Enhanced Photoluminescence from Organic Dyes Coupled to Periodic Array of Zirconium Nitride Nanoparticles

Noble metals, particularly gold, have been conventionally used for their suitable optical properties in the field of plasmonics. However, gold has a relatively low melting temperature, especially when nanosized, and the abundance of gold in the earth’s crust is low. These material-related limitations hinder the exploration of the use of plasmonics in several application areas. Transition metal nitrides are promising material alternatives because of their high mechanical and thermal stabilities, in addition to their acceptable plasmonic properties in the visible spectral region. Zirconium nitride (ZrN) is one such promising alternative owing to a higher carrier density than that of titanium nitride (TiN), which has been the most studied complementary material to gold. In this study, we have fabricated periodic arrays of ZrN nanoparticles and found that the ZrN array enhances the photoluminescence from an organic dye on the array; the photoluminescence intensity is increased by as much as 9.7× in the visible region. This result experimentally verifies that ZrN is useful as an alternative material to gold, to further develop plasmonics, and mitigate the conventional material-related limitations

Surface-Enhanced Infrared Absorption for the Periodic Array of Indium Tin Oxide and Gold Microdiscs: Effect of in-Plane Light Diffraction

Surface-enhanced infrared absorption (SEIRA) is an important phenomenon to achieve nondestructive, simplified, and <i>in situ</i> high-sensitivity infrared (IR) sensors. Conventionally, metal structures with nanogaps are employed to realize the high sensitivity owing to the extremely strong field enhancement in the hot spot. Although a library of surface modifiers has been developed, the manipulation of nanogaps and immobilization of target molecules in the hot spot are still complicated. In addition, target molecules immobilized at the positions other than the hot spot have relatively low sensitivity. A periodic array with pitch comparable to the wavelength of interest is an alternative structure in which the coupling of the plasmonic mode to in-plane light diffraction provides the hybrid mode accompanied by an enhanced electric field. Although the field enhancement by the hybrid mode depends on matching between localized surface plasmon resonance (LSPR) and diffraction, the contribution of the matching to SEIRA enhancement has never been clarified. In this work, we fabricated periodic arrays of indium tin oxide (ITO) and Au microdiscs (pitch: 3 μm, diameter: 2 μm) to analyze the contribution of the hybrid mode through varied LSPR and diffraction conditions. As a result, the ITO and Au arrays demonstrate a similar plasmonic–photonic hybrid mode in the mid-IR region despite the different excitation frequency of LSPR. To estimate the effect of the hybrid mode on SEIRA enhancement, the incident angular profiles of IR spectra of the polymer layer on the ITO and Au arrays were measured. The SEIRA enhancement factors for ITO and Au arrays are comparable in the IR measurement region (2200–1400 cm^–1). Our results verify that the plasmonic–photonic hybrid mode is very efficient for SEIRA enhancement, and the periodic array of microdiscs is very suitable for this application

Wavelength-Tunable Spasing in the Visible

A SPASER, short for surface plasmon amplification by stimulated emission of radiation, is key to accessing coherent optical fields at the nanoscale. Nevertheless, the realization of a SPASER in the visible range still remains a great challenge because of strong dissipative losses. Here, we demonstrate that room-temperature SPASER emission can be achieved by amplifying longitudinal surface plasmon modes supported in gold nanorods as plasmon nanocavities and utilizing laser dyes to supply optical gain for compensation of plasmon losses. By choosing a particular organic dye and adjusting the doping level, the resonant wavelength of the SPASER emission can be tuned from 562 to 627 nm with a spectral line width narrowed down to 5–11 nm. This work provides a versatile route toward SPASERs at extended wavelength regimes

Plasmonic–Photonic Hybrid Modes Excited on a Titanium Nitride Nanoparticle Array in the Visible Region

Conventionally used plasmonic materials generally have low thermal stability, low chemical durability (except gold), and are incompatible with complementary metal–oxide semiconductor processes. However, titanium nitride (TiN), an emerging plasmonic material, possesses gold-like optical properties, but displays relatively large ohmic losses. We fabricated a periodic array of TiN nanoparticles to effectively reduce these losses by coupling the localized surface plasmon resonance with light diffraction. The height of the nanoparticle and the periodicity of the array were designed to match the excitation conditions of both the localized surface plasmon resonance and light diffraction. As a result, the array supported a plasmonic–photonic hybrid mode in the visible region. For the loss mitigation effect to be assessed, photoluminescence (PL) from the light emitting layer on the array was measured. The PL intensity was larger than that from the same layer on a TiN thin film, demonstrating reduced loss. The angular and spectral profiles of the PL could be controlled by the hybrid mode. Our results thus pave the way toward plasmonic devices that can be fabricated using traditional complementary metal–oxide semiconductor processes

First Synthesis of EuS Nanoparticle Thin Film with a Wide Energy Gap and Giant Magneto-Optical Efficiency on a Glass Electrode

Novel magneto-optical thin films composed of europium sulfide (EuS) nanoparticles on a glass electrode exhibit large magneto-optical efficiency and a wide energy gap. EuS nanoparticle thin films are prepared by the electrochemical reduction of a single-source precursor, a Eu­(III) dithiocarbamate complex (tetraphenylphosphonum tetrakis­(diethyldithiocarbamate) europium­(III)). The EuS nanoparticle thin films were prepared on indium–tin oxide (ITO)-coated glass electrodes and characterized by electrochemical analysis, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, laser scanning microscopy, and absorption spectroscopy. Faraday rotation spectra for estimation of the magneto-optical efficiency have clear positive and negative peaks, which are attributed to the 4f–5d transitions of the EuS thin films. The positive and negative peaks of the Faraday rotation spectrum are 525 and 680 nm, which are directly related to the energy gap of the EuS nanoparticle thin film (2.4 eV). That spectrum indicates that the EuS nanoparticle thin films are blue shifted in comparison with 7 nm diameter EuS nanoparticles (2.2 eV). The Verdet constant of the thin film was 11 mdeg/cm Oe at 525 nm, which is approximately 10 times larger than that of previously reported EuS nanoparticles

AgCu₃V₄O₁₂: a Novel Perovskite Containing Mixed-Valence Silver ions

A novel silver-containing perovskite, AgCu₃V₄O₁₂, was synthesized under high-pressure and high-temperature conditions. It crystallizes in an A-site-ordered perovskite structure (space group <i>Im</i>3̅), in which silver ions occupy the 12-coordinated A sites forming regular icosahedra, and exhibits metallic behavior. Bond-valence-sum calculations and X-ray photoemission spectroscopy reveal that Ag ions are present in the mixed-valence state, most likely attributable to the coexistence of Ag⁺ and Ag³⁺, unlike the case of well-known perovskite-type AgNbO₃ and AgTaO₃ containing only Ag⁺ ions. We discuss metallic conduction in relation to electronic structure calculations

AgCu₃V₄O₁₂: a Novel Perovskite Containing Mixed-Valence Silver ions

A novel silver-containing perovskite, AgCu₃V₄O₁₂, was synthesized under high-pressure and high-temperature conditions. It crystallizes in an A-site-ordered perovskite structure (space group <i>Im</i>3̅), in which silver ions occupy the 12-coordinated A sites forming regular icosahedra, and exhibits metallic behavior. Bond-valence-sum calculations and X-ray photoemission spectroscopy reveal that Ag ions are present in the mixed-valence state, most likely attributable to the coexistence of Ag⁺ and Ag³⁺, unlike the case of well-known perovskite-type AgNbO₃ and AgTaO₃ containing only Ag⁺ ions. We discuss metallic conduction in relation to electronic structure calculations

Effective Optical Faraday Rotations of Semiconductor EuS Nanocrystals with Paramagnetic Transition-Metal Ions

Novel EuS nanocrystals containing paramagnetic Mn­(II), Co­(II), or Fe­(II) ions have been reported as advanced semiconductor materials with effective optical rotation under a magnetic field, Faraday rotation. EuS nanocrystals with transition-metal ions, EuS:M nanocrystals, were prepared by the reduction of the Eu­(III) dithiocarbamate complex tetraphenylphosphonium tetrakis­(diethyldithiocarbamate)­europium­(III) with transition-metal complexes at 300 °C. The EuS:M nanocrystals thus prepared were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), inductively coupled plasma atomic emission spectroanalysis (ICP-AES), and a superconducting quantum interference device (SQUID) magnetometer. Enhanced Faraday rotations of the EuS:M nanocrystals were observed around 550 nm, and their enhanced spin polarization was estimated using electron paramagnetic resonance (EPR) measurements. In this report, the magneto-optical relationship between the Faraday rotation efficiency and spin polarization is discussed

<i>A</i>‑Site-Ordered Perovskite MnCu₃V₄O₁₂ with a 12-Coordinated Manganese(II)

A novel cubic perovskite MnCu₃V₄O₁₂ has been synthesized at a high pressure and high temperature of 12 GPa and 1373 K. This compound crystallizes in the <i>A</i>-site-ordered perovskite structure (space group <i>Im</i>3̅) with lattice constant <i>a</i> = 7.26684(10) Å at room temperature. The most notable feature of this compound lies in the fact that the Mn²⁺ ion is surrounded by 12 equidistant oxide ions to form a regular icosahedron; the situation of Mn²⁺ is unprecedented for the crystal chemistry of an oxide. An anomalously large atomic displacement parameter <i>U</i>_iso= 0.0222(8) Ų is found for Mn²⁺ at room temperature, indicating that the thermal oscillation of the small Mn²⁺ ion in a large icosahedron is fairly active. Magnetic susceptibility and electric resistivity measurements reveal that 3d electrons of Mn²⁺ ions are mainly localized, while 3d electrons in Cu²⁺ and V⁴⁺ ions are delocalized and contribute to the metallic conduction

Enhancement of Optical Faraday Effect of Nonanuclear Tb(III) Complexes

The effective magneto–optical properties of novel nonanuclear Tb­(III) complexes with Tb–O lattice (specifically, [Tb₉(sal-R)₁₆(μ-OH)₁₀]⁺NO₃^–, where sal-R = alkyl salicylate (R = −CH₃ (Me), −C₂H₅ (Et), −C₃H₇ (Pr), or −C₄H₉ (Bu)) are reported. The geometrical structures of these nonanuclear Tb­(III) complexes were characterized using X-ray single-crystal analysis and shape-measure calculation. Optical Faraday rotation was observed in nonanuclear Tb­(III) complexes in the visible region. The Verdet constant per Tb­(III) ion of the Tb₉(sal-Me) complex is 150 times larger than that of general Tb­(III) oxide glass. To understand their large Faraday rotation, electron paramagnetic resonance measurements of Gd­(III) complexes were carried out. In this Report, the magneto–optical relation to the coordination geometry of Tb ions is discussed