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We report the high-performance continuous-wave (CW) operation of 10-μm-wide quantum-cascade lasers (QCLs) emitting at π ∼ 4.6 μm, based on the GaInAs-AlInAs material without regrowth, in epilayer-up and -down bonding configurations. The operational characteristics of QCLs such as the maximum average power, peak output power, CW output power, and maximum CW operating temperature are investigated, depending on cavity length. Also, important device parameters, i.e., the waveguide loss, the transparency current density, the modal gain, and the internal quantum efficiency, are calculated from length-dependent results. For a high-reflectivity (HR) coated 4-mm-long cavity with epilayer-up bonding, the highest maximum average output power of 633 mW is measured at 65% duty cycle, with 469 mW still observed at 100%. The laser exhibits the maximum wall-plug efficiencies of 8.6% and 3.1% at 298 K, in pulsed and CW operatons, respectively. From 298 to 393 K, the temperature dependent threshold current density in pulsed operation shows a high characteristic temperature of 200 K. The use of an epilayer-down bonding further improves the device performance. A CW output power of 685 mW at 288 K is achieved for the 4-mm-long cavity. At 298 K, the output power of 590 mW, threshold current density of 1.52 kA/cm², and maximum wall-plug efficiency of 3.73% are obtained under CW mode, operating up to 363 K (90 °C). For HR coated 3-mm-long cavities, laser characteristics across the same processed wafer show a good uniformity across the area of 2 × 1 cm², giving similar output powers, threshold current densities, and emission wavelengths. The CW beam full-width at half-maximum of far-field patterns are 25° and 46° for the parallel and the perpendicular directions, respectively. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) hierarchical cabbage-like β-cobalt hydroxide (β-Co(OH)2) nanostructures were fabricated onto conducive textiles composed of copper-coated polyethylene terephthalate fibers by a simple one-step electrochemical deposition (ED) method. Under an external applied voltage of -0.75 V for 4 h, the hierarchical cabbage-like β-Co(OH)2 nanostructures were well decorated on the conductive textiles. During the ED process, they were self-assembled by the tangled layers of nanoplate (thickness of ~45-55 nm) building blocks and exhibited a cabbage-shaped architecture. The structure and morphology of the as-prepared hierarchical cabbage-like β-Co(OH)2 nanostructures were characterized. The growth mechanism of cabbage like β-Co(OH)2 nanostructures was also investigated by varying the growth time. Moreover, the feasibility test for supercapacitors by measuring the electrochemical properties of the as-prepared nanostructures was performed by cyclic voltammetry and galvanic charge-discharge measurements. The obtained results show that the cabbage-like β-Co(OH)2 nanostructures on the conductive textile substrate exhibited superior energy storage performance compared to the nanoplate morphology. [ABSTRACT FROM AUTHOR]

The AgLa(PO3)4 phosphors activated with trivalent rare-earth (Eu3+, Tb3+) ions were prepared by a sol-gel synthesis method. The crystal structure of the compound was studied by X-ray diffraction patterns and found to be crystallized in the monoclinic system with a space group P21/c, indicating the calculated lattice parameters of a = 10.08 Å, b = 13.12 Å, and c = 7.314 Å. The Fourier-transform infrared spectrum, photoluminescence excitation/emission spectra, and decay curves were examined to study the optical properties. The analysis of the Eu3+ ions related emission spectrum revealed the presence of highly symmetric sites for the activator ions. The Tb3+ ions related emission spectrum exhibited a 5D3 emission due to the prolonged calcination at high temperatures, which reduces the residual hydroxyl ions. The optical properties show that this host material is suitable for phosphor materials and laser crystals. [ABSTRACT FROM AUTHOR]

Spindle shaped tetragonal La2(MoO4)3: Eu3+ phosphors were synthesized by a polyol mediated solvothermal synthesis method. Growth mechanism for the formation of spindles was explained by increasing the reaction temperature. Similarly, the effect of EDTA concentration and calcination temperature on the morphology of particles was studied. Structural properties of the samples were analyzed by X-ray diffraction patterns and Fourier transform infrared spectra. The emission richness in the red region was investigated by measuring both photoluminescence (PL) and cathadoluminescence (CL) emission spectra. The excitation spectra of the samples at different calcination temperatures exhibited intense excitation bands at different wavelengths in the ultraviolet (UV)-A, UV-B, UV-C and visible regions. This property makes the sample to be a promising red region component in UV or visible excitation based white light-emitting diodes. The lifetime variation as a function of calcination temperature was observed. The CL spectra exhibited similar behaviors as the PL spectra except the considerable emission intensities in lower wavelength region. The CIE coordinates obtained from the PL and CL spectra provided a good chromaticity in the red region. [ABSTRACT FROM AUTHOR]

Tm3+/Er3+/Eu3+/Er3+, Tm3+/Er3+/Eu3+ single, double and triple activator ion/ions doped nanocrystalline BaGd2O4 (BG) phosphors were prepared by a Pechini type sol-gel process. After annealing at 1300 °C, X-ray diffraction patterns confirmed their orthorhombic structure. Field-emission transmission electron microscope images of the BG sample indicated a nanoneedle-type morphology. Photoluminescence (PL) and cathodoluminescence (CL) measurements were utilized to establish the emission properties of rare-earth ions doped nanocrystalline BG host lattice. Under near-ultraviolet (NUV) excitations, BG:Tm3+ and BG:Er3+ exhibited their characteristic emissions in the blue and green regions, respectively, while BG:Tm3+/Er3+ and BG:Tm3+/Er3+/Eu3+ showed cyan and white light emissions, respectively, when doped with appropriate amounts of activator ions. In the PL, the cross-relaxation process is dominant rather than the energy transfer process. Due to the different mechanism from PL, the CL spectra showed different emission features of BG: Tm3+/Er3+/Eu3+ phosphor. The CL spectra of BG:Tm3+ and BG:Er3+ established the high purity blue and green emissions, respectively. From the PL and CL investigations, the white-light emission was realized from the single-phase BG:Tm3+/Er3+/Eu3+ phosphor under NUV and low voltage electron beam excitations. [ABSTRACT FROM AUTHOR]

Color-tunable CaWO4:xDy3+ phosphors were prepared via a simple conventional solid-state reaction and their luminescent properties were investigated as a function of Dy3+ ion concentration under 258 and 353 nm excitations. A gradual enhancement in the emission intensity was observed with the increment of Dy3+ ion concentration, reaching its maximum value when x=0.05. The main reason for the concentration quenching of Dy3+ emission in CaWO4 host lattice is due to the electric dipole-dipole interaction. The cathodoluminescence spectra, which were measured at different accelerating voltages and filament currents, were in consistent with the photoluminescence spectrum excited at 258 nm. Additionally, the emission color of CaWO4:xDy3+ phosphors can be suitably tuned from blue to green, and finally to yellow by the modulation of excitation wavelength and Dy3+ ion concentration. Ultimately, these color-tunable phosphors may have potential applications in the fields of miniature color displays. [ABSTRACT FROM AUTHOR]

A facile approach for shape-tunable synthesis of bismuth fluoride nanoparticles is reported. The approach is based on the homogeneous precipitation of precursor materials in mixed solvents (H2O and ethylene glycol) and only ethylene glycol. The influencing factors on the morphology of the particles, i.e., solvent ratio, F/Bi ratio, and ethylenediaminetetraacetic acid, are studied in detail, and are schematically illustrated. The morphology, crystallinity, structure, and optical properties of the prepared samples are characterized by using a field-emission scanning electron microscope, transmission electron microscope, X-ray diffractometer, Fourier transform infrared spectrometer, and spectrofluorometer, respectively. The hollow sphere-shaped nanoparticle doped with Eu3+ ions exhibit reddish orange emission under ultraviolet illumination due to the symmetric environment around the dopant ions. Subsequently, the effect of dopant concentration on the optical properties is also evaluated. The temperature-dependent photoluminescence emission spectra reveal good thermal stability. The obtained results provide an efficient strategy for synthesizing the shape-tunable nanoparticles with excellent optical properties. [ABSTRACT FROM AUTHOR]

We reported the titanium dioxide (TiO2) thin film-based metal-semiconductor-metal (MSM) ultraviolet (UV) photodetectors (PDs), fabricated by conventional photolithography and electron-beam evaporation processes, with additional annealing. The crystallinity and morphology of the thermally treated TiO2 layers were investigated. In order to optimize the performance of MSM UV PDs, the annealing temperature (Ta) and electrode spacing were adjusted. The qualified anatase TiO2 thin films without structural deformation were obtained at the Ta of 600 °C. At the bias of 5 V, the high on/off ratio of 6.0 × 105 was achieved from the device with the electrode spacing of 30 μm. By switching the light on/off, the device operation was also observed. The average rise and reset times were estimated to be 34.2 and 5.5 s, respectively. [ABSTRACT FROM AUTHOR]

Indirect band gap semiconductors are not efficient emitters of terahertz radiation. Here, we report strong emission of terahertz radiation from germanium wafers with nanostructured surfaces. The amplitude of THz radiation from an array of nano-bullets (nano-cones) is more than five (three) times larger than that from a bare-Ge wafer. The power of the terahertz radiation from a Ge wafer with an array of nano-bullets is comparable to that from n-GaAs wafers, which have been widely used as a terahertz source. We find that the THz radiation from Ge wafers with the nano-bullets is even more powerful than that from n-GaAs for frequencies below 0.6 THz. Our results suggest that introducing properly designed nanostructures on indirect band gap semiconductor wafers is a simple and cheap method to improve the terahertz emission efficiency of the wafers significantly. [ABSTRACT FROM AUTHOR]

Indirect band gap semiconductors are not efficient emitters of terahertz radiation. Here, we report strong emission of terahertz radiation from germanium wafers with nanostructured surfaces. The amplitude of THz radiation from an array of nano-bullets (nano-cones) is more than five (three) times larger than that from a bare-Ge wafer. The power of the terahertz radiation from a Ge wafer with an array of nano-bullets is comparable to that from n-GaAs wafers, which have been widely used as a terahertz source. We find that the THz radiation from Ge wafers with the nano-bullets is even more powerful than that from n-GaAs for frequencies below 0.6 THz. Our results suggest that introducing properly designed nanostructures on indirect band gap semiconductor wafers is a simple and cheap method to improve the terahertz emission efficiency of the wafers significantly. [ABSTRACT FROM AUTHOR]

Mesoporous particles are emerging as multifunctional biomaterials for imaging and drug delivery in several disease models, including cancer. We developed PEGylated α-Gd2(MoO4)3 marigold flower-like mesoporous particles for the purpose of drug delivery and, more specifically, evaluated their ability to deliver curcumin. The obtained mesoporous particles significantly conjugated the curcumin particles on their surfaces by inducing the formation of curcumin nanoparticles. In vitro studies of the PEGylated mesoporous particles filled with curcumin demonstrated that these particles could considerably facilitate the continuous and sustained release of curcumin into the cytoplasm and nucleus. As a result, the intracellular release of curcumin can inhibit proliferation in two human pancreatic cancer cell lines: MIA PaCa-2 and PANC-1. Additionally, the particles showed the increased inhibition of pIKKα, pIKKα/β and NF- κB-DNA binding activity as compared to pure curcumin. The curcumin conjugated mesoporous particles are concentrated in the cytoplasm and nucleus of the treated cancer cell lines. Consequently, these mesoporous particles are an effective method for drug delivery that can cross the biological barriers of the body targeting the cellular nucleoplasm. [ABSTRACT FROM AUTHOR]

Favorable temperature- and size-dependent device characteristics in mechanically flexible, thin (∼6.45 lm thick), microscale inorganic InGaN/GaN-based light-emitting diodes enable their use as highly efficient, robust devices that are capable of integration on diverse classes of unconventional substrates, including sheets of plastic. Finite element analysis and systematic studies of the operational properties establish important thermal, electrical, and optical considerations for this type of device. [ABSTRACT FROM AUTHOR]

We investigated the optoelectronic and thermal characteristics of InGaN/GaN monolithic light emitting diode (LED) arrays operating at l[?] 470 nm. The optical output power (Pout) and forward voltage (VF) were almost linearly increased with the number of LEDs for series arrays. In the case of parallel LED arrays, the maximum operating current was increased by increasing the number of devices, but the VF was kept almost constant. Around 235 mA, the maximum Pout of 55.6 mW was obtained for the 1 x 3 series LED array fabricated with a separation distance of 1000 um, while the Pout was 20.4 mW for the 1 x 3 parallel LED array. From the measured light-current-voltage data, the maximum internal temperature (Tmax), i.e. a maximum value of internal temperature rise within the devices under operation, was theoretically determined using a three-dimensional steady-state thermal heat dissipation model based on the finite element method. Also, the temperature profiles were obtained for various separation distances and array sizes. At injection current of 220 mA, the Tmax was theoretically calculated as 325.6 K and 306.6 K for 1 x 3 series and parallel LED arrays with a 1000 um separation distance, respectively. The Tmax was increased and decreased on decreasing the separation distance and substrate thickness, respectively, and its dependence on Tmax became more significant at higher injection current. [ABSTRACT FROM AUTHOR]

Rhenium disulfide (ReS2) is a transition metal dichalcogenide with a layer-independent direct bandgap. Notably, the weak interlayer coupling owing to its T-phase structure enables multi-layer ReS2 to behave similarly to decoupled monolayers. This inherent characteristic makes continuous multilayer ReS2 film a unique platform for large-area electronic applications. To date, the bulk of work on ReS2 has been conducted using mechanically exfoliated samples or small size flakes (<1 mm2) with no potential for large-scale electronics. A chemical vapor deposition (CVD) synthesis of a large area, continuous ReS2 film directly on a SiO2 substrate is also known to be more challenging compared with that of other 2D materials, such as MoS2 and WS2. This is partly due to its tendency to grow into discrete dendritic structures. In this study, a large-area (>1 cm2), continuous multilayer ReS2 film is directly synthesized on a SiO2 substrate without any transfer process. The polycrystalline ReS2 film synthesized by this method exhibits one of the fastest photoresponse speeds (0.03 s rise time and 0.025 s decay time) among the reported CVD films. The photoresponsivity Rλ was also the highest among large-area CVD films. The synthesis method for a continuous multilayer ReS2 film is amenable to large-scale integration and will pave the way for practical optoelectronic applications based on 2D layered materials. [ABSTRACT FROM AUTHOR]

Eu3+ ions activated Ca2La8(SiO4)6O2 (CLSO):Eu3+ nanophosphor samples were synthesized by a mixed solvothermal and hydrothermal method. The samples were carefully studied using various characterization techniques. The XRD patterns of CLSO:Eu3+ and CLSO confirmed that the samples were crystallized in hexagonal phase with a space group of P63/m (176). The morphology of the nanoparticles was studied by varying the reaction parameters such as growth, temperature and time. The photoluminescence (PL) excitation and PL emission spectra exhibited the typical Eu3+ bands in the wavelength range of 200–550 nm and 400–750 nm, respectively. The intensity of the electric dipole (ED) transition peak was strong in the PL emission spectrum which imparts the red color when observed under ultraviolet light. The ED transition peak intensity increased when the sample was calcined at an elevated temperature of 700 °C, indicating improved asymmetry ratio and good chromaticity coordinates. The electrical properties of the prepared materials were studied by spin-coating the powder dispersed solutions on the silica substrate. The output current values were also measured for the CLSO nanoparticles prepared under different growth conditions. These results showed the advantages of CLSO nanoparticles for their application in optics and feasibility in nanoelectronic and energy harvesting devices. [ABSTRACT FROM AUTHOR]

We fabricated various periodic nanostructures with a six-fold hexagonal symmetry on gallium arsenide (GaAs) substrates using simple process steps, together with a theoretical analysis of their antireflective properties. Elliptical photoresist (PR) nanopillars, which are inevitably generated by the asymmetric intensity distribution of the laser interference, were converted to rounded lens-like patterns by a thermal reflow process without any additional complex optic systems, thus leading to an exact six-fold hexagonal symmetry. Various shaped periodic nanostructures including nanorods, cones, truncated cones, and even parabolic patterns were obtained under different etching conditions using the rounded lens-like PR patterns formed by the reflow process. For the parabolic structure, the calculated lowest average reflectance of [?] 2.3% was obtained. To achieve better antireflection characteristics, an aluminum-doped zinc oxide (AZO) film was deposited on the GaAs parabolas, which forms an AZO/GaAs parabolic nanostructure. The structure exhibited a low average reflectance of [?] 1.2% over a wide wavelength region of 350-1800 nm and a hydrophobic surface with a water contact angle of thc [?] 115deg. The calculated reflectances were reasonably consistent with the measured results. [ABSTRACT FROM AUTHOR]