Yb-and Er concentration dependence of the upconversion luminescence of highly doped NaYF_(4):Yb,Er/NaYF_(4):Lu core/shell nanocrystals prepared by a water-free synthesis

High sensitizer and activator concentrations have been increasingly examined to improve the performance of multi-color emissive upconversion(UC)nanocrystals(UCNC)like NaYF_(4):Yb,Er and first strategies were reported to reduce concentration quenching in highly doped UCNC.UC luminescence(UCL)is,however,controlled not only by dopant concentration,yet by an interplay of different parameters including size,crystal and shell quality,and excitation power density(P).Thus,identifying optimum dopant concentrations requires systematic studies of UCNC designed to minimize additional quenching pathways and quantitative spectroscopy.Here,we quantify the dopant concentration dependence of the UCL quantum yield(ΦUC)of solid NaYF_(4):Yb,Er/NaYF_(4):Lu upconversion core/shell nanocrystals of varying Yb3+and Er3+concentrations(Yb3+series:20%‒98%Yb3+;2%Er3+;Er3+series:60%Yb3+;2%‒40%Er3+).To circumvent other luminescence quenching processes,an elaborate synthesis yielding OH-free UCNC with recordΦUC of~9%and~25 nm core particles with a thick surface shell were used.High Yb3+concentrations barely reduceΦUC from~9%(20%Yb3+)to~7%(98%Yb3+)for an Er3+concentration of 2%,thereby allowing to strongly increase the particle absorption cross section and UCNC brightness.Although an increased Er3+concentration reducesΦUC from~7%(2%Er3+)to 1%(40%)for 60%Yb3+.Nevertheless,at very high P(>1 MW/cm^(2))used for microscopic studies,highly Er3+-doped UCNC display a high brightness because of reduced saturation.These findings underline the importance of synthesis control and will pave the road to many fundamental studies of UC materials.

High Quantum Efficiency and High Concentration Erbium-Doped Silica Glasses Fabricated by Sintering Nanoporous Glasses

A new method was used to prepare erbium-doped high silica （SiO2 % 〉 96 % ） glasses by sintering nanoporous glasses. The concentration of erbium ions in high silica glasses can be considerably more than that in silica glasses prepared by using conventional methods. The fluorescence of 1532 nm has an FWHM （Full Wave at Half Maximum） of 50 nm, wider than 35 nm of EDSFA （erbium-doped silica fiber amplifer）, and hence the glass possesses potential application in broadband fiber amplifiers. The Judd-Ofelt theoretical analysis reflects that the quantum efficiency of this erbium-doped glass is about 0.78, although the erbium concentration in this glass （6 × 10^3） is about twenty times higher than that in silica glass. These excellent characteristics of Er-doped high silica glass will be conducive to its usage in optical amplifiers and microchip lasers.

Novel high- with low specific on-resistance high voltage lateral double-diffused MOSFET

A novel voltage-withstand substrate with high-K（HK, k 〉 3.9, k is the relative permittivity） dielectric and low specific on-resistance（Ron,sp） bulk-silicon, high-voltage LDMOS（HKLR LDMOS）is proposed in this paper. The high-K dielectric and highly doped interface N＋-layer are made in bulk silicon to reduce the surface field drift region. The high-K dielectric can fully assist in depleting the drift region to increase the drift doping concentration（Nd） and reshape the electric field distribution. The highly doped N＋-layer under the high-K dielectric acts as a low resistance path to reduce the Ron,sp. The new device with the high breakdown voltage（BV）, the low Ron,sp, and the excellent figure of merit（FOM = BV^2/Ron,sp） is obtained. The BV of HKLR LDMOS is 534 V, Ron,sp is 70.6 m？·cm^2, and FOM is 4.039 MW·cm^（-2）.

Environmentally stable,spectral-shape-controllable,GHz femtosecond Yb-doped fiber laser

We demonstrate an all-polarization-maintaining[PM]passively mode-locked Yb^(3+)-doped fiber laser[YDFL]with a fundamental repetition rate of 1.3 GHz.The optical spectra of a linearly polarized soliton exhibit different shapes by rotating the fast axis of the fiber optical pigtail of a dispersive dielectric mirror.The oscillator provides a series of laser performance,such as a threshold pump power for continuous wave laser oscillation of 3.1 mW,an optical-to-optical efficiency for modelocking of 29%,and an integrated relative intensity noise of 0.08%.To the best of our knowledge,this is the first report of>1 GHz ultrafast all-fiber YDFL with PM architecture.

First-principles study on the effect of high In doping on the conductivity of ZnO

Based on the density functional theory （DFT）, using first-principles plane-wave ultrasoft pseudopotential method, the models of the unit cell of pure ZnO and two highly In-doped supercells of Zn0.9375In0.0625O and Zn0.875In0.125O are constructed, and the geometry optimizations of the three models are carried out. The total density of states （DOS） and the band structures （BS） are also calculated. The calculation results show that in the range of high doping concentration, when the doping concentration is hihger than a specific value, the conductivity decreases with the increase of the doping concentration of In in ZnO, which is in consistence with the change trend of the experimental results.

Fairness in Olympic sports:How can we control the increasing complexity of doping use in high performance sports?

With the Rio Olympics just a few months past,we remember the excitement,the incredible performances,and the controversies.As happens so often,the Olympic Games focus attention not only on athletic achievements but also on how athletes may reach ever-increasing levels of performance.Doping,medical

Alloying cobalt with ruthenium in nitrogen doped graphene layers for developing highly active hydrogen evolution electrocatalysts in alkaline media

Subject Code:B01With the support by the National Natural Science Foundation of China,a creative study by the research group led by Prof.Chen Qianwang(陈乾旺)from the University of Science and Technology of China and High Magnetic Field Laboratory,Hefei Institutes of Physical Science,Chinese Academy of

High N-doped hierarchical porous carbon networks with expanded interlayers for efficient sodium storage

Sodium-ion batteries (SIBs) have been attracting considerable attention as a promising candidate for large-scale energy storage because of the abundance and low-cost of sodium resources. However, lack of appropriate anode materials impedes further applications. Herein, a novel self-template strategy is designed to synthesize uniform flowerlike N-doped hierarchical porous carbon networks (NHPCN) with high content of N (15.31 at.%) assembled by ultrathin nanosheets via a self-synthesized single precursor and subsequent thermal annealing. Relying on the synergetic coordination of benzimidazole and 2-methylimidazole with metal ions to produce a flowerlike network, a self-formed single precursor can be harvested. Due to the structural and compositional advantages, including the high N doping, the expanded interlayer spacing, the ultrathin two-dimensional nano-sized subunits, and the three-dimensional porous network structure, these unique NHPCN flowers deliver ultrahigh reversible capacities of 453.7 mAh·g^−1 at 0.1 A·g^−1 and 242.5 mAh·g^−1 at 1 A·g^−1 for 2,500 cycles with exceptional rate capability of 5 A·g^−1 with reversible capacities of 201.2 mAh·g^−1. The greatly improved sodium storage performance of NHPCN confirms the importance of reasonable engineering and synthesis of hierarchical carbon with unique structures.

A Bulky Pyridinylfluorene/Triphenylamine Hybrid Used as Host Material for Heavily-Doped Blue Electrophosphorescent Devices

In this work, a novel molecule pyridinylfluorene/triphenylamine hybrid （TPyFTPA） with bulky steric hindrance effects has been synthesized successfully by substituting 9-（pyridine-2-yl）-fluoren-9-yl with triphenylamine （TPA） via Friedel-Crafts reaction, which possesses good thermal stability and triplet energy （ET） of 420 ℃ with 5% weight loss and 2.86 eV, respectively. Moreover, the bulky steric hindrance material shows high stable morphology by heating to 200 ℃ without finding melting phenomena and crystallization that is demonstrated by differential scanning calorimetry （DSC） curve. The bulky pyridinylfluorene end-capped TPA has been used as host material for blue phosphorescent organic light-emitting diodes （PhOLEDs） with maximum external quantum efficiencies （EQEs） of 2.7%, 3.7%, and 3.5%, at the doping ratios of 10%, 30%, and 40%, respectively. The performances of TPyFTPA-based blue PhOLEDs own wide concentration ranging from 10% to 40%, which indicates the bulky TPyFTPA might be a potential candidate for inexpensive products with simplifying process for the applications in full-color display and solid state lighting.

A nanoporous nitrogen-doped graphene for high performance lithium sulfur batteries

A nanoporous N-doped reduced graphene oxide（p-N-rGO） was prepared through carbothermal reaction between graphene oxide and ammonium-containing oxometalates as sulfur host for Li-S batteries.The p-N-rGO sheets have abundant nanopores with diameters of 10-40 nm and the nitrogen content is 2.65 at%.When used as sulfur cathode,the obtained p-N-rGO/S composite has a high reversible capacity of 1110mAhg^-1 at 1C rate and stable cycling performance with 781.8 mAhg-1 retained after 110 cycles,much better than those of the rGO/S composite.The enhanced electrochemical performance is ascribed to the rational combination of nanopores and N-doping,which provide efficient contact and wetting with the electrolyte,accommodate volume expansion and immobilize polysulfides during cycling.

Improved dual-channel 4H-SiC MESFETs with high doped n-type surface layers and step-gate structure

An improved dual-channel 4H-SiC MESFET with high doped n-type surface layer and step-gate structure is proposed, and the static and dynamic electrical performances are analyzed.A high doped n-type surface layer is applied to obtain a low source parasitic series resistance, while the step-gate structure is utilized to reduce the gate capacitance by the elimination of the depletion layer extension near the gate edge, thereby improving the RF characteristics and still maintaining a high breakdown voltage and a large drain current in comparison with the published SiC MESFETs with a dual-channel layer.Detailed numerical simulations demonstrate that the gate-to-drain capacitance, the gate-to-source capacitance, and the source parasitic series resistance of the proposed structure are about 4%, 7%, and 18% smaller than those of the dual-channel structure, which is responsible for 1.4 and 6 GHz improvements in the cut-off frequency and the maximum oscillation frequency.

A High Power Conversion Efficiency L-Band Erbium Doped Fiber Amplifier

By using two sections of erbium doped fiber and a fiber optical reflector, a novel, highly efficient L-band amplifier is demonstrated with significantly power-conversion-efficiency enhancement and the gain increasing of as much as 13 dB.

A novel SOI pressure sensor for high temperature application

The silicon on insulator（SOI） high temperature pressure sensor is a novel pressure sensor with highperformance and high-quality. A structure of a SOI high-temperature pressure sensor is presented in this paper.The key factors including doping concentration and power are analyzed. The process of the sensor is designed with the critical process parameters set appropriately. The test result at room temperature and high temperature shows that nonlinear error below is 0.1%, and hysteresis is less than 0.5%. High temperature measuring results show that the sensor can be used for from room temperature to 350℃ in harsh environments. It offers a reference for the development of high temperature piezoresistive pressure sensors.