F. Bridges

Synthesis, Structural, and Optical Properties of Stable ZnS:Cu,Cl Nanocrystals †

Stable water-suspendable Cu+-doped ZnS nanocrystals (NCs) have been synthesized with mercaptopropionic acid (MPA) as a capping molecule. The nanocrystals have been characterized using a combination of experimental techniques including UV-vis and photoluminescence (PL) spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), inductively coupled plasma (ICP), and extended X-ray absorption fine structure (EXAFS). The UV-vis electronic absorption spectrum shows an excitonic peak at 310 nm, characteristic of quantum-confined ZnS NCs. This excitonic peak does not change noticeably with Cu+ doping. XRD confirms the formation of ZnS nanocrystals, and the average size of the NCs has been determined to be around 6 nm by TEM. The incorporation of Cu+ into the ZnS is manifested as a substantial red-shift of the emission band in the PL spectra upon addition of Cu2+ that was reduced into Cu+ during the synthesis reaction. EXAFS data were obtained to confirm copper doping as well as determine the local structure about Cu+ and Zn2+ in the NCs. Fitting to the EXAFS data for Cu+ suggests that most Cu+ ions are located near the surface within the ZnS NCs and that a significant fraction may be in the form of CuS as found in bulk material. These combined optical and structural studies have provided important new insight into the relevant electronic energy levels and their correlation to the optical and structural properties of ZnS:Cu,Cl NCs. This has important implications in potential applications of this phosphor material for solid state lighting, imaging, and other photonic devices.

X-RAY-ABSORPTION FINE STRUCTURE IN EMBEDDED ATOMS

Oscillatory structure is found in the atomic background absorption in x-ray-absorption fine-structure (XAFS) measurements. This atomic XAFS (AXAFS) arises from scattering within an embedded atom, and is analogous to the Ramsauer-Townsend effect. Calculations and measurements confirm the existence of AXAFS and show that it can dominate contributions such as multielectron excitations. The structure is sensitive to chemical effects and thus provides a probe of bonding and exchange effects on the scattering potential.

A Variation of the F‐Test for Determining Statistical Relevance of Particular Parameters in EXAFS Fits

A general problem when fitting EXAFS data is determining whether particular parameters are statistically significant. The F‐test is an excellent way of determining relevancy in EXAFS because it only relies on the ratio of the fit residual of two possible models, and therefore the data errors approximately cancel. Although this test is widely used in crystallography (there, it is often called a “Hamilton test”) and has been properly applied to EXAFS data in the past, it is very rarely applied in EXAFS analysis. We have implemented a variation of the F‐test adapted for EXAFS data analysis in the RSXAP analysis package, and demonstrate its applicability with a few examples, including determining whether a particular scattering shell is warranted, and differentiating between two possible species or two possible structures in a given shell.

LOCAL DISORDER IN THE OXYGEN ENVIRONMENT AROUND PRASEODYMIUM IN Y1-XPRXBA2CU3O7 FROM X-RAY-ABSORPTION FINE STRUCTURE

We present K-edge XAFS (X-Ray Absorption Fine Structure) data for various concentrations of Pr in Y

Structural information on Y ions in C82 from EXAFS experiments

_{1- x}

Spin-Orbital Short-Range Order on a Honeycomb-Based Lattice

Pr

The spectroscopy of crystal defects: a compendium of defect nomenclature

_{x}

Local lattice disorder in the geometrically frustrated spin-glass pyrochlore Y 2 Mo 2 O 7

Ba

Enhanced Cu emission in ZnS:Cu,Cl/ZnS core–shell nanocrystals

_{2}

Investigation of ferromagnetic filled skutterudite compounds EuT4Sb12 (T = Fe, Ru, Os)

Cu