Effect of local environment in resonant domains of polydisperse plasmonic nanoparticle aggregates on optodynamic processes in pulsed laser fields

Interactions of pulsed laser radiation with resonance domains of multiparticle colloidal aggregates having an increasingly complex local environment are studied via an optodynamic model. The model is applied to the simplest configurations, such as single particles, dimers, and trimers consisting of mono- and polydisperse Ag nanoparticles. We analyze how the local environment and the associated local feld enhancement by surrounding particles affect the optodynamic processes in domains, including their photomodification and optical properties.

Background and Research Prospect of Geo-ecological Survey and Monitor in the Critical Zone of Black Soil

The American Science journal,on the occasion of its 125 publication anniversary,in 2016,released 125 of the most challenging scientific issues(Kennedy et al.,2005)to the world.According to the basics,breadth and the influence,25 of the issues which considered to be the most important were screened,including"How many people can the Earth carry?"(Stokstad,2005;Dailyg et al.,1992;Cohen,1995)and"How high will the greenhouse effect make the earth temperature?

Review of the Book “Magnetooptical Spectroscopy of the Rare-Earth Compounds: Development and Application”

This book reviews and provides numerous theoretical calculations for the first time relevant to the optics and magneto-optics of the trivalent rare earth ions (RE3+) and their compounds. The RE3+ have unique spectroscopic properties that make them exceptionally attractive to both scientists, who probe the fundamental properties of these systems, and engineers, who develop these systems into photonic devices eagerly marketed in expanded technologies. Magneto-optical effects in compounds doped with RE3+ have been studied since the dawn of modern physics and have had a profound impact on their development in terms of practical opto-electronic devices. The authors of this new, exciting, and fresh text are world famous in this field, with over 150 years of experience in developing important theoretical and experimental contributions and over fifty years of more than 500 refereed publications in this field in the Soviet Union and the United States. They offer both a conceptual description of magneto-optical phenomena, as well as clear, detailed theoretical development published for the first time of many of the phenomena only briefly addressed in the literature. The book is based on the author’s original work in theoretical and experimental investigations in magneto-optics. Numerous graphs and simple examples model the phenomena described in the text, making it a highly desirable treatise for scientists beginning their studies in the field of magneto-optics.

Restructuring of plasmonic nanoparticle aggregates with arbitrary particle size distribution in pulsed laser fields

We have studied processes of interaction of pulsed laser radiation with resonant groups of plasmonic nanoparticles（resonant domains） in large colloidal nanoparticle aggregates having different interparticle gaps and particle size distributions.These processes are responsible for the origin of nonlinear optical effects and photochromic reactions in multiparticle aggregates.To describe photo-induced transformations in resonant domains and alterations in their absorption spectra remaining after the pulse action,we introduce the factor of spectral photomodification.Based on calculation of changes in thermodynamic,mechanical,and optical characteristics of the domains,the histograms of the spectrum photomodification factor have been obtained for various interparticle gaps,an average particle size,and the degree of polydispersity.Variations in spectra have been analyzed depending on the intensity of laser radiation and various combinations of size characteristics of domains.The obtained results can be used to predict manifestation of photochromic effects in composite materials containing different plasmonic nanoparticle aggregates in pulsed laser fields.

Processes underlying the laser photochromic effect in colloidal plasmonic nanoparticle aggregates

We have studied the dynamic and static processes occurring in disordered multiparticle colloidal Ag aggregates with natural structure and affecting their plasmonic absorption spectra under pico-and nanosecond pulsed laser radiations, as well as the physical origin responsible for these processes. We have shown that depending on the duration of the laser pulse,the mechanisms of laser modification of such aggregates can be associated both with changes in the resonant properties of the particles due to their heating and melting(picosecond irradiation mode) and with the particle shifts in the resonant domains of the aggregates(nanosecond pulses) which depend on the wavelength, intensity, and polarization of the radiation.These mechanisms result in formation of a narrow dip in the plasmonic absorption spectrum of the aggregates near the laser radiation wavelength and affect the shape and position of the dip. The effect of polydispersity of nanoparticle aggregates on laser photochromic reaction has been studied.

Giant magnetoresistance in Fe/SiO_2/p-Si hybrid structure under non-equilibrium conditions

The giant magnetoresistive（MR） effect was investigated in a simple Fe/Si O2/p-Si-hybrid-structure-based device from two back-to-back Schottky diodes. The effect was revealed only under the non-equilibrium conditions caused by optical radiation. It is demonstrated that the magnetoresistance ratio attains 100 or more. The main peculiarity of the MR behavior is its strong dependence on the magnitude and the sign of the bias current across the device and, most surprisingly, upon polarity of the magnetic field. It is important that the magnetoresistive effect is implemented exclusively in the subsystem of minority charge carriers transferred to the non-equilibrium states. The development of magneto-sensitive devices of this type can give grounds for a novel direction of semiconductor spintronics.

Lattice Doping of Lanthanide Ions in Cs_(2)AgInCl_(6)Nanocrystals Enabling Tunable Photoluminescence

Lead-free halide double perovskite Cs_(2)AgInCl_(6 )has become the research hotspot in the optoelectronic fields.It is a challenge to utilize the lattice doping by different lanthanide ions with rich and unique photoluminescence(PL)emissions for emerging photonic applications.Here,we successfully incorporated Dy^(3+),Sm^(3+),and Tb3+ions into Cs_(2)AgInCl_(6) nanocrystals(NCs)by the hot-injection method,bringing diverse PL emissions of yellowish,orange,and green light in Cs_(2)AgInCl_(6):Ln^(3+)(Ln^(3+)=Dy^(3+),Sm^(3+),Tb^(3+)).Moreover,benefiting from the energy transfer process,Sm^(3+)and Tb^(3+)ion-codoped Cs_(2)AgInCl_(6) NCs achieved tunable emission from green to yellow orange and a fluorescent pattern from the as-prepared NC-hexane inks by spray coating was made to show its potential application in fluorescent signs and anticounterfeiting technology.This work indicates that lanthanide ions could endow Cs_(2)AgInCl_(6) NCs the unique and tunable PL properties and stimulate the development of lead-free halide perovskite materials for new optoelectronic applications.

Manifestation of magnetoelastic interactions in Raman spectra of Ho_(x)Nd_(1-x)Fe_(3)(BO_(3))_(4) crystals

Raman spectra of Ho_(1-x)Nd_(x)Fe(BO_(3))4(x=1,0.75,0.5,0.25)have been studied in temperature range 10-400 K.Two compositions(x=1,x=0.75)demonstrate structural phase transition with soft mode restoration.The addition of Nd atoms increases interatomic spacing and decreases the temperature of structural phase transition.The solid solutions(x=0.75,0.5,0.25)demonstrate the emergence of the peaks corresponding to magnetoelastic interaction below Neel temperature.The order parameter of the magnetic phase transition has been determined.The equal concentrations of holmium and neodymium atoms prevent magnon soft modes condensation caused by exchange interactions in Fe-O-Fe chains are observed.Calculations confirm the data obtained in the experiment.

Influence of thermal conditions on the electrocaloric effect in a multilayer capacitor based on doped BaTiO_(3)

We present the results of studies of thermal expansion,heat capacity,permittivity,polarization and the influence of different thermal conditions on the intensive electrocaloric ffect(ECE),△T_(AD),in a commercial multilayer capacitor based on doped BaTiO_(3).Investigations in a wide temperature range revealed one anomaly in the behavior of the physical properties at about 290 K characteristic for the relaxors.Direct measurements showed a high reversibility of ECE under equilibrium thermal conditions.Good agreement was found between the values of△T_(AD) determined by direct and indirect measurements at the electric field up to 15.4 kV/cm.Quasi-isothermal conditions lead,firstly,to decrease of large△T_(AD)≈0.94 K obtained in adiabatic conditions under E=308 kV/cm to 0.87 K,and,secondly,the appearance of a difference between the values of △T^(ON) and△T^(OFF) determined when the electric field is applied and removed.Using this phenomenon and changing the frequency of the periodic electric field,E=15.4 kV/cm,the efect of cooling was obtained equal to[(OT^(ON)+AT^(OFF))/2]_(max)=-0.032 K.The results obtained are useful for further development of the electrocaloric refrigeration technique without thermal switches.

Negative thermal expansion in one-dimension of a new double sulfate AgHo(SO_(4))_(2)with isolated SO_4 tetrahedra

A double holmium-silver sulfate was obtained for the first time.The temperature intervals for the formation and stability of the compound were determined by differential scanning calorimetry.The crystal structure of AgHo(SO_(4))_(2)was determined by Rietveld method.The X-ray diffraction(XRD)analysis showed that the compound crystallizes in the monoclinic syngony,space group P2_1/m,with the unit cell parameters a=4.71751(4)A,b=6.84940(6)A and c=9.89528(9)A,β=95.1466(4)·,V=318.448(5)A^(3),Z=2,R_B=1.55%,T=303 K.Two types of sulfate tetrahedra were found in the structure,which significantly affected the spectral properties in the infrared range.In the temperature range of 143-703 K,a negative thermal expansion along the b direction accompanied by a positive thermal expansion along the a and c directions was observed.It was established that negative thermal expansion is the result of the deformation of sulfate tetrahedra,which is affected by the movement of holmium and silver atoms.The excitation in the blue spectral range(457.9 nm)produces a luminescence in light blue(489 nm),green(545 nm)and red(654 nm)spectral ranges,and the latter two were of comparable intensity that is favorable for WLED sources.The observed luminescent band distribution is ascribed to the specific crystal field at Ho^(3+)ion sites rather than a variation of radiationless probability.

Spin States of 2D Nanocomposites of Ni and V Nanoclusters on Hexagonal h-BN, BC_3 and Graphene

Atomic and electronic structures of adsorbed nickel and vanadium atoms and nanoclusters （Nin and Vn, n = 1-10） on hexagonal h-BN and BC3 lattices were studied using DFT PBE/PBC/PW （Perdew-Burke- Ernzerhof potential of density functional theory/periodic boundary conditions/plane wave basis set） technique. For the sake of comparison the structure and properties of the same nanoclusters deposited on pristine graphene were calculated as well. It was found that for all types of supports an increase of n from 1 to 10 leaded to decrease of coordination types from 776 to r/2 and 771. The h-BN- and BC3-based nanocomposites were characterized by high （up to 18 μ for Ni10/BC3） magnetic moments of the nanoclusters and featured by positive binding energies. The graphene-based nanocomposites revealed energetic stability and, in general, lower magnetic moments per unit cell. The direct potential energy barriers for migration of Ni η2/η21 and η6/η6 types of dimers on graphene were low （10.9-28.9 kJ/mol） with high reverse barriers for η6/η6 dimers, which favored dynamically equilibrated Ni clusterization on graphene.

Lattice distortion generates bound states in the continuum

High-Q optical cavity is an indispensable component of many photonic devices, such as lasers, sensors, harmonic generation and photon emission, and chiral dichroism.Conventional way of realizing ultrahigh Q-factor relies on Fabry-Pérot resonators, photonic crystal nanocavities fabricated by a CMOS-compatible process, or whispering gallery modes.

Elucidating elusive quaternary selenide EuCeCuSe3:Synthesis,crystal structure,properties and theoretical studies

We report on the novel heterometallic quaternary selenide EuCeCuSe3,the fabrication of which has been a challenge until this work.The structure of the reported selenide was elucidated from the powder X-ray diffraction data,which revealed the formation of EuCeCuSe3with excellent yield(96.7%)accompanied with a minor fraction of CeSe2(3.3%),and was best solved in orthorhombic space group Pnma with the BaLaCuS3structural type.Thus,the crystal structure of the title compound completes the row of the heterometallic quaternary selenides EuRECuSe3(RE=La,Pr,Nd,Sm,Eu,Gd,Tb,Dy,Ho,Er,Tm,Yb,Lu,Y),of which the cerium-based derivative exclusively belongs to the BaLaCuS3structural type.The distortion of the CuSe4polyhedron was compared for the whole series of EuRECuSe3compounds using theτ4-descriptor for four coordinated ions,which revealed the highest degree of distortion for the Ce3+-containing selenide,followed by the La3+-based derivative.Furthermore,the crystallographic and geometrical parameters of the reported selenide were discussed in comparison to the Ce3+-based sulfides SrCeCuS3and EuCeCuS3.Ab initio calculations of the crystal structure,a phonon spectrum and elastic constants for the crystal of EuCeCuSe3were also performed.The types and wavenumbers of fundame ntal modes were determined and the involvement of ions participating in the phonon modes was assessed.The experimental IR spectrum of the reported selenide was interpreted and found to be in agreement with the calculated spectrum.The experimental direct band gap of EuCeCuSe3was measured to be 1.36 eV that is consistent with the concept of its origin due to interband transitions between orbitals emerging mainly from 4f(valence band)and 5d(conduction band)levels of the Eu2+cation.The dependence of the Young’s modulus on the direction demonstrates the anisotropy of the elastic properties,while the Vickers hardness for EuCeCuSe3was calculated to be 5.2 GPa.Finally,the title compound is paramagnetic above 4 K.

Emerging ultra-narrow-band cyan-emitting phosphor for white LEDs with enhanced color rendition

Phosphor-converted white LEDs rely on combining a blue-emitting InGaN chip with yellow and red-emitting luminescent materials.The discovery of cyan-emitting(470-500 nm)phosphors is a challenge to compensate for the spectral gap and produce full-spectrum white light.Na_(0.5)K_(0.5)Li_(3)SiO_(4):Eu^(2+)(NKLSO:Eu^(2+))phosphor was developed with impressive properties,providing cyan emission at 486 nm with a narrow full width at half maximum(FWHM)of only 20.7 nm,and good thermal stability with an integrated emission loss of only 7% at 150℃.The ultra-narrow-band cyan emission results from the high-symmetry cation sites,leading to almost ideal cubic coordination for UCr_(4)C_(4)-type compounds.NKLSO:Eu^(2+) phosphor allows the valley between the blue and yellow emission peaks in the white LED device to be filled,and the color-rendering index can be enhanced from 86 to 95.2,suggesting great applications in full-spectrum white LEDs.

Non-stoichiometry in Ca2Al2SiO7 enabling mixedvalent europium toward ratiometric temperature sensing

Eu^2+/Eu^3+ mixed-valence couple co-doped material holds great potential for ratiometric temperature sensing owing to its different electronic configurations and electron-lattice interaction. Here, the correlation of nonstoichiometry in chemical composition, phase structures and luminescence propertis of Ca2 Al2 Si1-xO7:Eu is discussed, and controlled Eu^2+/Eu^3+ valence and tunable emission appear with decreasing Si content. It is found that the 2 Ca^2++ Si^4+←→ Eu^2++ Eu^3++ Al^3+ cosubstitution accounts for the structural stability and charge balance mechanism. Benefiting from the diverse thermal dependent emission behaviors of Eu^2+ and Eu^3+, Ca2 Al2 Si1-xO7:Eu thermometer exhibits excellent temperature sensing performances with the maximum absolute and relative sensitivity being 0.024 K-1(at 303 K) and 2.46% K-1(at 443 K) and good signal discriminability. We propose that the emission quenching of Eu^2+ is ascribed to 5 d electrons depopulation through Eu^2+/Eu^3+ intervalence charge transfer state, while the quenching of Eu^3+ comes from multiphonon relaxation. Our work demonstrates the potential of Ca2 Al2 Si1-xO7:Eu for noncontact optical thermometry, and also highlights mixed-valence europium-containing compounds toward temperature sensing.

Highly efficient Fe^(3+)-doped A_(2)BB′O_(6)(A=Sr^(2+),Ca^(2+);B,B′=In^(3+),Sb^(5+),Sn^(4+))broadband nearinfrared-emitting phosphors for spectroscopic analysis

Near-infrared(NIR)-emitting phosphor-converted light-emitting diodes have attracted widespread attention in various applications based on NIR spectroscopy.Except for typical Cr^(3+)-activated NIR-emitting phosphors,next-generation Cr^(3+)-free NIR-emitting phosphors with high efficiency and tunable optical properties are highly desired to enrich the types of NIR luminescent materials for different application fields.Here,we report the Fe^(3+)-activated Sr2−yCay(InSb)1−zSn_(2)zO_(6)phosphors that exhibit unprecedented long-wavelength NIR emission.The overall emission tuning from 885 to 1005 nm with broadened full-width at half maximum from 108 to 146 nm was realized through a crystallographic site engineering strategy.The NIR emission was significantly enhanced after complete Ca^(2+)incorporation owing to the substitution-induced lower symmetry of the Fe^(3+)sites.The Ca_(2)InSbO_(6):Fe^(3+)phosphor peaking at 935 nm showed an ultra-high internal quantum efficiency of 87%.The as-synthesized emission-tunable phosphors demonstrated great potential for NIR spectroscopy detection.This work initiates the development of efficient Fe^(3+)-activated broadband NIR-emitting phosphors and opens up a new avenue for designing NIR-emitting phosphor materials.

Glass crystallization making red phosphor for high-power warm white lighting

Rapid development of solid-state lighting technology requires new materials with highly efficient and stable luminescence,and especially relies on blue light pumped red phosphors for improved light quality.Herein,we discovered an unprecedented red-emitting Mg_(2)AI_(4)Si_(5)0_(18):Eu^(2+)composite phosphor(λex=450 nm,λem=620 nm)via the crystallization of MgO-AI_(2)O_(3)-Sio_(2) aluminosilicate glass.Combined experimental measurement and first-principles calculations verify that Eu^(2+)dopants insert at the vacant channel of Mg_(2)AI_(4)Si_(5)0_(18)crystal with six-fold coordination responsible for the peculiar red emission.Importantly,the resulting phosphor exhibits high internal/external quantum efficiency of 94.5/70.6%,and stable emission against thermal quenching,which reaches industry production.The maximum luminous flux and luminous efficiency of the constructed laser driven red emitting device reaches as high as 274 Im and 54lm W^(-1),respectively.The combinations of extraordinary optical properties coupled with economically favorable and innovative preparation method indicate,that the Mg_(2)AI_(4)Si_(5)0_(18):Eu^(2+)composite phosphor will provide a significant step towards the development of high-power solid-state lighting.

Unraveling the mechanochemical synthesis and luminescence in MnⅡ-based two-dimensional hybrid perovskite（C4H9NH3）2PbCl4

The mechanochemical route is a facile and fast way and has received much attention for developing versatile advanced functional materials. Herein, we reported a mechanochemical synthesis for incorporating divalent manganese ions (Mn^Ⅱ) into a two-dimensional (2D) hybrid perovskite (C4H9NH3)2PbCl4. The mild external stimuli originating from the grinding at room temperature enabled the formation of Mn^Ⅱ-doped 2D hybrid perovskites, and rapidly changed the luminescence characteristics. The photoluminescence analyses show that the violet and orange emissions are attributed to (C4H9NH3)2Pb1-xMnxCl4 band-edge emission and the T1→^6A1 transition of Mn^2+ resulting from an efficient energy transfer process, respectively. Site preference and distribution of the doped Mn^2+ cations on the locations of Pb^2+ were analyzed. The formation energy calculated by the density functional theory (DFT) indicates that the Mn^2+ ions can rapidly enter the crystal lattice due to the unique 2D crystal structure of the hybrid perovskite. Such a case of mechanochemical synthesis for the 2D hybrid perovskite motivates many novel emerging materials and the related applications.

利用电荷转移工程提高红色SrLa(Sc,Ga)O_(4):Ce^(3+)荧光粉的热稳定性

可被蓝光激发的高热稳定性红色荧光粉是制作高性能白光二极管(WLED)的关键材料.研究发现,Ce^(3+)掺杂的SrLaScO_(4)(SLO:Ce^(3+))荧光粉在440 nm激发下呈现峰值为640 nm的反常宽带红光发射.光谱学和结构分析证实Ce^(3+)离子在SLO中进入[LaO_(8)]多面体,产生强的晶体场劈裂和较大的Stokes位移,实现了比Eu^(2+)更低能量的红光发射.我们还设计并揭示了一种电荷转移相互作用的策略:在Sc^(3+)位置引入电负性较大的Ga^(3+),Ga^(3+)可以吸引更多邻位配合基团的电荷,以减少导带底部的电子占用而扩大带隙.Sc/Ga取代有效地抑制了热激活电离过程,使SrLa(Sc,Ga)O_(4):Ce^(3+)的热稳定性获得了显著提升,即在150℃的发光强度比(相对于20℃)从15%提升至31%.本研究为发现具有良好热稳定性的新型Ce^(3+)掺杂红色荧光粉提供了有效的设计原则.