In February 1980, the World Health Organization convened a meeting to consider information relevant to the nomenclature of influenza viruses and to make definitive proposals for the revision of the system which has been in use since 1971. The WHO recommendations are based on data derived from double immunodiffusion reactions involving haemagglutinin and neuraminidase antigens. The revised system of nomenclature is similar to the 1971 system in that it consists of two parts: (a) a type and strain designation, and (b) for influenza A viruses, a description of the antigenic specificity (subtype) of the surface antigens (H and N). The strain designation for influenza virus types A, B, and C contains information on the antigenic type of the virus (based on the antigenic specificity of the nucleoprotein), the host of origin (for strains isolated from non-human sources), geographical origin, strain number, and year of isolation. For influenza A viruses, the antigenic description, in parentheses, follows the strain designation and comprises two indices describing the antigenic subtype of the haemagglutinin and of the neuraminidase antigens. For the influenza A viruses from all species, the H antigens are grouped into 12 subtypes, H1-H12, while the N antigens are divided into 9 subtypes, N1-N9. Reference strains of influenza viruses are maintained by the WHO Collaborating Centres for Reference and Research on Influenza and the WHO Centres for the Study of Influenza Ecology in Animals, and are made available upon request.There is no provision for describing distinct subtypes of influenza B and C viruses. The existence of antigenic variation among influenza B strains is well established but the available information shows that a division into subtypes is not warranted.This revised system of nomenclature should be used universally from the date of publication of this Memorandum.

A revision of the system of nomenclature for influenzaviruses: a W.H.O. memorandum.

Abstract Tailored modifications of halide lead‐free perovskites (LFPs) via doping/alloying with metal cations have been recognized as a promising pathway to highly efficient inorganic phosphors with photoluminescence (PL) quantum yields of up to 100 %. Such materials typically display selective sensitivity to UV light, a broad PL range, and long PL lifetimes as well as a unique compositional variability and stability—an ideal combination for many light‐harvesting applications. This Minireview presents the state‐of‐the‐art in doped LFPs, focusing on the reports published mostly in the last two to three years. We discuss the factors determining the efficiency and spectral parameters of the broadband PL of doped LFPs depending on the dopant and host matrix, both in micro‐ and nanocrystalline states, address the most relevant challenges this rapidly developing research area is facing, and outline the most promising concepts for further progress in this field.

Doping/Alloying Pathways to Lead‐Free Halide Perovskites with Ultimate Photoluminescence Quantum Yields

The synthesis and photoluminescence properties of copper-doped Cs3ZnX5 (X = Cl, I) have been investigated. These materials have application prospects in white LEDs and X-ray scintillators.

Efficient emission in copper-doped Cs3ZnX5 (X = Cl, I) for white LEDs and X-ray scintillators

As a class of emerging photoluminescent materials, hybrid halide crystals have drawn research attention for their potential application in the fields of light‐emitting, security, and waveguide. Nevertheless, hybrid halide crystals containing antimony with long‐term stability and tunable light emission are still increasingly in demand. In this work, serial new hybrid halide crystals (BZA)2ZnCl4·2H2O:xSb3+ (x = 0–0.2, x represents the reaction ratio) and (BZA)2SbCl5 are synthesized (BZA = 2,4‐diamino‐6‐phenyl‐1,3,5‐triazine). In (BZA)2ZnCl4·2H2O:xSb3+ crystals, Sb3+ cations replace partial Zn2+ cations to form [SbCl4]− tetrahedron. Red light emission caused by the substitution of Sb3+ for Zn2+ enhances as the doping rate increases, resulting in the tunable emission from light blue to pink and finally to dark red. There are two kinds of Sb3+ in (BZA)2SbCl5 crystal. Sb(1) has a sixfold coordination with Cl to form a [Sb(1)Cl5]∞ 1D zigzag chain. Sb(2) atom adopts a fivefold coordination with Cl and is separated from each other by BZA+ cations. (BZA)2SbCl5 crystal shows bright orange‐yellow light emission with a photoluminescence quantum yield of 45%. Moreover, the organic–inorganic hybrid metal halide crystals containing antimony have excellent long‐term stability, with phase and luminescence keeping nearly unchanged after more than six months in ambient air.

Antimony Doped Hybrid Zinc Halide Crystals with Tunable Light Emission and Long‐Term Stability

Luminescent materials, also known as phosphors, have been widely used for applications such as emissive displays, fluorescent lamps, light-emitting diodes, and X-ray scintillation detectors. The energy-level diagram of a phosphor is extremely important for understanding its photoluminescence behavior. Here, we demonstrate through a combined density functional theory and experimental study that excited-state energy-level alignment accounts for the photoluminescence behaviors much better than ground-state energy-level alignment. An efficient doped phosphor should exhibit a type I excited-state dopant-host energy-level alignment, regardless of whether its ground-state alignment is type I. A type II excited-state dopant-host energy-level alignment implies that exciton dissociation, resulting in photoluminescence quenching. Our results provide not only a better understanding of the photoluminescence behaviors of the reported phosphors but also critical guidance for designing prospective luminescent materials.

Excited-State Dopant-Host Energy-Level Alignment: Toward a Better Understanding of the Photoluminescence Behaviors of Doped Phosphors.

Lead-free zero-dimensional (0D) perovskite nanocrystals (NCs) with isolated octahedral structures have attracted considerable attention due to their unique photoelectric properties, such as highly efficient emissions with broadband features. A series of phosphors composed of Sb3+-doped 0D perovskite crystals Cs3ZnCl5 with wavelength-tunable emission spectra have been obtained using a facile recrystallization method at room temperature in air. By controlling the doping concentration of Sb3+ in Cs3ZnCl5 lattice, bright emissions from red to orange have been achieved under excitation at 320 nm due to the expansion of the crystal lattice, and the emission excited at 275 nm is bluish-white, spanning the full visible region. Inductively coupled plasma emission spectrometry (ICP) demonstrates the Sb3+ substitutes for Zn2+ rather than Cs+ due to the similar charges and ionic radii. The luminescence performance of phosphor Cs3ZnCl5:Sb3+ can be improved obviously by replacing 3 mol% of Cs+ with Rb+ or K+ due to the further distortion of the crystal lattice. The present approach allows the synthesis of large-scale emissive lead-free 0D perovskites activated by Sb3+ with tunable luminescence color.

Bright tunable luminescence of Sb3+ doping in zero-dimensional lead-free halide Cs3ZnCl5 perovskite crystals.

Owing to its unique function to release the progeny virus particles from the surface of an infected cell, neuraminidase has drawn special attention for developing new drugs to treat influenza viruses. The 150-cavity that is adjacent to the active pocket of the group-1 neuraminidase (N1) renders the conformational change from ‘open’ form to ‘closed’ form when enzyme is binding with a ligand. Consequently, it would be a better strategy to design multi-binding-site inhibitors including X and R groups with proper shapes, sizes and electronic charges fitting into the active site. The NCI and ZINC fragment databases were screened for finding the optimal fragments with de novo design technique. By doing so, 24 derivatives of oseltamivir were obtained by linking the fragments at two different sites of the scaffold of oseltamivir. Molecular docking and dynamics showed that these compounds not only adopt more favourable conformation but also have stronger binding interaction with receptor. Most importantly, all com...

The derivatives of oseltamivir design passing through the important cleft of neuraminidase against influenza virus by de novo design

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Bright tunable luminescence of Sb3+ doping in zero-dimensional lead-free halide Cs3ZnCl5 perovskite crystals.

The derivatives of oseltamivir design passing through the important cleft of neuraminidase against influenza virus by de novo design