Michael W. Blair

Y2O3:Bi nanophosphor: Solution combustion synthesis, structure, and luminescence

Photoluminescence (PL), radioluminescence (RL), and thermoluminescence (TL) investigation of Y2O3:Bi nanophosphors prepared by solution combustion synthesis using urea, glycine, and hexamethylenetetramine (HMT) as fuels was carried out. The as-prepared nanopowders have increasing crystallinity and average crystallite sizes for urea, glycine, and HMT, respectively. Luminescence is composed of two emission bands centered at 408 and 505 nm due to two nonequivalent Bi3+ sites with symmetry S6 and C2, respectively. The occupancy of these sites depends on the synthesis conditions, in agreement with theoretical predictions. Annealing at 1000 °C for 1 h improves PL and RL efficiency due to enhanced crystallinity of the nanopowders and activation of recombination centers (Bi3+ ions). No shift in the PL peak position was observed as a function of average crystallite size. The concentration quenching was experimentally determined to have a maximum emission of around 3 mol % of the dopant. TL spectra present several ...

Science and Application of Oxyorthosilicate Nanophosphors

Nanophosphor Y2SiO5:Ce (n-YSO), Lu2SiO5:Ce (n-LSO), and Gd2SiO5:Ce (n-GSO) were prepared by solution-combustion synthesis yielding nanophosphor crystallite sizes between 20 nm - 80 nm. Ce dopant concentrations were varied between 0.1%-10% for each the nanophosphors and concentration quenching curves were measured by radioluminescence (RL) and photoluminescence (PL). n-YSO exhibits concentration quenching at 1 at% and 4 at% under UV and X-ray excitation, respectively. Red shifted emission with a larger Stokes shift is observed for nanophosphors as compared to bulk crystals. The measured PL lifetime depended on the refractive index of the media, indicating that the PL originates from the surface. Measurements of the RL/PL intensity indicate that the light output of these materials is comparable to the bulk crystal.

EPR and Luminescence of

The main thermally stimulated luminescence glow peak in irradiated oxyorthosilicates occurs near 360-400 K and has been postulated to comprise an electron trapped at an oxygen vacancy (F+ center). We have used electron paramagnetic resonance spectroscopy to identify this defect in Ln2SiO5:Ce (Ln = Lu and Y) and show that it consists of a single electron trapped at a non-silicon-bonded oxygen vacancy in both bulk and nanophosphor oxyorthosilicates. Both Lu- and Y-based nanophosphors form seven- and nine-oxygen coordinated structures (P21/c) whereas the bulk phosphors form six- and seven-oxygen coordinated structures (C2/c). In each case the F+ center predominately forms at the larger oxygen site. A typical resonance comprises a single Gaussian line broadened by hyperflne interaction with g-values near the free electron value and hyperflne coupling ~0.4 mT. The F+ center can be annealed and radiation-induced, consistent with the thermally stimulated luminescence glow peak behavior.

{\hbox {F}}^{+}

The structural, dielectric, and vibrational properties of pure and rare earth (RE)-doped Ba0.77Ca0.23TiO3 (BCT23; RE = Nd, Sm, Pr, Yb) ceramics obtained via solid-state reaction were investigated. The pure and RE-doped BCT23 ceramics sintered at 1450 °C in air for 4 h showed a dense microstructure in all ceramics. The use of RE ions as dopants introduced lattice-parameter changes that manifested in the reduction of the volume of the unit cell. RE-doped BCT23 samples exhibit a more homogenous microstructure due to the absence of a Ti-rich phase in the grain boundaries as demonstrated by scanning electron microscopy imaging. The incorporation of REs led to perturbations of the local symmetry of TiO6 octahedra and the creation of a new Raman mode. The results of Raman scattering measurements indicated that the Curie temperature of the ferroelectric phase transition depends on the RE ion and ion content, with the Curie temperature shifting toward lower values as the RE content increases, with the exception of...

Centers in Bulk and Nanophosphor Oxyorthosilicates

Herein we describe the unique luminescent behavior observed in [Ce(IV)(W(5)O(18))(2)](8-) clusters and examine the photophysical properties using density functional theory.

Structural and optical properties of rare earth–doped (Ba0.77Ca0.23)1−x(Sm, Nd, Pr, Yb)xTiO3

A novel synthetic route to a series of cerium bromide solvates is reported. The combination of bulk cerium bromide and the ionic liquid (IL) 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide results in a precursor paste that enhances the solubility of the cerium(III)bromide moiety in a number of donor solvents. Crystallization from these solvents has resulted in the isolation and characterization of CeBr(3)(THF)(4) (2), CeBr(3)(2-Me-THF)(4) (3), and CeBr(3)(MeCN)(5)·MeCN (4). Additionally, 2 is shown to be an efficient precursor for the new species CeBr(3)(py)(4) (5) and CeBr(3)(bipy)(py)(3) (6).

Luminescence in CeIV polyoxometalate [Ce(W5O18)2]8-: a combined experimental and theoretical study

The synthesis of Ce-doped Gd oxyorthosilicate nanoparticles using the solution combustion synthesis (SCS) method was investigated as a function of the amount of SiO2 in the precursor mixture. The SCS product consists of mixtures of Ce-doped Gd2SiO5, Gd4.67(SiO4)3O, and Gd2O3, whose relative concentrations depend on the amount of SiO2 in the precursor mixture; the synthesis of GSO:Ce was obtained with a reduction by 30% of the SiO2 content. Accordingly, this is the brightest material produced, with a photoluminescence signal that is comparable to that obtained from the bulk sample. Thermoluminescence (TL) results showed a considerably lower concentration of trapping defects in the nanoparticles than in the bulk sample. A previous study [E. G. Yukihara, L. G. Jacobsohn, M. W. Blair, B. L. Bennett, S. C. Tornga, and R. E. Muenchausen, J. Lumin. 130, 2309-2316 (2010)] reporting a comparison between photoluminescence and scintillation measurements, coupled to the TL characterization, suggests that surfaces pla...

An ionic liquid-mediated route to cerium(III) bromide solvates.

Nanophosphors correspond to nanostructured inorganic insulator materials that emit light under particle or electromagnetic radiation excitation. In this work we investigate the structure and luminescent properties of Ce-doped Lu2SiO5 (LSO) nanophosphors prepared by solution combustion synthesis with the Ce content 0.1 to 12 at. %. Samples were characterized by transmission electron microscopy (TEM), line scan electron energy-loss spectroscopy (EELS), xray diffraction (XRD), and electron paramagnetic resonance (EPR) spectroscopy. Photoluminescence excitation and emission spectra are composed of two major bands centered at 360 and 430 nm, respectively. These results reveal a red-shift and enhanced Stokes shift for the nanophosphors when compared to bulk. Ce content was also found to affect photoluminescence emission intensity and fluorescent lifetime. The nanophosphor concentration quenching curve presents a broad maximum centered at 1 at.%. Lifetime measurements show a continuous decrease from 34 to 21 ns as Ce content is increased.

Synthesis, structure, and scintillation of Ce-doped gadolinium oxyorthosilicate nanoparticles prepared by solution combustion synthesis

The role of transition-metal impurities in Yb3+-doped YLiF4 (YLF) laser-cooling crystals is studied. Divalent 3d transition-metal ions, in particular Fe2+, are found to have strong absorptions at the laser cooling pump wavelength and degrade the cooling efficiency by introducing background absorption. A set of eight substitutional and chargecompensated defects that form upon introduction of 1+, 2+, and 3+ transition-metal ions into the YLF crystal lattice is proposed. A calculation of solution energies for each defect type and for a range of 3d ions is carried out. It indicates that divalent 3d ions preferentially substitute for Y3+ accompanied by a fluoride vacancy for charge compensation. An electron paramagnetic resonance (EPR) study of a YLF crystal identifies Fe2+ in the crystal lattice, in agreement with the elemental analysis and the computational results. A strategy for purifying the YF3, LiF, and YbF3 starting materials for the YLF:Yb crystal growth is discussed. Chelate-assisted solvent extraction purification with pyrrolidine dithiocarbamate (APDC) for Y, Li, and Yb as well as ethylenediaminetetraacetic acid (EDTA) for Li was carried out.

Structure and Luminescence of Ce-doped Lu2SiO5 Nanophosphor

Electron paramagnetic resonance (EPR) spectroscopy has been used to study energy transport properties of both bulk and nanophosphor (nominally 30 nm) oxyorthosilicate samples, and we were able to separate the effects of crystal disorder and relaxation lifetime broadening on the EPR linewidths. The low temperature linewidths (T<10 K) were inhomogeneously broadened and dominated by crystal disorder effects and the nanophosphors showed an order of magnitude increase in crystal disorder. Both bulk and nanophosphor samples showed significant lifetime broadening involving direct relaxation via phonons and the Orbach relaxation process. At low temperatures, the lifetimes of the bulk samples displayed the influence of the lattice-bath relaxation time as well as the spin-lattice relaxation time while the lifetimes of the nanophosphor samples were not influenced by the lattice-bath relaxation time. The results imply that reduced dimensionality in insulators does reduce the lattice-bath relaxation time, although the...