The Effect of the Flux B203 and the Role of Ion RE3＊ in CaAI204： Eu2＋, Nd3＋, RE3＋ Phosphor （RE： Dy, Gd, Tb）

The long afterglow phosphors CaA1204： Eu2＋, Nd3＋, RE3＋ （RE： Dy, Gd, Tb） were prepared by the combustion method at 580℃ for 5 min. In this method, the B203 oxide was used as flux. The influences of the flux B203 quantity and the role of ion RE3＋ （RE： Dy, Gd, Tb） in the phosphor CaAI204： Eu2＋, Nd3＋ were studied systemically. The X-ray diffraction pattern, scanning electron microscopy graphic, the photoluminescence spectra and decay time were presented. The emission spectra of phosphors had a broad band with maximum at 444 nm due to electron transition from the 4f65dI to the 4f7 of ion Eu2＋. It is showed that Nd3＋ and RE3＋ ions generated traps that resulted in the long persistent phosphorescence. Simultaneously, when the concentration of RE3＋ ion was high, they generated also emission centers in the phosphor.     

CaMoO4:Dy3+,K+ near White Light Emitting Phosphor:Structural,Optical and Dielectric Properties

Undoped,Dy³⁺ doped and Dy³⁺,K⁺ codoped calcium molybdate phosphors have been synthesized by solid-state reaction method.X-ray diffraction studies reveal the tetragonal structure of the prepared phosphors having crystallite size 15-50 nm.Scanning electron microscopy（SEM） studies reveal the morphology and crystallite size of the prepared phosphors.Photoluminescence studies indicate that there are blue and yellow emissions at 489 and 576 nm,respectively corresponding to Dy³⁺ ion.The introduction of K⁺ ion significantly influences the blue and yellow emissions which causes the near white light emission from this codoped phosphor.The intense absorption peak of the codoped phosphor at 210 nm is attributed to the band gap and a shoulder at 240 nm appears due to charge transfer from oxygen ions to neighbouring molybdenum ions. The band gap of the codoped phosphor is calculated as 5.5 eV from the absorption studies.The dielectric properties such as permittivity and dielectric loss are studied as a function of frequency.     

Mo^6＋ Modified （K0.5Na0.5）NbO3 Lead Free Ceramics： Structural,Electrical and Optical Properties

Lead free polycrystalline ceramics （K0.5Na0.5）Nb（1-x）MoxO3 （x = 0, 0.02, 0.04, 0.06 and 0.08） have been synthesized via solid state reaction method. The formation of single phase perovskite structure up to 6 mol% of Mo^6＋ has been confirmed by X-ray diffraction pattern. Impedance spectroscopy reveals that bulk resistance decreases with increasing temperature, which indicates negative temperature coefficient of resistance （NTCR） behaviour of the compounds. The diffuse reflectance spectroscopy results indicate a red shift of the band gap energy of K0.5Na0.5NbO3 （KNN, from 4.28 to 3.61 eV） with increasing Mo^6＋ concentration due to structural modification. The photoluminescence spectra of doped samples are composed of two emission bands at room temperature. One emission band is near band edge ultraviolet （UV） emission （354 nm） and other is visible emission band （-397 nm） which may explore the possibility of these ceramics to be used in optical device applications.     

Co-Doped ZnO Nanoparticles:Structural,Morphological,Optical,Magnetic and Antibacterial Studies

Un-doped and Co-doped ZnO nanoparticles （NPs） with different weight ratios （0.5, 1.0, 1.5, and 2.0 wt% of Co） were synthesized by a facile and rapid microwave-assisted combustion method using urea as a fuel. The prepared NPs were characterized by X-ray diffraction （XRD）, high resolution scanning electron microscopy （HR-SEM）, energy dispersive X-ray analysis （EDX）, diffuse reflectance spectroscopy （DRS）, photoluminescence （PL） spectroscopy and vibrating sample magnetometry （VSM）. XRD patterns refined by the Rietveld method indicated that Co-doped ZnO had a single pure phase with wurtzite structure suggesting that Co^2＋ ions would occupy Zn^2＋ ionic sites within the ZnO crystal lattice. Interestingly, the morphology was found to convert substantially from grains to nanoparticles with close-packed periodic array of hexagonal-like shape and then into randomly distributed spherical NPs with the variation of Co-content. The optical band gap estimated using DRS was found to be red-shifted from 3.22 eV for the un-doped ZnO NPs then decrease up to 2.88 eV with increasing Co-content. PL spectra showed a strong green emission band thus confirming the formation of pure single ZnO phase. Magnetic studies showed that Co-doped ZnO NPs exhibited room temperature ferromagnetism （RTFM） and that the saturation magnetization attained a maximum value of 2.203 × 10^-3 emu/g for the highest Co-content. The antibacterial studies performed against a set of bacterial strains showed that the 2.0 wt% Co-doped ZnO NPs possessed a greater antibacterial effect.     

Chemical vapor deposition growth of monolayer MoSe2 nanosheets

The synthesis of two-dimensional （2D） layered materials with controllable thickness is of considerable interest for diverse applications. Here we report the first chemical vapor deposition growth of single- and few-layer MoSe2 nanosheets. By using Se and MoO3 as the chemical vapor supply, we demonstrate that highly crystalline MoSe2 can be directly grown on the 300 nm SiO2/Si substrates to form optically distinguishable single- and multi-layer nanosheets, typically in triangular shaped domains with edge lengths around 30 btm, which can merge into continuous thin films upon further growth. Micro-Raman spectroscopy and imaging was used to probe the thickness-dependent vibrational properties. Photoluminescence spectroscopy demonstrates that MoSe2 monolayers exhibit strong near band edge emission at 1.55 eV, while bilayers or multi-layers exhibit much weaker emission, indicating of the transition to a direct band gap semiconductor as the thickness is reduced to a monolayer.     

Blue-shift of Nano-Y_2O_3 : Eu~(3+) Emission Spectra Excited by X-ray

Nano-Y_2O_3:Eu~(3+) powder was prepared by the homogeneous precipitation. With controlling the conditions of the reaction, nano powders with different grain size were obtained. It is found that the blue-shift phenomena exist in the nano-Y2O3:Eu3+ emission spectra excited by X-ray. The wave lengths of the peak (5D0→7F2) are related with the grain size of the powder     

Room Temperature Ferromagnetism in Dual Doped (Mn 2+ , Ni 2+ ) ZnO Codoped with Li 1+ Prepared Using EDTASintered at Low Temperature

Nanopowders of Znl_x_y_zMnxNiyLizO [（x = 0.04, y = 0, z = 0）, （x = 0.04, y = 0.03, z = 0） and （x = 0.04, y = 0.03, z = 0.03）] have been synthesized by sol-gel precursor route using ethylene diamine tetraacetic acid （EDTA） as a metal chelating agent. X-ray diffraction analysis confirms the formation of wurtzite hexagonal structure for all the three compositions. Mn2＋ doped ZnO exhibits room temperature ferromagnetism （RTFM）, and it is found that further Ni2＋ doping has decreased Ms because of limit of solid solubility of transition metal in ZnO. But codoping of monovalent Li1＋, further increases the ferromagnetism （FM） value, due to introduction of free carriers compared to the dual doped samples. Photoluminescence （PL） spectra of the system, exhibit near band edge （NBE） emission peak at --464 nm due to the electron transition from interstitials to the valence band. Recombination of conduction electron with hole trapped at oxygen vacancy, leads to prominent defect emission peaks at --482 nm and 532 nm. The evidence of the formation of metaI-EDTA complexes are found from the Fourier transform infrared spectra at 2800-3800 cm-1 with shifting, splitting of the peak and also drastic variations in the intensity.     

Direct vapor phase growth process and robust photoluminescence properties of large area MoS2 layers

There has been growing research interest in the use of molybdenum disulfide in the fields of optoelectronics and energy harvesting devices, by virtue of its indirect-to-direct band gap tunability. However, obtaining large area thin films of MoS2 for future device applications still remains a challenge. In the present study, the amounts of the precursors （S and MOO3） were varied systematically in order to optimize the growth of highly crystalline and large area MoS2 layers by the chemical vapor deposition method. Careful control of the amounts of precursors was found to the key factor in the synthesis of large area highly crystalline flakes. The thickness of the layers was confirmed by Raman spectroscopy and atomic force microscopy. The optical properties and chemical composition were studied by photoluminescence （PL） and X-ray photoelectron spectroscopy. The emergence of strong direct excitonic emissions at 1.82 eV （A-exciton, with a normalized PL intensity of -55 × 10^3） and 1.98 eV （B-exciton, with a normalized PL intensity of -5 × 10^3） of the sample at room temperature clearly indicates the high luminescence quantum efficiency. The mobility of the films was found to be 0.09 cm^2/（V.s） at room temperature. This study provides a method for the controlled synthesis of high-quality two-dimensional （2D） transition metal dichalcogenide materials, useful for applications in nanodevices, optoelectronics and solar energv conversion.     

GaAs/AlGaAs heterostructure nanowires studied by cathodoluminescence

In this report we explore the structural and optical properties of GaAs/A1GaAs heterostructure nanowires grown by metalorganic vapour phase epitaxy using gold seed-particles. The optical studies were done by low-temperature cathodo- luminescence （CL） in a scanning electron microscope （SEM）. We perform a systematic investigation of how the nanowire growth-temperature affects the total photon emission, and variations in the emission energy and intensity along the length of the nanowires. The morphology and crystal structures of the nanowires were investigated using SEM and transmission electron microscopy （TEM）. In order to correlate specific photon emission characteristics with variations in the nanowire crystal structure directly, TEM and spatially resolved CL measurements were performed on the same individual nanowires. We found that the main emission energy was located at around 1.48 eV, and that the emission intensity was greatly enhanced when increasing the GaAs nanowire core growth temperature. The data strongly suggests that this emission energy is related to rotational twins in the GaAs nanowire core. Our measurements also show that radial overgrowth by GaAs on the GaAs nanowire core can have a deteriorating effect on the optical quality of the nanowires. Finally, we conclude that an in situ pre-growth annealing step at a sufficiently high temperature significantly improves the optical quality of the nanowires.     

Synthesis of Nanocrystalline FeS2 with Increased Band Gap for Solar Energy Harvesting

In this paper,we have reported the synthesis of FeS2 of higher band gap energy（2.75 eV） by using capping reagent and its successive application in organic-inorganic based hybrid solar cells.Hydrothermal route was adopted for preparing iron pyrite（FeS2） nanoparticles with capping reagent PEG-400.The quality of synthesized FeS2 material was confirmed by X-ray diffraction,field emission scanning electron microscopy,transmission electron microscopy,Fourier transform infrared,thermogravimetric analyzer,and Raman study.The optical band gap energy and electro-chemical band gap energy of the synthesized FeS2 were investigated by UV-vis spectrophotometry and cyclic voltammetry.Finally band gap engineered FeS2 has been successfully used in conjunction with conjugated polymer MEHPPV for harvesting solar energy.The energy conversion efficiency was obtained as 0.064%with a fill-factor of 0.52.     

Improvement of Optical Reactivity for Nano-TiO2 Film by Nitrogen ECR Plasma

Nitrogen ion was implanted into the nano-TiO2 film surfaces by electron cyclotron resonance （ECR） plasma modification to improve the optical reactivity in visible-light region for nano-TiO2. Diagnosing the N2 plasma by optical emission spectroscopy （OES） was applied to the process of plasma modification. X-ray photoelectron spectroscopy （XPS） was used for analysis of the binding of element after plasma modification. It is shown that the surface modification was caused by excitated N. The injecting of N2 and N＋ leads to the increase in the dissociative interstitial state N in the films. The doped N makes for TiO2-xNx appearing in the TiO2 films. TiO2-xNx forms the impurity energy state in the TiO2 energy band gap and reduces the energy band gap. This is the main reason leading to the red shift of absorption edge.     

Structural and Spectroscopic Characterizations of ZnO Quantum Dots Annealed at Different Temperatures

Here, we report the synthesis and characterizations of sol-gel derived zinc oxide （ZnO） quantum dots （QDs） using zinc acetate dihydrate （Zn（CH3COO）2.2H20） and lithium hydroxide monohydrate （LiOH.H20） as raw material. The as-prepared ZnO QDs was annealed at different temperature （400, 700, and 900 ℃） and the structural, optical properties were investigated by X-ray diffraction （XRD）, high resolution transmission electron microscopy （HRTEM）, UV-Vis and photoluminescence （PL） spectroscopy. The powder XRD patterns of the obtained samples showed the formation of single-phase wurtzite structure and the morphological changes have been observed with increasing annealing temperature. In the absorption spectra, the optical band gap of nanocrystalline ZnO QDs decreased from 3.18 to 3.11 eV and the particle size increased with increasing temperature. In the PL spectra, a broad green emission peak related to defect levels in the visible range of the spectra have been recorded.     

Evidence for structural phase transitions and large effective band gaps in quasi-metallic ultra-clean suspended carbon nanotubes

We report evidence for a structural phase transition in individual suspended metallic carbon nanotubes by examining their Raman spectra and electron trans- port under electrostatic gate potentials. The current-gate voltage characteristics reveal anomalously large quasi-metallic band gaps as high as 240 meV, the largest reported to date. For nanotubes with band gaps larger than 200 meV, we observe a pronounced M-shape profile in the gate dependence of the 2D band （or G＇ band） Raman frequency. The pronounced dip （or softening） of the phonon mode near zero gate voltage can be attributed to a structural phase transition （SPT） that occurs at the charge neutrality point （CNP）. The 2D band Raman intensity also changes abruptly near the CNP, providing further evidence for a change in the lattice symmetry and a possible SPT. Pronounced non-adiabatic effects are observed in the gate dependence of the G band Raman mode, however, this behavior deviates from non-adiabatic theory near the CNP. For nanotubes with band gaps larger than 200 meV, non-adiabatic effects should be largely suppressed, which is not observed experimentally. This data suggests that these large effective band gaps are primarily caused by a SPT to an insulating state, which causes the large modulation observed in the conductance around the CNP. Possible mechanisms for this SPT are discussed, including electron-electron （e.g., Mott） and electron-phonon （e.g., Peierls） driven transitions.     

Ar Pressure Dependence of the Properties of Molybdenum-doped ZnO Films Grown by RF Magnetron Sputtering

Transparent conducting oxide film of molybdenum-doped zinc oxide （MZO） with high transparency and relatively low resistivity was prepared by RF （radio frequency） magnetron sputtering at room temperature. The structural, electrical, and optical properties of the films deposited under different Ar pressure were investigated.XRD （X-ray diffraction） patterns show that the nature of the films is polycrystalline with a hexagonal structure and a preferred orientation along the c-axis. The resistivity increases as Ar pressure increases. The lowest range exceeds 88% for all the samples. The optical band gap decreases from 3.27 to 3.15 eV with increasing Ar pressure from 0.6 to 3.0 Pa.     

Field Emission Characteristics of Conducting Polymer Films Conditioned by Electric Discharge

A pure conducting polymer （PANI-CSA） film conditioned by an electric discharge was tentatively utilized as an cathode for emitting electrons under electric fields. The emission of electrons was observed using a phosphor （ZnO：Zn） screen excited by electrons from the conditioned film. The film morphology was investigated using a scanning electron microscope and it was found that undulate whisker-like sites formed on the surface. The emission was presumably due to the undulate whisker-like sites. The field enhancement factor was estimated to be as high as 1150. The electron emitting process of the PANI-CSA film conditioned by electric discharge was also discussed.     

Structural Morphological and Optical Properties of SnSb2S4 Thin Films Grown by Vacuum Evaporation Method

SnSb2S4 thin films were prepared from powder by thermal evaporation under vacuum of 1.33 × 10^-4 Pa （ 10^-6 Torr） on unheated glass substrates. The effect of thickness on the structural, morphological and optical properties of SnSb2S4 thin films was investigated. Films thickness measured by interference fringes method varied from 50 to 700 nm. X-ray diffraction analysis revealed that all the SnSb2S4 films were polycrystalline in spite without heating the substrates and the crystallinity was improved with increasing film thickness. The microstructure parameters： crystallite size, strain and dislocation density were calculated. It was observed that the crystallite size increased and the crystal defects decreased with increasing film thickness. In addition, by increasing the film thickness, an enhancement in the surface roughness root-mean-square （RMS） increased from 2.0 to 6.6 nm. The fundamental optical parameters like band gap, absorption and extinction coefficient were calculated in the strong absorption region of transmittance and reflectance spectrum. The optical absorption measurements indicated that the band （Eg） gap of the thin films decreased from 2.10 to 1.65 eV with increasing film thickness. The refractive indexes were evaluated in transparent region in terms of envelope method, which was suggested by Swanepoul. It was observed that the refractive index increased with increasing film thickness.     

Optical Spectra and Gain Properties of Ho3＋/Pr3＋ Co-doped LiYF4 Crystal

The LiYF4 single crystals singly doped Ho3＋ and co-doped Ho3＋, Pr3＋ ions were grown by a modified Bridgman method. The Judd-Ofelt strength parameters （Ω2, Ω4, Ω6） of No3＋ were calculated according to the absorption spectra and the Judd-Ofelt theory, by which the radiative transition probabilities （A）, fluorescence branching ratios （β） and radiative lifetime （τ rad） were obtained. The radiative lifetimes of 5/6 and 5/7 levels in Ho3＋ （1 mol%）：LiYF4 are 10.89 and 20.19 ms, respectively, while 9.77 and 18.50 ms in Ho3＋/pr3＋ doped crystals. Hence, the τ rad of 5/7 level decreases significantly by introduction of Pr3＋ into Ho3＋：LiYF4 crystal which is beneficial to the emission of 2.9 μm. The maximum emission cross section of Ho3＋：LiYF4 crystal located at 2.05 μm calculated by McCumber theory is 0.51 ×10-20 cm2 which is compared with other crystals. The maximum emission cross section at 2948 nm in Ho3＋/pr3＋ co-doped LiYF4 crystal obtained by Fuchtbauer- Ladenburg theory is 0.68 × 10-20 cm2, and is larger than the value of 0.53 × 10-20 cm2 in Ho3＋ singly doped LiYF4 crystal. Based on the absorption and emission cross section spectra, the gain cross section spectra were calculated. In the Ho3- ions singly doped LiYF4 crystal, the gain cross sections for 2.05 μm infrared emission becomes positive once the population inversion level reaches 30%. It means that the pump threshold for obtaining 2.05 μm laser is probably lower which is an advantage for Ho3＋-doped LiYF4 2.05 μm infrared lasers. The calculated gain cross section for 2.9 μm mid-infrared emission does not become positive until the population inversion level reaches 40% in Ho3＋/pr3＋：LiYF4 crystal, but 50% in Ho3＋ singly doped LiYF4 crystal, indicating that a low pumping threshold is achieved for the H03＋：5/6 → 5/7 laser operation with the introduction of Pr3＋ ions. It was also demonstrated that Pr3＋ ion can deplete rapidly the lower laser Ho3＋：5/7 level and has influence on t     

Heating graphene to incandescence and the measurement of its work function by the thermionic emission method

The work function （WF） of graphene is an essential parameter in graphene electronics. We have derived the WF of graphene by the thermionic emission method. Chemical vapor deposition （CVD）-grown single-layered polycrystalline graphene on copper foil is transferred to a cross-stacked carbon nanotube （CNT） film drawn from a super-aligned multiwalled CNT array. By decreasing the pore size of the CNT film, the as-prepared CNT-graphene film （CGF） can be Joule heated to a temperature as high as 1,800 K in vacuum without obvious destruction in the graphene structure. By studying the thermionic emission, we derive the WF of graphene, ranging from 4.7 to 4.8 eV with the average value being 4.74 eV. Because the substrate influence can be minimized by virtue of the porous nature of the CNT film and the influence of adsorbents can be excluded due to the high temperature during the thermionic emission, the measured WF of graphene can be regarded as intrinsic.     

Spatially-Resolved Crystallization of Amorphous Silicon Films on the Glass Substrate by Multi-beam Laser Interference

Laser interference induced crystallization of amorphous silicon （a-Si） on the glass substrate was performed using a Q-switched Nd：YAG （yttrium aluminum garnet） laser. White light interferometer （WLI） and atomic force microscope （AFM） were used to characterize the morphology of the structured films, while X-ray diffraction （XRD）, combined with the AFM, was used to analyse the crystalline structure of the film. The experimental results show that the laser energy density above a certain threshold, in the range of 400-500 mJ/cm2,triggers the patterned crystallizations which take the form similar to the laser intensity distribution. For the patterned crystallization under multipulse exposure, a definite polycrystalline structure with individual phases was observed by XRD. The difference in feature form, e.g., deepened craters or heightened lines, is related to the laser energy density relative to the threshold of evaporation of the material.     

Preparation and Characterisation of Sr2CeO_4:Eu~(3+) Rare Earth Luminescent Material by High Temperature Mechano-Chemical Method

A novel, high-temperature, mechano-chemical(HTMC) method was developed to synthesise singlephase Sr_2CeO_4:Eu~(3+)phosphor. Phosphors were characterised by X-ray diffraction(XRD), scanning electron microscopy(SEM), and luminescence spectra. Compared with phosphors prepared by the traditional hightemperature solid state method and citric acid gel method, single-phase Sr_2CeO_4:Eu~(3+)powders by using the HTMC method, with small average particle sizes of about 5 μm, a narrow size distribution range and uniform dispersion, were prepared at 800 ℃, and reached their maximum luminescent intensity at 900 ℃.Under ultraviolet excitation at 298 nm, the sample showed good luminescence with the strongest red light of 616 nm. However, Sr_2CeO_4:Eu~(3+)was prepared at the higher temperature of 1100 ℃ by solid state method and citric acid gel method. The particle size was too large and uneven with phosphor agglomeration by high-temperature solid state method. The luminescent intensity reached a maximum for Sr_2CeO_4:Eu~(3+)phosphor at a synthesis temperature of 1100 ℃ by using the high-temperature solid state method, and at 1200 ℃ by both citric acid gel and chemical precipitation methods. Furthermore, the advantages of the Sr_2CeO_4:Eu~(3+)powder prepared by HTMC method were discussed compared with that prepared using traditional high-temperature solid state and citric acid gel methods.