Improving the Five-Photon Absorption from Core-Shell Perovskite Nanocrystals.

It is necessary to improve the action cross section (η × σn) of high-order multiphoton absorption (MPA) for fundamental research and practical applications. Herein, the core-shell FAPbBr3/CsPbBr3 nanocrystals (NCs) were constructed, and fluorescence induced by up to five-photon absorption was observed. The value of η × σ5 reaches 8.64 × 10-139 cm10 s4 photon-4 nm-3 at 2300 nm, which is nearly an order of magnitude bigger than that of the core-only NCs. It is found that the increased dielectric constant promotes modulation of MPA effects, addressing the electronic distortion in high-order nonlinear behaviors through the local field effect. Meanwhile, the quasi-type-II band alignment suppresses the biexciton Auger recombination, ensuring the stronger MPA induced fluorescence. In addition, the core-shell structure can not only reduce the defect density but also promote the nonradiative energy transfer though the antenna-like effect. This work provides a new avenue for the exploitation of high-performance multiphoton excited nanomaterials for future photonic integration.

Lateral surface passivation of CdSe nanoplatelets through crown management.

Two-dimensional colloidal CdSe nanoplatelets (NPLs) have been considered as ideal emitting materials for high performance light-emitting devices due to their excellent optical properties. However, the understanding of defect related radiative and nonradiative recombination centers in CdSe NPLs is still far from sufficient, especially their physical distribution locations. In this work, CdSe core and CdSe/CdS core/crown NPLs have been successfully synthesized and their optical properties have been characterized by laser spectroscopies. It is found that the photoluminescence quantum yield of CdSe NPLs is improved by a factor of 4 after the growth of the CdS crown. At low temperatures, the change in the ratio of low and high energy emission intensities from NPLs suggests that the radiative recombination centers are mainly located on the lateral surface of the samples. This finding is further confirmed by the surface passivation experiment. Meanwhile, the nonradiative recombination centers of NPLs located on the lateral surface are also confirmed by ligand exchange. These results demonstrate the importance of understanding the optical properties of the lateral surface of NPLs, which are important for the design of material structures for optoelectronic applications.

Chiral Transition Metal Oxides: Synthesis, Chiral Origins, and Perspectives.

Transition metal oxides (TMOs) consist of a series of solid materials, exhibiting a wide variety of structures with tunability and versatile physicochemical properties. Such a statement is undeniably true for chiral TMOs since the introduction of chirality brings in not only active optical activities but also geometrical anisotropy due to the symmetry-breaking effect. Although progressive investigations have been made for accurately controlled synthesis and relevant explanations on the chirality origin of such materials, the overall field of chiral TMOs is still in its infancy with adequate space for interdisciplinary communications and development. Herein, therefore, recent advances in both experimental phenomena and theoretical calculations in this area are reviewed, to elucidate the underlying chiral origin with respect to their fabrications process, triggering new insights for further evolution of this field.

Towards Chinese clinical named entity recognition by dynamic embedding using domain-specific knowledge.

The task of electronic medical record named entity recognition (NER) refers to automatically identify all kinds of named entities in the medical record text. Chinese clinical NER remains a major challenge. One of the main reasons is that Chinese word segmentation will lead to the wrong downstream works. Besides, existing methods only use the information of the general field, not consider the knowledge from field of medicine. To address these issues, we propose a dynamic embedding method based on dynamic attention which combines features of both character and word in embedding layer. Domain knowledge is provided by word vector trained by domain dataset. In addition, spatial attention is added to enable the model to obtain more and more effective context encoding information. Finally, we conduct extensive experiments to demonstrate the effectiveness of our proposed algorithm. Experiments on CCKS2017 and Common dataset shows that the proposed method outperforms the baseline.

Chiral CdSe nanoplatelets as an ultrasensitive probe for lead ion sensing.

As opposed to traditional photoluminescence and ultra-violet based optical sensing, we present here a sensing system based on resolved optically active polarization with promising applications. It is based on the ultrathin CdSe nanoplatelets (NPLs) when modified with either l or d-cysteine molecules (l/d-cys) as bio-to-nano ligands. The chiral ligand transfers its chiroptical activity to the achiral nanoplatelets with an anisotropy factor of ∼10-4, which unlocks the chiral excitonic transitions and allows lead ion detection with a limit of detection (LOD) as low as 4.9 nM. Simulations and modelling based on time-dependent density functional theory (TD-DFT) reveal the chiral mechanism of l/d-cys capped CdSe NPLs. The presented CD-based sensing system illustrates an alternative possibility of using chiral CdSe NPLs as competitive chiral sensors for heavy metal ion detection.

Optical Characteristics of ZnS Passivated CdSe/CdS Quantum Dots for High Photostability and Lasing.

Nanocrystal quantum dots (QDs) have great potential for optoelectronic applications such as light emitting diodes and lasers due to their superior optical properties. The core-shell CdSe/CdS QDs can suppress Auger recombination effectively and enhance the emission efficiency. However, it will lead to poor photostability due to the small conduction band offset between CdSe core and CdS shell. For effective electron confinement, a thin shell of wide band gap ZnS semiconductor was grown on the CdSe/CdS core-shell QDs. The influence of ZnS shell has been investigated by comprehensive spectroscopic characterization. It is demonstrated that the CdSe/CdS/ZnS QDs show high photostable and temperature-insensitive emission. Moreover, room temperature lasing based on CdSe/CdS/ZnS QDs coated on a fiber was achieved. The lasing action can maintain under higher temperature up to 312.6 K. The experimental result is important for high performance optoelectronic device application based on colloidal QDs.

Optical waveguiding properties of colloidal quantum dots doped polymer microfibers.

QDs-doped polymer microfibers are fabricated through direct drawing method. By adding the polymethylmethacrylate into polystyrene, the surface quality and flexibility of microfiber are improved. Under direct excitation by the focused laser, the polymer microfibers doped with different quantum dots emit different colors and act as an optical waveguide. The waveguide properties of the microfiber are studied in detail. It is found that refractive index of the substrate and diameter of microfiber are the most important factors that affect the optical loss of this waveguide. The microfiber does not produce significant polarization after being deposited on the substrate. Moreover, exciting the QDs-doped polymer microfiber through a blue LED is demonstrated. This structure may find widespread applications in integrated photonic devices.