Lasing at 1065 nm in bulk Nd-doped telluride-tungstate glass

We have achieved, for the first time to our knowledge, lasing in a new type of telluride-tungstate glass host doped with neodymium: Nd³⁺:(0.8)TeO₂-(0.2)WO₃. Lasing was obtained at 1065 nm with two samples containing 0.5 mol% and 1.0 mol% Nd₂O₃. During gain-switched operation, slope efficiencies of 12% and 10% were obtained with the 0.5 mol% and 1.0 mol% doped samples, respectively, at a pulse repetition rate of 1 kHz. Judd-Ofelt analysis was further employed to determine the emission cross section σ_e at 1065 nm from the absorption spectra and lifetime data. The emission cross section from the Judd-Ofelt analysis came to 3.23 ± 0.09 × 10⁻²⁰ cm², in reasonable agreement with the value of 2.0 ± 0.13 × 10⁻²⁰ cm² obtained from the analysis of laser threshold data.     

Optical properties of and concentration quenching in Bi2O3-B2O3-Ga2O3 glasses

Er₂O₃-doped Bi₂O₃-B₂O₃-Ga₂O₃ glasses were prepared by the conventional melt-quenching method, and the Er³⁺:⁴I_13/2 → ⁴I_15/2 fluorescence properties are studied for different Er³⁺ concentrations. when the Er₂O₃ concentration increases from 0.03 to 3.0 mol%, the measured lifetime of Er³⁺:⁴I_13/2 level decrease from 2.24 to 0.9 m s, and from 0.25 to 0.20 m s for the Er³⁺:⁴I_11/2 level. The fast energy migration among Er³⁺ ions cause the reduction of lifetime of the ⁴I_13/2 level, whereas the change in the ⁴I_11/2 level is mainly due to a cooperative upconversion process (⁴I_11/2, ⁴I_11/2) → (⁴F_7/2, ⁴I_15/2). Based on the dipole-dipole interaction theory, the interaction parameter, C_Er,Er, for the migration rate of Er³⁺:⁴I_13/2 ↔ ⁴I_13/2 was calculated to be 32 × 10⁻⁴⁰ cm⁶ s⁻¹.     

Thermal diffusivity of rhodamine 6G incorporated in silver nanofluid measured using mode-matched thermal lens technique

Dual beam mode-matched thermal lens method has been employed to measure the heat diffusion in nanofluid of silver with various volumes of rhodamine 6G, both dispersed in water. The important observation is an indication of temperature dependent diffusivity and that the overall heat diffusion is slower in the chemically prepared Ag sol compared to that of water. The experimental results can be explained assuming that Brownian motion is the main mechanism of heat transfer under the present experimental conditions. Light induced aggregation of the nanoparticles can also result in an anomalous diffusion behavior.     

Sol-gel synthesis of erbium-doped yttrium silicate glass-ceramics

Yttrium silicate glasses and glass-ceramics were prepared by the sol-gel process. Yttrium nitrate was added to tetraethyl orthosilicate in amounts representing between 0.2 and 20 mol%, as well as amounts corresponding to the disilicate composition. Some samples were doped with erbium acetate. The solutions underwent gellation in 2-7 days and were dried for 2 weeks. Differential thermal analysis was used to design a multi-step heat treatment to 1000 °C to densify samples to transparent or translucent monoliths. Above 1000 °C, samples crystallized to yttrium disilicate and cristobalite. Phase separation before crystallization influenced the formation of the crystal phases.     

Synthesis of Y-junction carbon nanotubes within porous anodic aluminum oxide template

Y-junction carbon nanotubes with the average diameter about 200 nm were successfully synthesized within porous anodic aluminum oxide template, which was prepared by anodic anodizing aluminum sheet in 1.0 mol/l H₃PO₄ solution at a constant anodization voltage 90 V.     

Magnetic coupling in Co1−xPtx (x>0.5) nanowires electrodeposited on an AAO template

Thirty nanometer diameter Co-Pt nanowires of different composition were fabricated by electrodepositing the Co and Pt atoms to nanoporous anodized aluminium oxide (AAO) templates. The structure and magnetic properties are studied by transmission electron microscopy (TEM), induction-coupled plasma spectrometer (ICP), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). The as deposited nanowires with Pt content about 50 at.% present a single ferromagnetic phase of fcc CoPt. When the Pt content of the nanowires varies from about 55 to about 75 at.%, the nanowires include a soft phase of fcc CoPt₃ and a relatively hard phase of fcc CoPt and the two phases are separate as seen from the hysteresis loops. After annealing to 600 °C, the two phases coupled completely and the coupled phase has the same coercivity as the original hard one.     

Electrodeposition and magnetic properties of Ni nanowire arrays on anodic aluminum oxide/Ti/Si substrate

Ni nanowire arrays with different diameters have now been extended to directly fabricate in porous anodic alumina oxide (AAO) templates on Ti/Si substrate by direct current (DC) electrodeposition. An aluminum film is firstly sputter-deposited on a silicon substrate coated with a 300 nm Ti film. AAO/Ti/Si substrate is synthesized by a two-step electrochemical anodization of the aluminum film on the Ti/Si substrate and then used as template to grow Ni nanowire arrays with different diameters. The coercivity and the squareness in parallel direction of Ni nanowires with about 10 nm diameters are 664 Oe and 0.90, respectively. The Ni nanowire arrays fabricated on AAO/Ti/Si substrates should lead to practical applications in ultrahigh-density magnetic storage devices because of the excellent properties.     

Spectral hole burning and fluorescence in femtosecond laser induced Sm-doped glasses

The femtosecond laser was used to irradiate sol-gel derived Sm³⁺-doped Al₂O₃-SiO₂ glasses, in which the Sm³⁺ was reduced into Sm²⁺ ions. The fluorescence line narrowing was applied to investigate the coordination sphere of the Sm²⁺ ion. The spectral hole burning was performed on ⁷F₀→⁵D₀ transition of the Sm²⁺. The depth and width of the burnt holes were ∼27% and ∼4 cm⁻¹ FWHM at 7 K, respectively. Hole spectra were stable up to room temperature. The hole-burning efficiency was superior to that of Sm²⁺ in H₂ treated glasses and comparable to that in X-ray in terms of hole-burning dynamics.     

Structure and magnetic properties of CoxPb1−x nanowire arrays

Ordered Co_xPb_1−x nanowire arrays embedded in the porous anodic aluminum oxide (AAO) template have been fabricated by electrodeposition. XRD experiments prove that neither hexagonal-close-packed (hcp) nor face-centered-cubic (fcc) Co peaks are detected when the Co component (x) is below 0.91. The coercivity (H_c) and squareness (M_r/M_s) are found to increase with ferromagnetic Co component and the maximum value is at the position x=1 (pure Co nanowires). Annealing effects cause H_c and M_r/M_s increase, which surpasses the pure Co nanowires in the 0.2<x<0.6 at the annealing temperature of 700 °C. Microstructure change during annealing process is proposed to explain the magnetic properties change of samples.     

Photoluminescence characteristics from amorphous SiC thin films with various structures deposited at low temperature

Hydrogenated amorphous SiC thin films deposited at low substrate temperature (100 °C) show the different bonding configurations and microstructures which depend on the carbon concentrations in the films controlled by the gas ratio R of methane to silane during the deposition. Photoluminescence characteristics are investigated for these samples with different structures. A strong luminescence in red light region can be observed for samples deposited with low gas ratio R which is significantly reduced its intensity with increasing the carbon concentrations in the films. On the other hand, the luminescence bands located at blue-green light region are detected under UV light excitation for samples deposited with high gas ratio R, which can be associated with the existence of amorphous SiC clusters in the films.