Cathodoluminescence of Lu 2 O 3 :Tb

Spectroscopic properties of Lu 2 O 3 :Tb pellets sintered at 1000 v C or 1700 v C were investigated. The sintering temperature did not influence the optically excited emission and excitation spectra of the materials. However, the treatment temperature did influence the emission under cathode-rays stimulation. While the specimens sintered at 1000 v C showed only luminescent lines above 480 v nm resulting from a radiative relaxation of the 5 D 4 level, the samples heated at 1700 v C did show some luminescence in the blue region resulting from 5 D 3 M 7 F J emission. The blue emission could be recorded exclusively upon cathode-rays irradiation.     

Angular dependences of sputtering ratio,ion-electron emission coefficient and ion-induced photon emission yield at oblique ion incidence on crystalline targets

The angular dependences of the sputtering ratio, ion-induced photon emission yield and the ion-electron emission coefficient for two faces of a copper'crystal at glancing angles of ion incidence on the targets has been experimentally studied.     

Y2O3:Tm,Yb nanophosphors for correlative upconversion luminescence and cathodoluminescence imaging

We present a phosphor nanoparticle that shows both upconversion luminescence (UCL) and cathodoluminescence (CL). With this particle, low-autofluorescence, deep-tissue and wide-field fluorescence imaging can be achieved with nanometer-order high-spatial-resolution imaging. We synthesized Y₂O₃:Tm,Yb nanophosphors that emit visible and near-infrared UCL under 980 nm irradiation and blue CL via electron beam excitation. The phosphors were applied to fluorescent imaging of HeLa cells. The photostability of the phosphors was superior to that of a conventional organic dye. We show that after uptake by HeLa cells, the particles can be imaged with SEM and CL contrast in a cellular section. This indicates that correlative UCL and CL imaging of biological samples could be realized.     

Spatial luminescent properties and growth mechanism of one- and two-dimensional ZnO complexes

Unique ZnO nanocomplexes of one-dimensional nanorods combined with two-dimensional hexagonal plates are fabricated by a chemical vapor deposition method without using any catalysts. Cathodoluminescence images show that the green emission from the nanoplate is much stronger than that from the nanorod, which suggests the oxygen vacancies are more abundant in the ZnO nanoplates. Our study finds that the growth of one-dimensional ZnO nanorods and low-dimensional ZnO complexes can be switched by directly controlling the source oxygen.     

Effect of size variation on the cathodoluminescence characteristics of graphene quantum dots

Cathodoluminescence (CL) has been studied in graphene quantum dots (GQDs) by varying their average size (d) from 5 to 35 nm. The size dependence of CL peak wavelength is very analogous to that of photoluminescence (PL) peak wavelength unusually showing non-monotonic behaviors having a maximum at d = ∼17 nm. The CL behaviors can therefore be attributed to the novel feature of GQDs, i.e., the circular-to-polygonal-shape and corresponding edge-state variations of GQDs at d = ∼17 nm as d increases. However, the peak wavelengths of CL are especially much smaller than those of PL at both ends in the size range of GQDs, possibly resulting from the recombination of the electron-beam-excited e-h pairs at higher energy states before thermalization due to fast carrier-carrier scattering dominating over electron-phonon scattering in graphene.     

Energy transfer between doubly doped Er, Tmand Ho rare earth ions in SiO2 nanoparticles

Preparation of Er³⁺, Ho³⁺ and Tm³⁺ ions co-doped SiO₂ nanoparticle phosphor powders by sol gel method is reported. The morphology and the particle size of the SiO₂ host matrix were confirmed by field emission scanning electron microscopy (FESEM). Ultraviolet, visible (UV/VIS) and cathodoluminescence measurements were carried out in order to investigate the optical properties of our powder phosphors. Green emissions at 520 nm from Er³⁺ and 544 nm from Ho³⁺, and red emissions at 665 nm from both Er³⁺ and Ho³⁺ ions are reported. Another emission peak in the near infra-red (NIR) region at 875 nm from Er³⁺ was also measured. Blue emission at 460 nm, red at 705 nm and a NIR peak in the region of 865 nm from Tm³⁺ were observed. Red, green and blue (RGB) colours were measured from both SiO₂:Er³⁺,Tm³⁺ and SiO₂:Ho³⁺,Tm³⁺ systems. The change in the intensities of the emission peaks in both the SiO₂:Ho³⁺,Tm³⁺ and SiO₂:Er³⁺,Tm³⁺ systems with the change in accelerating beam voltage is shown. Energy transfer from Tm³⁺ ions to Er³⁺ and Ho³⁺ ions was observed. A mechanism explaining the increase and decrease behaviour of the emission with accelerating beam voltage from both systems is reported.     

Cathodoluminescence (CL) features of the Anatolian agates, hydrothermally deposited in different volcanic hosts from Turkey

Two different types of multi-colored gem-quality agate samples were investigated. They are both found in the same area in the Çubuk-Ankara region of Turkey although the first group is morphologically and geologically distinct from the second, being nodular-shaped agates occurring in cavity-spaces of a rhyolite host rock with an acidic character. They generally do not have any macroscopic inclusions, but the second group of rather block-shaped agates occurs in the fracture-spaces of an andesite host rock with a more neutral character, i.e. of lower free silica content, and they may display pseudomorphic bar-like macroscopic inclusions.Cathodoluminescence results at room temperature were obtained using measurements with alternating current (AC) (at energies of 14 and 24 keV) as well as direct current (DC) (at 14 keV energy), and they display remarkably different patterns between the two types of agates. It reveals a relation between the CL emissions and the presence of some transition metal elements. It is obvious that all trace elements do not play a direct role.Gaussian fitting of the cathodoluminescence AC experimental data at 14 keV energy obtained from the agates of rhyolite host indicates that there are three major spectral emissions, the dominant one being in the longer-visible wavelength region (red region) at about 690 nm. Additionally, two lesser emission lines occur in the middle-visible wavelength region (yellow region) at about 590 nm, and in the smaller-visible wavelength region (blue region) at about 430 nm. In spite of these, the same data from the agates of andesite host indicate that there is only one remarkable spectral emission which is in the in the middle-visible wavelength region (yellow region) at about 590 nm.On the other hand, Gaussian fitting of the cathodoluminescence AC experimental data at 24 keV energy obtained from the agates of rhyolite host indicates that these initial spectral emissions shift from the red and yellow regions to the orange and green regions respectively, even though the emission in the blue region is nearly constant. In spite of these, Gaussian fitting of the cathodoluminescence AC experimental data at 24 keV energy obtained from the agates of andesite host indicates that the initial spectral emission shifts from the yellow region to the green region, but also that a new minor emission develops in the blue region at about 430 nm. It is interpreted that these changes represent a maturation reaction in the microcrystalline quartz structure consisting of a condensation reaction eliminating water between neighboring paired silanol (Si-OH) groups to develop a strained Si-O-Si bond.     

Optical properties of nonpolar -plane GaN layers

We have studied optical properties of nonpolar a-plane GaN layers grown on r-plane sapphire by metalorganic chemical vapor deposition and hydride vapor phase epitaxy using different nucleation schemes. Several emission bands, which are not typical for c-plane GaN, are observed in the photoluminescence spectra and their excitation-intensity, temperature, and polarization dependencies are examined. In addition, the spatial distribution of the emissions was examined by cathodoluminescence imaging and relations of the different emissions with particular structural features in the layers are revealed. The results are discussed with emphasis on the origin of the emission line and particular recombination mechanisms.     

Effect of nanoscaled SnO2 coating on ZnS:Mn phosphors under electron irradiation

The luminescence properties of SnO₂-coated ZnS:Mn phosphors are investigated. In the case of photoluminescence, emission intensities show little change when SnO₂ is coated on the surface of ZnS:Mn, while in the case of cathodoluminescence (CL), emission intensities vary depending on excitation energies. In order to determine the luminescence behaviors, surface analyses of the phosphors were performed. Auger electron spectroscopy showed that the width of the SnO₂ layer on the ZnS:Mn phosphor was saturated at approximately 120 nm. Also, X-ray photoelectron spectroscopy indicated that the SnO₂ layers are well formed and saturated when the molar ratios of Sn/Zn are larger than 0.005. These results suggest that the changes in the CL emissions can be attributed to a lowering of the junction barrier.     

The origin of yellow band emission and cathodoluminescence of Au-catalyzed wurtzite GaN nanowires

GaN nanowires with large yield are directly synthesized by simply ammoniating the gallium oxide powders in the presence of ammonia gas at 1000 °C, under the assistance of Au nanocatalysts. The microstructure and crystallinity of as-synthesized GaN nanowires are well studied by using high-resolution transmission electron microscope (HRTEM) and some structural defects such as stacking faults are found in the GaN nano-crystal. Cathodoluminescence measurement shows that a strong near-band-edge (NBE) emission band centered at 384 nm and a broad yellow band in the range of 500–800 nm are observed. Finally, the growth mechanism and possible optical emission process of GaN nanowires are discussed.