Aggregation of ODC(I) and POL Defects in Bismuth Doped Silica Fiber.

First-principles calculations were used to simulate the aggregation of the peroxy chain defect POL and the oxygen vacancy defect ODC(I). Defect aggregation's electronic structure and optical properties were investigated. The two defects were most likely to accumulate on a 6-membered ring in ortho-position. When the two defects are aggregated, it is discovered that 0.75 ev absorption peaks appear in the near-infrared band, which may be brought on by the addition of oxygen vacancy defect ODC(I). We can draw the conclusion that the absorption peak of the aggregation defect of ODC(I) defect and POL is more prominent in the near infrared region and visible light area than ODC(I) defect and POL defect.

Synthesis, Crystal Growth, and Annealing of CdSxSe1-x and Cr:CdS0.8Se0.2 Single Crystals.

Mid-infrared laser in the 2-5 µm wavelength region is in the atmospheric transmission window range, and hence, it has important application prospects in the fields of optoelectronic countermeasures, space communication, environmental remote sensing, and molecular spectroscopy. One of the most promising technological approaches to achieve mid-infrared laser output is based on direct lasing of transition-metal (TM)-doped II-VI chalcogenide crystals. In this work, CdSxSe1-x and Cr:CdS0.8Se0.2 polycrystals were synthesized by a chemical vapor synthesis method from a stoichiometric mixture of vacuum-sublimed CdS and CdSe. The structure of the synthesized products was analyzed by X-ray diffraction (XRD). Using these synthesized products, CdSxSe1-x and Cr:CdS0.8Se0.2 single crystals were grown by the physical vapor transport (PVT) method. After annealing, the band gap becomes smaller and the transmission range widens to 17 µm. The composition of the single crystals was determined by energy-dispersive spectrometry (EDS) mapping and XPS, and it was found to be uniform throughout the ingot. In addition, the absorption peak maximum for the Cr2+ ion in the Cr:CdS0.8Se0.2 crystal is at 1.84 µm.

Optimizing Broadband Near-Infrared Emission in Bi/Sn-Doped Aluminosilicate Glass by Modulating Glass Composition.

The Bi/Sn-doped aluminosilicate glass samples were prepared using a melting-quenching method and their near-infrared (NIR) emission properties were studied. An ultra-broadband NIR emission ranging from 950 nm to 1600 nm was observed in all samples under 480 nm excitation, which covered the whole fiber low-loss window. The NIR emission spectrum showed that the maximum emission peak was about 1206 nm and the full width at half maximum (FWHM) was about 220 nm. Furthermore, the NIR emission intensity strongly depends on the composition of the glass, which can be optimized by modulating the glass composition. The Bi0 and Bi+ ions were the NIR luminescence source of the glass samples in this paper. The Bi/Sn-doped aluminosilicate glass has the potential to become a new type of core fiber material and to be applied to optical fiber amplifiers (OFAs), based on its excellent performance in ultra-broadband NIR emission.

Compact metalens-based integrated imaging devices for near-infrared microscopy.

With current trends to progressively miniaturize optical systems, it is now essential to look for alternative methods to control light at extremely small dimensions. Metalenses are composed of subwavelength nanostructures and have an excellent ability to manipulate the polarization, phase, and amplitude of incident light. Although great progress of metalenses has been made, the compact metalens-integrated devices have not been researched adequately. In the study, we present compact imaging devices for near-infrared microscopy, in which a metalens is exploited. The indicators including resolution, magnification, and image quality are investigated via imaging several specimens of intestinal cells to verify the overall performance of the imaging system. The further compact devices, where the metalens is integrated directly on the CMOS imaging sensor, are also researched to detect biomedical issues. This study provides an approach to constructing compact imaging devices based on metalenses for near-infrared microscopy, micro-telecopy, etc., which can promote the miniaturization tending of futural optical systems.

The n-type and p-type conductivity mechanisms of the bulk BiOCl photocatalyst from hybrid density functional theory calculations.

In this work, the n-type and p-type conductivity mechanisms of bulk BiOCl are systematically investigated using first-principles calculations. Under the O-rich growth conditions, BiOCl presents the intrinsic p-type conductivity, which primarily originates from the contributions of the antisite defects OCl. This is in excellent agreement with the observed p-type conductivity in BiOCl under high oxygen partial pressure or in oxygen-saturated solutions in experiments. While BiOCl displays the intrinsic n-type conductivity under the Bi-rich growth conditions, the vacancy defects VCl are responsible for the character. Nevertheless, the extrinsic means or effects could lead to the production and ionization of the O vacancies, which could contribute to the n-type conductivity in BiOCl. Therefore, the intrinsic n-type conductivity behavior reported in BiOCl in recent experiments is well explained. Under the Cl-rich growth conditions, the major donor defects VCl and the major acceptor defects VBi in BiOCl compensate each other, leading to an intrinsic insulator. However, it is shown that the usual unintentional H impurities HBi could form the p-type conductivity in BiOCl under Cl-rich growth conditions and enhance the p-type conductivity under O-rich growth conditions. This helps to understand the p-type conductivity behavior reported or mentioned in BiOCl in many experiments. At the same time, we found that Group II elements Ca and Sr are superior p-type doping elements for BiOCl under the Cl-rich and O-rich growth conditions. The defect physics in the bulk BiOCl photocatalyst is well understood. This work may inspire more magnificent studies on developing BiOCl-based photocatalysts.

From K[ZnBP2O8] to K[(Zn0.5Al0.5)2P2O8]: Substitution-Induced Microporous Zincoaluminophosphate with a Congruent-Melting Behavior.

An open-frame aluminophosphate, K[(Zn0.5Al0.5)2P2O8] (KZAPO), was rationally designed by a substitution design strategy and synthesized by a high-temperature molten salt method. Compared with the parent crystal of K[ZnBP2O8], KZAPO was characterized by similar 4 × 8 × 8 networks, a comparable short-wave ultraviolet transparency and a more regular tetrahedral frame with the mixing of (ZnO4)6- and (AlO4)5- anionic groups, highlighting the multifunctional roles that anionic group mixing played in structural and property modulations. In particular, KZAPO was characterized by a high thermal stability (over 850 °C) and a congruent-melting behavior, being conducive to practical applications.

Single Crystal CdSe X-ray Detectors with Ultra-High Sensitivity and Low Detection Limit.

CdSe single crystals (SCs), with a relatively high atomic number, large X-ray absorption coefficients, and high carrier mobility, are expected to provide high-performance detection for X-ray. However, the difficulty of growing high-quality CdSe SC has severely limited its application in X-ray detection. In this work, we develop an unconstrained physical gas phase method and in situ annealing process to grow high-quality CdSe SCs under unconstrained conditions. Using this method, CdSe SCs exhibit natural exposure planes, ultrahigh resistivity of 5.43 × 1012 to 1.29 × 1013 Ω cm and high µτ product of 1.3 × 10-2 to 1.5 × 10-2 cm2 V-1. It is also observed that CdSe SC X-ray detectors exhibit a record sensitivity of 2.08 × 105 µC Gyair-1 cm-2 and a low detection limit of 85 nGyair s-1, which are both desired in medical diagnostics. Moreover, those devices with different crystal directions provide anisotropic X-ray detection performance. Our findings pave a new avenue to exploit high-performance CdSe SC X-ray detectors.

K4Cu3(C3N3O3)2X (X = Cl, Br): strong anisotropic layered semiconductors containing mixed p-p and d-p conjugated π-bonds.

2D materials are gaining more and more interest owing to their promising applications in future electronic industry. Here, two new quasi-2D metal cyanurates, K4Cu3(C3N3O3)2X (X = Cl, Br), were grown and characterized for the first time. They belong to the trigonal P3[combining macron]m1 space group and feature an infinite layer, constructed by p-p conjugation in the (C3N3O3) planar six-membered-rings and d-p conjugation in the N-Cu-N linear chains. Moreover, they are indirect semiconductors with suitable bandgaps of 3.5 eV, locating between g-C3N4 and h-BN. The electronic states and anisotropic optical responses were also studied through theoretical calculations.

Hybrid density functional studies of native defects and H impurities in wurtzite CdSe.

In this study, the formation energies and electronic properties of six native defects as well as H impurities in wurtzite (wz) CdSe are systematically investigated using hybrid density functional calculations. It is shown that native defects, including antisite CdSe and interstitial Cdi, may be sources of the unintentional n-type conductivity in CdSe under Se-poor conditions; meanwhile, the vacancy defect VSe is not a good donor. However, when the common H impurity is considered, it is suggested that both the substitutional impurity HSe and the interstitial impurity Hi are the dominant and effective origins of the unintentional n-type conductivity in Se-poor conditions. However, unintentional p-type conductivity in CdSe is challenging to form regardless of the growth conditions. Moreover, hybrid functional calculations of the electronic structures show that the six native point defects and the extrinsic impurities Hi and HSe will cause more or fewer changes in the band gap. Among all considered defects and impurities, it is found that only the interstitial defect Cdi introduces impurity levels into the band gap. In particular, the present hybrid functional calculations theoretically affirm that the vacancy defect VCd in CdSe can induce a 2 µB magnetic moment; however, other native defects will not introduce any magnetic moment.

"Two in one": an unprecedented mixed anion, Ba2(C3N3O3)(CNO), with the coexistence of isolated sp and sp2π-conjugated groups.

The combination of different types of π-conjugated anions into one structure can lead to multifunctional materials with intriguing properties. Herein, we successfully developed a new mixed anion compound, Ba2(C3N3O3)(CNO) (I), containing two types of π-conjugated groups, planar (C3N3O3)3- six-membered rings and linear (CNO)- units, for the first time. The compound I exhibits the wide bandgap of 4.82 eV and high absorption coefficients in the wavelength range of 200-280 nm; this indicates that it is a potential optical detection material in the solar-blind region.

Facile Growth of an Ultraviolet Hydroisocyanurate Crystal with Strong Nonlinearity and a Wide Phase-Matching Region from π-Conjugated (HC3N3O3)2- Groups.

Mixed-alkali-metal hydroisocyanurate nonlinear-optical crystal RbLi(HC3N3O3)·2H2O was grown by a facile aqueous solution method. It exhibits a short phase-matching wavelength (λPM = 239 nm) and a strong second-harmonic-generation response (deff = 2.1KDP) benefitting from the well-aligned planar π-conjugated (HC3N3O3)2- anions, as confirmed by the first-principles calculations. Moreover, solar blind ultraviolet radiation can be reached using the title crystal via a fourth-harmonic-generation technique of a Nd-based laser, i.e., 1064 nm/4 = 266 nm.

Ba2M(C3N3O3)2 (M = Sr, Pb): Band Engineering from p-π Interaction via Homovalent Substitution in Metal Cyanurates Containing Planar π-Conjugated Groups.

The two new metal cyanurates Ba2M(C3N3O3)2 (M = Sr, Pb) were successfully grown by a solid-state cyclotrimerization reaction. The electronic energy bands of Ba2M(C3N3O3)2 are totally divergent in spite of their same structures and similar interlayer distances. Theoretical calculations show the narrowing band gap of Ba2Pb(C3N3O3)2 stems from the strong interaction between Pb 6p orbitals and anti-π orbitals in (C3N3O3)3- groups.

Parallel Alignment of π-Conjugated Anions in Hydroisocyanurates Enhancing Optical Anisotropy.

Birefringent crystals with optical anisotropy, which are employed to modulate the polarization of light, play a vital role in many fields of the optical industry. In this Communication, two mixed alkali metal hydroisocyanurates, RbLi(H2C3N3O3)2·2H2O (I) and CsLi(H2C3N3O3)2·2H2O (II), were synthesized by a simple aqueous solution method, and they feature layered structures composed of ∞2[H2C3N3O3]- ribbons through hydrogen bonds with the separation of water molecules and alkali cations. They exhibit a simultaneously short ultraviolet cutoff and giant birefringence, resulting from the perfect parallel alignment of π-conjugated (H2C3N3O3)- anions. Interestingly, the first-principles calculations elucidated that the electronic states and optical properties are slightly different owing to the distinct p-π interaction between alkaline metals and the (H2C3N3O3)- group despite the isostructural crystallographic lattice.

Cold atom-atom-anion three-body recombination of 4He4HexLi- (x = 6 or 7) systems.

Atom-atom-anion three-body recombination (TBR) in mixed 4He and xLi- (x = 6 or 7) is investigated in the adiabatic hyperspherical representation by quantum mechanically solving the Schrödinger equation. The distributions of product states following these TBR processes are found to be relatively different for the two systems when the collision energy is less than roughly 0.6 mK × kB or 0.3 mK × kB for 4He4He6Li- and 4He4He7Li- systems, respectively, with kB being the Boltzmann constant. For 4He4He6Li- systems, the rate of recombination into (v=0) l = 04He6Li- molecular anions is the largest with v and l denoting the rovibrational quantum numbers, while the TBR rate that leads to the formation of l = 14He6Li- molecular anions is a little smaller than that of neutral 4He2 molecules. For 4He4He7Li- systems, neutral 4He2 molecules tend to be the most products, following the yields of l = 0 and 1 4He7Li- molecular anions. However, in spite of these distinctly different distributions, the products of molecular anions, the sum of l = 0 and 1 4HexLi- products, are relatively larger than that of neutral 4He2 molecules for both the two systems.

Tailored dimensionality to regulate the phase stability of inorganic cesium lead iodide perovskites.

Inorganic CsPbI3 perovskites have shown promising potential for achieving all-inorganic photovoltaic (PV) devices. However, the black perovskite polymorph (α-phase) of CsPbI3 easily converts into yellow colour (δ-phase) in an ambient environment and it is only stable at high temperature (above 320 °C), which limits its practical application. Here we tailor the three-dimensional CsPbI3 perovskite into quasi-two-dimension through adding a large radius cation phenylethylammonium (PEA+). The incorporation of PEA+ into the CsPbI3 perovskite significantly improves the film morphology as well as the phase stability. An optimal CsxPEA1-xPbI3 perovskite film remains stable in the α-phase from room temperature to 250 °C in air and yields a power conversion efficiency of 5.7% for its solar device. The concept of using large radius cations in the 3D perovskite system provides a new perspective to further enhance the phase stability while retaining the device performance.