Solid-state Excitation Research Articles

Improved densification of SiCf/SiC composites by microwave-assisted chemical vapor infiltration process based on multifrequency solid-state sources excitation

This paper addresses the possibility of improving and controlling the temperature profile of a Ceramic Matrix Composite preform in a multiport Microwave-assisted Chemical Vapor Infiltration (MW-CVI) pilot-scale plant, based on a multifrequency excitation of the reactor by three solid-state sources. The choice of the most suited excitation frequencies is guided by rigorous numerical modeling of the reactor loaded by the sample, solving the coupled electromagnetic and thermal problems in a self-consistent way. The resulting infiltration front and residual porosity have been evaluated by a pseudo1D model, along the sample thickness, according to the previously computed heating pattern. The practical implementation and validation of the proposed technique are illustrated with MW-CVI trials on 10×10×0.3 cm3 SiCf/(SiC/BN)3/SiC preforms manufactured by Filament Winding method. The obtained results confirm the inside-out densification pattern, expected from the sample volumetric heating, along with an extension of the densification region by a factor of 2–3.

Polaritonic states trapped by topological defects

The miniaturization of photonic technologies calls for a deliberate integration of diverse materials to enable novel functionalities in chip-scale devices. Topological photonic systems are a promising platform to couple structured light with solid-state matter excitations and establish robust forms of 1D polaritonic transport. Here, we demonstrate a mechanism to efficiently trap mid-IR structured phonon-polaritons in topological defects of a metasurface integrated with hexagonal boron nitride (hBN). These defects, created by stitching displaced domains of a Kekulé-patterned metasurface, sustain localized polaritonic modes that originate from coupling of electromagnetic fields with hBN lattice vibrations. These 0D higher-order topological modes, comprising phononic and photonic components with chiral polarization, are imaged in real- and Fourier-space. The results reveal a singular radiation leakage profile and selective excitation through spin-polarized edge waves at heterogeneous topological interfaces. This offers impactful opportunities to control light-matter waves in their dimensional hierarchy, paving the way for topological polariton shaping, ultrathin structured light sources, and thermal management at the nanoscale.

Probing hyperbolic and surface phonon-polaritons in 2D materials using Raman spectroscopy

The hyperbolic dispersion relation of phonon-polaritons (PhPols) in anisotropic van der Waals materials provides high-momentum states, directional propagation, subdiffractional confinement, large optical density of states, and enhanced light-matter interactions. In this work, we use Raman spectroscopy in the convenient backscattering configuration to probe PhPol in GaSe, a 2D material presenting two hyperbolic regions separated by a double reststrahlen band. By varying the incidence angle, dispersion relations are revealed for samples with thicknesses between 200 and 750 nm. Raman spectra simulations confirm the observation of one surface and two extraordinary guided polaritons and match the evolution of PhPol frequency as a function of vertical confinement. GaSe appears to provide relatively low propagation losses and supports confinement factors matching or exceeding those reported for other 2D materials. Resonant excitation close to the 1s exciton singularly exalts the scattering efficiency of PhPols, providing enhanced scattering signals and means to probe the coupling of PhPols to other solid-state excitations.

Thermosensitive visible-light-excited visible-/NIR-luminescent complexes with lanthanide sensitized by the π-electronic system through intramolecular H-bonding.

Visible-luminescent lanthanide (LnL) complexes with a highly planar tetradentate ligand were successfully developed for a visible-light solid-state excitation system. L was designed by using two 2-hydroxy-3-(2-pyridinyl)-benzaldehyde molecules bridged by ethylenediamine, which was then coordinated to a series of Ln ions (Ln = Nd, Sm, Eu, Gd, Tb, Dy, and Yb). From the measurement of single-crystal X-ray analysis of EuL, two phenolic O atoms and two imine N atoms in L were coordinated to the Eu ion, and each π-electronic system took coplanar with the edged-pyridine moiety through an intramolecular hydrogen bond. The enol group on the phenolic skeleton changed to the keto form, and the pyridine was protonated. Thus, intramolecular proton transfer occurred in L after the complexation. Other complexes take isostructure. The space group is P-1, and the c-axis shrinks with decreasing temperature without a phase transition in EuL. The yellow color caused by the planar structure of L can sensitize ff emission by visible light, and the luminescence color of each complex depends on central Ln ions. Furthermore, a phosphorescence band also appeared at rt with ff emission in LnL. Drastic temperature dependence of luminescence was clarified quantitatively.

Combined neutron scattering and resonant ultrasound spectroscopy for lattice dynamics studies

Resonant ultrasound spectroscopy (RUS) and inelastic neutron scattering afford insight into solid state structures and excitations at vastly different frequency and length scales. We will discuss the combined use of these techniques to understand phase transitions in functional and structural materials. Structural complexity, such as chirality or incommensuration leads to emerging features in both techniques and modifies energy transport channels. Novel developments in techniques at the Oak Ridge neutron sources, that now enable in situ ultrasound spectrocopy in the neutron beam, and the RUSCal analysis software that now supports all Bravais classes and implements Monte-Carlo methods, will be discussed in example materials. [Work supported by the Deparment of Energy Office of Basic Energy Science and by Laboratory Directed Research at Oak Ridge National Laboratory. My thanks go to J. Torres, V. Fanelli, Y. Shinohara, E. Cakmak, C. Hua, A. Flores-Bettancourt, M. Ruis-Rodriguez for the collaboration and A. Zevalkink, D. Mandrus, V. Keppens, E. Lara-Curzio, and T. Watkins for fruitful discussions.]

Abundant stable wave structures for the nonlinear propagation of dislocations in crystals, phase differences across Josephson junctions

This study investigates the analytical solitary wave solutions of the nonlinear Sine–Gordon (SG) system by using two recent computational (Khater II and novel Kudryashov) schemes. The studied model is used as a model for various wave phenomena, including the propagation of dislocations in crystals, phase differences across Josephson junctions, torsion waves in strings and pendula, and waves along lipid membranes. It was already studied in the nineteenth century in connection with the theory of pseudospherical surfaces. The quantum version is used as a simple model for solid–state excitations. The solitonic property of the constructed solutions is also explained through some distinct graphs in two-, three-dimensional, contour, and polar plots. The stability property of the obtained soliton wave solutions is discussed based on the Hamiltonian system’s characterizations.

Near-IR Emission and upconversion luminescent properties of Tb3+/Yb3+ Co-doped HfO2/SiO2 nanoparticles

The luminescent characteristics of spherical hafnia/silica (HfO2/SiO2) nanoparticles (NPʼs) co-doped with Tb3+/Yb3+ were analysed. These NPʼs were synthesized using the spray pyrolysis technique. The addition of SiO2 and Tb3+/Yb3+ was found to induce a cubic phase in HfO2. The luminescent spectra presented the characteristic emission peaks for inter-electronic energy levels transitions of the Tb3+ and Yb3+ ions, with an excitation band centred at 270 nm. Under solid-state laser excitation at 980 nm an upconversion emission related to the Tb3+ ion was observed. The maximum emission peak in the visible region was at 543 nm, associated with 5D4 → 7F5 transitions of the Tb3+ ions and an IR emission peak at 970 nm (2F5/2 → 2F7/2) pertaining to Yb3+, with irradiation at 270 nm (UV). The energy transfer mechanism from Tb3+→Yb3+ (excitation at 270 nm), is discussed based on the time decay of the luminescence intensity analysis and the energy transfer efficiency (ηET) and was determined to be in the range of 29.2% to40.8%.

Acoustic and optical properties of a fast-spinning dielectric nanoparticle

Nanoparticles levitated in vacuum can be set to spin at ultimate frequencies, limited only by the tensile strength of the material. At such high frequencies, drastic changes to the dynamics of solid-state quantum excitations are to be expected. Here, we theoretically describe the interaction between acoustic phonons and the rotation of a nanoparticle around its own axis, and model how the acoustic and optical properties of the nanoparticle change when it rotates at a fixed frequency. As an example, we analytically predict the scaling of the shape, the acoustic eigenmode spectrum, the permittivity, and the polarizability of a spinning dielectric nanosphere. We find that the changes to these properties at frequencies of a few gigahertz achieved in current experiments should be measurable with presents technology. Our work aims at exploring solid-state quantum excitations in mesoscopic matter under extreme rotation, a regime that is now becoming accessible with the advent of precision control over highly isolated levitated nanoparticles.

(INVITED) Eu3+ activated molybdates – Structure property relations

Eu3+ activated phosphors have been a subject of scientific investigation for more than 100 years. Various host materials have been employed, among which molybdate hosts play an important role. They offer an array of advantageous properties such as high critical activator concentrations, facile solid state synthesis and excitation via the Mo6+/O2− charge transfer (CT) transition. This review paper discusses the basics of Eu3+ luminescence and presents the most important properties and synthesis conditions of various Eu3+ activated molybdates. Furthermore, relations between the crystallographic structure of the host and the optical properties of Eu3+ are shown. The point symmetry of the Eu3+ doping site can be determined from specific features of the Eu3+ emission spectrum and the number of crystallographic sites can be estimated. The concept of optical basicity is discussed in regard to the spectral position of the Mo6+/O2− charge transfer band. The influence of the CT band on the thermal quenching properties and consequently the photoluminescence efficiency of Eu3+ is investigated. Disadvantages of molybdates as phosphor host materials are discussed as well, such as the formation of Mo5+ defect states.

Design of beam scanning metamaterial antenna

A beam scanning metamaterial planar reflective array antenna is designed by combining square and octagonal rings. Compared with the traditional array antenna design, this array antenna adopts a new phase compensation method thus by combining the phase curve obtained by the reflective array unit when the material of the dielectric substrate is different, the phase compensation from 0~360 is realized, so that the phase curve of the array unit need not to completely cover 0~360, and Hermite interpolation way is used to make up for the poor linearity of the phase characteristics. The advantage of this method is its universality, which reduces the design requirements for the array unit. Using this method, several single-layer plane reflectarray antennas were designed. The simulation results show that the direction of the reflected beam is consistent with the expected setting, and the side lobe and the main lobe are at least 15 dB apart. By adjusting the range of the solid-state plasma excitation region of the metamaterial to change the resonance structure of the array unit, beam scanning in different spatial frequencies is achieved, which provides a new method for the design of the planar reflectarray antenna.

A 365 nm UV LED-excitable antenna ligand for switchable lanthanide luminescence.

The time-resolved luminescence of lanthanide complexes is a highly sensitive and widely used bioassay technology for clinical diagnostics. With the time-resolved luminescence detection the naturally occurring autofluorescence of biological matrices, solid supports and plastics can be avoided. A major drawback of the current technique is that the luminescent lanthanide labels require ultraviolet (UV) excitation, typically shorter than 360 nm, which is strongly absorbed and can damage living biological systems. The lack of cost-efficient high power solid state excitation light sources for UV excitation further limits the development of low-cost and more compact measurement instruments for time-resolved luminescence and the potential use of lanthanide luminescence in different applications. Switchable lanthanide luminescence is a binary probe technology that inherently enables a high signal modulation in a separation-free detection of targets. The intrinsically luminescent lanthanide chelate is split into two nonluminescent moieties, a lanthanide ion carrier chelate and a light harvesting antenna ligand, each of which can be attached to a separate molecular probe. A luminescent lanthanide complex is formed only when the two probes bind adjacently to the target molecule. Herein we describe a new 365 nm excitable antenna ligand (AL360) for switchable lanthanide luminescence of europium(iii) (EuIII) that would enable the use of 365 nm light emitting diodes (LEDs) as an excitation light source for time-resolved fluorescence imaging and detection. With the acquired subpicomolar assay sensitivity it would be applicable for solution or surface arrays and UV LED microscopy.

A repetitively pulsed xenon chloride excimer laser with all ferrite magnetic cores (AFMC) based all solid state exciter

Performance of repetitively pulsed xenon chloride excimer laser (λ~308nm) with solid state pulser consisting of magnetic pulse compression circuit (MPC) using all ferrite magnetic cores (AFMC) is reported. Laser system suitable for 100Hz operation with inbuilt pre-ionizer, compact gas circulation and cooling has been developed and presented. In this configuration, high voltage pulses of ~8µs duration are compressed to ~100ns by magnetic pulse compression circuit with overall compression factor of ~80. Pulse energy of ~18J stored in the primary capacitor is transferred to the laser head with an efficiency of ~85% compared to ~70% that is normally achieved in such configurations using annealed met-glass core. This is a significant improvement of about 21%. Maximum output laser pulse energy of ~100mJ was achieved at repetition rate of 100Hz with a typical pulse to pulse energy stability of ±5% and laser pulse energy of 150mJ was generated at low rep-rate of ~40Hz. This exciter uses a low current and low voltage solid state switch (SCR) that replaces high voltage and high current switch i. e, thyratron completely. The use of solid state exciter in turn reduces electromagnetic interference (EMI) effects particularly in excimer lasers where high EMI is present due to high di/dt. The laser is focused on a thin copper sheet for generation of micro-hole and the SEM image of the generated micro hole shows the energy stability of the laser at high repetition rate operation. Nearly homogeneous, regular and well developed xenon chloride (XeCl) laser beam spot was achieved using the laser.

Photoluminescence characteristics of Ce and Eu activated MBPO5 (M = Sr, Ca) phosphors

In this paper we have reported the luminescence characterizations of rare earths Ce and Eu activated MBPO5 (M=Sr, Ca) phosphors synthesized by modified solid state reaction and studied for photoluminescence (PL) studies. The incorporation of Ce and Eu in 3+ oxidation state was ascertained from PL studies. The spectral characteristics have revealed that the excitation spectra of Eu2+ activated SrBPO5 phosphor shows the strong broad peak observed at 354nm (monitored at 422nm) near UV region and is favorable to solid-state lighting excitation. The orange–red (589 and 591nm) emission in Eu3+ activated CaBPO5 is due to 5D0–7F1 transition of Eu3+ and this is permitted only in cases of Cs, Cn, and Cnv symmetries observed at Eu3+ sites. All these are the features of the f↔f transition of the trivalent europium ion. PL properties of Ce3+ activated MBPO5 (M=Sr, Ca) revealed the broad band emission at 375nm.

Solid-state optical absorption from optimally tuned time-dependent range-separated hybrid density functional theory

We present a framework for obtaining reliable solid-state charge and optical excitations and spectra from optimally tuned range-separated hybrid density functional theory. The approach, which is fully couched within the formal framework of generalized Kohn-Sham theory, allows for the accurate prediction of exciton binding energies. We demonstrate our approach through first principles calculations of one- and two-particle excitations in pentacene, a molecular semiconducting crystal, where our work is in excellent agreement with experiments and prior computations. We further show that with one adjustable parameter, set to produce the known band gap, this method accurately predicts band structures and optical spectra of silicon and lithium fluoride, prototypical covalent and ionic solids. Our findings indicate that for a broad range of extended bulk systems, this method may provide a computationally inexpensive alternative to many-body perturbation theory, opening the door to studies of materials of increasing size and complexity.

Synthesis, structure and fluorescence studies of the lanthanide complexes with 4-fluorobenzoic acid

Tb (1) and Eu (2) complexes with 4-fluorobenzoic acid have been synthesized by hydrothermal method. The structures of them were established by X-ray crystallography, which revealed that complexes 1 and 2 are isostructural and crystallized into one infinite 1D chains by bidentate bridging carboxyl groups. There are four coordinated and one free H2O molecules around each Tb3+ or Eu3+ centers. But the complexes present excellent luminescence under ultraviolet excitation. The photoluminescent properties of the two complexes were investigated by the solid state excitation, the emission spectra and the luminescent decay. The complexes exhibited strong green and red luminescence in visible spectral region on the broad excitation of the ultraviolet ligand absorption, which indicates the antenna effect might have taken place effectively. The overall quantum yields of complexes 1 and 2 are 41% and 14%, respectively, and the sensitization efficiency of the ligand in complex 2 is estimated to be 82%.

Molecular and electronic structure of cyclic trinuclear gold(I) carbeniate complexes: insights for structure/luminescence/conductivity relationships.

An experimental and computational study of correlations between solid-state structure and optical/electronic properties of cyclotrimeric gold(I) carbeniates, [Au3(RN═COR')3] (R, R' = H, Me, (n)Bu, or (c)Pe), is reported. Synthesis and structural and photophysical characterization of novel complexes [Au3(MeN═CO(n)Bu)3], [Au3((n)BuN═COMe)3], [Au3((n)BuN═CO(n)Bu)3], and [Au3((c)PeN═COMe)3] are presented. Changes in R and R' lead to distinctive variations in solid-state stacking, luminescence spectra, and conductive properties. Solid-state emission and excitation spectra for each complex display a remarkable dependence on the solid-state packing of the cyclotrimers. The electronic structure of [Au3(RN═COR')3] was investigated via molecular and solid-state simulations. Calculations on [Au3(HN═COH)3] models indicate that the infinitely extended chain of eclipsed structures with equidistant Au--Au intertrimer aurophilic bonding can have lower band gaps, smaller Stokes shifts, and reduced reorganization energies (λ). The action of one cyclotrimer as a molecular nanowire is demonstrated via fabrication of an organic field effect transistor and shown to produce a p-type field effect. Hole transport for the same cyclotrimer-doped within a poly(9-vinylcarbazole) host-produced a colossal increase in current density from ∼1 to ∼1000 mA/cm(2). Computations and experiments thus delineate the complex relationships between solid-state morphologies, electronic structures, and optoelectronic properties of gold(I) carbeniates.

Homochiral Zinc(II) Coordination Compounds Based on In-Situ-Generated Chiral Amino Acid–Tetrazole Ligands: Circular Dichroism, Excitation Light-Induced Tunable Photoluminescence, and Energetic Performance

We employed two pairs of new in-situ-generated chiral amino acid-tetrazole ligands in constructing homochiral Zn(II) coordination compounds: [Zn(tzet)]n (1a for (S)-tzet and 1b for (R)-tzet, H2tzet = N-[2-(1H-tetrazol-5-yl)ethyl]tryptophan) and [Zn(tzep)(H2O)2]·H2O (2a for (S)-tzep and 2b for (R)-tzep, H2tzep = N-[2-(1H-tetrazol-5-yl)ethyl]proline), which were hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction. Structural analysis reveals that 1 features a 2D homochiral framework generated by both tetrazolate and carboxylate bridges in tzet(2-) ligands. The isolated structure of 2 is stabilized by extensive hydrogen bonds, which leads to formation of a supramolecular 2D architecture. The absolute configuration induced at the nitrogen atoms of 1 and 2 is strictly related to the neighboring chiral carbon atoms by hydrogen-bond interactions. To further investigate their chirality, the combined experimental and theoretical analyses of circular dichroism spectra reveal the absolute configurations and nature of the Cotton effects. Solid-state excitation and emission spectra for 1 and 2 at room temperature were investigated with relevant density of states calculation, and tunable photoluminescence emission of 1 under different excitation wavelengths was discussed. As nitrogen-rich tetrazolate compounds, 1 and 2 possess higher enthalpies of combustion and may serve as a new family of promising energetic materials.

Portable optical-resolution photoacoustic microscopy with a pulsed laser diode excitation

Optical-resolution photoacoustic microscopy (OR-PAM) has been significantly improved in terms of spatial resolution, detection sensitivity, imaging speed, and penetration depth. However, the popular producibility of OR-PAM system is still limited by the size and cost of solid-state laser excitation. Here, we developed a portable laser-diode-based OR-PAM (LD-OR-PAM) system using a pulsed semiconductor laser source, which was operated at 905 ± 15 nm with a pulse energy as low as 4.9 μJ. The measured lateral resolution has been improved to ∼1.5 μm from hundreds of microns. The compact and inexpensive natures of LD-OR-PAM would promote the potential clinical applications such as in dermatology.

Hydrothermal syntheses, crystal structures and physical properties of a new family of energetic coordination polymers with nitrogen-rich ligand N-[2-(1H-tetrazol-5-yl)ethyl]glycine

Hydrothermal reaction of N-(2-cyanoethyl)glycine and NaN3 with corresponding metal salts yielded three energetic coordination polymers: [Zn(tzeg)]n1 and [M(tzeg)(H2O)]n (M = Cd2+ for 2, Cu2+ for 3) (H2tzeg = N-[2-(1H-tetrazol-5-yl)ethyl]glycine), which were characterized by single-crystal X-ray diffraction. Nitrogen-rich tzeg2− ligand is a new in situ generated organic compound through [2 + 3] cycloaddition reaction of nitrile and azide, which adopts two different coordination modes in 1–3. Polymer 1 features an achiral 3D network built up by interweaving of left/right-handed helical channels. Isostructural 2 and 3 exhibit an achiral 2D network formed alternately by left/right-handed helical chains. As nitrogen-rich energetic materials, 1 and 3 possess higher enthalpies of combustion (ΔHc), which are −12.054 and −11.583 kJ g−1, respectively, than the classical energetic compounds 1,3,5-trinitro-1,3,5,-triazine (RDX, −9.6 kJ g−1) and 1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX, −9.44 to −9.88 kJ g−1). The solid-state excitation and emission spectra for 1–3 were investigated at room temperature, which reveals ligand-centered luminescent emissions in the intensity order of 2 > 1 > 3. Variable-temperature magnetic susceptibility data show that 3 displays a weak antiferromagnetic interaction mainly resulting from magnetic exchange coupling between Cu2+ ions through double tetrazolato bridges.

Luminescence in Li3Al2(PO4)3:Eu2+

A series of efficient Li₃ Al ₂ (PO₄)₃ :Eu(2+) novel phosphors were synthesized by the facile combustion method. The effects of dopant on the luminescence behavior of Li₃ Al ₂ (PO₄)₃ phosphor were also investigated. The phosphors were characterized by X-ray diffraction, field emission scanning electron microscope and photoluminescence techniques. The result shows that all samples can be excited efficiently by near-ultraviolet excitation under 310 nm. The emission was observed for Li₃ Al ₂ (PO₄)₃ :Eu(2+) phosphor at 425 nm, which corresponded to the d → f transition. The concentration quenching of Eu(2+) was observed in Li₃ Al ₂ (PO₄)₃ :Eu(2+) when the Eu concentration was at 0.5 mol%. The prepared powders exhibited intense blue emission at the 425 nm owing to the Eu(2+) ion by Hg-free excitation at 310 nm (i.e., solid-state lighting excitation). Consequently, the availability of such a phosphor will significantly help in the development of blue-emitting solid-state lighting applications.