Annealing effect on structure and green emission of ZnO nanopowder by decomposing precursors

ZnO nanopowder is successfully synthesized by annealing the precursors in oxygen gas using the chemical precipitation method. Structural and optical properties of thus synthesized ZnO nanopowder are characterized by scanning electron microscopy （SEM） and photoluminescence （PL）. The morphology of ZnO nanopowders evolves from nanorod to cobble as annealing temperature increases from 500 to 1000℃, while spiral structures are observed in the samples annealed at 900 and 1000℃. The PL spectra of ZnO nanopowder consist of largely green and yellow emission bands. The green emission from ZnO nanopowder depends strongly on the annealing temperature with a peak intensity at a temperature lower than 800℃ while the yellow emission is associated with interstitial oxygen Oi.

Structural and Luminescent Properties of Mg_(0.25-x)Al_(2.57)O_(3.79)N_(0.21):xMn^(2+)Green-Emitting Transparent Ceramic Phosphor

A series of spinel-type Mg_(0.25-x)Al_(2.57)O_(3.79)N_(0.21):xMn^(2+)(MgAlON:xMn^(2+))phosphors were synthesized by the solid-state reaction route.The transparent ceramic phosphors were fabricated by pressureless sintering followed by hot-isostatic pressing(HIP).The crystal structure,luminescence and mechanical properties of the samples were systematically investigated.The transparent ceramic phosphors with tetrahedrally coordinated Mn^(2+)show strong green emission centered around 515 nm under blue light excitation.As the Mn^(2+)concentration increases,the crystal lattice expands slightly,resulting in a variation of crystal field and a slight red-shift of green emission peak.Six weak absorption peaks in the transmittance spectra originate from the spin-forbidden ^(4)T_(1)(^(4)G)→^(6)A_(1) transition of Mn^(2+).The decay time was found to decrease from 5.66 to 5.16 ms with the Mn^(2+)concentration.The present study contributes to the systematic understanding of crystal structure and properties of MgAlON:xMn^(2+)green-emitting transparent ceramic phosphor which has a potential application in high-power light-emitting diodes.

Study of Structural, Optical, Electrical and Dielectric Properties of Gd-Doped ZnO Composites Synthesized by Solid State Reaction Method

In this manuscript, we are reporting structural, bonding, optical, dielectric, and electrical properties of Gd-doped ZnO composite samples (Zn1−xGdxO, x = 0, 0.05, 0.10) prepared by solid-state reaction method. XRD spectra confirm the wurtzite hexagonal phase with a grain size distribution of 42 - 47 nm. The FT-IR spectra confirm bonding behavior like Zn-O, O=C=O, and O-H stretching modes. FESEM micrographs show that the grains of crystallites possess nearly spherical morphology. Optical absorption spectra confirm that the optical band gap decreases systematically from 3.19 eV to 3.15 eV for x = 0.0 to x = 0.10 samples. For all samples, PL spectra exhibited near-band emission, blue emission, and green emission peaks. The dielectric constant decreases as the applied frequency increases. Hall effect results show that with increasing doping concentration of Gd, mobility and resistivity increase while bulk concentration decreases. Current-Voltage study shows that current increases when temperature is increased. Rare earth-doped ZnO is potential material used for optoelectronics and spintronics device applications. Properties of Gd-doped ZnO are studied by various research groups, but dielectric studies are limitedly reported. Therefore, the present research work aims to study the change of electrical, optical, and dielectric properties of Gd-doped ZnO for device applications.

Fabrication of Green Electroluminescent Devices

A gadolinium ternary complex, tris(1 phenyl 3 methyl 4 isobutyryl 5 pyrazolone) (2, 2′ dipyridyl) gadolinium Gd(PMIP) 3(Bipy) was synthesized and used as a light emitting material in the organic electroluminescent devices. The devices exhibited the green electroluminescent (EL) emission peaking at 513 nm, originating from the Gd(PMIP) 3(Bipy). By improving the configuration, the device with a structure of ITO/poly(N vinylcarbazole) (PVK) (40 nm)/Gd(PMIP) 3(Bipy) (40 nm)/tris (8 hydroxyquinoline) aluminum (ALQ) (40 nm)/Mg∶Ag(200 nm)/Ag(100 nm) showed higher performance and a maximum luminance of 340 cd·m -2 at 18 V.

Photoluminescence of green nanophosphors Sr_(2)MgSi_(2)O_(7)doped with Tb^(3+)under 374-nm excitation

A series of Sr_(2)MgSi_(2)O_(7):Tb^(3+)nanophosphors is prepared using a high-temperature solid-state reaction.The x-ray diffraction patterns show that the crystal structure of the sample is not significantly affected by Tb^(3+)ions.However,the images of the scanning electron microscope illustrate that the average size of nanoparticles becomes larger with the increase of Tb^(3+)concentration.Unlike earlier investigations on down-conversion emission of Tb^(3+)ion excited by deep ultraviolet light,in this work,the photoluminescence characteristics of Sr_(2)MgSi_(2)O_(7)nanophosphors doped with different Tb^(3+)concentrations are analyzed under 374-nm excitations.The intense green emission at 545 nm is observed at an optimal doping concentration of 1.6 mol%.The main reason for the concentration quenching is due to the electric dipole-electric dipole interaction among Tb^(3+)ions.

Green up-conversion Luminescence in Nd^(3+)-Ho^(3+) Co-doped Oxyfluorotellurite Glasses

Blue, green and red up-conversion luminescence at around 490, 545 and 650 nm, which result from the Ho^3＋5F3→5I8, （5F4,5S2）→3. 5I8 and 5F5→ 5I8 transitions, respectively, were observed in Nd3＋-Ho3. co-doped oxyfiuorotellurite glasses under 800 nm excitation. Among these up-conversion luminescence, the green emission was extremely strong and the blue and red emission intensities were very weak. Selectively strong green up-conversion luminescence of these glasses indicate a high possibility for realizing a green upconversion laser. Up-conversion processes for the blue, green and red emissions are two-photon processes assisted by Nd3^＋→Ho^3＋ energy transfer. It is proposed that the up-conversion mechanism for the blue and green emissions is different from that for the red emission. The respective mechanisms are discussed.

Green-emissive carbon quantum dots with high fluorescence quantum yield:Preparation and cell imaging

High fluorescence quantum yield(QY),excellent fluorescence stability,and low toxicity are essential for a good cellular imaging fluorescent probe.Green-emissive carbon quantum dots(CQDs)with many advantages,such as unique fluorescence properties,anti-photobleaching,low toxicity,fine biocompatibility and high penetration depth in tissues,have been considered as a potential candidate in cell imaging fluorescent probes.Herein,N,S-codoped green-emissive CQDs(QY=64.03%)were synthesized by the one-step hydrothermal method,with m-phenylenediamine as the carbon and nitrogen source,and L-cysteine as the nitrogen and sulfur dopant,under the optimum condition of 200℃ reaction for 2 h.Their luminescence was found to originate from the surface state.In light of the satisfactory photobleaching resistance and the low cytotoxicity,CQDs were used as a cell imaging probe for HeLa cell imaging.The results clearly indicate that cells can be labeled with CQDs,which can not only enter the cytoplasm,but also enter the nucleus through the nuclear pore,showing their broad application prospect in the field of cell imaging.

Green-emitting Polyfluorenes Containing Hexylthiophen-dibenzothiophene-S,S-dioxide Unit with Large Two-photon Absorption Cross Section

Green light-emitting polyfluorenes containing 3,7-bis（4-hexylthiophen-2-yl）dibenzo[b,d]thiophene 5,5-dioxide（DHTSO）unit were synthesized.All the resulted polymers show high thermal stability with the decomposition temperatures（T_d）over 420°C and the glass transition temperatures（T_g）over 75°C.The polymers exhibit the enhanced highest occupied molecular orbital（HOMO）energy levels and the depressed lowest unoccupied molecular orbital（LUMO）energy levels with the increase of DHTSO unit in polymers.The photoluminescence（PL）spectra of the polymers show positive solvatochromism in solution with the variation of solution polarities,indicating remarkable intramolecular charge transfer（ICT）effect in the polymers containing DHTSO moiety.The fluorescence quantum yields（（37）_（PL））are in the range of 34%-67%for PF-DHTSOs in film.All polymers possess two photon absorption（TPA）properties,and the TPA cross sections（？_2）are enhanced with increasing DHTSO unit in polymers.The highest？_2 is 2392 GM for PF-DHTSO15 in chloroform solution upon 740 nm excitation.The device of PF-DHTSO15 shows green emission with the Commission Internationale de L’.Eclairage（CIE）coordinates of（0.26,0.59）,and the maximum luminous efficiency（LE_（max））of 10.8 cd·A^（-1） with the configuration of ITO/PEDOT：PSS/EL/Cs F/Al.These results indicate that introducing DHTSO unit into polyfluorene backbone could be a promising molecular design strategy for TPA and effective green-light emission.

Multiple-quantum-well perovskite for hole-transport-layer-free light-emitting diodes

We demonstrate hole-transport-layer-free light-emitting diodes(LEDs) based on solution-processed multiple-quantum-well(MQW) perovskite. The MQW perovskite can self-assemble to a unique structure of vertically graded distribution with two-dimensional layered perovskite covered by three-dimensionallike perovskite at top, which can naturally form a barrier of electron transporting to the anode interface,thereby enhancing the charge capture efficiency. This leads to hole-transport-layer-free MQW perovskite LEDs reaching an external quantum efficiency(EQE) of 9.0% with emission peak at 528 nm, which is over6 times of LEDs based on three-dimensional perovskite with the same device structure, representing the record EQE of hole-transport-layer-free perovskite LED.

Wastewater treatment in 2050:Challenges ahead and future vision in a European context

1.Introduction The current state of the wastewater industry is one of transition.In Europe,in the last 2 decades,we have seen a significant improvement on river water quality after implementation of the Urban Waste Water Treatment European Directive(91/271/EEC)[1],and the European Water Framework Directive[2].Up to 97% of the population have now access to safely managed wastewater treatment services.

Deep Eutectic Solvent-assisted Synthesis of Nitrogen-doped Carbon Quantum Dots for Cell Imaging

Carbon quantum dots(CQDs)are widely used in fluorescence imaging due to their negligible toxicity,low-cost and excellent Huorescence properties.The fluorescence properties of CQDs are greatly a fleeted by the synthesis method,passivation agent and reaction media.In this study,the nitrogen-doped CQDs(N-CQDs)were synthesized by a facile microwave-assisted method with citric acid(CA)as a carbon source and deep eutectic solvents as a N-dopaiit as well as the reaction solvent.After detailed characterizations,the as-prepared N-CQDs exliibited near spherical morphology with an average size of(2.64±0.55)nm.Besides,the abundant hydrophilic limctional groups including hydroxyl,carboxyl,amine and quaternary-ammonium were present on the surface of the N-CQDs.TheN-CQDs displayed the excitation-dependent fluorescence feature under the excitation wavelength of 350—80 nm.Moreover,the N-CQDs could be efficiently uptaken by RAW264.7 cells and emitted bright green light.Meanwhile,the resultant N-CQDs showed the low cytotoxicity in living cells,suggesting the great potential in bio-imaging applications.