2.1μm Emission Spectral Properties of Tm and Ho Doped Transparent YAG Ceramic

Highly transparent Tm:Ho:YAG transparent ceramics were prepared using advanced ceramic technology and their spectroscopic properties were studied for infrared laser applications. Following the Judd-Ofelt procedure several spectroscopic properties such as the radiative transition probability (Arad), radiative decay time (τrad) and fluorescence branching ratio (β) are quantitatively obtained from the absorption spectrum. The absorption and emission cross sections corresponding to the 5I7 → 5I8 transition of Ho3+ at 2.1 μm have been evaluated following Mc Cumber theory and found that the obtained emission spectrum very well correlates to the simulated emission spectral data. The optical gain spectrum spread from 1800 nm to 2150 nm with a spectral width of over 107 nm and maximum gain coefficient of 0.44 cm–1. Thus it is expected that the Tm3+:Ho3+:YAG ceramics would be an appropriate host material to achieve infrared laser applications at 2.1 μm

Synthesis and Upconversion Spectroscopy of Yb Er Doped M2O2S (M = La, Gd, Y) Phosphors

Yb and Er doped M2O2S (M = Y, Gd, La) phosphor was synthesized by solid state flux fusion method and their up conversion spectral properties were studied as a function different Yb concentrations. The solid state flux fusion results in well crystallized hexagonal shaped phosphor particles of average size 4–6 μm. Upconversion spectral studies shows that all the compositions are stronger in green emission with the green emission intensity 1.7 times than the red in composition Gd2O2S:Yb(8)Er(1), Y2O2S:Yb(9)Er(1), La2O2S:Yb(3)Er(7) (All mol%). The internal upconversion efficiency for the green emission bands was calculated to be 74, 62, 100% respectively in Gd2O2S:Yb(8)Er(1), Y2O2S:Yb(8)Er(1), La2O2S:Yb(8)Er(1). Mechanisms of up conversion by two photon and energy transfer processes are interpreted and explained. The x, y color coordinates are measured and the color tunability was analyzed as a function of the 980 nm excitation power. Results shows that all phosphor offers power dependent color tuning properties where the emission color can be tuned from 490 nm to 550 nm by simply changing the 980 nm excitation power from 10–50 mW

Exploring the optical properties of La 2 Hf 2 O 7 :Pr 3+ nanoparticles under UV and X-ray excitation for potential lighting and scintillating applications

New optical materials with efficient luminescence and scintillation properties have drawn a great deal of attention due to the demand for optoelectronic devices and medical theranostics. Their nanomaterials are expected to reduce the cost while incrementing the efficiency for potential lighting and scintillator applications. In this study, we have developed praseodymium-doped lanthanum hafnate (La2Hf2O7:Pr3+) pyrochlore nanoparticles (NPs) using a combined co-precipitation and relatively low-temperature molten salt synthesis procedure. XRD and Raman investigations confirmed ordered pyrochlore phase for the as-synthesized undoped and Pr3+-doped La2Hf2O7 NPs. The emission profile displayed the involvement of both the 3P0 and 1D2 states in the photoluminescence process, however, the intensity of the emission from the 1D2 states was found to be higher than that from the 3P0 states. This can have a huge implication on the design of novel red phosphors for possible application in solid-state lighting. As a function of the Pr3+ concentration, we found that the 0.1%Pr3+ doped La2Hf2O7 NPs possessed the strongest emission intensity with a quantum yield of 20.54 ± 0.1%. The concentration quenching, in this case, is mainly induced by the cross-relaxation process 3P0 + 3H4 → 1D2 + 3H6. Emission kinetics studies showed that the fast decaying species arise because of the Pr3+ ions occupying the Hf4+ sites, whereas the slow decaying species can be attributed to the Pr3+ ions occupying the La3+ sites in the pyrochlore structure of La2Hf2O7. X-ray excited luminescence (XEL) showed a strong red-light emission, which showed that the material is a promising scintillator for radiation detection. In addition, the photon counts were found to be much higher when the NPs are exposed to X-rays when compared to ultraviolet light. Altogether, these La2Hf2O7:Pr3+ NPs have great potential as a good down-conversion phosphor as well as scintillator material

Dataset for electronic and optical properties of Y2O2S and Er dopped Y2O2S calculated using density functional theory and simulated x-ray near edge spectra

The computational data presented in this paper refer to the research article “Optical properties and simulated x-ray near edge spectra for Y2O2S and Er doped Y2O2S”. We present the data used to calculate the structural, electronic, and optical properties of the Y2O2S and its Er+3 doped counterparts at various concentrations using density functional theory (DFT) and simulated X-ray near edge (XANES) spectra. We report electronic information from DFT and DFT+U generated from the Vienna Ab initio Simulation Package (VASP) using PAW pseudopotentials. We also report VASP calculated optical properties for the host Y2O2S using the independent particle approximation (IPA), the random phase approximation (RPA), the many-body GW0 approximation, and the Bethe-Salpeter equation (BSE) approximation, under the 10-atom unit cell. The IPA calculations are repeated using the 80-atom unit cell for both the host Y2O2S and the Y2O2S:Er+3 counterparts. The optical properties data include the frequency-dependent real and imaginary parts of the dielectric function, the absorption and extinction coefficients, the refractive index, and the reflectivity. FEFF10 XANES calculations are performed on the Y K-, L1-, L2-, and L3-edges, as well as on the Er M5-edge

Forcespinning: A new method for the mass production of Sn/C composite nanofiber anodes for lithium ion batteries

The development of nanostructured anode materials for rechargeable Lithium-ion Batteries has seen a growing interest. We herein report the use of a new scalable technique, Forcespinning (FS) to produce binder-free porous Sn/C composite nanofibers with different Sn particle size loading. The preparation process involves the FS of Sn/PAN precursor nanofibers and subsequently stabilizing in air at 280 °C followed by carbonization at 800 °C under an inert atmosphere. The Sn/C composite nanofibers are highly flexible and were directly used as binder-free anodes for lithium-ion batteries. The produced Sn/C composite nanofibers showed an improved discharge capacity of about 724 mA h g− 1 at a current density of 100 mA g− 1 for over 50 cycles compared to most nanofiber electrodes prepared by electrospinning and centrifugal spinning. The FS method clearly produces Sn/C nanofiber composite electrodes that have a high specific capacity and excellent cyclic performance, owing to the unique structure and properties of the nanofibers. The FS technology is thus a viable method for the large scale production of nano/micro fibers for battery electrodes, separators, and other applications. To the best of our knowledge, this is the first time to report results on the use of Forcespinning technology to produce composite nanofiber anodes for lithium-ion batteries

Structural evolution and magnetic properties of Gd2Hf2O7 nanocrystals: Computational and experimental investigations

Structural evolution in functional materials is a physicochemical phenomenon, which is important from a fundamental study point of view and for its applications in magnetism, catalysis, and nuclear waste immobilization. In this study, we used x-ray diffraction and Raman spectroscopy to examine the Gd2Hf2O7 (GHO) pyrochlore, and we showed that it underwent a thermally induced crystalline phase evolution. Superconducting quantum interference device measurements were carried out on both the weakly ordered pyrochlore and the fully ordered phases. These measurements suggest a weak magnetism for both pyrochlore phases. Spin density calculations showed that the Gd3+ ion has a major contribution to the fully ordered pyrochlore magnetic behavior and its cation antisite. The origin of the Gd magnetism is due to the concomitant shift of its spin-up 4f orbital states above the Fermi energy and its spin-down states below the Fermi energy. This picture is in contrast to the familiar Stoner model used in magnetism. The ordered pyrochlore GHO is antiferromagnetic, whereas its antisite is ferromagnetic. The localization of the Gd-4f orbitals is also indicative of weak magnetism. Chemical bonding was analyzed via overlap population calculations: These analyses indicate that Hf-Gd and Gd-O covalent interactions are destabilizing, and thus, the stabilities of these bonds are due to ionic interactions. Our combined experimental and computational analyses on the technologically important pyrochlore materials provide a basic understanding of their structure, bonding properties, and magnetic behaviors

Suppression of optical damage at 532 nm in Holmium doped congruent lithium niobate

Optical damage experiments were carried out in a series of Holmium doped congruent lithium niobate (Ho:cLN) crystals as a function of dopant concentration and laser intensity. The light induced beam distortion was recorded with a camera and a detector under the pseudo-Zscan configuration. At 532 nm, strong suppression of the optical damage was observed for the 0.94 mol. % doped crystal. Increased resistance to optical damage was also observed at 488 nm. The suppression of the optical damage is predominantly attributed to the reduction of the Nb antisites due to the holmium doping

Effect of Polymer Concentration, Rotational Speed, and Solvent Mixture on Fiber Formation Using Forcespinning

Polycaprolactone (PCL) fibers were produced using Forcespinning® (FS). The effects of PCL concentration, solvent mixture, and the spinneret rotational speed on fiber formation were evaluated. The concentration of the polymer in the solvents was a critical determinant of the solution viscosity. Lower PCL concentrations resulted in low solution viscosities with a correspondingly low fiber production rate with many beads. Bead-free fibers with high production rate and uniform fiber diameter distribution were obtained from the optimum PCL concentration (i.e., 12.5 wt%) with tetrahydrofuran (THF) as the solvent. The addition of N, N-dimethylformamide (DMF) to the THF solvent promoted the gradual formation of beads, split fibers, and generally affected the distribution of fiber diameters. The crystallinity of PCL fibers was also affected by the processing conditions, spinning speed, and solvent mixture

Effect of Polymer Concentration Rotational Speed and Solvent Mixture On Fiber Formation Using Forcespinning®

Polycaprolactone (PCL) fibers were produced using Forcespinning® (FS). The effects of PCL concentration, solvent mixture, and the spinneret rotational speed on fiber formation were evaluated. The concentration of the polymer in the solvents was a critical determinant of the solution viscosity. Lower PCL concentrations resulted in low solution viscosities with a correspondingly low fiber production rate with many beads. Bead-free fibers with high production rate and uniform fiber diameter distribution were obtained from the optimum PCL concentration (i.e., 12.5 wt%) with tetrahydrofuran (THF) as the solvent. The addition of N, N-dimethylformamide (DMF) to the THF solvent promoted the gradual formation of beads, split fibers, and generally affected the distribution of fiber diameters. The crystallinity of PCL fibers was also affected by the processing conditions, spinning speed, and solvent mixture

Pyrochlore Rare-Earth Hafnate RE2Hf2O7 (RE = La and Pr) Nanoparticles Stabilized by Molten-Salt Synthesis at Low Temperature

Complex oxides of the RE2Hf2O7 series are functional materials that exist in the fluorite or pyrochlore phase depending on synthesis method and calcination temperature. In this study, we investigate the process of synthesis, crystal structure stabilization, and phase transition in a series of RE hafnate compounds, synthesized by the coprecipitation process of a single-source complex hydroxide precursor followed with direct calcination or molten-salt synthesis (MSS) method. Phase pure RE2Hf2O7 (RE = Y, La, Pr, Gd, Er, and Lu) ultrafine nanostructured powders were obtained after calcinating the precursor in a molten salt at 650 °C for 6 h. Moreover, we demonstrate that the MSS method can successfully stabilize ideal pyrochlore structures for La2Hf2O7 and Pr2Hf2O7 in the nanodomain, which is not possible to achieve by direct calcination of the coprecipitated precursor at 650 °C. We propose mechanisms to elucidate the differences in these two synthesis methods and highlight the superiority of the MSS method for the production of RE hafnate nanoparticles