Fluorosilicate and fluorophosphate superfluorescent multicore optical fibers co-doped with Nd3+/Yb3+

In the paper spectroscopic properties of two fluorosilicate and fluorophosphate glass systems co-doped with Nd³⁺/Yb³⁺ ions are investigated. As a result of optical excitation at the wavelength of 808 nm strong and wide emission in the 1 μm region corresponding to the superposition of optical transitions ⁴F_3/2 → ⁴I_11/2 (Nd³⁺) and ²F_5/2 → ²F_7/2 (Yb³⁺) can be observed. The optimization of Nd³⁺ → Yb³⁺ energy transfer in both glasses allows to manufacture multicore optical fibers with narrowing and red-shifting of amplified spontaneous emission (ASE) at 1.1 μm.     

Improvement of 1.53 μm emission and energy transfer of Yb3+/Er3+ co-doped tellurite glass and fiber

To improve the 1.53 μm band emission of Er³⁺, the trivalent Yb³⁺ ions were introduced into the Er³⁺ single-doped tellurite glass with composition of TeO₂–ZnO–La₂O₃, a potential gain medium for Er³⁺-doped fiber amplifier (EDFA). The improved effects were investigated from the measured 1.53 μm band and visible band spontaneous emission spectra together with the calculated 1.53 μm band stimulated emission (signal gain) spectra under the excitation of 975 nm laser diode (LD). It was found that Yb³⁺/Er³⁺ co-doping scheme can remarkably improve the visible band up-conversion and the 1.53 μm band fluorescence emission intensity, and meanwhile improves the 1.53 μm band signal gain to some extent, which were attributed to the result of the effective energy transfer of Yb³⁺:²F_5/2 + Er³⁺:⁴I_15/2 → Yb³⁺:²F_7/2 + Er³⁺:⁴I_11/2. The quantitative study of energy transfer mechanism was performed and microscopic energy transfer parameters between the doped rare-earth ions were determined. In addition, the spectroscopic properties of Er³⁺ were also investigated from the measured absorption spectrum according to the Judd–Ofelt theory, and the structure behavior and thermal stability of the prepared tellurite glass were analyzed based on the X-ray diffraction (XRD) and differential scanning calorimeter (DSC) measurements, respectively.     

Photoluminescence properties of novel white phosphor of Dy3+-doped LaBSiO5 glass

A single-phased white emitting phosphor LaBSiO₅:Dy³⁺ was successfully synthesized via a solid state reaction. The X-ray diffraction results confirmed that the doped Dy³⁺ ions did not change the lattice structure. Several strong excitation peaks of LaBSiO₅:Dy³⁺ were found around 300–450 nm. Under excitation of 350 nm, the LaBSiO₅:Dy³⁺ exhibited white emission by combining the two emission peaks at 478 and 574 nm corresponding to the typical ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 transitions. The optimal substitution proportions of Dy³⁺ for La³⁺ was determined to be 1 mol% and the critical distance of Dy³⁺ was 25.9628 Å. Moreover, the CIE chromaticity coordinates of LaBSiO₅:Dy³⁺ phosphor was (0.3116, 0.3474) which is close to the ideal white light coordinates (0.333, 0.333), indicating that the phosphor has a potential application as a single component ultraviolet-convertible white light emitting phosphor.     

Effect of different ethanol/water solvent ratios on the morphology of SnO2 nanocrystals and their electrochemical properties

We report on the effect of different ethanol/water solvent ratios on the morphology of SnO₂ nanocrystals prepared by the conventional hydrothermal method and their electrochemical properties. The nanocrystals were structurally and morphologically characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), surface area measurements, and transmission electron microscopy. The XRD patterns indicate that the sphere-like SnO₂ microcrystals have a rutile-type tetragonal structure and FESEM images show that the microspheres have a diameter of 2–5 μm. We found that the ethanol/water volume ratio plays an important role in formation of the final product. Electrochemical tests revealed that the SnO₂ microspheres had a high initial capacity of 1546 mAh g^?1 at a current density of 100 mA g^?1 and retained a reversible capacity of 439 mAh g^?1 after 30 discharge cycles.     

Ultra-low-energy ion-beam-synthesis of Ge nanocrystals in thin ALD Al2O3 layers for memory applications

Structural and electrical properties of ALD-grown 5 and 7 nm-thick Al₂O₃ layers before and after implantation of Ge ions (1 keV, 0.5–1 × 10¹⁶ cm^?2) and thermal annealing at temperatures in the 700–1050 °C range are reported. Transmission Electron Microscopy reveals the development of a 1 nm-thick SiO₂-rich layer at the Al₂O₃/Si substrate interface as well as the formation of Ge nanocrystals with a mean diameter of ～5 nm inside the implanted Al₂O₃ layers after annealing at 800 °C for 20 min. Electrical measurements performed on metal–insulator–semiconductor capacitors using Ge-implanted and annealed Al₂O₃ layers reveal charge storage at low-electric fields mainly due to location of the Ge nanocrystals at a tunnelling distance from the substrate and their spatial dispersion inside the Al₂O₃ layers.     

Fabrication and study of properties of the PLA/Sr2MgSi2O7:Eu2+, Dy3+ long-persistent luminescence composite thin films

In this paper, Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ (SMS) particles were first synthesized by sol–gel method and then modified with 3-aminopropyltriethoxysilane (APS) to improve their dispersibility and compatibility in the polylactic acid (PLA) matrix. The structure of pure SMS particles was analyzed by XRD and XPS. The properties of SMS particles before and after modification were characterized by FT-IR and SEM. PLA/SMS composite films containing 15 wt% of SMS particles were prepared by spin coating on silicon wafer. Their morphology and luminescence properties were examined. It was found that the composite films can be excited by a broad band from 330 nm to 425 nm with the highest excitation intensity at 360 nm. The fluorescent and phosphorescent emission bands of the composite films and SMS particles all have a major emission peak at 468 nm. Decay curves of the composite films have a similar tendency with that of the pure SMS particles, except for the lower intensity.     

Preparation and luminescence of europium-doped lanthanum fluoride–benzoic acid hybrid nanostructures

Europium-doped lanthanum fluoride (LaF₃:Eu³⁺) nanoparticles were synthesized using a solvothermal method, and they were then capped with benzoic acid (BA) ligands to form LaF₃:Eu³⁺–BA hybrid nanostructures. The LaF₃:Eu³⁺–BA hybrid nanostructures showed strong luminescence as a result of energy transfer from BA to the Eu³⁺ ions of the LaF₃:Eu³⁺ nanoparticles. The dominant excitation band for the LaF₃:Eu³⁺–BA hybrid nanostructures ranged from 200 nm to 300 nm. It has been shown that the luminescence of LaF₃:Eu³⁺–BA hybrid nanostructures strongly depends on the pH value and content of benzoic acid used in the preparation of the hybrid nanostructures. An X-ray diffraction technique, transmission electron microscopy, luminescence spectroscopy, Fourier transform infrared spectroscopy and a UV–vis spectrophotometer were used to characterize the products.     

Preparation and luminescent properties of novel red phosphors for white-light emitting diodes (W-LEDs) application

A series of Eu³⁺–Gd³⁺ co-doped solid solution of Ca_0.54Sr_{0.46–1.5x–1.5z}Eu_zGd_x (MoO₄)_y (WO₄)_1−y (x=0.01–0.20, y=0–1.0, z=0.01–0.30) have been prepared by solid-state reactions. It is found that appropriate amount of Mo⁶⁺ or W⁶⁺, Eu³⁺ and Gd³⁺concentrations can enhance the luminescent intensity and improve crystal structure. These phosphors can be effectively excited by ultraviolet light at 394 nm and blue light at 465 nm (f–f transition) and emits red light (616 nm) with line spectrum. The wavelengths at 394 and 465 nm are nicely fitted in with the widely applied output wavelengths of ultraviolet or blue LED chips.     

Antimony sulfide (Sb2S3) thin films by pulse electrodeposition: Effect of thermal treatment on structural,optical and electrical properties

Antimony sulfide films have been deposited by pulse electrodeposition on Fluorine doped SnO₂ coated glass substrates from aqueous solutions containing SbCl₃ and Na₂S₂O₃. The crystalline structure of the films was characterized by X-ray diffraction, Raman spectroscopy and TEM analysis. The deposited films were amorphous and upon annealing in nitrogen/sulfur atmosphere at 250 °C for 30 min, the films started to become crystalline with X-ray diffraction pattern matching that of stibnite, Sb₂S₃, (JCPDS 6-0474). AFM images revealed that Sb₂S₃ films have uniformly distributed grains on the surface and the grain agglomeration occurs with annealing. The optical band gap calculated from the transmittance and the reflectance studies were 2.2 and 1.65 eV for as deposited and 300 °C annealed films, respectively. The annealed films were photosensitive and exhibited photo-to-dark current ratio of two orders of magnitude at 1 kW/m² tungsten halogen radiation.     

Enhanced luminescence of CaSb2O6:Bi3+ blue phosphors by efficient charge compensation

This paper reported an enhanced photoluminescence of CaSb₂O₆:Bi³⁺ by efficient charge compensation. Charge compensated CaSb₂O₆:Bi³⁺,M⁺ (M=Li, Na and K) phosphors were prepared using a co-precipitation technique followed by heat-treatment. The structure and morphology of the as-prepared CaSb₂O₆:Bi³⁺,M⁺ samples were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The results revealed that the obtained CaSb₂O₆:Bi³⁺,M⁺ samples are hexagonal crystal structure and this structure was retained regardless of co-doping by Li⁺, Na⁺ or K⁺. All samples showed sphere-like shape with particle size of 40–80 nm. The optical properties of products were studied by UV–vis diffuse reflectivity, photoluminescence spectra and luminescence decay measurements. Under the excitation of 336 nm light, all of the samples exhibited a strong blue emission peaking around 437 nm, which is attributed to the ³P₁–¹S₀ transition of the Bi³⁺ ion. It was found that the charge compensation has significant effect on the photoluminescence properties of CaSb₂O₆:Bi³⁺ and the best luminescence properties have been achieved for CaSb₂O₆:0.75Bi³⁺,0.75 Na⁺. The mechanism for the enhancement of the blue emission has also been studied in detail. Our results suggested that the optical properties of oxide nanostructures can be tailored through co-doping with aliovalent ions and the favorable luminescence properties of CaSb₂O₆:Bi³⁺,Na⁺ make it potential for lighting and display applications.     

Enhanced efficiency of organic photovoltaic cells with Sr2SiO4:Eu2+ and SrGa2S4:Eu2+ phosphors

We report the effect of yellow Sr₂SiO₄:Eu²⁺ and green SrGa₂S₄:Eu²⁺ phosphors on the efficiency of organic photovoltaic (OPV) cells. Each phosphor was coated on the back side of indium tin oxide (ITO)/glass substrates by spin coating with poly(methyl methacrylate) (PMMA). The maximum absorption wavelength of the active layer in the OPV cells was ～512 nm. The emission peaks of Sr₂SiO₄:Eu²⁺ and SrGa₂S₄:Eu²⁺ were maximized at 552 nm and 534 nm, respectively. The short circuit current density (J_sc) and power conversion efficiency (PCE) of the OPV cells with Sr₂SiO₄:Eu²⁺ (8.55 mA/cm² and 3.25%) and with SrGa₂S₄:Eu²⁺ (9.29 mA/cm² and 3.3%) were higher than those of the control device without phosphor (7.605 mA/cm² and 3.04%). We concluded that phosphor tuned the wavelength of the incident light to the absorption wavelength of the active layer, thus increasing the J_sc and PCE of the OPV cells.     

Substrate temperature effect on structural,optical and electrical properties of vacuum evaporated SnO2 thin films

Tin oxide (SnO₂) thin films were deposited on glass substrates by thermal evaporation at different substrate temperatures. Increasing substrate temperature (T_s) from 250 to 450 °C reduced resistivity of SnO₂ thin films from 18×10⁻⁴ to 4×10⁻⁴▒ Ω ▒cm. Further increase of temperature up to 550 °C had no effect on the resistivity. For films prepared at 450 °C, high transparency (91.5%) over the visible wavelength region of spectrum was obtained. Refractive index and porosity of the layers were also calculated. A direct band gap at different substrate temperatures is in the range of 3.55−3.77 eV. X-ray diffraction (XRD) results suggested that all films were amorphous in structure at lower substrate temperatures, while crystalline SnO₂ films were obtained at higher temperatures. Scanning electron microscopy images showed that the grain size and crystallinity of films depend on the substrate temperature. SnO₂ films prepared at 550 °C have a very smooth surface with an RMS roughness of 0.38 nm.     

Exploration of electrochemical properties of zinc antimonate nanoparticles as supercapacitor electrode material

Synthesis and Electrochemical properties of zinc antimonate nanoparticles have been explored and the strategy was to engage zinc antimonate towards supercapacitors. Cyclic voltammetry measurements were done at different sweep rates and the inclusion of two heterovalent metal cations such as Zn²⁺ and Sb⁵⁺ in the nanostructure participates in the electrochemical phenomena thereby exhibiting pseudocapacitance behavior with a significant specific capacitance of 140.8 F/g at the sweep rate of 10 mV/s was achieved. Further, from galvanostatic charge-discharge measurements, it is apparent that the capacitor characteristics were found to be phenomenal in 1 M H₂SO₄ electrolyte with good electrochemical constancy over 500 cycles with an incredible capacity retention of 100% at a current density of 1 A/g respectively. The results suggest that the obtained zinc antimonate could be a promising, inexpensive and electrochemically active candidate in supercapacitor application.     

2-Mercaptobenzothiazolate complexes of rare earth metals and their electroluminescent properties

We have demonstrated the electroluminescent (EL) properties of 2-mercaptobenzothiazolate complexes of rare earth metals [Ln(mbt)₃, Ln = Y, Sm, Eu, Gd, Tb, Dy, Tm] using simple non-doped two-layer organic light emitting diode with the configuration of indium tin oxide/N,N′-bis(3-methylphenyl)-N,N′-diphenylbenzidine/Ln(mbt)₃/Yb. It was found that 2-mercaptobenzothiazolate complexes have highly efficient intra-energy transfer from the singlet to the triplet state of the ligand, and then to the excited state of the central lanthanide ions. Thus Y(mbt)₃ and Gd(mbt)₃ exhibit the broad ligand-centered emission with maximum near 600 nm and Dy(mbt)₃, Tb(mbt)₃ and Tm(mbt)₃ complexes exhibit pure sharp emission bands from the intra f–f transitions of lanthanide ions Tb³⁺: ⁵D₄ → ⁷F₆ (492 nm), ⁵D₄ → ⁷F₅ (547 nm), ⁵D₄ → ⁷F₄ (589 nm), ⁵D₄ → ⁷F₃ (624 nm); Dy³⁺: ⁴F_9/2 → ⁶H_13/2 (575 nm) and Tm³⁺: ³H₄–³H₆ (795 нм).     

High-performance pentacene field-effect transistors using Al2O3 gate dielectrics prepared by atomic layer deposition (ALD)

High-performance pentacene field-effect transistors have been fabricated using Al₂O₃ as a gate dielectric material grown by atomic layer deposition (ALD). Hole mobility values of 1.5 ± 0.2 cm²/V s and 0.9 ± 0.1 cm²/V s were obtained when using heavily n-doped silicon (n⁺-Si) and ITO-coated glass as gate electrodes, respectively. These transistors were operated in enhancement mode with a zero turn-on voltage and exhibited a low threshold voltage (< −10 V) as well as a low sub-threshold slope (<1 V/decade) and an on/off current ratio larger than 10⁶. Atomic force microscopy (AFM) images of pentacene films on Al₂O₃ treated with octadecyltrichlorosilane (OTS) revealed well-ordered island formation, and X-ray diffraction patterns showed characteristics of a “thin film” phase. Low surface trap density and high capacitance density of Al₂O₃ gate insulators also contributed to the high performance of pentacene field-effect transistors.     

Effect of europium doping levels on photoluminescence and thermoluminescence of strontium yttrium oxide phosphor

The present paper deals with the effect of europium (Eu³⁺) doping concentration (0.1–2.5 mol%) on photoluminescence (PL) and thermoluminescence (TL) of strontium yttrium oxide (SrY₂O₄) phosphor. The sample was prepared by the modified solid state reaction method, which is the most suitable method for large-scale production. The prepared phosphor sample was characterized by using X-ray Diffraction (XRD), field emission gun scanning electron microscopy, fourier transform infrared spectroscopy, high resolution transmission electron microscopy, photoluminescence, thermoluminescence and commission internationale de I׳Eclairage techniques. The PL emission was observed in the range of 410–630 nm for the SrY₂O₄ phosphor doped with Eu³⁺. Excitation spectrum was found at 254 and 325 nm, sharp peaks were found around 593, 615 and 625 nm with high intensity. From the XRD data, using Scherrer׳s formula, calculated average crystallite size of Eu³⁺ doped SrY₂O₄ phosphor is around 32 nm. Thermoluminescence study was carried out for the phosphor with UV and gamma irradiation. The TL response of SrY₂O₄:Eu³⁺ phosphor for two different radiations was compared and studied in detail. The present phosphor can act as a single host for white light emission in display devices. The detailed process and possible mechanisms for PL and TL are studied and discussed. For the variable concentration of Eu³⁺ on PL studies the PL intensity increases with increasing the concentration of dopant and the concentration quenching found after 2 mol% of Eu³⁺ the optimized concentration was 2 mol%, which is suitable for the display device application. In TL glow curve the optimized concentration was 1 mol% for the UV irradiated sample and 0.2 mol% of Eu³⁺ for the gamma irradiated sample and beta irradiated sample for 10 Gy dose. The kinetic parameters were calculated by the computerized glow curve deconvolution (CGCD) technique.     

Defect characterization of Tl4GaIn3Se2S6 layered single crystals by photoluminescence

Photoluminescence (PL) spectra of Tl₄GaIn₃Se₂S₆ layered crystals grown by the Bridgman method have been studied in the energy region of 2.02–2.35 eV and in the temperature range of 16–45 K. A broad PL band centered at 2.20 eV was observed at T=16 K. Variations of emission band has been studied as a function of excitation laser intensity in the 0.1 to 149.9 mW cm⁻² range. Radiative transitions from shallow donor level located at 10 meV below the bottom of conduction band to moderately deep acceptor level located at 180 meV above the top of the valence band were suggested to be responsible for the observed PL band. An energy level diagram showing transitions in the band gap of the crystal was plotted taking into account the results of present work and previously reported paper on thermally stimulated current measurements carried out below room temperature. Analysis of the transmission and reflection measurements performed in the wavelength range of 400–1030 nm at room temperature revealed the presence of indirect transitions with 2.22 eV band gap energy.     

Synthesis and luminescent properties of ternary complexes EuXLa1−X(TTA)3Dipy

Rare-earth ternary complexes Eu_XLa_1?X(TTA)₃Dipy (X = 0, 0.1, 0.25, 0.5, 0.75, 0.9, 1.0) were synthesized. Characterization with DTA-TG, IR, elemental analysis and fluorescent spectra had also been carried out. It is found that the enhanced luminescence of Eu³⁺ ions by La³⁺ ions occurs in ternary complexes, and when X = 0.25, Eu_0.25La_0.75(TTA)₃Dipy has the highest luminescence efficiency and lifetime. It is proved by TG curve that the complexes are stable, and we monitored the spectra of Eu_XLa_1?X(TTA)₃Dipy[PVK:Eu_XLa_1?X(TTA)₃Dipy/BCP/AlQ/Al] at the different rate r min^?1. The results showed that the La³⁺ ion acts as an energy transfer bridge that helps energy transfer from PVK to Eu³⁺.     

Novel GaAs enhancement-mode/depletion-mode pHEMTs technology using high-k praseodymium oxide interlayer

In this study, a novel metal–semiconductor gate enhancement-mode (E-mode) and a metal–insulator-metal–semiconductor (MIMS) gate depletion-mode (D-mode) AlGaAs/InGaAs pseudomorphic high electron mobility transistor (pHEMT) on a single GaAs substrate have been developed by using high dielectric constant praseodymium insulator layer. The epitaxial layers were design for an enhancement-mode pHEMT after gate recess process. To achieve E/D-mode pHEMTs on single GaAs wafer, traditional Pt/Ti/Au metals were deposited as Schottky contact for E-mode pHEMTs and Pr/Pr₂O₃/Ti/Au were deposited as MIMS-gate for D-mode pHEMTs. This AlGaAs/InGaAs E-mode pHEMTs exhibit a gate turn-on voltage (V_ON) of +1 V and a gate-to-drain breakdown voltage of ?5.6 V, and these values were +7 V and ?34 V for MIMS-gate D-mode pHEMTs, respectively. Therefore, this high-k insulator in D-mode pHEMT is beneficial for suppressing the gate leakage current. Comparing to previous E/D-mode pHEMT technology, this E-mode pHEMTs and MIMS-gate D-mode pHEMTs exhibit a highly potential for high uniformity GaAs logic circuit applications due to its single recess process.     

Optical characterization of mechanically alloyed PbSnS3 nanocrystals

The present study explains the preparation of PbSnS₃ nanocrystals using mechanical alloying as the processing technique and elemental powders as the starting material. The elemental powders of Pb, Sn and sublimed sulphur (S) were mechanically alloyed for 40 h. Phases evolved during mechanical alloying are explored by X-ray diffraction (XRD). The morphology and microstructural features have been investigated using High-resolution Transmission Electron Microscopy (HRTEM). UV–Vis–NIR spectroscopy has been used to measure the optical absorption characteristics. The mechanically alloyed powders show particle sizes in the range of 3–12 nm. The absorption edge extends from 503 nm to the visible region to 1360 nm near infrared region with a sudden change in slope at 860 nm, indicating the feature of indirect band gap semiconductors. The intersection point with the x-axis of extrapolating (αE)² line as a function of E gives a direct band gap of 1.33 eV and an indirect gap of 0.59 eV.