Peter A. Tanner

Some misconceptions concerning the electronic spectra of tri-positive europium and cerium

Tripositive europium attracts wide interest in diverse fields such as phosphors, sensors, and time-gated bioimaging agents based upon its optical emission spectra. Some inaccurate descriptions of these spectra are being amplified throughout the literature. In this tutorial review the background of electronic states, energy levels and transition intensities is provided as a pre-requisite for clarifying these misconceptions. The topics discussed encompass the electric dipole nature of intraconfigurational 4f electronic transitions, the use of europium as site symmetry and centrosymmetry probe, as well as an indicator of nephelauxetic effects. The frequently mis-used term Stokes shift is also clarified and alternative terms are given for the situations where it is incorrectly applied.

Upconversion for White Light Generation by a Single Compound

A new multiphoton upconversion process for rare earth oxide powders is reported, using infrared laser diodes. In vacuum, multiphoton excitation produces intense upconversion emission in the visible spectral range, and Tm(2)O(3) or Yb(2)O(3) achieves pure white upconversion using 808 or 975 nm excitation, respectively.

Preparation and luminescence properties of sol-gel hybrid materials incorporated with europium complexes

Microporous silica gel has been prepared by the sol-gel method utilizing the hydrolysis and polycondensation of tetraethylorthosilicate (TEOS). The gel has been doped with the luminescent ternary europium complex Eu(TTA)3·phen: where HTTA = 1-(2-thenoyl)-3,3,3-trifluoracetone and phen = 1,10-phenanthroline. By contrast to the weak f-f electron absorption bands of Eu3+, the complex organic ligand exhibits intense near ultraviolet absorption. Energy transfer from the ligand to Eu3+ enables the production of efficient, sharp visible luminescence from this material. Utilizing the polymerization of methyl methacrylate or ethyl methacrylate, the inorganic/polymer hybrid materials containing Eu(TTA)3·phen have also been obtained. SEM micrographs show uniformly dispersed particles in the nanometre range. The characteristic luminescence spectral features of europium ions are present in the emission spectra of the hybrid material doped with Eu(TTA)3·phen.

Contamination of Heavy Metals in Marine Sediment Cores from Victoria Harbour, Hong Kong

The physical characteristics, and concentrations of major and trace metals, in 6 m long sediment cores from five marine locations in Hong Kong have been determined. Core chronologies have been reconciled with dredging, construction, and other anthropogenic activities taking place since 1900. Sedimentation rates varied by an order of magnitude, from the more open harbour environments to enclosed ones. The most critical pollutant in the cores, copper, had normalized enrichment factors between 2.8 and 312 at the five sites, and surficial concentrations >6 g kg−1 in the upper sediment of the Typhoon Shelter sampling site. Whereas the Cu, Ni and Cr pollution largely dates from the post-industrial period, Zn and Pb pollution have a longer history from the construction, maintenance and anchorage of ships. Individual trace metal fluxes varied from one location to another by factors >1500, and the magnitudes in the Typhoon Shelter were generally greater than values at other polluted harbour environments.

Advanced red phosphors for white light-emitting diodes

White light-emitting diodes (WLEDs) with high luminous brightness, low energy consumption, long lifetime and environmental friendliness can be applied in various fields. However, low colour rendering index and high correlated colour temperature have seriously limited the quality of white light, resulting from the deficiency of the red light component in commercial phosphors. New phosphors that can emit suitable red light are needed. The improvement of red emitters has gradually become a hot topic in WLED applications such as good colour rendering lighting and full colour displays. This review summarizes recent achievements concerning red phosphors mainly from three aspects. They are: intensifying absorption bands and reducing lattice defects to increase quantum efficiency; selecting an appropriate coordination environment and altering the lattice symmetry to fine-tune the luminescence spectra; and reducing the nonradiative transition rate and preventing charge imbalance of a luminescence centre to enhance thermal stability.

Analysis of spectral data and comparative energy level parametrizations for Ln3+ in cubic elpasolite crystals

Abstract Comparative analyses have been made of the 4f n lanthanide ion (Ln 3+ ) energy level structures in a variety of cubic elpasolite crystals. The systems can be grouped into two sets, namely (i) Ln 3+ in the neat compounds: Cs 2 NaLnCl 6 (LnCeYb, except for Nd, Pm and Sm), Cs 2 LiErCl 6 Cs 2 NaLnBr 6 (LnPr, Ho, Tm), Cs 2 KPrF 6 and Rb 2 NaEuF 6 ; and (ii) Ln 3+ diluted into elpasolite host crystals: Cs 2 NaYCl 6 :Ln 3+ (LnPr, Sm, Eu), Cs 2 NaGdCl 6 :Ln 3+ (LnHo, Nd) and Cs 2 KYF 6 :Eu 3+ . New energy level data obtained from low temperature absorption, emission and electronic Raman studies are presented for these systems to provide more accurate and extensive data sets. The new energy level data were analysed in terms of a 4f n “free-ion” Hamiltonian and a parametric crystal field Hamiltonian model, with octahedral ( O h ) site symmetry for the Ln 3+ ion. The empirical energy level data were fitted to the parametrized total Hamiltonian and the resulting “best-fit” parameter sets are presented and discussed. Examination of the parameter values obtained from least-squares fittings reveals significant differences in the crystal field perturbations experienced by the 4f electrons of Ln 3+ at octahedral sites: the fluoride ligands interact with the 4f electrons somewhat more strongly than do the bromide ligands. The phenomenological (fitted) crystal field parameters of Cs 2 NaLnCl 6 do not exhibit a clear trend across the series of lanthanide elements, partly because of the uncertainty in determination due to the term dependence. The magnitude of the B k 0 ( k = 4,6) parameters follow different patterns in the LaCl 3 :Ln 3+ , LaF 3 :Ln 3+ and LiYF 4 :Ln 3+ systems. However, the magnitudes of the “free-ion” parameters resulting from free variation in the elpasolite system data fits exhibit clearer trends and the spin-orbit coupling constant is found to fit well to a second-order polynomial in atomic number. The standard deviations of the data fits as defined herein are between 0 and 43 cm −1 , so that the energy level schemes of the Ln 3+ ions in elpasolite lattices are reasonably well reproduced.

Comparison of Methods for Determination of Organic Carbon in Marine Sediment

Abstract Assessment of two methods for the determination of organic carbon (OC) in the silt-clay fraction of marine sediment has been carried out with reference to values from the decarbonated sediment, using a CHN analyzer. Although the mass loss on ignition (MLOI) was lower at 440°C than at 550°C or 600°C, the OC contents were overestimated by a factor near three from these results, and the rank order of OC in different sediments was not reproduced. Wet oxidation using the revised Walkley–Black titration overestimated OC in anoxic sediments, but gave an underestimation for oxic sediment. The need for sediment reference material with certified OC content is stressed.

What Use Are Crystal Field Parameters? A Chemist’s Viewpoint

Although first principles methods are gaining interest, the crystal field model is at present the only practicable model to analyze and simulate the energy level structures of lanthanide ions (Ln(3+)) in crystal hosts at the accuracy level of approximately 10 cm(-1). Three criteria are suggested to assess the use of energy parameters, especially crystal field parameters, from the crystal field parametrization of 4f(N) energy level data sets for the entire lanthanide ion (Ln(3+)) series, except Pm(3+). Systematic analyses have been performed upon the most complete energy level data sets available for Ln(3+) situated at sites of high symmetry in crystals of Cs(2)NaLnCl(6). This presents a stringent test for theory because the number of energy parameters is considerably reduced, and the data sets are representative and fairly complete. The results from these data set fittings are shown to comply with the three criteria put forward. First, the fittings of data sets are accurate, and a predictive capability has been employed to calculate the energy levels of Pm(3+) and to elucidate and list all of the potentially luminescent levels of Ln(3+) in the hexachloroelpasolite hosts. Second, the systematic and smooth variations of parameter values over the lanthanide series have been described by simple equations and rationalized. Third, a physical insight of the crystal field parameter variation across this series of elements has been achieved by utilizing a simple semiquantitative model considering the distributions of the 4f radial wave functions at the edge of the Ln(3+) ions, where the ligand orbitals extend. The parameter trends for an individual Ln(3+) ion have been shown to be consistent also for the Cs(2)NaLnF(6) host lattice, and predictions of the individual crystal field parameter values are made.

The acidification process under the cloud in Southwest China : Observation results and simulation

Abstract Mean ionic concentrations in rain water (RW) and cloud water (CW) for urban, suburban and rural locations in southwest (SW) and eastern (E) China, from sampling periods between 1985 and 1989 are reported. In SW China the ammonium, calcium and hydrogen cations, and the sulphate anion are present at elevated levels in urban RW. The mean concentrations of these ions are all lower in CW, so that washout is the predominant process leading to acidification. Washout is also important over suburban regions but rainout provides most of the acidity of precipitation in rural areas. Simultaneous observations of CW and RW concentrations over short time intervals have confirmed the dominance of washout processes in the large cities Chongqing and Guiyang. The chemical compositions of CW and RW exhibit changes with the weather system behaviour as well as with the sampling location. In E China the acidity of rainfall is largely neutralized by alkaline particulates. The mean ionic concentrations in RW show an increasing trend from 1985 to 1988. The ambient air quality in China has deteriorated over the same period, with concentrations of sulphur dioxide and suspended particulates at high levels. The below-cloud acidification process has been simulated by a model which includes scavenging of both gas and aerosol species. The importance of rainout, gas washout or aerosol washout processes is found to vary with the location and with the different ion species considered. Gas washout always leads to overall acidification. Aerosol alkalization has been identified in some suburban areas. The effects on the rainwater acidification predicted from the reduction of sulphur dioxide gas emissions have also been simulated, and are expected to be negligible at Chongqing and Guiyang. The concentration of the hydrogen peroxide oxidant, not that of the pollutant sulphur dioxide, is the controlling factor for the pH of the rainfall in these regions.

Functionalized europium nanorods for in vitro imaging.

Emissive europium hydroxide nanorods (ENR) (20 nm x 500 nm) functionalized by a surface coating of chromophore-containing organically modified silicate (ORMOSIL) layer, have been synthesized and characterized by high-resolution transmission electron microscopy (TEM). Low-temperature photophysical characterization of the functionalized nanorods (FENR) demonstrated a strong red 5D0 luminescence both in solid and in suspended solutions. Potentials of this nanorod material for live cell imaging have also been explored. Both the bare and functionalized nanorods are able to enter living human cells with no discernible cytotoxicity. Chromophore-to-Eu3+ energy-transfer in the functionalized nanorods enables staining of the cytoplasm of living human cells. This is confirmed by costaining with fluorescent dextran. The red chromophore-sensitized luminescence from the internalized nanorods in live human lung carcinoma cells (A549) can be observed by confocal microscopy 2 h after loading and reaches maximal emission after 24 h.