Enhancement of Vibrant Up-Conversion in (Ca,Sr)F2:Er,Yb,Al Phosphors via Energy Transfer, Localized Interstitial Distortion, and Au Nanostructures.

A remarkable increase in the luminescent intensity of Er3+-doped CaF2 up-conversion phosphors was achieved, showing an approximate enhancement of over 1100-fold. This enhancement was realized by incorporating Yb3+, Al3+, Sr2+, and gold nanospheres and nanorods. The substantial improvement in up-converting luminescence effectively enhances sensitivity and efficiency at low excitation power densities. The up-conversion phosphors, consisting of (Ca,Sr)F2:Er,Yb,Al, were easily prepared using excess NH4F flux at 950 °C for 30 min. The structural confirmation of interstitial Al3+ ions within the CaF2 lattice was achieved through synchrotron powder X-ray powder diffraction. The significant enhancement of up-conversion emission and their mechanisms in the phosphors were vividly represented through energy transfer, interstitials and local distortions, and localized surface plasmon resonances when excited with a 980 nm diode laser.

Insights of Peculiar Green-Yellow Emission Occurrence in Ce3+-Doped Barium Yttrium Orthogermanate Phosphors.

The Ba8.8Ce0.1Na0.1Y2Ge6O24 orthogermanate phosphor, prepared by LiCl flux assistance under a reducing atmosphere, exhibited a mysterious green-yellow emission at 298 K. A blue-emitting orthogermanate phosphor was expected to be achieved through the lower d-band of Ce3+ ions in the host structure owing to their optical structure geometry. Oxygen vacancies were observed in the phosphors through investigating bond-length fluxations, the oxygen 1s profile, and the Ge2+/Ge4+ oxidation state, using synchrotron X-ray diffraction refinement, X-ray photoelectron spectroscopy, and Ge K-edge X-ray absorption near-edge structure spectra, respectively. The Ba-M4,5 edge shift, bonding limitation, and distortion index discovery reveal the oxygen-coordinating environment variation around the Ba2+(Ce3+) ions in the phosphors. The green-yellow emission results from the active 6-coordinated antiprism oxygen geometry around the Ce3+ ions in the phosphors.

Spectral-converting study of Ba((9-3)(m+n)/2)Er(m)Yb(n)Y2Si6O24 (m = 0.005 - 0.2, n = 0 - 0.3) orthosilicate phosphors.

Optical materials composed of Ba((9-3)(m+n)/2)Er(m)Yb(n)Y2Si6O24 (m = 0.005-0.2, n = 0-0.3) were prepared using a solid-state reaction. The X-ray diffraction patterns of the obtained phosphors were examined to index the peak positions. The photoluminescence (PL) excitation and emission spectra of the Er(3+)-activated phosphors and the critical emission quenching as a function of Er(3+) content in the Ba(9-3m/2)Er(m)Y2Si6O24 structure were monitored. The spectral conversion properties of Er(3+) and Er(3+)-Yb(3+) ions doped in Ba9Y2Si6O24 phosphors were elucidated under diode-laser irradiation at 980 nm. Up-conversion emission spectra and the dependence of the emission intensity on pump power for the Ba8.55Er0.1Yb0.2Y2Si6O24 phosphor were investigated. The desired up-conversion of the emitted light, which passed through the green, yellow, orange and red regions of the spectrum, was achieved through the use of appropriate Er(3+) and/or Yb(3+) concentrations in the host structure and 980 nm excitation light. The up-conversion mechanism in the phosphors is described by an energy-level schematic.

Photoluminescence Spectra Correlations with Structural Distortion in Eu3+- and Ce3+-Doped Y3Al5-2x(Mg,Ge)xO12 (x = 0, 1, 2) Garnet Phosphors.

Garnet-type materials consisting of Y3Al5-2x(Mg,Ge)xO12 (x = 0, 1, 2), combined with Eu3+ or Ce3+ activator ions, were prepared by a solid-state method to determine the structural and optical correlations. The structure of Y3Al5-2x(Mg,Ge)xO12 (x = 1, 2) was determined to be a cubic unit cell (Ia-3d), which contains an 8-coordinated Y3+ site with octahedral (Mg,Al)O6 and tetrahedral (Al,Ge)O4 polyhedra, using synchrotron powder X-ray diffraction. When Eu3+ or Ce3+ ions were substituted for the Y3+ site in the Y3Al5-2x(Mg,Ge)xO12 host lattices, the emission spectra showed a decrease in the magnetic dipole f-f Eu3+ transition and a redshift of the d-f Ce3+ transition, related to centrosymmetry and crystal field splitting, respectively. These changes were monitored according to the increase in Mg2+ and Ge4+ contents. The dodecahedral and octahedral edge sharing was identified as a key distortion factor for the structure-correlated luminescence in the Eu3+/Ce3+-doped Y3Al5-2x(Mg,Ge)xO12 garnet phosphors.

Self-Activating Strontium Orthoborate Blue Phosphors Induced by Cation and Anion Deficiencies and Their Rare-Earth-Free White Ultraviolet Light-Emitting Diodes.

Self-activating blue-light-emitting strontium orthoborate phosphors, viz., Sr3B2+xO6+3x/2 and Sr3B2+xO6+3x/2-δ (x ranges from -0.3 to 0.1), were obtained by varying the number of BO3/2 and anion deficiencies. The integrated intensity observed from the oxygen 1s profile obtained via X-ray photoelectron spectroscopy indicated the relative concentrations of the oxygen vacancies in the Sr3B2+xO6+3x/2 (x = 0, -0.1, and -0.3) and Sr3B2O6-δ phosphors. The structures of Sr3B2O6, Sr3B2.1O6.15, Sr3B1.9O5.85, and Sr3B2O6-δ with crystal orientations were analyzed based on high-resolution synchrotron powder X-ray diffraction data. A mixture of rare-earth-free blue Sr3B2O6-δ and yellow Sr2.45Ba0.5Na0.05Al0.95Sn0.05O4-αF1-δ phosphors, incorporated on a 315 nm UV-LED chip, can generate a white-light UV-LED.

Nonstoichiometric LaO0.65F1.7 Structure and Its Green Luminescence Property Doped with Bi3+ and Tb3+ Ions for Applying White UV LEDs.

Red-green-blue phosphors excited by ultraviolet (UV) radiation for white light LEDs have received much attention to improve the efficiency, color rendering index (CRI), and chromatic stability. The spectral conversion of a rare-earth ion-doped nonstoichiometric LaO0.65F1.7 host was explored with structural analysis in this report. The nonstoichiometric structure of a LaO0.65F1.7 compound, synthesized by a solid-state reaction using La2O3 and excess NH4F precursors, was analyzed by synchrotron X-ray powder diffraction. The crystallized LaO0.65F1.7 host, which had a tetragonal space group of P4/nmm, contained 9- and 10-coordinated La3+ sites. Optical materials composed of La1-p-qBipTbqO0.65F1.7 (p = 0 and 0.01; q = 0-0.2) were prepared at 1050 °C for 2 h, and the single phase of the obtained phosphors was indexed by X-ray diffraction analysis. The photoluminescence spectra of the energy transfer from Bi3+ to Tb3+ were obtained upon excitation at 286 nm in the nonstoichiometric host lattice. The desired Commission Internationale de l'Eclairage (CIE) values of the phosphors were calculated. The intense green La0.89Bi0.01Tb0.1O0.65F1.7 phosphor with blue and red optical materials was fabricated on a 275 nm UV-LED chip, resulting in white light, and the internal quantum efficiency, CRI, correlated color temperature, and CIE of the pc LED were characterized.

Enhancement in Electromagnetic Wave Shielding Effectiveness through the Formation of Carbon Nanofiber Hybrids on Carbon-Based Nonwoven Fabrics.

The selective hybrid formation of numerous tiny carbon nanofibers (CNFs) in carbon-based nonwoven fabrics (c-NFs), namely CNFs formed only on the surfaces of individual carbon fibers (i-CFs) constituting c-NFs and not on the surfaces of carbon microcoils (CMCs), could be formed by the incorporation of H2 gas flow into the C2H2 + SF6 gas flow in a thermal chemical vapor deposition system. On the other hand, the nonselective hybrid formation of numerous tiny CNFs in c-NFs, that is, tiny CNFs formed on the surfaces of both i-CFs and CMCs, could be achieved by simply modulating the SF6 gas flow on and off in continuous cycles during the reaction. Detailed mechanisms are suggested for the selective or nonselective formation of tiny CNFs in c-NFs. Furthermore, the electromagnetic wave shielding effectiveness (SE) values of the samples were investigated across operating frequencies in the 8.0-12.0 GHz range. Compared with previously reported total SE values, the presently measured values rank in the top tier. Although hybrid formation reduced the electrical conductivity of the native c-NFs, the total SE values of the native c-NFs greatly increased following hybrid formation. This dramatic improvement in the total SE values is ascribed to the increased thickness of c-NFs after hybrid formation and the electromagnetic wave absorption enhancement caused by the intrinsic characteristics of CMCs and the numerous intersections of tiny CNFs.

Near UV excited line and broad band photoluminescence of an anion-ordered oxyfluoride.

A near UV excitable phosphor Sr(2.85)Eu(0.1)Al(0.9)In(0.1)O(4-alpha)F(1-delta) was made by reducing as-made Sr(2.85)Eu(0.1)Al(0.9)In(0.1)O(4)F. This material reveals defect-induced broad-band photoluminescence emissions centered at 600 nm and a line emission at 619 nm due to the(5)D(0) --> (7)F(2) transition of the Eu activator (curve 1). Such combined line and broad-band emitters have the potential when combined with another broad-band emitting phosphor with emissions near 500 nm to create white light by converting near-UV light from a Ga(1-x)In(x)N light-emitting device.

Bi3+ and Eu3+ Activated Luminescent Behaviors in Non-Stoichiometric LaO0.65F1.7 Structure.

Optical materials composed of La1-p-qBipEuqO0.65F1.7 (p = 0.001-0.05, q = 0-0.1) were prepared via a solid-state reaction using La(Bi,Eu)2O3 and NH4F precursors at 1050 °C for two hours. X-ray diffraction patterns of the phosphors were obtained permitting the calculation of unit-cell parameters. The two La3+ cation sites were clearly distinguished by exploiting the photoluminescence excitation and emission spectra through Bi3+ and Eu3+ transitions in the non-stoichiometric host lattice. Energy transfer from Bi3+ to Eu3+ upon excitation with 286 nm radiation and its mechanism in the Bi3+- and Eu3+-doped host structures is discussed. The desired Commission Internationale de l'Eclairage values, including emissions in blue-green, white, and red wavelength regions, were obtained from the Bi3+- and Eu3+-doped LaO0.65F1.7 phosphors.

Enhancement of Electromagnetic Wave Shielding Effectiveness of Carbon Fibers via Chemical Composition Transformation Using H2 Plasma Treatment.

H2 plasma treatment was performed on carbon-based nonwoven fabrics (c-NFs) in a 900 W microwave plasma-enhanced chemical vapor deposition system at 750 °C and 40 Torr. Consequently, the electromagnetic wave shielding effectiveness (SE) of the c-NFs was significantly enhanced across the operating frequency range of 0.04 to 20.0 GHz. We compared the electromagnetic wave SE of the H2 plasma-treated c-NFs samples with that of native c-NFs samples coated with nano-sized Ag particles. Despite having a lower surface electrical conductivity, H2 plasma-treated c-NFs samples exhibited a considerably higher electromagnetic wave SE than the Ag-coated c-NFs samples, across the relatively high operating frequency range of 7.0 to 20.0 GHz. The carbon component of H2 plasma-treated c-NFs samples increased significantly compared with the oxygen component. The H2 plasma treatment transformed the alcohol-type (C-O-H) compounds formed by carbon-oxygen bonds on the surface of the native c-NFs samples into ether-type (C-O-C) compounds. On the basis of these results, we proposed a mechanism to explain the electromagnetic wave SE enhancement observed in H2 plasma-treated c-NFs.

EuKNaTaO5: crystal growth, structure and photoluminescence property.

The synthesis, structure determination, and intrinsic luminescent properties of a new tantalate, EuKNaTaO(5), are reported. Single crystals of the title compound were grown out of a reactive KOH/NaOH eutectic melt. Luminescence in many materials is activated by doping a rare earth cation into the solid matrix; we report undoped, all-rare earth EuKNaTaO(5), which exhibits bright orange room temperature photoluminescence.

Facile synthesis of sub-10 nm-sized bright red-emitting upconversion nanophosphors via tetrahedral YOF:Yb,Er seed-mediated growth.

Ultrasmall and uniform tetrahedral-shaped YOF:Yb,Er upconversion nanophosphors (UCNs) are synthesized and sub-10 nm YOF:Yb,Er/YOF core/shell UCNs are formed via YOF:Yb,Er seed-mediated synthesis. The ultrasmall YOF:Yb,Er/YOF core/shell UCNs realize intense red emission under near infrared light (λex = 980 nm).

Effects of the Carbon Fiber-Carbon Microcoil Hybrid Formation on the Effectiveness of Electromagnetic Wave Shielding on Carbon Fibers-Based Fabrics.

Carbon fiber-carbon microcoil (CF-CMC) hybrids were formed on carbon fiber (CF)-based fabric. The morphologies of CF-based fabrics and CF-CMC hybridized fabrics were investigated. The electrical conductivities of the CF-CMC hybridized fabrics were examined and compared with those of native CF-based fabrics. Furthermore, the electromagnetic wave shielding effectiveness (SE) of the CF-CMC hybridized fabrics was investigated across operating frequencies in the 8.0⁻12.0 GHz range, and the results were compared with those for native CF-based fabrics. For the CF-based nonwoven fabrics, the SE values were improved by the CF-CMC hybridization reaction, although the electrical conductivities of the nonwoven fabric were reduced by the CF-CMC hybrid formation. For the CF-based woven fabrics, the SE values were improved by more than twofold throughout the entire range of frequencies, owing to the CF-CMC hybrid formation. This dramatic improvement was partly ascribed to the enhanced electrical conductivity, particularly in the transverse direction to the individual CFs. Owing to the increased thickness of the woven or nonwoven fabrics after the CF-CMC hybrid formation and the intrinsic characteristics of CMCs, the absorption mechanism for the SE was determined for the main factor that contributed to the improvement of the SE values.

Synthesis and structure of the bilayer hydrate Na0.3NiO2.1.3D2O.

The metal oxide bilayer deuterate (hydrate) Na(0.3)NiO2.1.3D2O (Na(0.3)NiO2.1.3H2O) were prepared from NaxNiO2 by extracting Na+ cations and simultaneously intercalating fully and nondeuterated water. High-resolution neutron powder diffraction, thermogravimetric analysis, and inductively coupled plasma atomic emission spectroscopy were used to show that a Na(0.3)(D2O)(1.3) network separates layers of edge-sharing NiO6 octahedra.