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Herein, 5,5′‐bis(4‐biphenylyl)‐2,2′‐bithiophene (BP2T or PPTTPP) nanocrystals are prepared via a modified miniemulsion technique. X‐ray diffraction and selected area electron diffraction analyses reveal that the BP2T molecules stand almost upright against the crystal basal plane. With decreasing nanocrystal size, the peak energies of photoluminescence (PL) spectra are blue‐shifted in the photon energy range from the bulk crystal to the monomer state. Energy‐wavevector dispersion plots reproduced using the data of size‐dependent PL spectra indicate that the size dependence of optical properties cannot be explained by the conventional quantum confinement effect used in inorganic nanocrystals. The micro‐PL and time‐resolved PL measurements of the BP2T nanocrystals reveal that the size‐dependent optical properties can be attributed to a combined effect based on the surface effects as well as lattice softening, and quantum effects involving specific surface area‐dependent site shift effect and exciton confinement. Moreover, amplified spontaneous emission is observed from the nanocrystals ≈600–1000 nm in size, which is smaller than the size previously reported for organic systems.

Micro-ring structures with methylammonium lead bromide (CH3NH3PbBr3)/poly(ethylene oxide) (PEO) composites are fabricated by using a microcapillary as a template. By the fast-drying process, the CH3NH3PbBr3/PEO composite films with a high PEO concentration are deposited to homogeneously cover the inner surface of the microcapillaries. Under optical pumping, whispering gallery mode lasing is observed from the inner circumference of microcapillaries, which works as a micro-ring cavity. With a reduction in ϕ, the mode number and lasing threshold fluence decrease, suggesting that the stimulated emission is enhanced based on cavity quantum electrodynamics in the CH3NH3PbBr3/PEO composite films uniformly covering the inside of microcavities.

Organic single-crystal self-cavities are prepared by solution growth of p-sexiphenyl (p-6P). Based on Fabry-Pérot feedback inside a quasi-lozenge-shaped platelet crystal, edge-emitting laser is obtained under optical pumping. The multimode lasing band appears at the 0-1 or 0-2 vibronic progressions depending on the excitation conditions which affect the self-absorption effect. Cavity-size dependence of amplified spontaneous emission (ASE) is investigated with laser-etched single crystals of p-6P. As the cavity length of square-shaped crystal is reduced from 100 to 10 μm, ASE threshold fluence is decreased probably due to size-dependent light confinement in the crystal cavity.

Herein we experimentally study magnetic multilayer metamaterials with broken translational symmetry. Epitaxially-grown iron-gold (Fe-Au) multilayers modulated using Fibonacci sequence—referred to as magnetic inverse Fibonacci-modulated multilayers (IFMs)—are prepared using ultra-high-vacuum vapor deposition. Experimental results of in-situ reflection high-energy electron diffraction, magnetization curves, and ferromagnetic resonance demonstrate that the epitaxially-grown Fe-Au IFMs have quasi-isotropic magnetization, in contrast to the in-plane magnetization easy axis in the periodic multilayers.

Strong exciton-photon coupling has been observed in a highly oriented organic single crystal microcavity. This microcavity consists of a thiophene/phenylene co-oligomer (TPCO) single crystal laminated on a high-reflection distributed Bragg reflector. In the TPCO crystal, molecular transition dipole was strongly polarized along a certain horizontal directions with respect to the main crystal plane. This dipole polarization causes significantly large anisotropies in the exciton transition and optical constants. Especially the anisotropic exciton transition was found to provide the strong enhancement in the coupling with the cavity mode, which was demonstrated by a Rabi splitting energy as large as ∼100 meV even in the "half-vertical cavity surface emitting lasing" microcavity structure. [ABSTRACT FROM AUTHOR]

A simple "cast-capping" method is adopted to prepare single-crystal perovskites of methyl ammonium lead bromide (CH3NH3PbBr3). By capping a CH3NH3PbBr3 solution casted on one substrate with another substrate such as glass, mica, and distributed Bragg reflector (DBR), the slow evaporation of solvent enables large-size cubic crystals to grow between the two substrates. Under optical pumping, edge-emitting lasing is observed based on Fabry-Pérot resonation between parallel side facets of a strip-shaped crystal typically with a lateral cavity length of a few tens of lm. On the other hand, vertical-cavity surface-emitting lasing (VCSEL) is obtained from a planar crystal grown between two DBRs with a cavity thickness of a few lm. Simultaneous detection of those edge- and surface-emissions reveals that the threshold excitation fluence of VCSEL is higher than that of the edge-emitting lasing due to thickness gradient in the planar crystal. [ABSTRACT FROM AUTHOR]

Vertical-cavity organic lasers are fabricated with melt-grown crystals of a cyano-substituted thiophene-phenylene co-oligomer. Due to lying molecular orientation, surface-emitting lasing is achieved even in the half-cavity crystal grown on a distributed Bragg reflector (DBR) under optical pumping at room temperature. Anticrossing splits in angle-resolved photoluminescence spectra suggest the formation of exciton-polaritons between the cavity photons and the confined Frenkel excitons. By constructing the full-cavity structure sandwiched between the top and bottom DBRs, the lasing threshold is reduced to one order, which is as low as that of the half cavity. Around the threshold, the time profile of the full-cavity emission is collapsed to a pulsed shape accompanied by a finite turn-on delay. We discuss these observed characteristics in terms of a polariton contribution to the conventional photon lasing. [ABSTRACT FROM AUTHOR]

We have achieved to observe vertical cavity surface emitting lasing (VCSEL) from an optically pumped organic single crystal. A vapor-grown thiophene/phenylene co-oligomer (TPCO) single crystal with in-plane polarization component was used as the gain medium in an optical microcavity. Since the top and bottom surfaces of the TPCO crystal serve as high-quality resonators, well-defined Fabry-Pérot resonance is achieved. Furthermore, by using high reflectivity distributed Bragg reflector as the cavity resonator, we have observed lasing emissions with a line width of 0.9 nm and a threshold of ~3 mJ/cm². The VCSEL-type optical feedback configuration demonstrated in this study is expected to be one of the available means to realize the electrically pumped organic laser device. [ABSTRACT FROM AUTHOR]

We report on the fabrication and characterization of low-dimensional single crystals of hexyl-substituted thiophene/phenylene co-oligomer, 5,5′-Bis(4′-n-hexyl-4-biphenylyl)-2,2′-bithiophene (BP2T-Hx). X-ray diffraction measurements of the single crystals reveal that BP2T-Hx molecules crystallize in a monoclinic form. Temperature dependence of photoluminescence (PL) decay profiles of the BP2T-Hx crystal results in a PL quantum yield of 39%. Above an excitation threshold of 262 μJ cm−2, amplified spontaneous emission is obtained in a disk-shaped crystal of BP2T-Hx based on the self-waveguiding effect of fluorescence light. Owing to two-dimensional light confinement supported by high group refractive index of 3.4 and high quality factor of 3800, the one-dimensional needle crystal with a cavity length of 70 μm realizes a Fabry–Pérot lasing at a threshold of 186 μJ cm−2 which is 29% lower than that of the disk-shaped crystal. [ABSTRACT FROM AUTHOR]

Organic light-emitting diodes with trilayer PIN structures are fabricated using only thiophene/penylene co-oligomer derivatives: 5,5′-bis(4-biphenylyl)-2,2′-bithiophene (BP2T), 5″′-bis(4-trifluoromethylphenyl)[2,2′;5′,2″;5″,2″′]quaterthiophene (P4T-CF3), and 5,5′-bis-(4′-cyanobiphenyl-4-yl)-2,2′-bithiophene (BP2T-CN) as the P, I, and N materials, respectively. As designed from their expected frontier orbital energies, electroluminescence (EL) is obtained from the P4T-CF3 layer. When the BP2T layer is first deposited on an indium-tin-oxide (ITO) substrate, the device (Al:Li/BP2T-CN/P4T-CF3/BP2T/ITO) shows homogeneous EL. On the other hand, the device with an opposite deposition order (Au/BP2T/P4T-CF3/BP2T-CN/ITO) shows dotted EL with higher efficiency at lower bias voltages. By decreasing the deposition rate of the P4T-CF3 layer in the latter device, its morphological change results in homogeneous EL with increased density of dotted emission. [ABSTRACT FROM AUTHOR]

Organic electroluminescence (EL) devices with surface-emitting microcavity structure were fabricated using vapor-deposited films of thiophene/phenylene co-oligomer derivatives, aiming at polariton formation under electrical excitation. Owing to strong coupling between excitons and photons in the device, we demonstrated the formation of cavity polaritons with a large Rabi-splitting energy (2ħΩ = 250 meV). Furthermore, efficient relaxation into the bottom of lower polariton branch was confirmed from angle-resolved EL spectra. In excitation-density dependence, the luminance of microcavity EL devices showed a superlinear increase with an elevation of current density indicating a contribution of triplet excitons. [ABSTRACT FROM AUTHOR]

Organic semiconductor microcavities forming strongly coupled exciton-polaritons are interesting systems due to their nonlinear coherent emission observed even at room temperature. Here, we investigate the incident angle and photon-energy-dependent photoemission from a planar organic microcavity to evaluate the relaxation efficiency towards the bottom of the lower polariton branch. We observe nonlinear increase in the vertical emission from the microcavity when the sample is pumped resonantly to the lower polariton branch with an incident angle of 30 to 55°. The observed results support the fast and efficient relaxation of organic microcavity polaritons within the lower polariton branch. [ABSTRACT FROM AUTHOR]

Optically pumped lasing is observed in cyano-substituted thiophene/phenylene co-oligomer (TPCO) microcrystals fabricated by the slide boat method. Dot-shaped crystals approximately 10 μm in size are obtained. Needle- and platelet-like crystals are also obtained in other TPCO derivatives. The needle and platelet crystals show a lower lasing threshold than that of the dot-shaped crystals with clear multimode lasing spectra. A brief discussion follows on how to improve film fabrication from microdot and platelet crystals to film-like morphology. [ABSTRACT FROM AUTHOR]

In this study, electroluminescence from single crystals of CH3NH3PbBr3 perovskite is explored. The cast capping method was applied to fabricate simple devices with an ITO/CH3NH3PbBr3/ITO structure. The devices showed a low operation voltage of 2 V and a pure green luminescence with full width at half maximum of ∼20 nm. However, the emission occurring at the crystal edges demonstrated blinking with a subsecond time interval, which is similar to the previously reported photoluminescence behavior of nanocrystal perovskites. This electroluminescence blinking may provide new insight into the recombination processes depending on the carrier traps and defects of emission layers in perovskite light-emitting devices. [ABSTRACT FROM AUTHOR]

Optically pumped lasing and electroluminescence (EL) have been observed in solution-processed perovskite semiconducting materials of formamidinium lead bromide, CH(NH2)2PbBr3. Microcavities with flat surfaces and sharp edges have been easily obtained by the simple solution process called the “cast-capping method”. The crystals show clear multimode lasing of Fabry–Pérot cavities. The mode intervals are well explained by the optical constants with large dispersions of the materials. We have also fabricated EL devices and obtained clear EL in a single layer of the materials, but the EL intensity has been quenched rapidly. [ABSTRACT FROM AUTHOR]

We study the magneto-optical (MO) response of permalloy/silver/bismuth (Py/Ag/Bi) trilayer samples in reference to a control Py film by means of spectroscopic generalized MO ellipsometry. The trilayer structures show enhanced MO Kerr amplitude values compared to optical multilayer calculations based upon the Py film reference measurements, especially in the near-infrared region. This indicates that the optical interference conditions accounted for in the model are not sufficient to explain the influence of the Ag/Bi bilayer in the structure. Instead, the local optical and MO properties of the Py layer itself must be modified by the presence of the Ag/Bi bilayer, which could be caused by enhanced effective spin–orbit coupling. [ABSTRACT FROM AUTHOR]

Photoluminescence from an organic microcavity is investigated using vapor-grown single crystals of 5,5′-bis(4′-cyano-biphenyl-4-yl)-2,2′-bithiophene (BP2T-CN). A vertical half-cavity structure is fabricated with thin platelet crystals of BP2T-CN placed on a distributed Bragg reflector (DBR). Lying orientation of the BP2T-CN molecules is suitable for effective surface emission from the cavity. Angle-resolved photoluminescence spectra show anticrossing splits, suggesting the formation of cavity polaritons induced by coupling between confined photons and excitons. Phenomenological analysis well reproduces the dispersion characteristics with a Rabi splitting energy of 90 meV at room temperature. With increasing excitation fluence under optical pumping, one of the cavity photon modes is gain-narrowed, and amplified emission is obtained from the surface-emitting half-cavity structure. [ABSTRACT FROM AUTHOR]

Optically pumped lasing has been observed in solution-processed perovskite semiconducting materials, CH3NH3PbX3 (X = Cl, Br, I). Self-assembled Fabry–Pérot (FP) cavities have been easily obtained by using a simple “cast-capping method”, where we can obtain single-crystal-like optical cavities. The observed spectra show clear multimode lasing of the FP cavities under pulsed optical excitation. The mode intervals are well explained by the optical constants with large dispersions of the materials. The obtained refractive index around the lasing area coincides with the results in the previous reports. [ABSTRACT FROM AUTHOR]

Organic electroluminescence (EL) devices were fabricated with bilayered thiophene/phenylene co-oligomer (TPCO) derivatives: p-type 5,5′-bis(4-biphenylyl)-2,2′-bithiophene (BP2T) and n-type 5,5′-bis(4′-cyanobiphenyl-4-yl)-2,2′-bithiophene (BP2T-CN). Two types of EL device, Al:Li/BP2T-CN/BP2T/ITO (device A) and Au/BP2T/BP2T-CN/ITO (device B), were investigated using vapor-deposited films of BP2T and BP2T-CN by changing the order of deposition onto the indium–tin-oxide (ITO)/glass substrate. The EL performance was significantly improved for device B in which the two molecules had a lying orientation suitable for efficient carrier injection and transport as well as surface emission. In device A, on the other hand, the standing BP2T orientation resulted in much lower current density and EL intensity. [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) nanorod arrays for inorganic/organic hybrid solar cells were electrochemically deposited on indium tin oxide (ITO) substrates with a rotating disk electrode setup. The addition of a ZnO seed layer on the ITO prior to electrochemical deposition improved the morphology of the nanorods, resulting in nanorods with smaller and homogenous diameters as well as a higher degree of vertical orientation on to the substrate. The ZnO films deposited on the seeded ITO substrates had higher optical transmittance and lower concentration of defects. Chronoamperometric transient curves show that nucleation and coalescence occurred later for bare ITO substrates, indicating lower densities of initial nuclei, resulting in the growth of nanorods with larger diameters. The solar cell characteristics of the devices fabricated from the seeded ITO substrates were better. The seed layer also acts as a hole-blocking layer, preventing the direct contact between the hole-transporting polymer material and the ITO. [ABSTRACT FROM AUTHOR]

Enhancement of light-matter interaction of a quantum emitter with sub wavelength quasiperiodic metamaterials is proposed and demonstrated. The quasiperiodic metamaterials consist of subwavelength metal-dielectric multilayers, which are arranged into a Fibonacci lattice. The influence of Fibonacci metamaterials (FM) on the dipole emission is analyzed with a semiclassical model. The local density of states near FM is evaluated and a characteristic mode in higher wave numbers is revealed; a strong enhancement of the decay rate was predicted. A lifetime measurement is carried out and a reduction of lifetime of quantum dots on the surface of FM is observed. The enhancement of light-matter interaction arises from the localized latticelike state inherent for self-similar quasiperiodic order. [ABSTRACT FROM AUTHOR]

Solid parahydrogen, which is known to have an exceptionally long vibrational coherence lifetime as a molecular solid, offers an ideal testbed to perform coherent control experiments in the condensed phase. Here we demonstrate the spatial manipulation and visualization of the relative phase of vibrational wave functions in solid parahydrogen. Spatial distribution of vibrational excitation is generated by femtosecond impulsive Raman excitation. It is shown that the imprinted initial phase can be manipulated by wave-front modulation of the excitation laser pulses with a spatial light modulator. An interferometric measurement is used to convert the spatial phase distribution of the vibrational wave functions to the amplitude distribution. We have confirmed that the spatial profile of the scattered anti-Stokes pulse reveals the spatial phase distribution of the wave functions. The read-and-write scheme demonstrated in this experiment is applicable to a broad range of Raman memory systems accessible by Λ-type transitions. [ABSTRACT FROM AUTHOR]