Broad Absorption Bandwidth Research Articles

Optimizing the aqueous phase synthesis of CdTe quantum dots using mixed-ligands system and their applications for imaging of live cancer cells and tumors in vivo

Quantum dots (QDs) exhibit unique optical properties including size-tunable fluorescence, superior brightness, broad absorption and tiny emission bandwidth. These properties have made QDs promising candidates for bioimaging and biosensing applications. In this work, CdTe QDs were synthesized in aqueous phase using both mercaptopropionic acid (MPA) and Cysteine (Cys) as capping agents. Growth kinetics and optical properties of the resulted QDs were found to be dependent on both species and concentration of surfactant molecules. Considering the distinct nature and advantages of MPA and Cys, a mixed-ligands system was proposed as a potential approach to fabricate QDs with specific optical property and functions for in vitro and in vivo bioimaging applications.

Electromagnetic wave absorption properties of multi-walled carbon nanotubes decorated with La-doped BaTiO 3 nanocrystals synthesized by a solvothermal method

Ba 1− x La x TiO 3/multi-walled carbon nanotube (MWCNT) nanocomposites with different concentrations of La 3+ doping, were synthesized by a solvothermal process. The prepared nanocomposites had a hybrid microstructure in which Ba 1− x La x TiO 3 nanocrystals with diameter of 10–30 nm were firmly immobilized on the MWCNTs sidewalls. Electromagnetic (EM) wave absorption properties of La-doped BaTiO 3/MWCNT nanocomposites were investigated in the 7.5–18 GHz frequency range for an absorber thickness of 1 mm. The reflection loss (RL) calculated from the EM parameters of the samples, moved to low frequencies with increasing La 3+ doping. The widest absorption bandwidth, with the lowest frequency range, was observed in a nanocomposite doped with 1.5 at% La 3+. An RL exceeding −5 dB for this sample was obtained in the frequencies ranging from 9.6 to 16.3 GHz, with the optimal RL of −17.4 dB at 10.9 GHz, due to enhanced interfacial polarization resulting in developed ε ″ r . In addition, the RL for the sample shifted to the low frequency region and the peaks became sharper in the 2–18 GHz frequency range with increasing absorber thickness. For BaTiO 3/MWCNT nanocomposites, La 3+ doping can greatly improve the EM wave absorbing ability in a thin absorber thickness and the donor-doped nanocomposites show promise for application in EM wave shielding materials with broad absorption bandwidths.

Skin collagen fiber-based radar absorbing materials

By using skin collagen fiber (CF) as raw material, Schiff base structure containing CF (Sa-CF) was synthesized through CF-salicylaldehyde reaction. Then a novel radar absorbing material (Fe-Sa-CF) was prepared by chelating reaction between Sa-CF and Fe3+. The coaxial transmission and reflection method was used to analyze the complex permittivity and complex magnetic permeability of these CF-based materials, and the radar cross section (RCS) method was used to investigate their radar absorbing properties in the frequency range of 1.0–18.0 GHz. Experimental results indicated that the conductivity of CF increased from initial 1.08×10−11 to 2.86×10−6 S/cm after being transferred into Fe-Sa-CF, and its dielectric loss tangent (tanδ) in the frequency range of 1.0–17.0 GHz also increased. These facts suggest that the Fe-Sa-CF is electric-loss type radar absorbing material. In the frequency range of 3.0–18.0 GHz, Sa-CF (1.0 mm in thickness) exhibited somewhat radar absorbing property with maximum radar reflection loss (RL) of −4.73 dB. As for Fe-Sa-CF, the absorbing bandwidth was broadened, and the absorbing intensity significantly increased in the frequency range of 1.0–18.0 GHz where a maximum radar RL of −9.23 dB was observed. In addition, the radar absorbing intensity of Fe-Sa-CF can be further improved by increasing membrane thickness. When the thickness reached to 2.0 mm, the RL values of Fe-Sa-CF were −15.0–−18.0 dB in the frequency range of 7.0–18.0 GHz. Consequently, a kind of novel radar absorbing material can be prepared by chemical modification of collagen fiber, which is characterized by thin thickness, low density, broad absorption bandwidth and high absorption intensity.

Synthesis of La 3+ and Nd 3+ co-doped yttria nanopowder for transparent ceramics by oxalate precipitation method

Polycrystalline Nd 3+ and La 3+ co-doped yttria nanopowder Nd 3+:Y 1.90La 0.10O 3 for transparent ceramics was synthesized by co- precipitation method using oxalate acid as the precipitant and (NH 4) 2SO 4 as the electrical stabilizer under ultrasonic radiation. Nanopowders calcined at different temperatures were characterized with thermal gravimetric-differential thermal analysis (TG/DTA), X-ray diffraction (XRD), transmitting electron microscopy (TEM), energy dispersive spectrometry (EDS) and spectral analysis techniques. The results indicated that nanopowders calcined at 1100 °C for 4 h were 40–70 nm in size with spherical morphology, the powder had the strongest emission peak centered at 1078 nm, corresponding to the transition of 4F 3/2→ 4I 11/2 of Nd 3+ ion. The highest optical transmittance of the ceramics sintered at 1500 °C for 13 h was about 48% in near IR waveband, and the sintered ceramics had a broad absorption bandwidth of about 12.6 nm at the laser diode (LD) pump wavelength of 808 nm.

Surface-modified micrometre nickel hollow spheres and their microwave characteristics

To improve the magnetic properties, nickel hollow spheres (NHSs) were surface-modified with a cellular Co structure by a facile electroless cobalt plating route. The microstructures and properties of the modified NHSs were characterized by field emission scanning electron microscopy, x-ray diffraction, Brunauer–Emmett–Teller specific surface area and a vibrating sample magnetometer. Microwave properties were evaluated by mixing NHSs with polyvinyl butyral as coaxial samples. The SEM images showed that the NHSs were coated by the Co cellular films, which not only increased the specific surface area but also enhanced the coercivity and magnetization. Also, the modified NHSs composites presented low RL min values below −30 dB at thicknesses between 1.0 and 2.0 mm, and exhibited a broad absorption bandwidth ΔW at ‘thin’ thickness.

Microwave Permittivity, Permeability, and Absorption of Ni Nanoplatelet Composites

The Ni nanoplatelets with an average diameter of 75 nm and an average thickness of 10 nm are coated with MnO2 by a simple solution phase chemical method. The MnO2-coated Ni nanoplatelets are dispersed in paraffin wax to form the composite samples of the magnetic filler dispersed in the nonmagnetic insulating matrix. The effect of the Ni nanoplatelet volume fraction on the complex permittivity, complex permeability, and microwave absorption of the composites has been studied in the frequency range of 0.1-10 GHz. The complex permittivity of the composites with different volume fractions of the Ni nanoplatelets is almost constant in the 0.1-10 GHz frequency range. The complex permeability of the composites shows several resonance peaks. Besides the natural resonance peak, the exchange resonance peaks are observed. The composite with 17% volume fraction of Ni nanoplatelets has excellent microwave absorption properties of a minimum reflection loss value -31 dB at 9.1 GHz for a thickness of 2 mm and a broad absorption bandwidth of 2.3-10 GHz (R < -10 dB). The Ni nanoplatelets are a possible candidate as high performance microwave absorption filler. For the Ni nanoplatelet composites, the magnetic loss is the dominant term for microwave absorption.

Fabrication and spectral properties of Nd3+-doped yttrium lanthanum oxide transparent ceramics

Transparent 1at% Nd3+:Y1.9La0.1O3 ceramics were fabricated with nanopowders prepared by carbonate coprecipitation method. The powder compacts were sintered in H2 atmosphere at 1550°C for 30h. The Nd3+:Y1.9La0.1O3 ceramics display uniform grains of about 50μm and high transparency. The highest transmittance of the ceramics reaches 67%. The strongest absorption peak is in the wavelength of 820nm with absorption cross section of 2.48×10−20cm2. The absorption is still high at LD wavelength 806nm with absorption cross section of 1.78×10−20cm2 and broad full width at half maximum (FWHM) of about 6.3nm. The strongest emission peak was centered at 1078nm with large stimulated emission cross section of 9.63×10−20cm2 and broad FWHM of about 7.8nm. The broad absorption and emission bandwidth of Nd3+:Y1.9La0.1O3 transparent ceramics are favorable to achieve the miniaturized LD pumping apparatus and ultrashort modelocked pulse laser output, respectively.

Spectral investigation of Yb-doped calcium pyroniobate crystal

Ytterbium-doped calcium pyroniobate single crystal has been grown for the first time. Spectral properties of Yb: Ca 2Nb 2O 7 were investigated by emission and absorption spectra. Its cooperative luminescence and fluorescence lifetime were also studied. Yb ions in Ca 2Nb 2O 7 showed very broad absorption and emission bandwidth and relatively large absorption and emission cross-sections. Along with other optical properties, this Yb-doped crystal would be a potential self-frequency doubling femtosecond laser gain material.

Spectroscopy and efficient laser action from diode pumping of a new broadly tunable crystal: Yb^3+:Sr_3 Y(BO_3)_3

The first demonstration of laser action in a Yb3+:Sr3Y(BO3)3 crystal is reported. This new material exhibits particularly broad absorption and emission bandwidths (6 and 60 nm, respectively) and hence is of particular interest for diode-pumped femtosecond and tunable laser sources. Efficient operation from diode pumping (1.4 W of cw laser power obtained with 3.6 W of diode pump power and as much as 3.4 W of peak power from high-power quasi-cw pumping) together with smooth tunability (over 50 nm FWHM) is reported. For the comparison, efficiency and thermal limitations of Yb:glass and Yb:Ca4GdO(BO3)3 have been investigated under the same conditions.

Optical spectroscopy and diode-pumped laser performance of Nd/sup 3+/ in the CNGG crystal

We have exploited the broad absorption and emission bandwidth of the laser crystal Ca/sub 3/(NbGa)/sub 2-x/Ga/sub 3/O/sub 12/ doped with Nd/sup 3+/ to develop a tunable and mode locked diode-pumped 1.06 /spl mu/m laser. We also present the fluorescence and excitation spectra at different crystal temperatures from 10 to 298 K. The spontaneous transition probabilities, the branching ratios, and the radiative lifetime are calculated by means of the Judd-Ofelt theory and compared with the experimental results. The stimulated emission cross-sections of the most important transitions have been calculated and compared with laser results. Employing a 2-W laser diode as a continuous-wave pump source, we have been able to tune the emission wavelength in the range 1053-1074 nm. Active mode-locking yielding pulses of 9.6, 18, and 19.7 ps at the three main emission peaks of 1058.6, 1061.2, and 1065.3 nm, respectively. was also demonstrated.

Efficient laser-diode-pumped neodymium-doped calcium–niobium–gallium–garnet laser

Efficient lasing of Nd:Ca (Nb, Ga)(2-x) Ga(3)-garnet (CNGG) disordered crystal pumped by a laser diode was demonstrated. In the end-pumped cw lasing experiment with a single-stripe diode, a slope efficiency of 24.2% and a maximum optical conversion efficiency of 19.3% were obtained. It was shown that the dependence of cw output power on the pump wavelength is insensitive compared with Nd:YAG because of the broad pump absorption bandwidth of Nd:CNGG. From the diode-bar-pumped experiment, it was confirmed that Nd:CNGG is a promising material for diode-bar pumping to obtain high average power with good beam quality, because of its advantages of a broader pump absorption band compared with that of Nd:YAG and the higher thermal conductivity compared with Nd-doped glasses.

Infrared Spectrum of Solid Carbon Monoxide

The infrared spectrum of solid carbon monoxide at 20°K has been examined in the fundamental and overtone regions. Sharp features (bandwidths about one cm−1) are assigned to vibrational modes of the various isotopic species: C12O16, 2138.1 cm−1; C12O17, 2112.3 cm−1; C13O16, 2092.2 cm−1; and C12O18, 2088.4 cm−1. These frequencies are examined with the aid of existing theories of frequency shifts in condensed phases. A broad absorption (bandwidth about 40 cm−1) centered at 2208 cm−1 is assigned to combinations of the fundamental mode with lattice modes. Calculations suggest that the lattice modes involved probably include translations as well as librations.