The Photoluminescence Spectra of the Aeschynite Group Minerals

Raman and photoluminescence spectra of the metamict and annealing recrystallization titanoaeschynite-(Nd) and nioboaeschynite-(Ce), found in Baiyunobo mineral deposit in China, were measured and discussed. The peaks or bands in the spectra of the metamic minerals are weak, broad and diffuse, but sharpen notably after heating. The results show that the distortion of the structure and disorder state of the elements exists in the minerals when natural crystalline minerals transformed in-to metamict minerals after a long period of self-irradiation structure damaging. And all bands in the photoluminescence spectra of the aeschynite group mineral stem from emission transitions of Nd3+, when 514.5 nm laser is used as the excitation source.

Fabrication and photoluminescence characteristics of nonuniform Yb-Er codoped films

The nonuniform Yb-Er Codoped Al2O3 films were prepared on SiO2/Si substrates using a medium frequency magnetron sputtering system. Two asymmetry targets in the system were introduced to realize the nonuniform dopant. Some curves of Photoluminescence （PL） peak intensity were obtained by adjusting the deposition parameters, such as, the pillar number of erbium and ytterbium in the mixed target and the distance between a sample table and targets. Typically, the curve of PL peak intensity against the offset distance was approximately linear. The ratio of the PL intensity at the two ends of the same sample was 12.6 and the slope was 71.83/mm when the pillar numbers of the erbium and ytterbium in the mixed target are 5 and 60, respectively, and the distance between targets and the sample table is 2.9 cm.

Effect of different catalysts and growth temperature on the photoluminescence properties of zinc silicate nanostructures grown via vapor-liquid-solid method

We explore the photoluminescence properties of zinc silicate(Zn_(2)SiO_(4)) nanostructures synthesized by vapor-liquidsolid(VLS)mode of growth using three different catalysts(Sn,Ag,and Mn).Different catalysts significantly influence the growth rate which in turn has an impact on the structure and hence the photoluminescence of the prepared zinc silicate nanostructures.Zn_(2)SiO_(4) has a wide bandgap of about 5.5 eV and in its pure form,it does not emit in visible region due to its inner shell electronic transitions between the 3 d5 energy levels.However,the incorporation of different catalysts(Sn,Ag and Mn)at different growth temperatures into the Zn_(2)SiO_(4) crystal growth kinetics provides wide visible spectral range of photoluminescence(PL)emissions.PL analysis shows broad multi-band spectrum in the visible region and distinct colors(red,yellow,green,blue,cyan and violet)are obtained depending on the crystalline structure of the prepared nanostructures.The allowed transitions due to the effect of different catalysts on zinc silicate lattice offer a huge cross-section of absorption that generates strong photoluminescence.The correlation between the structural and optical properties of the synthesized nanostructures is discussed in detail.The synthesized photoluminescent nanostructures have potential applications in solidstate lighting and display devices.

A New Yellow Long Lasting Phosphor Y_2O_2S∶Ti

A new kind of doped rare earth free phosphor Y 2O 2S∶xTi (0<x≤0.10) with doped Ti as activative center was synthesized by solid state reaction and sintered at 1200 ℃ for 2.5 h under reducing atmosphere. XRD patterns, photoluminescence spectra, time-resolved phosphorescence spectra and decay curves of the phosphor were investigated. XRD results reveal that a single Y 2O 2S phase exists with Ti content up to 6% (mol fraction). Yellow long lasting phosphorescence for present materials was observed in the dark with naked eye after the removal of the excitation light. From the time-resolved phosphorescence spectra the broad emission band centered at 565 nm was confirmed to be responsible for the long lasting phosphorescence which could maintain above 1 h. The possible mechanism responsible for the long lasting phosphorescence of the Y 2O 2S∶Ti phosphor was proposed.

The influence of nickel dopant on the microstructure and optical properties of SnO2 nano-powders

The microstructure and optical properties of Ni-doped SnO2 nano-powders are studied in detail. By Ni-doping, not only the grain size reduces, but also the grain shape changes from nano-rods to spherical particles. The crystallization becomes better with annealing temperature increasing. The band gap energy decreases as nickel doping level increases. The sp-d hybridization and alloying effect due to amorphous SnO2-x phase should be responsible for the band gap narrowing effect. Nickel dopant does not change the photoluminescence （PL） peak positions.

Influence of annealing conditions on impurity species in arsenic-doped HgCdTe grown by molecular beam epitaxy

Based on our previous work, the influence of annealing conditions on impurity species in in-situ arsenic （As）- doped Hg1-xCdxTe （x ≈ 0.3） grown by molecular beam epitaxy has been systematically investigated by modulated photoluminescence spectra. The results show that （i） the doped-As acting as undesirable shallow/deep levels in asgrown can be optimized under proper annealing conditions and the physical mechanism of the disadvantage of high activation temperature, commonly assumed to be more favourable for As activation, has been discussed as compared with the reports in the As-implanted HgCdTe epilayers （x ≈ 0.39）, （ii） the density of VHg has an evident effect on the determination of bandgap （or composition） of epilayers and the excessive introduction of VHg will lead to a short-wavelength shift of epilayers, and （iii） the VHs prefers forming the VHg-ASHg complex when the inactivated-As （AsHg or related） coexists in a certain density, which makes it difficult to annihilate VHg in As-doped epilayers. As a result, the bandedge electronic structures of epilayers under different conditions have been drawn as a brief guideline for preparing extrinsic p-type epilayers or related devices.

The Site Symmetry of Eu^(3+) in ZnS:Eu Nanoparticle

Nanosized ZnS doped with different concentrations of Eu3+ were prepared andanalyzed by x-ray diffraction technique. The experimental results show that ZnS belongs to thecubic structure. From the photoluminescence (PL) emission spectra, it can be seen that the ratioof the emission intensity of Eu3+ at 616 nm to that at 590 nm increases as the increasing of Eu3+.This phenomenon reveals that the site symmetry of Eu3+ reduces as the increasing of Eu3+.

Synthesis, Crystal Structure and Characterization of the Host-guest Type UOF

A new uranium（Ⅵ）-polycarboxylate framework with honeycomb（6,3） nets {[Zn（phen）_2（H_2O）_2][（UO_2）_2（BDC）_3]·2H_2O}n（1, BDC = benzene-1,4-dicarboxylate） was hydrotherrmally synthesized by the reactions of Zn（NO_3）_2·6H_2O with phenanthroine, UO_2（NO_3）_2·6H_2O and benzene-1,4-dicarboxylate. The complex was structurally characterized by FT-IR spectroscopy, powder XRD and X-ray single-crystal diffraction. Crystal data for 1： monoclinic, space group Cc with M_r = 1522.19, a = 14.9385（10）, b = 20.4922（13）, c = 15.9728（10） ？, β = 100.1240（10）°, V = 4813.5（5） ？~3, Z = 4, D_c = 2.100 g？cm^（–3）, μ = 7.293 mm^（–1）, F（000） = 2872, the final R = 0.0224 and w R= 0.0677 for 6522 observed reflections with I 〉 2σ（I）. Hydrogen bonds and π-π stacking interactions contribute to the structural extension and stabilization. Experimental band gap of about 3.57 e V indicates its broad gap semiconductor nature. UV-Vis spectra and solid-state luminescence were discussed in detail. The compound exhibits photocatalytic activities for the degradation of rhodamine B.

Fluorescence Properties of Eu^(3+) :Y_2SiO_5 Single Crystal

Fluorescence properties of Eu 3+ :Y 2SiO 5 have been investigated. Transitions between 5D and 7Fwere were studied with transmission spectra, fluorescence spectra, photoluminescence excitation ( or absorption ) spectra and site selective fluorescence spectra. The X ray powder diffraction pattern of Eu 3+ :Y 2SiO 5 shows that the crystal belong to monoclinic, and lattice's constants a, b, c and β are obtained by a simulation with the measured diffraction angles.

Photoanode Activity of ZnO Nanotube Based Dye-Sensitized Solar Cells

Vertical ZnO nanotube （ZNT） arrays were synthesized onto an indium doped tin oxide （ITO） glass substrate by a simple electrochemical deposition technique followed by a selective etching process. Scanning electron microscopy （SEM） showed formation of well-faceted hexagonal ZNT arrays spreading uniformly over a large area. X-ray diffraction （XRD） of ZNT layer showed substantially higher intensity for the （0002） diffraction peak, indicating that the ZnO crystallites were well aligned with their c-axis. Profilometer measurements of the ZNT layer showed an average thickness of -7 μm. Diameter size distribution （DSD） analysis showed that ZNTs exhibited a narrow diameter size distribution in the range of 65-120 nm and centered at -75 nm. The photoluminescence （PL） spectrum measurement showed violet and blue luminescence peaks that were centered at 410 and 480 nm, respectively, indicating the presence of internal defects. Ultra-violet （UV） spectroscopy showed major absorbance peak at ,-348 nm, exhibiting an increase in energy gap value of 3.4 eV. By employing the formed ZNTs as the photo-anode for a dye-sensitized solar cell （DSSC）, a full-sun conversion efficiency of 1.01% was achieved with a fill factor of 54%. Quantum efficiency studies showed the maximum of incident photon-to-electron conversion efficiency in a visible region located at 590-550 nm range.

Effect of red emitting fluorescent pigment on fluorescent color of SrAl2O4：Eu2＋,Dy3＋ phosphors

Green-blue fluorescence emitting SrAl_2O_4：Eu^（2＋）,Dy^（3＋） phosphors（SAOED） were coated by SiO_2 and a coumarin type red-emitting fluorescent pigment（FP）.The effects of the FP on the morphology,crystal structure,photoluminescence properties and fluorescent color of the SAOED phosphors were systematically investigated by scanning electron microscopy（SEM）,FT-IR,X-ray diffraction（XRD）,photoluminescence spectra and CIE-1931 chromaticity coordinates characterization.Even though the surface of the SAOED phosphors became rough after being coated with SiO_2 and FP,crystal lattice of SrAl_2O_4 did not have any obvious lattice distortions.The photoluminescence spectra indicated that the SAOED phosphors could be used as the excitation light source to excite the FP to emit red fluorescence.The emission spectrum of the FP-coated SAOED consisted of a broad band with two emission peaks at 520 and 610 nm,and its fluorescence emission color was a mixed color of the SAOED phosphors and FP.The fluorescence color of the SAOED/SiO_2/FP composites tended to transfer to red area with the increase of the FP content varying from 0.1%to 0.9%.

Why the hydrothermal fluorinated method can improve photocatalytic activity of carbon nitride

Carbon nitride(CN) photocatalysts have attracted much attention due to their excellent photocatalytic properties.And hydrothermal fluorination is a common method to improve the photocatalytic effect of CN photocatalyst.Here,the influence of the band gap was first revealed of fluorination and hydroxylation of CN photocatalyst based on the first theoretical principle.Here,the effect of fluorination and hydroxylation on the CN band gap was discussed for the first time using the first theoretical principle.With F atoms and OH doping,the band gap of CN was significantly improved,conduction band and valence band moved up.Then,F-CN photocatalyst with F atoms and OH was successfully synthesized by a hydrothermal fluorinated method.Next,the reasons why F-CN photocatalyst was more effective than that of traditional CN photocatalyst were fully discussed.From the photocatalytic effect of photocatalyst(12,593.2 μmolg^(-1) h^(-1)to the morphology(super-small nanosheets),structure(homojunctions),composition(metal-free),specific surface area(54.1 m^(2)/g),visible light absorption response(AQE is10.9% at 420 nm) and photo-induced carrier life(14.13 ns).Therefore,this work has a great guiding effect on the development of CN photocatalyst.

Fabrication of titania thin film with composite nanostructure and its ability to photodegrade rhodamine B in water

A titania nanorod filmwas synthesized by direct oxidation of metallic Ti with hydrogen peroxide solution under a low temperature.Titania nanoparticles were then filled into the gaps among the nanorods through an infiltration sol-gel procedure to form a composite titania film with an ordered nanostructure.X-ray diffraction spectra indicate that the composite film was a mixture of anatase and rutile while the titania film obtained by only using a sol-gel procedure was pure anatase.Field emission scanning electron microscopy observations show that titania nanoparticles were embedded into the titania nanorod film.Photoluminescence spectra suggest the enhanced separation of electron and hole pairs for the obtained composite titania film over the corresponding titania nanorod film.The composite titania film exhibited improved ability to photodegrade rhodamine B in water compared with the titania nanorod film.The apparent photodegradation rate constant,fitting a pseudo-first-order,was 3 times of that obtained by the sol-gel derived titania film at the same weight.The improved photocata-lytic activity for the composite titania film could be attributed to the enhanced separation of electron and hole pairs due to the embedding of the titania nanoparticles within the titania nanorods.

Effects on the emission discrepancy between two-dimensional Sn-based and Pb-based perovskites

Two-dimensional (2D) Sn-based perovskites are a kind of non-toxic environment-friendly emission material with low photoluminescence quantum yields (PLQYs) and enhanced emission linewidths compared to that of 2D Pb-based perovskites.However,there is no work systematically elucidating the reasons for the differences in the emission properties.We fabricate (BA)_(2)SnI_(4)and (BA)_(2)PbI_(4)having different defect densities and different exciton-phonon scattering intensities.We also reveal that 2D Sn-based perovskites have stronger exciton-phonon scattering intensity and higher defects density,significantly broadening the emission linewidth and accelerating the exciton relaxation process,which significantly reduces the PLQY of 2D Sn-based perovskites.