, was prepared by coprecipitation of metal nitrates with sodium hydroxide. The material is a loose powder composed of irregular particles formed from aggregation of particles of a few nanometers, as shown in scanning electron microscope (SEM) images. It was found that the photoluminescence intensity reached the maximum when the calcination temperature was 1350 deg. C and the concentration of Eu³⁺ was 1.0%. The material emits bright red emission at 614 nm under a radiation of λ=250 nm. - Graphical abstract: Calcination of a layered double hydroxide precursor produces Ca₃Al₂O₆:Eu³⁺, which is very easy to be pulverized. It is proposed that Eu³⁺ takes the place of one Ca²⁺ (green spheres in the picture, pink pyramids are [AlO₄] tetrahedrons) in the cell of Ca₃Al₂O₆. The Ca²⁺ could be any one of the bigger green spheres without inversion symmetry, and emits red light under a UV radiation of λ=250 nm. Display Omitted