Imaging of Individual Eu Doped Y2O3 Sub-microspheres Using Photoluminescence Yield: An Application of Scanning Transmission X-ray Microscopy in Luminescent Materials

Abstract

Scanning transmission X-ray microscopy (STXM) employs a nano-sized X-ray beam and provides spectro-microscopic information by measuring the absolute absorption of the specimen in transmission; thus both chemical images and detailed absorption spectroscopic features of a single nanostructure (including its thickness) can be revealed [1]. STXM-Ptychography reaches a spatial resolution of 10 nm in the hard X-ray and below 5 nm in the soft X-ray [2,3]. Recently STXM using X-ray fluorescence yield (FY) and total electron yield (TEY) mode has been developed to visualize local element segregation, chemistry and conductivity variation among different crystal facets of LiNi1/3Fe1/3Mn4/3O4 micro-sized particles at the transition metal L-edges and O K-edge, which do not suffer from the sample thickness limitation because soft X-ray cannot penetrate thick samples [4]. Jacobsen et. al. have demonstrated that scanning luminescence X-ray microscopy (SLXM) can be used to form high-resolution images of ZnS based phosphor P31 microparticles and polystyrene microspheres loaded with fluorescent dye based on the visible light emission from the sample and the fluorescent dye, respectively [5]. More recently, Vaz et. al. demonstrated imaging of the magnetic domain configuration of cobalt microstructures fabricated on MgO(001) using the photoluminescence from the MgO substrate in STXM [6]. These encourage further development of STXM with the capability of photoluminescence yield (PLY) mode for studying luminescent nanomaterials. Here we demonstrate the imaging of individual Eu doped Y2O3 submicrospheres using STXM based on the optical luminescence from the sub-microspheres. Furthermore, PLY-X-ray absorption near edge structures (PLY-XANES) can be isolated from individual submicrospheres.Eu-doped Y2O3 submicrospheres were prepared by homogeneous precipitation and post-annealing with CO(NH2)2, Y(NO3)3 and Eu(NO3)3 as starting materials. STXM measurement was carried out at the SM beamline of the Canadian Light Source (CLS). A 25 nm outermost-zone zone plate (CXRO, Berkeley Lab) is used and the diffraction-limited spatial resolution for this zone plate is 30 nm. As shown in Figure 1, the detector was modified to only collect the optical luminescence emitted from the sample. More details of STXM measurement and data analysis can be found elsewhere [7]. Figure 2a shows a STXM image of Eu doped Y2O3 submicrospheres that monitored the optical luminescence emitted from the submicrospheres when excited at 540 eV. The morphology of the sample is well resolved, showing spherical shape with diameter of about 250-500 nm. The luminescence intensity is much stronger at the center than the edge area of single submicrospheres (e.g.: as marked by green dashed circle), suggesting that the sample is solid, not a hollow structure. The STXM image is consistent

Emerging X-ray imaging technologies for energy materials

“…As the synchrotron pulse is typical ~30 ps and X-ray Free Electron Laser (XFEL) is ~100 fs with tunable repetition rates, time-resolved imaging via different energy transfer channel is a possibility. Figure 11 below shows a couple of examples of XEOL imaging of rare-earth phosphors excited in the tender (Ce and Tb L3-edge) and soft X-ray (O K-edge) region, respectively [98,99]. It can be seen from Figure 11 that XEOL with a given emission channel, has different depth and site selectivity than XRF hence it produces slightly different maps, left panel) and that an individual nanostructure can be mapped with optical yield (right panel).…”

Combining X-ray excited optical luminescence and X-ray absorption spectroscopy for correlative imaging on the nanoscale

“…The three main motivations for exploiting XEOL in imaging studies are its low background signal and high penetrability in biological systems, the previously discussed site-selectivity, and the ability to probe optical luminescence at scales below the diffraction limit. These motivations have led to the development of laboratory-based, low-dose, 2D and 3D imaging systems for monitoring drug release and biomolecular processes in vivo (Pratx et al, 2010;Chen et al, 2011Chen et al, , 2013Carpenter et al, 2012), full-field optically detected XAS microscopes (Poolton et al, 2006;Sabbe et al, 2014), and scanning XEOL microscopes that make use of soft and hard X-ray nanoprobes (Sham et al, 2010;Jacobsen et al, 1993;Martı ´nez-Criado et al, 2006, 2012a,b, 2017Wang et al, 2018).…”