Cathodoluminescence mapping and thermoluminescence of Pr3+ doped in a CaTiO3/CaGa2O4 composite phosphor

In order to probe the properties of the one pot prepared composite phosphor of CaTiO₃ and CaGa₂O₄, cathodoluminescence mapping, thermoluminescence and lifetime measurements were carried out. The structural study showed both irregular and rod shaped particles, which match with CaTiO₃ and CaGa₂O₄, respectively, according the x-ray maps. The cathodoluminescence spectrum showed emission peaks from ³P₀→³H₄ and ¹D₂→³H₄ transitions, with the earlier transition completely absent in CaTiO₃:Pr emission at room temperature. The diffuse reflectance spectrum showed a shifted band of the inter-valence charge transfer from 360 nm to 388 nm, which is not observable for CaTiO₃:Pr³⁺and CaGa₂O₄:Pr³⁺. Additionally, the phosphorescence decay curve was recorded and the presence of electron trapping centers was confirmed using thermoluminescence spectroscopy.     

Structural and optical properties of neodymium-doped lutetium fluoride thin films grown by pulsed laser deposition

Neodymium-doped lutetium fluoride (Nd³⁺:LuF₃) thin films were successfully grown on MgF₂ (0 0 1) substrates by pulsed laser deposition (PLD). It is void of cracks that are otherwise prevalent due to structural phase transitions in Nd³⁺:LuF₃ during thin film deposition and bulk crystal growth. Cathodoluminescence (CL) spectra revealed multiple emission peaks, with a dominant peak in the vacuum ultraviolet (VUV) region at 179 nm. This peak has a decay time of 6.7 ns. The ability to grow high quality Nd³⁺-doped fluoride thin films would enable fabrication of VUV light-emitting devices that will enhance applications requiring efficient VUV light sources.     

Spatially-resolved cathodoluminescence spectroscopy of ZnO defects

Spatially-resolved cathodoluminescence spectroscopy has contributed significant new information to our understanding of native point defects in ZnO micro- and nanoscale structures. This paper aims to review representative examples of this work and the new perspectives gained from spatially resolving these defects both laterally and depth-wise. Results obtained from many groups worldwide include studies of Schottky diodes, polycrystalline ceramics, nanostructures, and microwires. The nature and spatial distribution of native point defects in these materials together with their strong dependence on growth and processing suggest new avenues for their control in transport and optoelectronic device structures.     

Investigation of properties of ZnO ceramics sintered from ZnO-Zn nanopowders produced by pulsed electron beam evaporation

In this paper we have studied the properties of ZnO ceramics sintered from the ZnO-Zn nanopowders (NPs) produced by a pulsed electron beam evaporation of heterogeneous targets (oxide or metal) and to establish the influence of NPs prehistory on the luminescence and dilatometry properties of ceramics produced from them. Pressing was performed on uniaxial presses: static and the magnetic pulsed one. Sintering of ceramics was produced in air by heating to 1200 °C in 60 min. Maximal density of the ceramics did not exceed 81,25% of the theoretical density. The behavior of the shrinkage curves of ZnO-Zn NPs depends on their prehistory. Evolution of properties of ZnO-Zn nanoparticles (NPles) during annealing in air is studied by XRD and pulsed cathodoluminescence methods. The suppression of the ultraviolet emission in NP obtained by electron beam evaporation, and in ceramics sintered of them was established.     

Catalytic coating of virus particles with zinc oxide

We show that the rod-shaped Tobacco mosaic virus (TMV) can be coated with the wide band gap semiconductor zinc oxide by electroless deposition under mild reaction conditions. The process involves pretreatment with aqueous Pd(II), followed by nucleation of ZnO, directed to palladium centers formed on the surface of TMV. The mechanism is based on the local pH change due to the reduction of nitrate by dimethylamine borane at the palladium. Morphology and chemical composition have been analyzed by transmission electron microscopy (TEM) and by energy filtering TEM, respectively. The optical properties were elucidated by cathodoluminescence, which showed the desired near-band edge emission.     

Luminescent properties of ZnO structures grown with a vapour transport method

ZnO structures were synthesised on the sapphire (112?0) substrate by a vapour transport method in a gas flowing furnace. The influence of the oxygen content in the gas mixture on the morphology and luminescent properties of ZnO structures grown on a strip-like substrate was investigated, with all other growth parameters being kept nominally identical. Integrated electron microscopy and cathodoluminescence analysis shows gradual variations of structural and optical emission properties for ZnO structures grown on the long substrate. Defect-related green luminescence of ZnO is found to be highly dependent on the oxygen vapour in the growth region of the furnace. Our findings demonstrate that the green luminescence is associated with oxygen deficiency in ZnO.     

Scanning electron microscopy study of twins in ZnSe single crystals grown by solid-phase recrystallization

ZnSe single crystals were grown from n-type microcrystalline boules by a solid phase recrystallization (SPR) method. During SPR, twinned regions appear with different electronic recombination properties. The recrystallizations were performed under different atmospheres, Ar or Se, and pressures to investigate the influence of growth conditions on these structural features. Recombination properties were studied by means of cathodoluminescence (CL) and remote-electron beam induced current (REBIC). Wavelength dispersive X-ray (WDX) mappings were also performed to analyze possible differences in stoichiometry related to the presence of extended defects.     

Cathodoluminescence study in AlxGa1 − xN structures

In this work, we consider a 2D model for calculation of cathodoluminescence in GaN-based structures. This model is developed using an extended generation profile and taking into account the influence of the carrier diffusion process, internal absorption and some radiative recombination processes. First, we have investigated the effect of hole diffusion length and the surface recombination velocity on the CL spectra of GaN sample grown at 800 °C by MOVPE method. Then, we have calculated the dependence of CL intensity from AlGaN alloys as a function of Al content and the electron beam energy.

Results show a red shift of the CL peaks when the beam energy is varied from 2 to 10 keV at room temperature. The band-edge emission of Al_xGa_1 − xN shifts about 0.49 eV when the Al composition is increased from x = 0.18 to 0.38. Comparison of the experimental spectra with simulations shows a good agreement.     

Cathodoluminescence study of crystalline quality of (Al, In, Ga)N heterostructures

Wurtzite InGaN/GaN and AlGaN/GaN heterostructures grown by metal organic vapor phase epitaxy were studied using cathodoluminescence (CL) combined with secondary electron microscopy (SEM) and scanning transmission electron microscopy (STEM). The surface morphology of samples containing InGaN layers is dominated by three types of defects: mesa-like hexagonal structures, hexagonal pyramids and micropipes. At the positions of pyramids the whole epilayer is thicker than at defect free positions, while at the positions of micropipes the whole epilayer is much thinner. The luminescence efficiency as well as the emission wavelength are influenced by these defects. In SL structures an increasing SL period thickness in the growth direction was observed. Panchromatic CL images show intensity inhomogeneity in both InGaN/GaN and AlGaN/GaN heterostructure, which are related to local variations of the interface quality. In AlGaN/GaN SQW structures a broad deep-level luminescence band at around 543 nm was observed, which is generally absent in InGaN/GaN heterostructures. This deep-level emission is strongly enhanced in defect positions.