Drop shaped zinc oxide quantum dots and their self-assembly into dendritic nanostructures: Liquid assisted pulsed laser ablation and characterizations

Complex nanostructures and nano-assemblies have exhibited their potential application in the fabrication of future molecular machines and molecular devices. Liquid phase pulsed laser ablation is an easy, versatile, environmental friendly and rapidly growing method for the synthesis of nanostructured materials. Nanosecond pulsed laser ablation of zinc rod placed on the bottom of glass vessel containing methanol is used to produce colloidal solution of drop shaped zinc oxide quantum dots and their self-assembly into various dendritic nanostructures. UV-vis absorption, diffuse reflectance, transmission electron microscopy, and photoluminescence spectroscopy techniques are used for the optical, microscopic, structural and defect diagnosis of obtained colloidal quantum dots and their nano-assemblies. The average length, width and aspect ratio of drop shaped zinc oxide quantum dots are 6 ± 2.4 nm, 3.5 ± 1.4 nm and 1.69 ± 0.4 nm, respectively. Careful investigation of assemblies shows that most of them have linear growth, i.e. growth in longitudinal direction is higher as compared to the transverse direction with three types of classifications as (i) linear axis symmetrical branching, (ii) linear axis asymmetrical branching and (iii) curvilinear axis asymmetrical branching. Photoluminescence spectrum has emission peaks in UV, violet, blue and green spectral region corresponding to the excitonic and various defect related emissions.     

Effect of surface roughness on nucleation and growth of vanadium pentoxide nanowires

The effect of surface roughness on subsequent growth of vanadium pentoxide (V₂O₅) nanowires is examined. With increasing surface roughness, both the number density and aspect ratio of V₂O₅ nanowires increase. Structures and morphology of obtained nanowires were characterized by field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). The nanowires are approximately 40-90 nm in diameter and 2 μm in length. X-ray diffraction (XRD) analysis indicates that the obtained nanowires are orthorhombic structure with (0 0 1) out-of-plane orientation. The luminescence property of V₂O₅ nanowires has been investigated by photoluminescence (PL) at 150 K and 300 K. PL results show intense visible emission, which is attributed to different inter-band transitions between the V 3d and O 2p band. This simple fabrication approach might be useful for fabrication of large area V₂O₅ nanowires arrays with high density.     

Spectroscopy of defects in irradiated alpo 4 and GaPO 4 crystals

The time-resolved luminescence spectra in energy region of 2.0-6.0 v eV, as well as the excitation spectra (4-35 v eV), reflectivity and the decay kinetics were studied at T =10 v K and 295 v K using selective vacuum ultraviolet excitation in nominally pure crystals as well as crystals with intrinsic defects and radiation defects induced by fast electrons.     

Luminescent patterns based on color centers generated in lithium fluoride by extreme ultraviolet radiation and soft X-rays

Primary and aggregate color centers in lithium fluoride (LiF) crystals and polycrystalline LiF films were produced by an innovative irradiation technique using extreme ultraviolet radiation and soft X-rays generated by a laser-plasma source. This irradiation facility allowed the efficient formation of active color centers on luminescent patterns with submicron spatial resolution on large areas and short exposure times. The method looks promising for the realization of low-dimensionality photonic devices. The optical characterization of the colored structures was performed by means of absorption and photoluminescence measurements on LiF samples colored under different irradiation conditions.     

Optical properties of oxygen-deficiency related centers in amorphous SiO 2 investigated by synchrotron radiation

We report an investigation of the photoluminescence activity at 4.4 v eV in g -irradiated silica under UV and vacuum-UV excitation by synchrotron radiation. Our results evidence two iso-energetic contributions which can be related to two oxygen-deficient centers variants: ODC(I) and ODC(II). The first, excited within the 7.6 v eV absorption, is detected only at low temperature and has a lifetime of about 2 v ns. The second exhibits two excitation maxima peaked at 5.0 and 6.8 v eV, its amplitude decreases by a factor 2 on increasing the temperature whereas its lifetime has a value of about 4 v ns. These features give new insights on the excitation pathway of the 4.4 v eV emission involving the conversion from ODC(I) towards ODC(II).     

Luminescence enhancement by energy transfer from Ce ions in Ba1.6Ca0.4P2O7:Ce:Tb phosphor

The optical properties of Ba_1.6Ca_0.4P₂O₇ doped with Ce³⁺ and Tb³⁺ are investigated. Under excitation at 280 nm the emission spectrum of Ba_1.6Ca_0.4P₂O₇:Ce³⁺ consists of a peak at 370 nm and a shoulder at the longer wavelength side. The emission spectra of Ba_1.6Ca_0.4P₂O₇:Tb³⁺ shows the well-known emission lines due to ⁵D₄-⁷F_J transitions of Tb³⁺. The green emissions of Tb³⁺ ions are enhanced upon UV excitation through energy transfer from Ce³⁺ to Tb³⁺ ions. The efficiency of such an energy transfer is estimated based on spectroscopic data. The dependence of photoluminescence (PL) intensities of Ce³⁺ and Tb³⁺ emissions on Ce³⁺ or Tb³⁺ concentrations in the systems (Ba_1.6Ca_0.4P₂O₇:0.04Ce³⁺,xTb³⁺ and Ba_1.6Ca_0.4P₂O₇:xCe³⁺,0.04Tb³⁺) and the temperature dependence of PL emission spectra of Ba_1.6Ca_0.4P₂O₇:0.06Ce³⁺,0.04Tb³⁺ is also investigated.     

Synthesis, structure, and photoluminescence properties of ZnSSe alloy nanorods

ZnSSe alloy nanorods were prepared on gold (Au)-coated Si (100) substrates by the thermal evaporation of a mixture of ZnSe and ZnS powders. The nanorods were straight, 70-150 nm in width, and up to a few tens of micrometers in length. Transmission electron microscopy and X-ray diffraction indicated that the nanorods were ZnSSe single crystals with a wurtzite-type hexagonal close-packed structure. The photoluminescence measurements showed that the ZnSe nanorods had a strong emission band centered at approximately 500 nm in the blue-green region. The blue-green emission band corresponding to the deep-level emission of the ZnSSe nanorods showed no shift. On the other hand, a shoulder of the band in the blue region corresponding to the near-band edge (NBE) emission band shifted continuously from 466 nm to a lower wavelength region with increasing composition x in ZnSe_1−xS_x from 0 to 0.41. The blue-green emission intensity of the ZnSSe nanrods also increased with increasing composition x. The enhancement of blue-green emission might be due to the increase in structural defects, such as dislocations and stacking faults in the nanorods.     

Cu掺杂Ga2O3薄膜的光学性能

采用射频磁控溅射和N2气氛退火处理制备了多晶Ga2O3薄膜和Cu掺杂Ga2O3薄膜.用X射线衍射仪、紫外-可见分光光度计、荧光光谱仪对Ga2O3薄膜和Cu掺杂Ga2O3薄膜的结构和光学性能进行了表征.结果表明,Cu掺杂后Ga2O3薄膜的结晶质量变差,透过率明显降低,吸收率增加,光学带隙减小.本征Ga2O3薄膜在紫外、蓝光和绿光出现了发光带,Cu掺杂后紫外和蓝光发射增强,且在475nm处出现了一个新的发光峰.     

N掺杂ZnO薄膜的荧光特性研究

以N2为掺杂源,通过改变O2∶N2比,利用射频磁控溅射法在玻璃衬底上制备了具有[002]择优取向的N掺杂ZnO薄膜,研究了ZnO薄膜的光致发光谱随着N掺入量的不同而变化的规律.结果表明,薄膜主衍射峰为402 nm处的发光峰;由于N掺杂量的不同,有的薄膜在445 nm和524 nm处也有发光发存在,但随着薄膜N含量的不同,其发光峰强度明显不同,其峰位也发生了相应的红移或者蓝移.当O2∶N2为10∶ 15时,制备的薄膜N掺杂量最大,光学性能最好,此工艺为研究ZnO薄膜的缺陷类型及导电类型提供了重要的研究参考.     

Evidence for barrier-to-well injection of carriers in high quality ZnO/Zn0.9Mg0.1O multiple quantum wells grown on (111) Si

High quality ZnO/Zn_0.9Mg_0.1O multiple quantum wells were grown on (111) Si employing epitaxial Lu₂O₃ buffer layer and a thin ZnO nucleation layer. The linewidth of the low temperature ZnO well emission is only 17 meV. The effective recombination lifetime of emission from ZnO wells is 183 ps. Temperature-dependent photoluminescence is investigated to reveal the behavior of the carriers in the multiple quantum wells. Evidence for the barrier-to-well injection is indicated from the thermal quenching of both the barrier and well emissions. Carrier localization and thermal delocalization are observed in ZnMgO cap/barriers. The depth of the local potential well is determined to be ∼7 meV$\sim 7\text{meV}$.