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A series of natural zircon samples (with U concentrations of 140-2600 ppm and ranging from well crystalline to severely radiation damaged) were investigated by means of REE3+ photoluminescence spectroscopy. We found systematic changes in REE3+ emissions depending on the accumulated radiation damage expressed by the effective time-integrated a-dose of zircon samples. Structural reconstitution as caused by dry annealing resulted in intensity gains and decreases of half-widths of REE3+ emissions. The band half-widths of distinct luminescence Stark's levels of the 4F9/2 → 6H13/2 transition of Dy3+ (~17 250 cm-1; ~580 nm wavelength) and the 4F3/2 → 4I9/2 transition of Nd3+ (~11 300 cm-1; ~885 nm wavelength) were found to correlate sensitively with the degree of radiation damage accumulated. These REE3+ emissions are proposed as potential measure of the irradiation-induced structural disorder of zircon. The two emissions are considered particularly suitable because (1) they are commonly detected in PL spectra of natural zircon, and (2) they are hardly biased by other emissions or Stark's levels. Preliminary calibration curves that relate band-width increases to the a dose were established using a suite of well-characterized Sri Lankan zircon. Band broadening upon increasing corpuscular self-irradiation is assigned to increasing structural destruction, i.e., the increasing perturbation of REE3+ cationic lattice sites. Possible advantages of REE3+ luminescence spectroscopy, complementary to Raman spectroscopy, as method to quantify structural radiation damage are discussed. [ABSTRACT FROM AUTHOR]

The photoluminescence (PL) and PL excitation (PLE) spectra of Si6-zAlzOzN8-z ([beta]-sialon):Eu2+ phosphors with small z values (z = 0.025-0.24) were studied at room temperature and 6 K. The PL and PLE spectra exhibit fine structure with the PL lines being as sharp as 45-55 nm even at room temperature; this fine structure was enhanced by decreasing the z value. These results can be used for expanding the color gamut of liquid crystal displays, particularly in the blue-green region. From low-temperature measurements, the fine PLE structure was ascribed to discrete energy levels of 7FJ states. The 4f65d excited states of Eu2+ are considered to be localized near the 4f orbital. This is because the bonding of Eu2+ with surrounding atoms is ionic rather than covalent. Lattice phonon absorptions were also observed in the PLE spectrum, revealing that the optically active Eu2+ ions are located in the [beta]-sialon crystal. The PL spectrum of the sample with the smallest z value (0.025) consists of a sharp zero-phonon line and lattice phonon replicas, which results in a sharp and asymmetric spectral shape. [ABSTRACT FROM AUTHOR]

Recently, fluorescence spectra of rare-earth ions in oxide materials are very attractive for the applications of the optical amplification in optical fiber communications, white LED, etc. However, it has been difficult to calculate the fluorescence spectra of rare-earth ions by the first principle method. In this study, we used the relativistic discrete-variational multielectron (DVME) method, which is a configuration-interaction (CI) calculation program using the molecular orbitals obtained by the relativistic DV-Xα method. We applied this method for the calculation of the fluorescence spectrum of the Pr3+ ions in phosphate materials. The transition probability of the fluorescence was calculated in the same manner of the absorption. The obtained theoretical fluorescence spectrum was in good agreement with the experimental one, though the intensity of each peak was deeply dependent on the configuration of the surrounding structural units. The results suggested that the DVME method was useful for the calculation of not only absorption but also fluorescence spectra of rare-earth ions in oxide materials. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [ABSTRACT FROM AUTHOR]

The article discusses a study on the preparation of poly vinyl alcohol (PVA) films with Sm³+ and Dy³+ ions using a conventional solution cast technique. The study also used absorption spectral measurements to assess these doped PVA films. It also recorded the excitation and emission spectra and decay curve to understand emission performance of the polymers. It also explained the emission performances of these films in terms of relevant energy level schemes.

During the first measurement campaign of the EU FORMAT project in summer 2002 near Milan, northern Italy, ground-based scattered light differential optical absorption spectroscopy (DOAS) measurements were performed using a new multi-axis instrument. From the data set of this four week measurement period, the detailed analysis results of three days, 12-14 August, are presented exemplary. Slant column densities for formaldehyde (HCHO) and the oxygen dimer (O4) have been retrieved, employing fitting windows from 335 nm to 357 nm and 350 nm to 360 nm respectively. In order to convert slant into vertical columns radiative transfer calculations were perfomred using aerosol parameters derived from the actual O4 measurements. By analysing the measurements from different viewing directions (zenith, 4x off-axis) vertical profile information, and in particular mixing ratios for the boundary layer have been derived for the first time for HCHO with a multi-axis DOAS (MAX-DOAS) instrument. HCHO vertical columns are in the range of 5 to 20⋅1015 molec/cm² with an relative error of about 15%. This corresponds to HCHO mixing ratios in the boundary layer of 0.7 ppb to 4.2 ppb, which is in excellent agreement with simultaneous measurements from both a Hantzsch in-situ and a long-path DOAS instrument operated at the same place. [ABSTRACT FROM AUTHOR]

Praseodymium doped lanthanum metaborate, La(BO2)3, is synthesized by solution chemistry. The title compound crystallizes in the monoclinic space group 12/c. The ten-fold coordinated rare earth ion is located in the C2 low point symmetry site. The optical and crystal field analyses of Pr3+ in this host lattice are presented. The absorption spectra are recorded from the visible to the far IR domain at 300 and 9 K. The low temperature absorption spectra show only one electronic line for ³H4→³P9 transition confirming a unique local environment for the rare earth ion in this metaborate phase. Under various Ar+ laser excitations, the emission of Pr3+ ion is detected from the ³P0 and ¹D2 excited levels of the 4f² ground configuration. A selective excitation in the ¹D2 level as also performed. The electrostatic crystal field (cf) effect on the 4f² configuration has been evaluated on the basis of the cf theory with nine phenomenological Bkq crystal field parameters (cfp) in the C2y point symmetry, using 54 (52) experimental cf levels deduced from the absorption and emission spectra. The final simulation is achieved with an r.m.s. of 16.1 (12.6) cm-1. [ABSTRACT FROM AUTHOR]

CsCdBr 3 consists of linear chains of [CdBr 6 ] 4- octahedra separated by Cs + ions. The excited states of the covalently bound [CdBr 6 ] 4- octahedra form the lowest excitonic states of the crystal lattice. The trivalent Pr ions substitute for the divalent Cd ions. For reasons of charge compensation in the linear Cd 2+ chains, pair centers of the form Pr 3+ -(Cd vacancy)-Pr 3+ are predominantly formed. In CsCdBr 3 the optical band gap is wider than the electronic one. This allows to study the interaction between Pr 3+ ions and excitons by means of optical spectroscopy. The interaction leads to quantum up- and down-conversion generating one photon from two lower ones in energy and vice versa. Related experiments are discussed. [ABSTRACT FROM AUTHOR]

In this article, we report on some of the fundamental chemical and physical processes responsible for the deposition of graphene by microwave plasma-enhanced chemical vapor deposition. The graphene is grown by plasma decomposition of a methane and hydrogen mixture (CH4/H2) at moderate pressures over polycrystalline metal catalysts. Different conditions obtained by varying the plasma power (300–400 W), total pressure (10–25 mbar), substrate temperature (700 °C–1000 °C), methane flow rate (1–10 sccm) and catalyst nature (Co–Cu) were experimentally analyzed using the in situ optical emission spectroscopy technique to assess the species rotational temperature of the plasma and the H-atom relative concentration. Then, two modeling approaches were developed to analyze the plasma environment during graphene growth. As a first approximation, the plasma is described by spatially averaged bulk properties, and the species compositions are determined using kinetic rates in the transient zero-dimensional (0D) configuration. The advantage of this approach lies in its small computational demands, which enable rapid evaluation of the effects of reactor conditions and permit the identification of dominant reactions and key species during graphene growth. This approach is useful for identifying the relevant set of species and reactions to consider in a higher-dimensional model. The reduced chemical scheme was then used within the self-consistent two-dimensional model (2D) to determine auto-coherently the electromagnetic field, gas and electron temperatures, heavy species, and electron and ion density distributions in the reactor. The 0D and 2D models are validated by comparison with experimental data obtained from atomic and molecular emission spectra. [ABSTRACT FROM AUTHOR]

Rare-earth silicates are highly efficient materials for silicon-based light sources. Here we report a novel light-emitting device based on Ce2Si2O7. Intense violet/blue electroluminescence was observed, with a turn-on voltage of about 13 V. The violet/blue emission is attributed to 4f-5d transitions of the Ce3+ ions in Ce2Si2O7, which are formed by interfacial reaction of CeO2 and Si. Electroluminescence and photoluminescence mechanisms of the Ce2Si2O7 light-emitting device are also discussed. [ABSTRACT FROM AUTHOR]