Band-edge Effect Research Articles

A dual-mode biosensor based on silica inverse opal photonic crystals modulated electrochemiluminescence and dye displacement colorimetry for the sensitive detection of synthetic cathinone in water environment

To address the challenges posed by signal capacity limitations and the reliance of sensing methods on single analytical information, this study developed an electrochemiluminescence (ECL) and colorimetric dual-mode sensing platform for the precise detection of 4-chloroethcathinone (4-CEC) in water environments. Firstly, the accurate alignment of the reflection wavelength of appropriately sized silica inverse opal photonic crystals (SIOPCs) with the ECL emission wavelength of luminescent metal-organic frameworks (PCN-224) has been achieved via diameter modulation. This innovative design, which cleverly utilized the band-edge effect, improved the luminous intensity of the ECL sensor, leading to a significant boost in analytical performance. Secondly, the establishment of a colorimetric detection method for confirming the presence of 4-CEC in samples through visual observation of color changes was achieved by employing an aptamer-based dye displacement reaction, utilizing differential binding affinities between the aptamer and both the sulforhodamine B (SRB) and 4-CEC. Under the optimal experimental conditions, the dual-mode sensor demonstrated ECL detection of limits (LOD) of 2.6 × 10−13 g/L and colorimetric LOD of 6.5 ng/L for 4-CEC. These findings highlighted the tremendous potential of developing streamlined and efficient dual-signal readout platforms using ECL aptamer sensors for the precise determination of other Synthetic cathinones (SCs) in water environments.

Indirect magnetic signals in Weyl semimetals mediated by a single Fermi arc

Recently, abundant transport phenomena characterizing the surface states of Weyl semimetals (WSMs) have been reported. To generate these phenomena, electrons have to complete a closed intersurface orbit. Due to the unavoidable impurities in real materials, this orbit could be destroyed by the impurity scattering, which limits the detection of the surface states in WSMs. Here, we investigate the RKKY interaction between magnetic impurities, solely mediated by a single surface band, in semi-infinite WSMs. It is found that peculiar oscillations and slowly decaying laws of the RKKY interaction can act as the signals to capture the dispersive nature of the surface states of WSMs. The underlying physics is attributed to two effects: the band-edge effect and the bending effect of the surface band, which can control the RKKY interaction individually or compete with each other to produce more complex magnetic behaviors. In addition, the band-edge effect together with the finite Fermi energy would result in another interesting oscillation with battering pattern. All the results are significantly different from that in previous literatures where surface states have to couple with bulk states (or other surface states of different spins) to generate nonzero magnetic interaction. Compared to the previous models of surface states, the model here is more practical and is helpful for the deeper understanding of the surface magnetic properties in WSMs.

Luminescence regulation of lanthanide-doped nanorods in chiral photonic cellulose nanocrystal films

A new design for chiral photonic cellulose nanocrystal films was developed by co-assembling lanthanide-doped nanorods (NRs) into chiral cellulose nanocrystals, in which the photonic band gap (PBG) could be tuned in the visible range by changing the mass fraction of flexible agents, such as polyvinyl alcohol (PVA) and ethylene glycol (EG). Due to the PBG effect, the luminescence modulation in such nanocrystal films had been realized. The down-conversion luminescence from NaGd30Y60F4:5%Tb3+, 5%Eu3+ NRs and up-conversion luminescence from NaGd40Y40F4:18%Yb3+, 2%Er3+ NRs could be enhanced by 28 % and 18 % respectively, on account of the band edge effect. The luminescence would be inhibited when the luminescence overlapped with the stop band of the PBG. These results implied that the biocompatible photonic cellulose nanocrystal films are ideally suited for applications in optical coding, optical resonators and biocompatible lasers.

Research on dual-functional characteristics of piezoelectric metamaterial beams for vibration reduction and power generation

A piezoelectric metamaterial beam composed of metamaterials and piezoelectric energy harvesting is proposed to realize the dual-functional characteristics of vibration reduction and power generation simultaneously. Based on the theoretical derivation of the electrical domain and the structural domain, the transfer matrix of the piezoelectric metamaterial beam is constructed using the charge accurate integration method and the transfer matrix method. The energy band structure of the infinite periodical model and the vibration transmission of the finite periodical model are analyzed numerically to illustrate the low frequency bandgaps of the piezoelectric metamaterial beam. An external load circuit for energy harvesting is introduced, and its influence on the vibration characteristics of the original system is analyzed. On this basis, Kirchhoff’s law is used to derive accurate analytical solutions for the output voltage and output power of each piezoelectric oscillator, and the relationship between the local resonance bandgap and band-edge effect and the power generation performance of the piezoelectric metamaterial beam is investigated in detail. Finally, the theoretical analysis results are verified by finite element simulation analysis. It is shown that the introduction of an external load circuit for energy harvesting results in the vanishing of the dense resonant frequency range at the lower band edge of the local resonance bandgap and the modal peaks near the upper and lower band edges are effectively suppressed, consequently expanding the range of the bandgap. In addition, an excellent power generation performance is observed in the local resonant bandgap and the passband of the upper and lower band edges.

Simulation of 1D edge-emitting organic photonic crystal lasers based on conjugated polymer

A 1D edge-emitting organic semiconductor photonic crystal laser is designed and demonstrated based on conjugated polymer MEH-PPV as the gain medium. The bandgap and band-edge effect of photonic crystals are applied to construct an organic resonant cavity as the high reflective mirror and output coupler. Besides, the photonic crystal with a defect is introduced as the mode-selector inside the cavity to achieve the single longitudinal mode output. The simulation results show the edge-emitting laser outputs signals at the wavelength 588 nm with the full width at half maximum of 0.131 nm. All photonic crystal components of lasers are integrated on an organic ridge waveguide, which makes it compact and reliable for the potential application in all-optics integration in future.

Gigantic electric-field-induced second harmonic generation from an organic conjugated polymer enhanced by a band-edge effect

Electric-field-induced second harmonic generation (EFISH), a third-order nonlinear process, arises from the interaction between the electric field of an external bias and that of two incident photons. EFISH can be used to dynamically control the nonlinear optical response of materials and is therefore promising for active nonlinear devices. However, it has been challenging to achieve a strong modulation with EFISH in conventional nonlinear materials. Here, we report a large tunability of an EFISH signal from a subwavelength-thick polymer film sandwiched between a transparent electrode and a metallic mirror. By exploiting the band-edge-enhanced third-order nonlinear susceptibility of the organic conjugated polymer, we successfully demonstrate a gigantic EFISH effect with a modulation ratio up to 422% V−1 at a pumping wavelength of 840 nm. The band-edge-enhanced EFISH opens new avenues for modulating the intensity of SHG signals and for controlling nonlinear electro-optic interactions in nanophotonic devices.

Wavelength-Tunable and Highly Stable Perovskite-Quantum-Dot-Doped Lasers with Liquid Crystal Lasing Cavities.

This study applies a low-cost solvothermal method to synthesize all-inorganic (lead-free cesium tin halide) perovskite quantum dots (AIPQDs) and to fabricate AIPQD-doped lasers with cholesteric liquid crystal (CLC) lasing cavities. The lasers present highly qualified lasing features of low threshold (150 nJ/pulse) and narrow line width (0.20 nm) that are attributed to the conjunction of the suppression of photoluminescence (PL) loss caused by the quantum confinement of AIPQDs and the amplification of PL caused by the band-edge effect of the CLC-distributed feedback resonator. In addition, the lasers possess highly flexible lasing-wavelength tuning features and a long-term stability under storage at room temperature and under high humidity given the protective role of CLC. These advantages are difficult to confer to typical light-emitting perovskite devices. Given these merits, the AIPQD-doped CLC laser device has considerable potential applications in optoelectronic and photonic devices, including lighting, displays, and lasers.

Enhancement of fluorescent emission in photonic crystal film and application in photocatalysis

Fluorescent photonic crystal films composed of monodisperse NaYF4:15Yb,0.5Tm@SiO2 (where 15 and 0.5 represent the mole percentage of reactants) core–shell spheres were successfully fabricated and applied in photocatalysis. The core–shell spheres were prepared using a modified Stober method, and fluorescent photonic crystal films were fabricated via a simple self-assembly method. The morphologies, structures and upconversion fluorescent properties of the fluorescent photonic crystal films with different photonic band gaps were characterized. Moreover, their photocatalytic capability in decomposing rhodamine B using near-infrared light was studied. Results indicate that the band edge effect plays a critical role in the enhancement of short wave emission intensity of fluorescent photonic crystal films. Specifically, in comparison to the reference sample without a band edge effect, the 363 nm emission intensity was enhanced by 5.97 times, while the percentage of UV upconversion emission was improved by 6.23%. In addition, the 451 nm emission intensity was enhanced by 5.81 times, and the percentage of visible upconversion emission was improved by 8.88%. Furthermore, fluorescent photonic crystal films with enhanced short wave emission exhibited great photocatalytic performance in the degradation of rhodamine B aqueous solutions under near-infrared light.

Nonlinear digital out-of-plane waveguide coupler based on nonlinear scattering of a single graphene layer

A new mechanism for out-of-plane coupling into a waveguide is presented and numerically studied based on nonlinear scattering of a single nano-scale Graphene layer inside the waveguide. In this mechanism, the refractive index nonlinearity of Graphene and nonhomogeneous light intensity distribution occurred due to the interference between the out-of-plane incident pump light and the waveguide mode provide a virtual grating inside the waveguide, coupling the out-of-plane pump light into the waveguide. It has been shown that the coupling efficiency has two distinct values with high contrast around a threshold pump intensity, providing suitable condition for digital optical applications. The structure operates at a resonance mode due to band edge effect, which enhances the nonlinearity and decreases the required threshold intensity.

Real-Time Fluorescence Detection in Aqueous Systems by Combined and Enhanced Photonic and Surface Effects in Patterned Hollow Sphere Colloidal Photonic Crystals.

Hollow sphere colloidal photonic crystals (HSCPCs) exhibit the ability to maintain a high refractive index contrast after infiltration of water, leading to extremely high-quality photonic band gap effects, even in an aqueous (physiological) environment. Superhydrophilic pinning centers in a superhydrophobic environment can be used to strongly confine and concentrate water-soluble analytes. We report a strategy to realize real-time ultrasensitive fluorescence detection in patterned HSCPCs based on strongly enhanced fluorescence due to the photonic band-edge effect combined with wettability differentiation in the superhydrophobic/superhydrophilic pattern. The orthogonal nature of the two strategies allows for a multiplicative effect, resulting in an increase of two orders of magnitude in fluorescence.

Impurity-related nonlinear optical absorption under combined effects of intense laser field and band-edge nonparabolicity on InGaN QW

Conduction band-edge nonparabolicity effect on linear and nonlinear optical properties related to 1s–1p intra-conduction band transition in unstrained wurtzite (In, Ga)N–GaN symmetric quantum well (QW) is investigated incorporating an additional external probe as well as the nonresonant intense laser field (ILF) effect. Using the compact density matrix approach and the iterative procedure, the analytical expressions of optical absorption coefficients (ACs) are calculated. The numerical results are obtained within the single-band effective mass and the one-parabolic-band approximations under finite potential barrier. It is found that the internal and external perturbations show an important impact on the optical spectrum. A critical value of the laser-dressed parameter (LDP) is obtained by limiting two behaviors. Moreover, the ILF can be used as a way to control the optical properties of the QW structures and to reduce the lift of the conduction band-edge.

Theoretical Aspects of Minority Carrier Extraction in Unipolar Barrier Infrared Detectors

We have examined, theoretically, minority carrier collection in unipolar barrier infrared photodetectors. In barrier infrared detectors, for example the nBn, the unipolar barrier should block only majority carriers and allow unimpeded flow of minority carriers. However, an imperfect barrier would also block minority carriers, resulting in higher than expected turn-on bias. Minority carrier blocking can be caused by barrier doping or unintended band offset between the barrier and the absorber. The distinct manner in which these two mechanisms affect device performance were investigated. We found that introduction of an appropriate amount of barrier doping can reduce depletion dark current without increasing turn-on bias. We examined the effects of band structure on conductivity effective masses when the n-type absorber was a type-II superlattice (T2SL). We showed that for a long-wavelength infrared InAs/GaSb T2SL the vertical conductivity hole effective mass can be much smaller than that predicted by the simple band-edge effect mass picture, implying that the vertical hole mobility estimated from the band-edge effective mass can be unduly pessimistic.

Intense laser field and conduction band-edge nonparabolicity effects on hydrogenic impurity states of InGaN QW

In this paper, hydrogenic impurity ground-state binding energy in unstrained wurtzite (In, Ga)N symmetric quantum well is investigated. The heterostructure is considered under the action of an intense laser field (ILF) incorporating an additional internal probe as well as the conduction band-edge nonparabolicity effect (CBENP). The variational approach is used within the framework of single band effective-mass approximation with two-parametric 1S-hydrogenic trial wavefunction. The competition effect between internal and external perturbations is also shown. Our results reveal that the binding energy is the largest for the well width around the effective Bohr radius and is strongly influenced by both parameters. Moreover, the principle effect of ILF (CBENP) is to reduce (enhance) the binding energy. It is found that the lift of the conduction band-edge can be easily eliminated by adjusting the ILF-parameter.

Ultralow-threshold single-mode lasing based on a one-dimensional asymmetric photonic bandgap structure with liquid crystal as a defect layer.

In this Letter, we propose defect-mode lasing from a one-dimensional asymmetric photonic structure with dye-doped nematic liquid crystal as a central defect layer. The local field intensity of the distinguished single defect mode at the overlapped photonic band edges is drastically enhanced by the asymmetric structure consisting of two distinct multilayer photonic crystals. With high density of states of photons, effective output lasing emission and maximum input excitation are ensured. As a result, the single-mode lasing with a low excitation threshold of 0.2 μJ/pulse is achieved due to the combination of the defect layer and the photonic band edge effect.

Enhancement of broadband optical absorption in photovoltaic devices by band-edge effect of photonic crystals

We numerically investigate broadband optical absorption enhancement in thin, 400-nm thick microcrystalline silicon (µc-Si) photovoltaic devices by photonic crystals (PCs). We realize absorption enhancement by coupling the light from the free space to the large area resonant modes at the photonic band-edge induced by the photonic crystals. We show that multiple photonic band-edge modes can be produced by higher order modes in the vertical direction of the Si photovoltaic layer, which can enhance the absorption on multiple wavelengths. Moreover, we reveal that the photonic superlattice structure can produce more photonic band-edge modes that lead to further optical absorption. The absorption average in wavelengths of 500-1000 nm weighted to the solar spectrum (AM 1.5) increases almost twice: from 33% without photonic crystal to 58% with a 4 × 4 period superlattice photonic crystal; our result outperforms the Lambertian textured structure.

Efficient light amplification in low gain materials due to a photonic band edge effect

One of the possibilities of increasing optical gain of a light emitting source is by embedding it into a photonic crystal (PhC). If the properties of the PhC are tuned so that the emission wavelength of the light source with gain falls close to the photonic band edge of the PhC, then due to low group velocity of the light modes near the band edge caused by many multiple reflections of light on the photonic structure, the stimulated emission can be significantly enhanced. Here, we perform simulation of the photonic band edge effect on the light intensity of spectrally broad source interacting with a diamond PhC with low optical gain. We show that even for the case of low gain, up to 10-fold increase of light intensity output can be obtained for the two-dimensional PhC consisting of only 19 periodic layers of infinitely high diamond rods ordered into a square lattice. Moreover, considering the experimentally feasible structure composed of diamond rods of finite height - PhC slab - we show that the gain enhancement, even if reduced compared to the ideal case of infinite rods, still remains relatively high. For this particular structure, we show that up to 3.5-fold enhancement of light intensity can be achieved.

Effects of GaN Thin Layer on InGaN at Electrolyte-Semiconductor Interface for the Application of Photoelectrochemical Water Splitting

ABSTRACTPhotoelectrochemical properties of nitride semiconductors are paid attention due to their possibilities of water splitting by visible light absorption. However, the photocurrent density of InxGa1-xN, which absorbs visible light, is usually lower than that of GaN, which has larger band-gap and absorbing only UV light. The reasons of this are thought to be the band-edge position at the semiconductor-electrolyte interface and the crystal quality. The conduction band-edge decreases with increasing of indium composition and across the hydrogen generation energy at around the indium composition of 0.2. This means that the hydrogen generation ability decreases with increasing of indium composition. Low crystal quality is obtained because the lower growth temperature of InxGa1-xN than that of GaN to achieve the indium incorporation. In order to improve the photocurrent density, band-edge energy control and quantum tunneling effect are tried using the structure of thin GaN layer on InxGa1-xN here. The effect for the photocurrent densities is also discussed.

Photonic crystal lasers—ultimate nanolasers and broad-area coherent lasers [Invited

Photonic crystals in which the refractive index changes periodically provide an exciting tool for the manipulation of photons and have seen substantial progress in recent years. In this article, we discuss two topics regarding photonic crystal lasers: (i) ultimate nanolasers based on the photonic bandgap effect and high-Q nanocavities, and (ii) broad-area photonic crystal lasers based on the photonic bandedge effect.

Room temperature photonic crystal band-edge lasing from nanopillar array on GaN patterned by nanosphere lithography

An ordered GaN nanopillar array fabricated by nanosphere lithography exhibited room temperature photopumped lasing via the photonic crystal band-edge effect. With a monolayer of self-assembled nanospheres as hard mask, the ordered pattern was transferred to the sample to form nanopillars by inductively coupled plasma dry etch. Under pulsed optical excitation, room temperature lasing with a low lasing threshold of 30 mJ/cm2 was achieved. The dominant lasing peak, centered at 415.6 nm, corresponds to a band-edge mode at the Γ-point of the band diagram. A Q factor in the range of 600–700, and spontaneous emission coupling factor of 0.021 were evaluated.

Ferromagnetic resonance linewidth mechanisms in polycrystalline ferrites: Role of grain-to-grain and grain-boundary two-magnon scattering processes

The frequency dependence of the ferromagnetic resonance linewidth $\ensuremath{\Delta}H$ in polycrystalline hot isostatically pressed pure and Ca-Ge substituted yttrium iron garnet (YIG) spheres was measured between 1.95 and 6 GHz and analyzed. The linewidths for these ultradense ferrite materials are in the 5--40 and 5--25 Oe ranges for the pure and the substituted YIG samples, respectively. The $\ensuremath{\Delta}H$ vs frequency data show especially sharp Buffler peaks due to the band-edge crossover effect that is the signature for grain-to-grain (GG) two-magnon scattering (TMS) [C. R. Buffler, J. Appl. Phys. 30, S172 (1959)]. Both the GG and recent grain-boundary (GB) TMS models were used to obtain quantitative fits to the data. The fits demonstrate the expected GG TMS contribution to the linewidth for frequencies above the Buffler peak. They also reveal two unexpected results: (1) a dominant GB TMS role for frequencies below the Buffler peak where the GG TMS linewidth contribution is essentially zero and (2) a significant GB TMS role for frequencies above the peak where the linewidth has generally been associated with GG processes only. In the high-frequency regime, the GB scattering term appears to explain about half of the overall linewidth.