Gallium Concentration Optimisation of Gallium Doped Zinc Oxide for Improvement of Optical Properties

The near-band luminescence of doped ZnO is promising for advanced scintillators; however, the dopant type and concentration effects require a detailed study. Undoped and Ga-doped ZnO nanopowders were prepared by a microwave-assisted solvothermal method and the gallium concentration effect on luminescence properties was studied. The near-band luminescence peak position dependence on gallium concentration was observed. Near-band luminescence intensity versus defect luminescence intensity ratio was explored for different gallium concentrations and the optimal value was determined. Samples were prepared with dopant concentrations between 0.2 and 1.5 at%, XRD analysis confirmed that samples contained only zinc oxide hexagonal wurtzite phase. The results of the research showed that ZnO:Ga containing 0.9 at.% gallium was promising for scintillators.

Синтез наноразмерных люминофоров Gd-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=-:Nd-=SUP=-3+-=/SUP=- полимерно-солевым методом и исследование их основных характеристик

The article considers the aspects of nanoscale Gd2O3:Nd3+ phosphors synthesis using the liquid polymer-salt method. Within the framework of the method, the double role of polyvinylpyrrolidone (PVP) as an organic solvent in the process of synthesis was determined. On the one hand, PVP stabilizes the process of Gd2O3 crystals formation, preventing their uncontrolled growth and aggregation. On the other hand, PVP serves as a fuel during decomposition (combustion) increasing the temperature of reaction and thus influencing the structural and emission properties of phosphors. It is shown that drying of the initial homogeneous solution containing gadolinium and neodymium salts and PVP at the room temperature for 24 hours followed by thermal treatment at the temperature of 1000 °C for 2 hours allow formation of highly luminescent Gd2O3:Nd3+ near-infrared phosphors. The crystals grown are characterized mainly by the cubic structure and an average size of 40 nm. Experimental results confirmed that the developed method is appropriate for modification of a structure of silica hollow-core antiresonant fibers with thin-film coatings based on the synthesized material and does not result in structural and phase conversion of Gd2O3 crystals. It is found out that emission spectra of nanoscale Gd2O3:Nd3+ phosphors formed by the polymer-salt method at the temperatures of 550 °C and 1000 °C are identical, as follows: 1) the shape of the luminescence peaks is the same for the two mentioned regimes of thermal treatment regardless of intensity, 2) the main luminescence peak is located near the wavelength of 1064 nm and corresponds to a 4F3/2-4I11/2 electron transition, 3) additional luminescence peaks are located close to 900 nm and 1340 nm and refer to 4F3/2-4I9/2 and 4F3/2-4I13/2 electron transitions respectively.

Excitation Density Dependent Photoluminescence Studies on Homo-Epitaxial GaN Nanowall Networks Grown by Laser Assisted Molecular Beam Epitaxy

The optical properties of laser-assisted molecular beam epitaxy grown homo-epitaxialGaN nanowall networks (NWNs) were investigated using power dependent photoluminescence (PL) spectroscopy and compared with homo-epitaxial GaN thin film. The pore size and tip width of GaN NWN sample is ˜120–180 nm and 10–15 nm, respectively. The ultraviolet-visible spectroscopy study shows that the GaN NWNs have low optical light reflection and minimum Fabry-Perot cavity effect than GaN film. The room temperature PL spectroscopy reveals that the GaN NWNs possesses enhanced band gap of 3.51 eV with blue shift of 90 meV than the GaN film (3.42 eV). The excitation density dependent PL spectroscopy measurements reveal that the GaN NWNs nanowall and near band emission (NBE) peak position and its linewidth invariant. The intensity of NBE peak for GaN film and nanowalls varies linearly whereas NBE to defect related yellow luminescence peak intensity ratio shows a non-linear variation on the excitation density. The excitation density in PL measurements plays a key role when the sample quality compared on the basis of PL data.

Fractal Properties of CdTe Quantum Dots Dendrites-=SUP=-*-=/SUP=-

Here we present the analyses of fractal properties of CdTe dendrites. The spectral characteristics of dendrites obtained at different acids of the initial solution were investigated. We demonstrate the displacement of the local luminescence peak depended on the branches of the dendritic structure. The fractal dimension has been calculated by the box-counting method. We obtained the correlation between the local peak of luminescence and the Minkowski dimension.

First-principles study on the optical spectra of ZrO2 crystal with oxygen vacancy

In this paper, we present the optical spectra of the ZrO2 crystal containing oxygen vacancy based on the Density Functional Theory (DFT). The finite-size correction scheme (FNV) is employed to eliminate the artificial interactions and correct the defect formation energy of oxygen vacancies with three different charges (0, +1, +2). Besides, we use hybrid density functionals to relieve the band edge problem. Finally, we obtain the optical spectra for the F center and F[Formula: see text] center containing the electron–phonon coupling. The absorption peak of F center of threefold coordinate oxygen vacancy (V[Formula: see text]) near 446 nm (2.78 eV) agrees well with the experimental value (2.83 eV), which can enhance the visible light photocatalytic ability of ZrO2. The luminescence peak of the F[Formula: see text] center of fourfold coordinate oxygen vacancy (V[Formula: see text]) is 561 nm (2.21 eV), which is close to the experimental value (2.5 eV).

Thin film characterization of Ce and Sn co-doped CdZnS by chemical bath deposition

Cerium and tin co-doped cadmium zinc sulfide nanoparticles (CdZnS:Ce)Sn were synthesized by chemical bath deposition method with a fixed concentration of Ce (3.84 mol%) and three different concentrations of Sn (2 mol % and 4 mol% and 6 mol%). They showed broad photoluminescence spectra in the visible region under the ultraviolet excitation with a wavelength of 325 nm. The photoluminescence emission peaks were obtained at 540 nm, 560 nm and 570 nm for CdZnS, CdZnS:Ce and (CdZnS:Ce)Sn thin films, respectively having different concentrations of Sn. It has been observed that the photoluminescence emission peak shifted to higher wavelength region with an increase in intensity by Ce doping and Ce–Sn co-doping. Further enhancement in luminescence peak intensity has been observed by increasing concentration of Sn in (CdZnS:Ce)Sn films. Average crystallite size, measured from XRD data, was found to be increased with increasing concentration of Sn. An increase in the concentration of Sn shifted the UV-Vis absorption edge toward the higher wavelength side. Energy band gap for undoped CdZnS and Ce–Sn co-doped CdZnS varied from 2.608 eV to 2.405 eV. The SEM micrographs of CdZnS and (CdZnS:Ce)Sn films showed the leafy-like and ball-like structures. The presence of Sn and Ce was confirmed by EDAX analysis.

Synthetic Control of the Photoluminescence Stability of Organolead Halide Perovskites

An optimized synthetic procedure for preparing photostable nanocrystalline methylammonium lead halide materials is reported. The procedure was developed by adjusting the lead halide to methylammonium/octylammonium halide precursor ratio. At a high precursor ratio (1:3), a blue-shifted photoinduced luminescence peak is measured at 642 nm for CH3NH3PbI3 with 0.01 to 12 mJ pulsed-laser irradiation. The appearance of this peak is reversible over 300 min upon blocking the irradiation. In order to determine if the peak is the result of a phase change, in situ x-ray diffraction measurements were performed. No phase change was measured with an irradiance that causes the appearance of the photoinduced luminescence peak. Luminescence microscpectroscopy measurements showed that the use of a lower precursor ratio (1:1.5) produces CH3NH3PbI3 and CH3NH3PbBr3 perovskites that are stable over 4 min of illumination. Given the lack of a measured phase change, and the dependence on the precursor ratio, the photoinduced luminesce peak may derive from surface trap states. The enhanced photostability of the resulting perovskite nanocrystals produced with the optimized synthetic procedure supports their use in stable optoelectronic devices.