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This article presents a recognition mechanism for nitro-explosives by the luminescent metal-organic framework 1 (LMOF-1) with the aid of density functional theory (DFT) and time-dependent density functional theory (TDDFT). The behavior of hydrogen bonding between the LMOF-1 and nitro-explosives in the S 1 state is closely associated with the fluorescence properties of the LMOF-1. In our research, we calculated the geometric configuration, 1 H NMR and IR spectra of the Complex 2 formed by LMOF-1 and nitrobenzene in the S 0 and S 1 states. The results showed that the hydrogen bond in the S 1 state was increased, which was unfavorable for the luminescence of LMOF-1. Furthermore, the fluorescence rate of LMOF-1 decreased after encapsulating nitrobenzene into it. These calculated results collectively suggest that LMOF-1 is a potential fluorescence sensor for the detection of nitro-explosives. This research was aiming to provide a better understanding of the recognition mechanism by LMOFs for nitro-explosives., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Red phosphor is indispensable to achieve warm white light in the white light diode (WLED) application. However, the current red phosphors suffer from high cost and harsh synthesis conditions. In this study, an oxide‐based rare‐earth‐free red‐emitting phosphor Li3Mg2NbO6:Mn4+ (LMN:Mn4+) has been successfully synthesized by a simple solid‐state reaction method. The relationship between crystal structure and luminescence was investigated in detail. The site occupancy of the doping Mn4+ ion in the LMN host has been discussed from the point of bond valence sum. How the coordination environment of doping Mn4+ affects the energy level of doping Mn4+ ion has been illustrated via the Tanabe‐Sugano energy‐level diagram. Moreover, warm white light has been obtained using LMN:Mn4+ as compensator to the YAG:Ce3+. [ABSTRACT FROM AUTHOR]

White light-emitting diodes (WLEDs) have been considered as the next generation lighting technology due to their advantages such as high efficiency and environmental friendliness. However, current mainstream WLEDs, which are based on blue chips and the Y3Al5O12:Ce3+ yellow phosphor, suffer from the problem of low color rendering index (CRI). To solve this problem, a yellowish-green phosphor Ca1.5Y1.5Al3.5Si1.5O12:Ce3+ (CYAS:Ce3+) based on the garnet structure has been designed in this study. Its crystal structure, band structure, and luminescence properties have been investigated in detail. CYAS:Ce3+ exhibits efficient and thermal-stable yellowish-green emission. The 5d centroid shift and crystal splitting of the Ce3+ ion in CYAS have been analyzed together with the structure. Moreover, good warm white light with a low correlated color temperature (3210 K), high color rendering index (85.1) and luminous efficacy (88.5 lm W−1) has been obtained by combining CYAS:Ce3+ and the red phosphor CaAlSiN3:Eu2+ with a blue LED chip. [ABSTRACT FROM AUTHOR]

The rare-earth free tunable full-color-emitting Si-BCNO phosphors were synthesized at low temperature (below 800 °C) for 45 min by solid state reaction method using urea, boric acid, polyethylene glycol and silica as raw materials. The prepared samples exhibited single, distinct and broad photoluminescence emission bands varied from blue (470 nm) to red (620 nm) upon excitation at 370 nm by varying the concentrations of Si and sintering temperatures. The decay curves signified that the luminescence was induced by two luminescence centers, related to longer lifetime τ 1 and shorter lifetime τ 2 . The temperature-dependent PL intensity of the phosphor has been also investigated, which performs good thermal stability. It is believed that the Si-BCNO phosphor could be a possible material for multicolor light-emitting diodes. [ABSTRACT FROM AUTHOR]

Using the solid-state reaction method, Ce3+, Tb3+-coactivated Si5 AlON7 ( Si6− z Al z O z N8− z, z = 1) phosphors were successfully synthesized. The obtained phosphors exhibit high absorption and strong excitation bands in the wavelength range of 240-440 nm, matching well with the light emitting-diode ( LED) chip. The ET from Ce3+ to Tb3+ ions in Si5 AlON7: Ce3+, Tb3+ has been studied and demonstrated by the luminescence spectra and decay curves. Moreover, the phosphors show tunable emissions from blue to green by tuning the relative ratio of the Ce3+ to Tb3+ ions. Thermal quenching properties of Si5 AlON7: Ce3+, Tb3+ had also been investigated and the quenching temperature is ~190°C. These results show that Si5 AlON7: Ce3+, Tb3+ could be a promising candidate for a single-phased color-tunable phosphor applied in UV-chip pumped LEDs. [ABSTRACT FROM AUTHOR]

Abstract: Bi3+ doped Ca12Al14O32Cl2 series were successfully synthesized by conventional solid-state reaction method and their luminescence properties have been investigated in detail. Crystallographic parameters of the refinement structure with cubic space group I-43d were obtained by XRD refinement as a =12.0183(3)Å and V (cell volume)=1735.93(1)Å3. The resulting phosphors absorb ultraviolet (UV) light (240–400nm) and show a single intense broad emission band in the wavelength range of 400–600nm with maximum intensity at 483nm. The Commission Internationale de 1’Eclairage (CIE) chromaticity coordinates are about x =0.185, y =0.306. Thus, the novel light blue-emitting phosphor Ca12Al14O32Cl2:Bi3+ could be potentially applied in UV white light-emitting diodes. [Copyright &y& Elsevier]

Abstract: Rare-earth-doped β-SiAlON phosphors, with the compositions of Si6− z Al z O z N8− z :xRe (z =1, Re=Sm or Dy, 0.01⩽ x ⩽0.05), were prepared by a solid-state reaction at high temperature. The photoluminescence properties were investigated as functions of the rare earths (i.e., x) concentration. In β-SiAlON:Sm2+, broad 4f 55d 1 →4f 6 emission and line 5 D 0 → 7 FJ emission were observed at room temperature. The characteristic 4 F 9/2 →6 H 15/2 (blue) and 4 F 9/2 →6 H 13/2 (yellow) transitions of Dy3+ were detected in the emission spectra. And the thermal quenching properties of β-SiAlON:Sm2+ and β-SiAlON:Dy3+ were investigated. [Copyright &y& Elsevier]

Abstract: β-SiAlON:Ln3+ (Ln=Yb/Ho, Yb/Er) microparticles with up-conversion (UC) luminescence properties were successfully synthesized via a solid-state reaction method by employing Si3N4 (nanopowder), Al2O3 (nanopowder) and rear-earth oxides. The results show that the β-SiAlON:Ln3+ microparticles have a size ranging from 100 to 400nm. Under the 980nm NIR laser excitation, Yb/Er and Yb/Ho codoped samples exhibit UC luminescence centered at 658 and 660nm, respectively. The power dependency and the dynamics of the UC luminescence confirm the existence of two-photon UC processes in Yb/Er and Yb/Ho codoped samples respectively, and the UC mechanisms were given. [Copyright &y& Elsevier]

Abstract: A novel ZrO2:Sm3+,Sn4+ phosphor is synthesized by solid state reaction. The ZrO2:Sm3+ does not show afterglow. But, after doping Sn4+, intense red afterglow luminescence is firstly observed in ZrO2:Sm3+,Sn4+ and it can last more than 1000s at maximum. The afterglow decay curves of ZrO2:Sm3+,Sn4+ are fitted by three exponential components and the decay process consists of initial fast, intermediate and slow decay. The thermoluminescence indicates that the Sn4+ ions induce suitable traps with the depth of 0.436eV and result in efficient afterglow luminescence of ZrO2:Sm3+,Sn4+. The thermoluminescence filling and fading experiments further confirm the important role of the proper shallow traps induced by doping Sn4+ on the afterglow of ZrO2:Sm3+,Sn4+. [Copyright &y& Elsevier]

Large quantities of hexagonal boron nitride ( h-BN) nanoplates with hexagonal morphologies have been successfully synthesized by a simple two-step route without using any template or catalyst, including combustion synthesis and then annealing processes. The phase content, morphology, and optical properties of the products have been characterized. It reveals that the obtained products are pure and of high crystallinity. The UV-vis absorption spectrum indicates that the h-BN nanoplates have an optical band gap of ~6.07 eV. Strong violet-blue photoluminescence ( PL) emission with a broad band ranging from 400 nm to 475 nm has been observed, indicating that the nanoplates as-grown by this simple route are promising for application in nanosize optical devices ( LEDs, blue-light source, UV detector, etc.). The phonon lines features are obviously found in the PL spectra, the phonon frequency involved in these transitions is consistent with the B-N E2g vibrational mode, which has been measured by the Raman spectroscopy. [ABSTRACT FROM AUTHOR]

Novel Ca 1.96 (B 1- y Si y)(O 3- y N y)Cl:0.04Eu2+ phosphors were designed and synthesized by introducing [Si4++N3−]/[B3++O2−] co-substitutions into Ca 2 BO 3 Cl:Eu2+ lattice. Fourier Transform Infrared Spectroscopy (FTIR) show that typical planar [BO 3 ]3− units gradually transformed into [BO 4 ]5− units with the increase of y , which was firstly realized in luminescence materials. Uneven expansion of cell parameters a,b, and c were confirmed by the combination of X-ray diffraction spectra (XRD) and results of Rietveld refinement. Structure variation caused smaller centroid shift (ε c) and 5 d energy level splitting (ε cfs), inducing the narrowing of excitation spectra (y = 0 → y = 0.2, 168 → 144 nm) and blue-shift of emission spectra (y = 0 → y = 0.2, 582 → 525 nm). Excellent thermal stability (6% loss at 150 °C) was obtained, which resulted from more covalent bonding. Using the combination of representative sample CBSOCN 0.2 : 0.04Eu2+ and red K 2 SiF 6 :Mn4+ in a blue LED driven lamp, white light with high CRI ~92.8 and color temperature closed to the summer sun (5770 K) was obtained. Unlabelled Image • [Si4++N3−]/[B3++O2−] co-substitution was applied to synthesize the Ca 2 (B 1- y Si y)(O 3- y N y)Cl:Eu2+ series. • Luminescence color change from yellow to green with the increase of y. • Thermal stability of samples increased with the increase of y. • White light with high CRI can be synthesized by using the optimal sample CBSOCN 0.2 : 0.04Eu2+. [ABSTRACT FROM AUTHOR]

Luminescent covalent organic frameworks (COFs) as fluorescent sensor materials provide a distinct advantage over other materials. In this work, we investigated the hydrogen bonding between the luminescent COF Ph-An-COF and formaldehyde in its excited electronic state by using density functional theory and time-dependent density functional theory to determine whether this type of COF can be used for formaldehyde detection. Hydrogen bonding significantly changed the nature of the frontier orbital and the luminescent properties. Our study reveals that the hydrogen bonding was strengthened in the excited state and the fluorescence rate coefficient was significantly reduced, which is not favorable for the luminescence of this type of COF and would lead to a luminescence decrease or quenching phenomenon. Therefore, this type of luminescent COF can be used as a potential chemical sensor to detect formaldehyde. This work provides an insight into the design of luminescence covalent organic frameworks. [ABSTRACT FROM AUTHOR]

This paper investigates the luminescent properties of luminescent metal-organic framework (LMOF) [Zn 2 (oba) 2 (bpy)], and its selectivity for the detection of nitro-explosives via fluorescence quenching, using the density functional and time-dependent density functional theories. The luminescent mechanism of the LMOF follows the electron transfer from ligand to ZnO quantum dot. The hydrogen bondings formed between LMOF and electron-withdrawing nitro-explosives as well as electron-donating aromatic compounds have different influences on the luminescent mechanism of the LMOF. The hydrogen bonding in the excited state was investigated to display the relationship between hydrogen bonding and fluorescence. [ABSTRACT FROM AUTHOR]

Abstract: Yellow-orange oxynitride Ca-α-SiAlON: Eu2+ phosphors with the compositions of Ca0.8Si9.2Al2.8O1.2N14.8: xEu2+ (x =0–0.24) were obtained via carbothermal reduction and nitridation method. Crystallographic parameters of the refinement structure with triclinic space group P31c (159) were obtained by XRD refinement as a = b =7.8859(3)Å, c =5.7336(2)Å, V =308.7915(3)Å3, Z =1. The resulting phosphors can absorb light in the range of 300–500nm efficiently and show a single intense broad emission band in the wavelength range of 500–700nm with maximum intensity at 580–601nm. The chromaticity coordinates of the synthesized Ca-α-SiAlON: Eu2+ phosphors can be tailored by simply controlling the activator concentration. All the results show that Ca-α-SiAlON: Eu2+ phosphors can be a candidate for warm white LEDs. [Copyright &y& Elsevier]