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The total radiation pattern is evaluated for nanoantenna phosphors comprising a periodic array of TiO2 particles on the phosphor plate. The antenna redistributes the spatial radiation pattern while the total emission intensity remains unchanged.

Zirconia is transparent from near-ultraviolet through the entire visible region, and here we utilize the periodic arrays of zirconia nanoparticle to excite electric and magnetic SLRs in the visible.

The stable magnetic structure of EuZrO3 solid solution is tuned with the change of lattice volume. In particular, the ferromagnetic state is stabilized by the increase in lattice volume, which experimentally verifies the theoretical prediction.

To date, the plasmonic nanostructure utilized for magneto-optical (MO) enhancement has been limited to noble metals with resulted enhancement in the green-red part of visible spectrum. In this study, we fabricated a diffractive hexagonal array composed of Al nanoparticles (NPs) with a thin 7.5 nm ferromagnetic film and pushed the enhanced Faraday rotation (FR) into the blue to green range of the visible light. The freedom and ability to control the working spectral region in the whole visible range from 400 to 800 nm were also demonstrated by changing the lattice constant and the dielectric environment of plasmonic nanostructures. Particularly, in the blue range we obtained the maximum FR 0.57° at 410 nm with a broad boosting region around 0.5° from 400 to 500 nm. Moreover, the largest FR 1.66° was shown at 638 nm by tuning the dielectric environment into a higher refractive index medium. The results of our investigation demonstrate the potential of Al-based magnetoplasmonic effect and offer opportunities to push the MO spectral response out of visible range into the ultraviolet-blue range.

8 pags., 5 figs., 1 tab., Various optical phenomena can be induced in periodic arrays of nanoparticles by the radiative coupling of the local dipoles in each particle. Probably the most impressive example is bound states in the continuum (BICs), which are electromagnetic modes with a dispersion inside the light cone but infinite lifetime, that is, modes that cannot leak to the continuum. Symmetry-protected BICs appear at highly symmetric points in the dispersion of periodic systems. Although the addition of nonequivalent lattice points in a unit cell is an easy and straightforward way of tuning the symmetry, BICs in such particle lattice, that is, non-Bravais lattice, are less explored among periodic systems. Starting from a periodic square lattice of Si nanodisks, three non-Bravais lattices are prepared by detuning size and position of the second disk in the unit cell. Diffraction-induced coupling excites magnetic/electric dipoles in each nanodisk, producing two surface lattice resonances at the Γ point with a band gap in between. The high/low energy branch becomes a BIC for the size/position-detuned array, respectively, while both branches are bright (or leaky) when both size and position are detuned simultaneously. The unexplored role of the interplay between magnetic and electric dipoles in dielectric nanoparticles in connection with the change of BIC to bright character in the detuned arrays is discussed with the aid of a coupled electric and magnetic dipole model. This study gives a simple way of tuning BICs at telecom wavelengths in non-Bravais lattices, including both plasmonic and dielectric systems, thus scalable to a wide range of frequencies., This work was partly supported by the Nanotechnology Hub, Kyoto University (JPMXP09 F19NMC042) and Kitakyusyu FAIS in the “Nanotechnol-ogy Platform Project,” sponsored by MEXT, Japan. The authors gratefully acknowledge the financial support from Kakenhi (21H04619, 22H01776),JSPS Bilateral Program (JPJSBP120219920), and the Netherlands Organisation for Scientific Research (NWO) through Gravitation grant “ResearchCentre for Integrated Nanophotonics” and Innovational Research Activities Scheme (Vici project SCOPE no. 680-47-628). J.A.S.-G. and D.R.A. ac-knowledge support from the Spanish Ministerio de Ciencia e Innovaciónthrough grants MELODIA PGC2018-095777-B-C21 and FPU Ph.D. Fellow-ship FPU15/03566 (MCIU/AEI/FEDER, UE)

A novel Ruddlesden–Popper-related compound, Gd3Ba2Fe4O12, was discovered and its crystal structure was determinedviasingle-crystal X-ray diffraction. The structure has an ordered structure of octahedra and pyramids along thecaxis. Gd3Ba2Fe4O12belongs to the tetragonal systemP42/ncm, witha= 5.59040 (10) Å andc= 35.1899 (10) Å. TheA-site ions in the Ruddlesden–Popper structure,i.e.Gd3+and Ba2+, exhibit an ordering along thecaxis. The perfect oxygen deficiency is accommodated at the GdO layers in the proper Ruddlesden–Popper structure. Using the bond-valence-sum method, the Fe ions in the FeO6octahedra and FeO5pyramids represent valence states of +3 and +2.5, respectively, demonstrating a two-dimensional charge disproportionation. The corner-sharing FeO6octahedra and FeO5pyramids are tilted in opposite directions, with the neighbours around one axis of the simple perovskite configuration, which, using Glazer's notation, can be represented asa−b0c0/b0a−c0. In the perovskite blocks, the facing FeO5pyramids across the Gd layer rotate in the same sense, which is a unique rotation feature related to oxygen deficiency.

We have examined the effect of synthesis conditions on α-Ga2O3 film, one of the ultra-wide bandgap semiconductors, on c-plane sapphire substrate via mist CVD process. The resultant film is dominantly composed of α-Ga2O3 phase, but a small amount of κ-Ga2O3 phase coexists when the growth temperature is higher. The source solution containing higher concentration of HCl expands the range of temperatures at which single-phase α-Ga2O3 is grown and suppresses the inclusion of κ-Ga2O3 at higher growth temperatures. Moreover, the growth with higher concentration of HCl up to 0.66 mol l−1 increases the growth rate and improves the surface roughness. Thus, HCl has a crucial role in the selective growth of α-Ga2O3 and the quality of the film. Also, some pits are observed at the surface of α-Ga2O3 and κ-Ga2O3 is precipitated inside the pit defect when the concentration of HCl is low and the growth temperature is high.

We demonstrated selective-area growth of r-SnO2 on a SiO2-masked r-TiO2 (110) substrate. The heteroepitaxy on a window started with a Volmer–Weber mode to grow islands with {100}-, {11̄0}-, and {011}-faceted sidewalls, whose growth shapes were consistent with the rutile structure’s equilibrium shape. The islands coalesced each other to make a flat (110) top surface on a striped window, and lateral overgrowth started after the complete coverage of the window. Cross-sectional transmission-electron-microscopy observation of the stripe revealed that misfit dislocations propagated perpendicularly to the facet planes by the image force effect and that the dislocation density reduced substantially in the wing regions.

Rare-earth-doped up-converters with Yb3+ as a sensitizer show a high internal conversion efficiency under the excitation at wavelength λ = 980 nm. For the solar cell applications of up-converters, ...

High optical absorptivity or a large absorption cross-section is necessary to fully utilize the irradiation of light for photothermal heating. Recently, titanium nitride (TiN) nanostructures have been demonstrated to be robust optical absorbers in the optical range owing to their nonradiative decay processes enhanced by broad plasmon resonances. Because the photothermally generated heat dissipates to the surroundings, suppressing heat transfer from TiN nanostructures is crucial for maximizing the photothermal temperature increase. In the current work, compared to the planar TiN film, high-aspect-ratio TiN nanostructures with subwavelength periodicities have been demonstrated to enhance the photothermal temperature increase by a 100-fold using nanotube samples. The reason is attributed to the extremely anisotropic effective thermal conductivities. Our work has revealed that high-aspect-ratio TiN nanostructures are effective in improving photothermal heating, and they can be used in various applications, such as solar heating, chemical reactions, and microfluidics.

A novel A-site deficient quadruple perovskite (Pv) oxide, CuNb2O6, has been successfully obtained by a combination of high-pressure synthesis techniques and topochemical structural transformation. Post-annealing of high-pressure-synthesized Pv-CuNbO3 above 470 K at ambient pressure leads to the formation of Pv-CuNb2O6 due to the topochemical deinsertion of half of the copper ions, which is accompanied by changes in the valence state and coordination environment of the remaining copper ions from triangular coordinated Cu+ into square-planar coordinated Cu2+. A combined structural analysis using synchrotron X-ray and electron diffraction and optical second harmonic generation shows that Pv-CuNb2O6 crystallizes into a non-centrosymmetric cubic structure with the space group I23. Magnetic characterization reveals an antiferromagnetic order below 12 K. We find that this compound exhibits a colossal dielectric constant up to the order of 104. The topochemical cation deinsertion is also found in another high-pressure-synthesized Pv-CuTaO3, which produces cubic Pm Pv-CuTa2O6. The present results are expected to provide a guideline for developing new functional materials.

Manipulating the plasmonic properties of metal nanocrystals (NCs) is key to many modern nanophotonic technologies. Here, the strategy of combining Ag+ ↔ Li+ ion exchange and controlled thermal crystallization is proposed as an effective means to prepare transparent nano-glass composites (nano-GCs) embedded with hybrid Ag–metal and γ-Ga2O3:Ni2+ NCs. Only by this method can a large amount of Ag–metal NCs (1.1 mol%) be implanted and well dispersed in the glass matrix without sacrificing their optical transmission properties. The broadband near-infrared (NIR) emission of Ni2+ is enhanced by 100% in the presence of Ag–metal NCs, which is otherwise impossible by raising the Ni2+ concentration due to the limited solubility and intrinsically weak absorption of Ni2+ in nano-GCs. The mechanisms responsible for the enhanced NIR emissions of Ni2+ are comprehensively discussed in the context of both experimental investigations and theoretical simulations. The present study not only provides a promising robust nano-GC-based gain medium for integrated optics but also offers some insights into the plasmonic metal-enhanced photoluminescence for enriched optical functions.

Optical performance of surface plasmon resonance critically depends on the material loss of the metals, which deteriorates the quality factor of the resonance. In addition to intrinsic loss that co...

Layered double hydroxides (LDHs) are a class of materials that act as adsorbents of anionic molecules because of their positively charged layered structure. One appealing application is optical sen...

Mesoporous silica features open and accessible pores that can intake substances from the outside. The combination of mesoporous silica with plasmonic nanostructures represents an interesting platform for an optical sensor based on the dependence of plasmonic modes on the refractive index of the medium in which metallic nanoparticles are embedded. However, so far only a limited number of plasmonic nanostructures are combined with mesoporous silica, including random dispersion of metallic nanoparticles and flat metallic thin films. In this study, we make a mesoporous silica layer on an aluminum nanocylinder array. Such plasmonic arrangements support both localized surface plasmon resonances (LSPRs) and extended modes which are the result of the hybridization of LSPRs and photonic modes extending into the mesoporous layer. We investigate in situ optical reflectance of this system under controlled pressure of isopropanol vapor. Upon exposure, the capillary condensation in the mesopores results in a gradual spectral shift of the reflectance. Our analysis demonstrates that such shifts depend largely on the nature of the modes; that is, the extended modes show larger shifts compared to localized ones. Our materials represent a useful platform for the field of environmental sensing

LuFe2O4 has been the most extensively studied among a series of RFe2O4 (R = Sc, Y, In and Dy to Lu) compounds, which possess both dielectric and magnetic orderings originating in equal numbers of Fe2+ and Fe3+ ions in a triangular lattice. We have prepared LuFe2O4 thin films epitaxially grown on a (111)-oriented YSZ (yttria-stabilized zirconia) substrate via a pulsed laser deposition method and found that the resultant thin film comprises a curious self-assembled interface structure. Our structural analysis at an atomic level by using high-angle annular dark-field scanning transmission electron microscopy and energy dispersive X-ray spectrometry reveals that very thin layers of LuFe2O4 lacking Fe–O layers, corresponding to the hexagonal LuFeO3 and Lu2Fe3O7 compositions, are formed at the interface between the c-axis oriented LuFe2O4 thin film and YSZ substrate with a Lu-rich region just on the surface of the substrate. Such an interfacial structure leads to an exchange bias effect peculiarly observed for an interface formed by different types of magnetic materials. The LuFe2O4 thin film itself shows spin glass transition similar to bulk LuFe2O4 with an off-stoichiometric oxygen ratio. Also, a change in electronic transport behavior between Arrhenius-type and variable range hopping schemes has been observed in the temperature dependence of electrical resistivity around the three-dimensional charge ordering temperature.

TmFe2O4, a member of the RFe2O4 family (R = Sc, Y, In, and Dy to Lu), shows both charge and spin orderings and exhibits interesting dielectric and magnetic phenomena. We have grown epitaxial thin films of TmFe2O4 on (111)-oriented YSZ (yttria-stabilized zirconia) substrates via the pulsed laser deposition method and explored their interfacial structure at the atomic level and magnetic properties. The out-of-plane X-ray diffraction and reciprocal space mapping results reveal that the TmFe2O4 thin film grows with the c-axis perpendicular to the (111) surface of the YSZ substrate. The structure of the TmFe2O4/YSZ interface was investigated by using scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). Interestingly, the hexagonal TmFeO3−δ phase has been found at the interface between the TmFe2O4 thin film and the YSZ substrate with the Tm3+-rich region at the upper side of the substrate. We suggest the possible growth mechanism based on the structural analysis. TmFe2O4 itself exhibits a spin or cluster glass transition, as verified by the fact that the external magnetic field dependence of irreversible transition temperature is described well in terms of the de Almeida–Thouless line and that the aging-memory effect is clearly observed. Furthermore, the field-cooled hysteresis loops and training effect clearly demonstrate the presence of the intrinsic exchange bias at 100 K due to the unique magnetic structure of the interface.

Magneto-optical glass with a large Verdet constant has been developed. The glass was utilized as a Faraday rotator in the optical isolator, and the downsizing of the isolator was achieved.

We have grown single crystals of RFe2O4−δ (R = Y, Tm, Yb), proposed to be electronic ferroelectrics, by using the floating-zone melting technique under rather moderate conditions. For the crystal g...

High-power white-light-emitting diodes (WLEDs) comprising binderless bulk phosphors and ultraviolet (UV) LED chips as next-generation illumination sources were intensively studied. The main challen...

The combination of metasurface with optical emitters provides a unique opportunity to control the emission. The metasurface effect strongly depends on the spectral overlap between the internal electronic transitions of the emitter and the optical resonances of the metasurface. Elaborate design of the metasurface could realize the resonances at both absorption and emission wavelengths of the emitter, but it usually leads to complexity in fabrication. In this work, we propose a very simple strategy to obtain the resonances at both wavelengths by sandwiching the emitter layer with a pair of metasurfaces designed for absorption and emission, respectively. For this purpose, we use a sticker of Al metasurface, which is the array of Al nanoparticles embedded in a flexible polymer film that can be stuck on any clean surfaces. The metasurface stack is prepared by simply placing the sticker, resonating at the emission wavelength, on the emitter layer deposited on the TiO₂ metasurface resonating at the absorption wavelength. The overall enhancement achieved for the stack of the metasurfaces can be understood roughly as the multiplication of contributions from the respective metasurfaces. Employing a sticker provides an easy-to-make way of constructing a stack of metasurfaces, which increases the degree of freedom in designing the metasurface-coupled emitters., 貼るだけで3次元ナノアンテナを作製 --サンドイッチでもっと明るく--. 京都大学プレスリリース. 2021-05-10.

International audience; A single metallic nanodisk is the simplest plasmonic nanostructure, but it is robust enough to generate a Fano resonance in the forward and backward scattering spectra by the increment of nanodisk height in the symmetric and asymmetric dielectric environment. Thanks to the phase retardation effect, the non-uniform distribution of electric field along the height of aluminum (Al) nanodisk generates the out-of-plane higher-order modes, which interfere with the dipolar mode and subsequently result in the Fano-lineshape scattering spectra. Meanwhile, the symmetry-breaking effect by the dielectric substrate and the increment of refractive index of the symmetric dielectric environment further accelerate the phase retardation effect and contribute to the appearance of out-of-plane modes. The experimental results on the periodic Al nanodisk arrays with different heights confirm the retardation-induced higher modes in the asymmetric and symmetric environment. The appearance of higher modes and blueshifted main dips in the transmission spectra prove the dominant role of out-of-plane higher modes on the plasmonic resonances of the taller Al nanodisk.

A novel Ruddlesden-Popper-related compound, Gd

TmFe

Upconversion photoluminescence (UCPL) of rare-earth ions has attracted much attention due to its potential application in cell labeling, anti-fake printing, display, solar cell and so forth. In spite of high internal quantum yield, they suffer from very low external quantum yield due to poor absorption cross-section of rare-earth ions. In the present work, to increase the absorption by rare earth ions, we place the emitter layer on a diffractive array of Al nanocylinders. The array is designed to trap the near infrared light in the emitter layer via excitation of the plasmonic-photonic hybrid mode, a collective resonance of localized surface plasmons in nanocylinders via diffractive coupling. The trapped near-infrared light is absorbed by the emitter, and consequently the intensity of UCPL increases. In sharp contrast to the pure localized surface plasmons which are bound to the surface, the hybridization with diffraction allows the mode to extend into the layer, and the enhancement up to 9 times is achieved for the layer with 5.7 µm thick. This result explicitly demonstrates that coupling the excitation light to plasmonic-photonic hybrid modes is a sensible strategy to enhance UCPL from a thick layer.

Coupling layers of light emitters to arrays of plasmonic particles provides an opportunity to tailor the photoluminescence, both spectrally and spatially, and opens new venues for the design of phosphors in solid-state-lighting applications. While a significant enhancement of the photoluminescence for certain frequencies and in defined directions has been reported and described in terms of pump enhancement and emission outcoupling, the effect of optical absorption by metals on the conversion efficiency and total photoluminescence intensity is less well studied. Here, we investigate the optical absorption for emitter layers deposited on diffractive arrays of silver and titanium dioxide using an integrating sphere. The results show that absorption at the excitation wavelengths of the emitter has a critical impact on the conversion efficiency, while the absorption at luminescence wavelengths does not modify significantly the total radiation intensity. The evaluation technique used in this manuscript to quantify the optical absorption by the array, leads to a working recipe to design resonant systems that can be exploited in solid-state-lighting applications.

International audience; We report a perovskite oxide with a new type of polar structure, CuNbO3, thanks to the use of high-pressure and high-temperature synthesis. The perovskite-type CuNbO3 was previously obtained under high-pressure and high-temperature conditions, but its crystal structure has not been solved yet. Our structural analysis reveals that CuNbO3 perovskite crystallizes in a polar monoclinic space group (Pc) with a root 2 a(pc) x root 2 a(pc ) x 2a(pc) unit cell (a(pc) being the pseudo-cubic lattice parameter), which VT, is one maximal nonisomorphic subgroup of the polar rhombohedral space group, R3c. This compound exhibits a remarkable "noncollinear ferrielectric" structure due to parallel displacements of Cu+ and antiparallel displacements of Nb5+ along different axes, representing a new type of polar phase in the perovskite structure. We also observe that the noncollinear ferrielectric Pc s tructure transforms around 470 K into the collinear ferroelectric R3c structure that features parallel displacements of Cu+ and Nb5+ in the same direction. The present work extends the accessible composition range of the perovskite niobate series and demonstrates the role of A-O covalency in determining their crystal structures.

Sm3+-doped aluminoborate glasses containing Ag nanoparticles have been synthesized via a melt-quenching technique. After heat treatment, the surface plasmon resonance (SPR) absorption peak of Ag nanoparticles appears approximately at the wavelength λ = 425 nm. With the precipitation of the Ag nanoparticles, the intensities of visible (λ = 600 nm) and near-infrared (λ = 950 nm) photoluminescence are enhanced under excitation at λ = 400 nm up to 39.8% and 25% that of the as-made glass, respectively. Moreover, the excitation of Sm3+ at λ = 473 nm for the sample heat-treated at 500 °C shows higher enhancement in near-infrared photoluminescence by 55.5% (λ = 950 nm). This enhancement is attributable to the intensified localized electromagnetic field accompanied by the excitation of SPR. The presence of Ag nanoparticles assists the conversion of UV light into visible and near-infrared light, which can induce a photoelectric effect for Si and other semiconductors used in solar cells.

Hybrid improper ferroelectricity, which utilizes nonpolar but ubiquitous rotational/tilting distortions to create polarization, offers an attractive route to the discovery of new ferroelectric and multiferroic materials because its activity derives from geometric rather than electronic origins. Design approaches blending group theory and first principles can be utilized to explore the crystal symmetries of ferroelectric ground states, but in general, they do not make accurate predictions for some important parameters of ferroelectrics, such as Curie temperature (TC). Here, we establish a predictive and quantitative relationship between TC and the Goldschmidt tolerance factor, t, by employing n = 2 Ruddlesden–Popper (RP) A3B2O7 as a prototypical example of hybrid improper ferroelectrics. The focus is placed on an RP system, (Sr1–xCax)3Sn2O7 (x = 0, 0.1, and 0.2), which allows for the investigation of the purely geometric (ionic size) effect on ferroelectric transitions, due to the absence of the second-ord...