Bluish-green afterglow and blue photoluminescence of undoped BaAl2O4.

Undoped BaAl2O4 was derived via sol-gel combustion technique. The afterglow and photoluminescence (PL) properties of undoped BaAl2O4 were explored with the combination of experiments and density functional theory (DFT) calculations. Undoped BaAl2O4 is found to display bluish-green afterglow that is discernible to naked eye in dark for about 20 s. The broad afterglow spectrum of undoped BaAl2O4 is peaked at around 495 nm. As a contrast, the broad PL spectrum of undoped BaAl2O4 can be decomposed into a bluish-green PL band peaking at about 2.53 eV (490 nm) and a blue PL band centered at about 3.08 eV (402.6 nm). DFT calculations indicate that the defect energy levels generated by oxygen and barium vacancies are critical to the afterglow and PL of undoped BaAl2O4. This work demonstrates that the oxygen and barium vacancies in undoped BaAl2O4 are liable for the bluish-green afterglow and blue PL of undoped BaAl2O4. The recorded bluish-green afterglow of BaAl2O4 is particularly important to understand the afterglow mechanisms of rare-earth doped BaAl2O4.

Photoluminescence and afterglow of Dy3+ doped CaAl2O4 derived via sol-gel combustion.

With doping concentration varying from 0.1 to 5.0 mol%, a series of Dy3+ doped calcium aluminate (CaAl2O4:Dy3+) phosphors were synthesized via a sol-gel combustion technique. The phase, morphology, photoluminescence (PL), afterglow, and thermoluminescence (TL) glow curves of CaAl2O4:Dy3+ were investigated by means of X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, PL spectroscopy, afterglow spectroscopy, and TL dosimetry, respectively. It is found that: (i) oxygen vacancies and Dy3+ work as two independent sets of luminescence centers of PL for CaAl2O4:Dy3+; (ii) Dy3+ works as the luminescence center of afterglow for CaAl2O4:Dy3+; (iii) the afterglow of CaAl2O4:Dy3+ lasts for about 115 min at the optimal doping concentration of around 0.8 mol%; and (iv) multiple traps, which are sensitive to doping concentration, are present in CaAl2O4:Dy3+. The PL and afterglow mechanisms of CaAl2O4:Dy3+ are discussed to reveal the processes of charged carrier excitation, migration, trapping, detrapping, and radiative recombination in CaAl2O4:Dy3+.

Diffusing Mn4+ into Dy3+ Doped SrAl2O4 for Full-Color Tunable Emissions.

Dy3+ and Mn4+ codoped SrAl2O4 (SrAl2O4:Dy3+,Mn4+) phosphors were obtained by diffusing Mn4+ ions into Dy3+-doped SrAl2O4 via the constant-source diffusion technique. The influences of diffusion temperature and diffusion time on the emissions of SrAl2O4:Dy3+,Mn4+ were investigated. It was found that: (i) efficient red emission peaking at 651 nm can be readily achieved for SrAl2O4:Dy3+ by simply diffusing Mn4+ into SrAl2O4:Dy3+ at 800 °C and above; (ii) the red emission of Mn4+ becomes dominant over the characteristic emissions of Dy3+ when the diffusion temperature is 900 °C or higher; and (iii) the intensity of the red emission of SrAl2O4:Dy3+,Mn4+ is far more sensitive to diffusion temperature than to diffusion time. Our results have demonstrated that full-color tunable emissions can be realized for SrAl2O4:Dy3+, Mn4+ by tuning the parameters of diffusion temperature and diffusion time, which opens up a space for realizing easy color control of Dy3+-doped inorganic materials.

Green Afterglow of Undoped SrAl2O4.

Undoped SrAl2O4 nanocrystals were obtained via solution combustion using urea as fuel. The afterglow properties of undoped SrAl2O4 were investigated. Green afterglow from undoped SrAl2O4 is visible to the human eye when the 325 nm irradiation of a helium-cadmium laser (13 mW) is ceased. The afterglow spectrum of undoped SrAl2O4 is peaked at about 520 nm. From the peak temperature (321 K) of the broad thermoluminescence glow curve, the trap depth of trap levels in undoped SrAl2O4 is estimated to be 0.642 eV using Urbach's formula. Based on first-principles density functional calculations, the bandstructures and densities of states are derived for oxygen-deficient SrAl2O4 and strontium-deficient SrAl2O4, respectively. Our results demonstrate that the green afterglow of undoped SrAl2O4 originates from the midgap states introduced by oxygen and strontium vacancies. The observation of green afterglow from undoped SrAl2O4 helps in gaining new insight in exploring the afterglow mechanisms of SrAl2O4-based afterglow materials.

Blue Photoluminescence and Cyan-Colored Afterglow of Undoped SrSO4 Nanoplates.

Undoped SrSO4 nanoplates were synthesized via the composite hydroxide-mediated approach. The products were characterized by means of X-ray diffractometry, scanning electron microscopy, X-ray energy-dispersive spectroscopy, X-ray photoelectron spectroscopy, photoluminescence (PL) spectroscopy, electron spin resonance technique, afterglow spectroscopy, and thermoluminescence dosimetry. The steady-state PL spectrum of undoped SrSO4 nanoplates can be deconvoluted into two distinct Gaussian bands centered at 2.97 eV (417.2 nm) and 2.56 eV (484.4 nm), respectively. The nature of the defect emissions is confirmed through the emission-wavelength-dependent PL decays as well as the excitation-wavelength-dependent PL decays. A cyan-colored afterglow from undoped SrSO4 nanoplates can be observed with naked eyes in the dark, and the afterglow spectrum of the undoped SrSO4 nanoplates exhibits a peak at about 492 nm (2.52 eV). The duration of the afterglow is measured to be 16 s. The thermoluminescence glow curve of the undoped SrSO4 nanoplates shows a peak at about 40.1 °C. The trapping parameters are determined with the peak shape method, the calculated value of the trap depth is 0.918 eV, and the frequency factor is 1.2 × 1014 s-1. Using density functional calculations, the band structures and densities of states of oxygen-deficient SrSO4 and strontium-deficient SrSO4 are presented. The mechanisms of the cyan-colored afterglow are discussed for undoped SrSO4, and the oxygen vacancies in SrSO4 are proposed to be the luminescence center of the afterglow.

Intrinsic Defect Engineering in Eu3+ Doped ZnWO4 for Annealing Temperature Tunable Photoluminescence.

Eu3+ doped ZnWO4 phosphors were synthesized via the co-precipitation technique followed by subsequent thermal annealing in the range of 400⁻1000 °C. The phase, morphology, elemental composition, chemical states, optical absorption, and photoluminescence (PL) of the phosphors were characterized by X-ray diffraction, scanning electron microscopy, dispersive X-ray spectroscopy, X-ray photoelectron spectrometry, diffuse UV⁻vis reflectance spectroscopy, PL spectrophotometry, and PL lifetime spectroscopy, respectively. It is found that the PL from Eu3+ doped ZnWO4 is tunable through the control of the annealing temperature. Density functional calculations and optical absorption confirm that thermal annealing created intrinsic defects in ZnWO4 lattices play a pivotal role in the color tunable emissions of the Eu3+ doped ZnWO4 phosphors. These data have demonstrated that intrinsic defect engineering in ZnWO4 lattice is an alternative and effective strategy for tuning the emission color of Eu3+ doped ZnWO4. This work shows how to harness the intrinsic defects in ZnWO4 for the preparation of color tunable light-emitting phosphors.

Eu2+ and Eu3+ Doubly Doped ZnWO4 Nanoplates with Superior Photocatalytic Performance for Dye Degradation.

Eu2+ and Eu3+ doubly doped ZnWO4 nanoplates with highly exposed {100} facets were synthesized via a facile hydrothermal route in the presence of surfactant cetyltrimethyl ammonium bromide. These ZnWO4 nanoplates were characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectrometry, diffuse UV-vis reflectance spectroscopy, photoluminescence spectrophotometry, and photoluminescence lifetime spectroscopy to determine their morphological, structural, chemical, and optical characteristics. It is found that Eu-doped ZnWO4 nanoplates exhibit superior photo-oxidative capability to completely mineralize the methyl orange into CO2 and H2O, whereas undoped ZnWO4 nanoparticles can only cleave the organic molecules into fragments. The superior photocatalytic performance of Eu-doped ZnWO4 nanoplates can be attributed to the cooperative effects of crystal facet engineering and defect engineering. This is a valuable report on crystal facet engineering in combination with defect engineering for the development of highly efficient photocatalysts.

Effect of enterohaemorrhagic Escherichia coli O157:H7-specific enterohaemolysin on interleukin-1ß production differs between human and mouse macrophages due to the different sensitivity of NLRP3 activation.

Enterohaemorrhagic Escherichia coli (EHEC) O157:H7 infection in humans can cause acute haemorrhagic colitis and severe haemolytic uraemic syndrome. The role of enterohaemolysin (Ehx) in the pathogenesis of O157:H7-mediated disease in humans remains undefined. Recent studies have revealed the importance of the inflammatory response in O157:H7 pathogenesis in humans. We previously reported that Ehx markedly induced interleukin-1ß (IL-1ß) production in human macrophages. Here, we investigated the disparity in Ehx-induced IL-1ß production between human and mouse macrophages and explored the underlying mechanism regarding the activation of NOD-like receptor family, pyrin domain containing 3 (NLRP3) inflammasomes. In contrast to the effects on human differentiated THP-1 cells and peripheral blood mononuclear cells, Ehx exerted no effect on IL-1ß production in mouse macrophages and splenocytes because of a disparity in pro-IL-1ß cleavage into mature IL-1ß upon caspase-1 activation. Additionally, Ehx significantly contributed to O157:H7-induced ATP release from THP-1 cells, which was not detected in mouse macrophages. Confocal microscopy demonstrated that Ehx was a key inducer of cathepsin B release in THP-1 cells but not in mouse IC-21 cells upon O157:H7 challenge. Inhibitor experiments indicated that O157:H7-induced IL-1ß production was largely dependent upon caspase-1 activation and partially dependent upon ATP signalling and cathepsin B release, which were both involved in NLRP3 activation. Moreover, inhibition of K(+) efflux drastically diminished O157:H7-induced IL-1ß production and cytotoxicity. The findings in this study may shed light on whether and how the Ehx contributes to the development of haemolytic uraemic syndrome in human O157:H7 infection.

[Excitation-wavelength dependent photoluminescence from porous silicon].

With the technique of fluorescence spectral analysis, the dependence of the fluorescence from porous silicon on the excitation wavelength was investigated. It was found when the excitation wavelength decreases from 650 to 340 nm, the fluorescence spectrum of porous silicon blue shifts continuously from 780 to 490 nm. Using scanning electron microscopy (SEM) and computer simulation, the cross-sectional structures of porous silicon were studied. The authors' results showed that the microstructures of porous silicon exhibit fractal characteristics. With the additional information extracted from the excitation spectra of porous silicon, the authors' results can be interpreted in terms of the quantum size effect and the fractal structures of porous silicon.

[Study on photoelectric dispersion characteristic of liquid crystal light valve].

The electro-optical properties and dispersion characteristics of a liquid crystal light valve (LCLV) were investigated. A 90 degrees twisted light valve (model TB3639) was used as a typical LCLV in the authors' experiment. At 27 degrees C and a fixed frequency of 1000 Hz, the transmitted light intensities (T) of the LCLV were measured as a function of wavelength (lamda) at different applied voltages. From the measured T-lamda curves, the dependence of contrast ratio k on the wavelength can be derived. The authors' results showd that the TB3639 LCLV has a comparatively high contrast ratio and low dispersion within the visible region. In the range of 450-750 nm, the contrast ratio, with its value higher than 0.8, does not change much with the wavelength. Particularly the contrast ratio is higher than 0.95 with a minimum dispersion in the range of 550-670 nm.