Cathodoluminescence of Rare Earth Doped Zircons. I. Their Possible Use as Reference Materials

Synthetic zircon crystals (ZrSiO4), undoped and doped with Y3+, La3+, Ce3+, Pr3+, Nd3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, Er3+, Tm3+, Yb3+, Lu3+, were grown from a flux consisting of a mixture of Li2MoO4 and MoO3 heated to 1125°C and then cooled to 750°C. The cathodoluminescence (CL) spectra of these zircons were analyzed at room-temperature and near liquid nitrogen temperature with a CL spectrometer attached to a scanning electron microscope (SEM). This study highlights the complexity of the intrinsic emission band extending from 200 to 500 nm. The relative intensities of the major emission band centered at 230 nm (5.4 eV) and peaks of less energy were found to depend upon the crystallographic orientation of the crystals. Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, Er3+ and Tm3+-doped zircons display sharp emission peaks being characteristic of the doping rare-earth element (REE). These lines are frequently multiplets but only the average position of the peaks are reported because of the instrumental conditions used in this study. The CL intensities of the intrinsic and extrinsic features were found to depend on the crystal orientation, and numerous experimental factors such as the electron beam energy and the beam current density

Cathodoluminescence of Rare Earth Doped Zircons. II. Relationship Between the Distribution of the Doping Elements and the Contrasts of Images

Cathodoluminescence (CL) color photographs using an optical CL microscope with a cold cathode electron gun are compared with non-spectrally resolved (polychromatic) and selected wavelength CL images obtained by means of a scanning electron microscope equipped with a CL spectrometer. It is the aim of this paper to show how the interpretation of the contrasts of CL images depends on the knowledge of the CL photon energy distributions participating to the observed contrasts as well as the matrix effects modifying the number of emitted photons compared to that of generated photons. It is shown that the impurities different from the rare earth elements (REE) activators are responsible for charge trapping mechanisms leading to the development of internal electric fields modifying the energy and spatial distribution of the electrons within the insulators and consequently modifying the relative intensities of the intrinsic (host lattice) emission and characteristic emission of a REE activator. In addition, the mechanisms of production of photons must be better understood before trying to express the CL intensity of a monochromatic line as a function of the corresponding REE activator

A Genome Wide Association Study of arabinoxylan content in 2-row spring barley grain

In barley endosperm arabinoxylan (AX) is the second most abundant cell wall polysaccharide and in wheat it is the most abundant polysaccharide in the starchy endosperm walls of the grain. AX is one of the main contributors to grain dietary fibre content providing several health benefits including cholesterol and glucose lowering effects, and antioxidant activities. Due to its complex structural features, AX might also affect the downstream applications of barley grain in malting and brewing. Using a high pressure liquid chromatography (HPLC) method we quantified AX amounts in mature grain in 128 spring 2-row barley accessions. Amounts ranged from ~ 5.2 μg/g to ~ 9 μg/g. We used this data for a Genome Wide Association Study (GWAS) that revealed three significant quantitative trait loci (QTL) associated with grain AX levels which passed a false discovery threshold (FDR) and are located on two of the seven barley chromosomes. Regions underlying the QTLs were scanned for genes likely to be involved in AX biosynthesis or turnover, and strong candidates, including glycosyltransferases from the GT43 and GT61 families and glycoside hydrolases from the GH10 family, were identified. Phylogenetic trees of selected gene families were built based on protein translations and were used to examine the relationship of the barley candidate genes to those in other species. Our data reaffirms the roles of existing genes thought to contribute to AX content, and identifies novel QTL (and candidate genes associated with them) potentially influencing the AX content of barley grain. One potential outcome of this work is the deployment of highly associated single nucleotide polymorphisms markers in breeding programs to guide the modification of AX abundance in barley grain