Junpei Zhang

AgInSbTe memristor with gradual resistance tuning

A chalcogenide material with Ag/Ag5In5Sb60Te30/Ag structure was proposed as a memristor. Reproducible gradual resistance tuning in bipolar/unipolar modes was demonstrated. The resistance variation was tuned more precisely by controlling the polarity, the amplitude, the width, and the number of applied voltage pulses. The bipolar memristive switch was attributed to the coexistence of intrinsic space charge limited conduction and extrinsic electrochemical metallization effect. Moreover, the unipolar gradual resistance tuning reconfirmed the electrochemical metallization effect. The gradual resistance tuning characteristics will promote this memristor to potential application in mimicking biological plastic synapses.

Near Field Enhanced Photocurrent Generation in P-type Dye-Sensitized Solar Cells

Over the past few decades, the field of p-type dye-sensitized solar cell (p-DSSC) devices has undergone tremendous advances, in which Cu-based delafossite nanocrystal is of prime interest. This paper presents an augment of about 87% improvement in photocurrent observed in a particular configuration of organic dye P1 sensitized CuCrO2 delafossite nanocrystal electrode coupled with organic redox shuttle, 1-methy-1H- tetrazole-5-thiolate and its disulfide dimer when Au nanoparticles (NPs, with diameter of about 20 nm) is added into the photocathode, achieving a power convert efficiency of 0.31% (measured under standard AM 1.5 G test conditions). Detailed investigation shows that the local electrical-magnetic field effect, induced by Au NPs among the mesoporous CuCrO2 film, can improve the charge injection efficiency at dye/semiconductor interface, which is responsible for the bulk of the gain in photocurrent.

The influence of high magnetic field on electric-dipole emission spectra of Eu3+ in different single crystals

In this work, the effect of pulsed high magnetic field on the integral intensity of the electric-dipole emission spectrum of Eu3+ in YVO4:Eu3+ and GdVO4:Eu3+ single crystals was studied and the results showed magnetic field induced luminescence suppression in YVO4:Eu3+ and luminescence expansion in GdVO4:Eu3+. The single crystals were prepared by the optical floating zone method. The strong effect of the magnetic field on the splitting and emission of 5D0–7F2 and 5D0–7F4 transitions in Eu3+ was investigated. The integral luminescence intensities of Eu3+ are proportional to the magnetic field at higher than 15 T. For GdVO4:Eu3+, the integral intensity increases with the strengthening of magnetic field, and is completely opposite to that for YVO4:Eu3+. In this study, the dependence of luminescence integral intensity on the magnetic field was proposed to be the result of the structural change induced by high magnetic field which changes the symmetry of Eu3+ ions in single crystals.

Simultaneous luminescence modulation and magnetic field detection via magneto-optical response of Eu3+-doped NaGdF4 nanocrystals

Non-agglomerated and uniform Eu3+-doped NaGdF4 nanocrystals were synthesized via a facile one-step precipitation method at room temperature. Under pulsed magnetic fields, the luminescence properties of the as-prepared samples have been recorded and discussed in detail. Particularly, “controllable eliminating luminescence” of 5D0–7F0 transition in Eu3+ was achieved during the magneto-optical interaction. Magnetic field assisted cross-relaxation of excited electrons was derived from Zeeman splitting of the higher 5D energy level, and the magnetic confinement of f electron wave functions was proposed which were responsible for the change in luminescence intensity with a variation of magnetic field strength. The characteristic variation of the emission band under pulsed magnetic fields promises an optical probe for magnetic field detection.

Magnetic field induced great photoluminescence enhancement in an Er 3+ :YVO 4 single crystal used for high magnetic field calibration

An optical technique is proposed for the accurate calibration of pulsed high magnetic fields utilizing the magnetic field dependent photoluminescence (PL) properties in an Er(3+):YVO(4) single crystal at 80 K. Bright green PL emissions are excited by a 487.5 nm laser line and can be enhanced greatly by a magnetic field at certain field values (B(c)). Since the B(c)s under 10 T are extremely stable for a given sample at a certain temperature, and the FWHM of the enhancement peaks are less than 0.9 T, an Er(3+):YVO(4) single crystal is proven to be a good candidate for pulsed high magnetic field calibration. The detailed processes and numerous advantages of the technique are presented in this work.

Enhanced room temperature magnetoresistance in La0.7 Ca0.2 Sr0.1 MnO3/Ag composites

The effect of added Ag on the electro-magnetic properties and enhanced room temperature magnetoresistance in (La0.7Ca0.2Sr0.1MnO3)1−x/Agx composites has been studied systematically. According to the results of x-ray diffraction, scanning electron microscopy and magnetic measurement, we can suggest that Ag segregates at the grain surface of La0.7Ca0.2Sr0.1MnO3. The results of electronic measurements show that the intrinsic insulator/metal transition temperature (TP) does not change, which is in accordance with the results for the Curie temperature (TC). It is very interesting to note that the magnetoresistance at room temperature is enhanced, which is encouraging for potential applications. These phenomena can be explained by considering that Ag, which segregated at the grain boundaries or surfaces, does not change the intrinsic structure of La0.7Ca0.2Sr0.1MnO3 and lead to a modification of grain boundaries.

Intrinsic memristance mechanism of crystalline stoichiometric Ge2Sb2Te5

The bipolar memristive switching of stoichiometric crystalline Ge2Sb2Te5 (GST) thin film has been demonstrated. In contrast to the filamentary switching reported previously for a GST memristor, the intrinsic memristance is interpreted as arising from a trap-associated space-charge limited current mechanism, which is confirmed by the frequency-dependent resistance and capacitance. The contributions of charge trapping in grain defects and grain boundary defects are analyzed, and the latter ones may dominate the resistance variation. Unraveling the intrinsic memristance of GST will help us further understand the conduction mechanism of chalcogenides and promote the design of future nonvolatile memory and neuromorphic devices.

Narrowband spectrally selective near-infrared photodetector based on up-conversion nanoparticles used in a 2D hybrid device

A narrowband wavelength-selective near-infrared photodetector based on lanthanide-doped up-converting nanoparticles (UCNPs) and monolayer MoS2 was fabricated via a novel, simple strategy. This UCNPs/transition metal dichalcogenide design could revitalize photodetection research, particularly in the selective response field.

High magnetic field and temperature tuning of up-conversion luminescence in Mn2+-doped (Er3+/Yb3+): NaYF4

Upconversion luminescence properties of (Yb3+/Er3+): NaYF4 and Mn2+ doped (Yb3+/Er3+): NaYF4 nanocrystals have been investigated under pulsed high magnetic field. The emission ratio of red to green of the bare (Yb3+/Er3+): NaYF4 nanocrystals increases by about 42% as the magnetic field increases from 0 T to 40 T. While for Mn2+ doped (Yb3+/Er3+): NaYF4 nanocrystals, the ratio keeps almost unchanged due to the energy transferring between Mn2+ and Yb3+/Er3+. The effects of temperature on the upconversion emissions are also compared for the two types of nanocrystals. Our observations have prospective applications in biological imaging and magnetic field detection.

Influence of high magnetic field on the luminescence of Eu3+-doped glass ceramics

Rare earth (RE) doped materials have been widely exploited as the intriguing electronic configuration of RE ions offers diverse functionalities from optics to magnetism. However, the coupling of magnetism with photoluminescence (PL) in such materials has been rarely reported in spite of its fundamental significance. In the present paper, the effect of high pulsed magnetic field on the photoluminescence intensity of Eu3+-doped nano-glass-ceramics has been investigated. In our experiment, Eu-doped oxyfluoride glass and glass ceramic were prepared by the conventional melt-quenching process and controlled heat treatment. The results demonstrate that the integrated PL intensity of Eu3+ decreases with the enhancement of magnetic field, which can be interpreted in terms of cooperation effect of Zeeman splitting and magnetic field induced change in site symmetry. Furthermore, as a result of Zeeman splitting, both blue and red shift in the emission peaks of Eu3+ can be observed, and this effect becomes more promin...