Microwave‐assisted sintering synthesis of greenish‐yellow emitting Sr2SiO4:Eu2+ phosphors

Europium ion (Eu²⁺) doped Sr₂SiO₄ phosphors with greenish‐yellow emission were synthesized using microwave‐assisted sintering. The phase structure and photoluminescence (PL) properties of the obtained phosphor samples were investigated. The PL excitation spectra of the Sr₂SiO₄:Eu²⁺ phosphors exhibited a broad band in the range of 260 nm to 485 nm with a maximum at 361 nm attributed to the 5f‐4d allowed transition of the Eu²⁺ ions. Under an excitation at 361 nm, the Sr₂SiO₄:Eu²⁺ phosphor exhibited a greenish‐yellow emission peak at 541 nm with an International‐Commission‐on‐Illumination (CIE) chromaticity of (0.3064, 0.4772). The results suggest that the microwave‐assisted sintering method is promising for the synthesis of phosphors owing to the decreased sintering time without the use of additional reductive agents.     

Synthesis and luminescent properties of novel BaGd2O4:Eu3+ scintillating phosphor

BaGd_2‐xO₄:xEu³⁺ and Ba_1‐yGd_1.79‐2yEu_0.21Na_3yO₄ phosphors were synthesized at 1300°C in air by conventional solid‐state reaction method. Phosphors were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence excitation (PLE) spectra, photoluminescence (PL) spectra and thermoluminescence (TL) spectra. Optimal PL intensity for BaGd_2‐xO₄:xEu³⁺ and Ba_1‐yGd_1.79‐2yEu_0.21Na_3yO₄ phosphors at 276 nm excitation were found to be x = 0.24 and y = 0.125, respectively. The PL intensity of Eu³⁺ emission could only be enhanced by 1.3 times with incorporation of Na⁺ into the BaGd₂O₄ host. Enhanced luminescence was attributed to the flux effect of Na⁺ ions. However, when BaGd₂O₄:Eu³⁺ phosphors were codoped with Na⁺ ions, the induced defects confirmed by TL spectra impaired the emission intensity of Eu³⁺ ions. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis and luminescence properties of Ca3Ga2Si3O12:RE3+ (RE = Eu/Tb) powder phosphors

Rare earth ions (Eu³⁺ or Tb³⁺)‐activated Ca₃ Ga₂ Si₃O₁₂ (CaGaSi) phosphors were synthesized by using a sol–gel method. Photoluminescence spectra of Eu³⁺:CaGaSi phosphors exhibited five emission bands at 578, 592, 612, 652 and 701 nm, which were assigned to the transitions (⁵D₀ → ⁷F₀, ⁷F_1, ⁷F₂, ⁷F₃ and ⁷F₄), respectively, with an excitation wavelength of λ_exci = 392 nm. Among these, the transition ⁵D₀ → ⁷F₂ (612 nm) displayed bright red emission. In the case of Tb³⁺:CaGaSi phosphors, four emission bands were observed at 488 (⁵D₄ → ⁷F₆), 543 (⁵D₄ → ⁷F₅), 584 (⁵D₄ → ⁷F₄) and 614 nm (⁵D₄ → ⁷F₃) from the measurement of PL spectra with λ_exci = 376 nm. Among these, the transition ⁵D₄ → ⁷F₅ at 543 nm displayed bright green emission. The structure and morphology of the phosphors were studied from the measurements of X‐ray diffraction (XRD), scanning electron microscopy (SEM) and energy‐dispersive X‐ray analysis (EDAX) results. Copyright © 2011 John Wiley & Sons, Ltd.     

Rapid synthesis of BaMoO4:Eu3+ red phosphors using microwave irradiation

This study synthesized BaMoO4:Eu³⁺ red phosphors using the microwave method. In addition, the phase composition, morphology, and luminescence properties of the red phosphors were characterized using X-ray diffraction, field-scanning electron microscopy, and photoluminescence spectroscopy. The results revealed that doping red phosphors with different concentrations of Eu³⁺ does not change the crystal structure of the matrix material. The BaMoO₄:Eu³⁺ phosphors exhibited micron-scale irregular polyhedra, which could be excited by ultraviolet light with a wavelength of 395 nm to induce red-light emission. The optimal dosage of Eu³⁺ was 0.08, and the chromaticity coordinates of BaMoO₄:0.08Eu³⁺ phosphors were (0.5869, 0.3099). White light-emitting diode (w-LED) devices manufactured by using a combination of BaMoO₄:0.08Eu³⁺ phosphor and commercially available phosphors exhibited good white-light emission under the excitation of an ultraviolet chip. The BaMoO₄:0.08Eu³⁺ red phosphors that rapidly synthesized under the microwave field are expected to be used in w-LED devices.     

Genome modeling: From chromatin fibers to genes

The intricacies of the 3D hierarchical organization of the genome have been approached by many creative modeling studies. The specific model/simulation technique combination defines and restricts the system and phenomena that can be investigated. We present the latest modeling developments and studies of the genome, involving models ranging from nucleosome systems and small polynucleosome arrays to chromatin fibers in the kb-range, chromosomes, and whole genomes, while emphasizing gene folding from first principles. Clever combinations allow the exploration of many interesting phenomena involved in gene regulation, such as nucleosome structure and dynamics, nucleosome-nucleosome stacking, polynucleosome array folding, protein regulation of chromatin architecture, mechanisms of gene folding, loop formation, compartmentalization, and structural transitions at the chromosome and genome levels. Gene-level modeling with full details on nucleosome positions, epigenetic factors, and protein binding, in particular, can in principle be scaled up to model chromosomes and cells to study fundamental biological regulation.     

Rare earth Eu3+/Tb3+-doped hollow microspheres (LaPO4) and core-shell nanocomposite luminescent materials with different transmittance (SiO2@LaPO4 Eu3+) preparation and research on luminescence performance

For the manufacture of hollow nanospheres that had different shapes, three distinct templates—urea, carbon microspheres, and polyethylene glycol 20,000—were used. The relationship between microspheres with various hollow structures and their luminescent properties were investigated. Furthermore, the effects of annealing temperature and the proportion of rare earth Eu³⁺/Tb³⁺ions in the reaction were investigated using the structural characteristics of the microspheres and fluorescent materials. The fluorescent materials were wrapped on the outer surface of the microspheres. The ideal balance between the best structure and superior luminescent performance was found, to create reasonably good white light.     

Structural characterization and optical properties of Ca2MgSi2O7:Eu2+,Dy3+ phosphor by solid‐state reaction method

Ca₂MgSi₂O₇:Eu²⁺,Dy³⁺ phosphor was prepared by the solid‐state reaction method under a weak reducing atmosphere. The obtained phosphor was characterized using X‐ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy dispersive X‐ray spectroscopy (EDX) and Fourier transform infrared (FT‐IR) techniques. The phase structure of the Ca₂MgSi₂O₇:Eu²⁺,Dy³⁺ phosphor was akermanite type, which is a member of the melilite group. The surface morphology of the sintered phosphor was not uniform and phosphors aggregated tightly. EDX and FT‐IR spectra confirm the elements present in the Ca₂MgSi₂O₇:Eu²⁺,Dy³⁺ phosphor. Under UV excitation, a broadband emission spectrum was found. The emission spectra observed in the green region centered at 535 nm, which is due to the 4f–5d transition. The mechanoluminescence (ML) intensity of the prepared phosphor increased linearly with increases in the mechanical load. The ML spectra were similar to the photoluminescence (PL), which indicates that ML is emitted from the same emitting center of Eu²⁺ ions as PL. Copyright © 2014 John Wiley & Sons, Ltd.     

Luminescence characteristics and X-ray-induced defects in BaFBr:Eu2+ storage phosphor

Three different approaches used to synthesize a sensitive BaFBr:Eu²⁺ X-ray storage photostimulated luminescence (PSL) phosphor at 850°C for 1 h in a reducing atmosphere are reported. The effects of F/Br and Eu concentration on photoluminescence (PL) and PSL sensitivities synthesized by the three approaches were compared. In the first recipe, BaFBr:Eu²⁺ prepared using a BaF₂, BaBr₂ and EuF₃ mixture using solid-state diffusion (Recipe I), even in a reducing atmosphere, yielded a low PL and PSL intensity due to oxygen contamination that acted as competing hole traps. When BaFBr:Eu²⁺ was prepared using ammonium bromide and ammonium fluoride by two different recipes (Recipes II and III), oxygen contamination was eliminated, resulting in enhanced PSL efficiency. The proposed PSL process in BaFBr:Eu²⁺ was consistent with the experimental results. Increased F/Br molar ratios would incorporate fluorine ion interstitials that act as hole traps accompanied by bromine ion vacancies that act as electron traps. Although two types of F centres, F(Br⁻) and F(F⁻) are possible, F(Br⁻) centres formed during X-irradiation are only vital for the PSL process. Structural, morphology, and thermoluminescence (TL) properties of the samples were also examined using XRD, field emission scanning electron microscope (FESEM), energy-dispersive X-ray spectroscopy (EDAX), and TL studies.     

The influence of preparation conditions on the fluorescence properties of Eu(Sal)(3)Phen.

The influence of the synthesis conditions (method and sequence of adding reagents, reaction temperature, stirring rate) on the luminescence performance of the rare earth ternary complex compound europium-salicylic acid-(1,10-phenanthroline) [Eu(Sal)(3)Phen] was studied. We show that the method and sequence of adding reagents greatly affects the luminescence properties of the products. Within the range of synthesis temperatures (30-70 degrees C), the complex has a better luminescence performance at the lower temperature. However, performance decreased when the temperature decreased to 20 degrees C. Increase of stirring rate led to better performance in the range 200-700 r.p.m. Infrared (IR) spectroscopy, scanning electron microscopy (SEM) and wide-angle X-ray diffraction (WAXD) were utilized to characterize the structure and morphology of Eu(Sal)(3)Phen. The studies demonstrate that the crystallization of the product increased with increasing luminescence of the product. Therefore, it is proposed that increasing the crystallization of the product will enhance its luminescence performance.     

Origin and evolution of the panarthropod head – A palaeobiological and developmental perspective

The panarthropod head represents a complex body region that has evolved through the integration and functional specialization of the anterior appendage-bearing segments. Advances in the developmental biology of diverse extant organisms have led to a substantial clarity regarding the relationships of segmental homology between Onychophora (velvet worms), Tardigrada (water bears), and Euarthropoda (e.g. arachnids, myriapods, crustaceans, hexapods). The improved understanding of the segmental organization in panarthropods offers a novel perspective for interpreting the ubiquitous Cambrian fossil record of these successful animals. A combined palaeobiological and developmental approach to the study of the panarthropod head through deep time leads us to propose a consensus hypothesis for the intricate evolutionary history of this important tagma. The contribution of exceptionally preserved brains in Cambrian fossils – together with the recognition of segmentally informative morphological characters – illuminate the polarity for major anatomical features. The euarthropod stem-lineage provides a detailed view of the step-wise acquisition of critical characters, including the origin of a multiappendicular head formed by the fusion of several segments, and the transformation of the ancestral protocerebral limb pair into the labrum, following the postero-ventral migration of the mouth opening. Stem-group onychophorans demonstrate an independent ventral migration of the mouth and development of a multisegmented head, as well as the differentiation of the deutocerebral limbs as expressed in extant representatives. The anterior organization of crown-group Tardigrada retains several ancestral features, such as an anterior-facing mouth and one-segmented head. The proposed model aims to clarify contentious issues on the evolution of the panarthropod head, and lays the foundation from which to further address this complex subject in the future.