Search Results (197)

Semiconductor photonic nanowires are critical components for nanoscale light manipulation in integrated photonic and electronic devices. Optimizing their optical performance requires enhanced photon conversion efficiency, for which a promising solution is to combine semiconductors with noble metals, using the surface plasmon resonance of noble metals to enhance the photon absorption efficiency. Here, we report plasmon-enhanced light emission in a hybrid nanowire device composed of perovskite semiconductor nanowires and silver nanoparticles formed using superfluid helium droplets. A cesium lead halide perovskite-based four-layer structure (CsPbBr₃/PMMA/Ag/Si) effectively reduces the metal’s plasmonic losses while ensuring efficient surface plasmon–photon coupling at moderate power. Microphotoluminescence and time-resolved spectroscopy techniques are used to investigate the optical properties and emission dynamics of carriers and excitons within the hybrid device. Our results demonstrate an intensity enhancement factor of 29 compared with pure semiconductor structures at 4 K, along with enhanced carrier recombination dynamics due to plasmonic interactions between silver nanoparticles and perovskite nanowires. This work advances existing approaches for exciting photonic nanowires at low photon densities, with potential applications in optimizing single-photon excitations and emissions for quantum information processing. Full article

A single crystal of YAl₃(BO₃)₄ was grown using the top-seeded solution growth method. The vacuum ultraviolet (VUV) excitation spectrum, monitored at the emission wavelength of 312 and 372 nm, showed a narrow excitation band at around 162 nm, which is located near the absorption edge of the YAl₃(BO₃)₄ host. Upon VUV excitation at 162 nm, the characteristic self-trapped exciton (STE) emission bands were observed at 312 and 372 nm. The X-ray excited scintillation spectrum shows a broad emission band peaking at 310 nm with a weak shoulder band at around 375 nm, which is consistent with photoluminescence, and can thus be assigned to the STE emission. The scintillation light yield under irradiation at a ²⁵²Cf-thermal neutron reached 2700 photons/thermal neutron. Full article

Due to the equipartition exciton property of graphene metamaterials, researchers have applied them to the design of absorbers and developed a series of absorbers covering different wavebands (including narrowband and broadband). In this paper, an absorber based on surface-isotropic excitations was designed with the help of graphene metamaterials and relevant simulations. The absorber exhibited six perfect absorption peaks in the mid-infrared band and had an extremely simple structure consisting of only three layers: a gold layer at the bottom, a dielectric layer made of silica in the middle, and patterned graphene at the top. This absorber possesses excellent tuning ability, and by applying an external bias to the graphene layer, the Fermi energy level of graphene can be adjusted, and thus the resonance frequency of the absorption peak can be tuned. Meanwhile, the effect of the graphene relaxation time on the absorber performance was investigated. In addition, the refractive index of the dielectric layer was found to be linearly related to the resonance frequency of the absorption peak. It is worth mentioning that the absorber structure possessed polarization insensitivity due to its central symmetry. Even when incident light with different polarizations was incident over a wide range of angles, the change in absorbance of the absorption peaks was negligible, demonstrating significant insensitivity to the angle of incidence. The sensor possesses excellent characteristics such as tunability, polarization insensitivity, incident angle insensitivity, and high sensitivity. This paper demonstrates the feasibility of a six-frequency sensor and opens up more ideas for the design of multi-frequency sensors. Full article

This paper presents a systematic absorption and circular dichroism spectroscopy study of short single strands of DNA, from 2 to 20 bases. They are composed of a sequence-specific nucleobase composition, either adenine (A), thymine (T), or AT repeats. The absorption spectra hypochromism and the circular dichroism one show butterfly-shaped spectra. Data analysis conducted on the spectra of these oligomers provides evidence for the formation of excitons and their delocalization length along the strand of DNA in relation to how many bases are involved in the excitonic coupling. In particular, the extent of this coupling is limited to adjacent nucleobases in the case of pure adenine strands but spans multiple nucleobases in the case of pure thymine strands. Predictably, AT repeats show a mixed behavior between the two. Full article

Chalcogenide perovskites have shown great potential for photovoltaic applications. Most researchers have begun to pay close attention to the crystal synthesis, phase stability, and optoelectronic properties of chalcogenide perovskites AMX₃ (A = Ca, Sr, Ba; M = Ti, Zr, Hf, Sn; X = S, Se). At present, the A-site metal cations are mainly limited to alkaline earth metal cations in the literature. The replacement of the alkaline earth metal cations by Yb²⁺ is proposed as an alternative for chalcogenide perovskites. In this study, the phase stability, and mechanical, electronic, optical, and photovoltaic properties of novel chalcogenides YbMX₃ (M = Zr, Hf; X = S, Se) are theoretically evaluated in detail for the first time. It is mentioned that YbZrS₃ and YbHfS₃ are marginally thermodynamically stable while YbZrSe₃ and YbHfSe₃ exhibit superior phase stability against decomposition. Good mechanical and dynamical stability of these chalcogenide perovskites are verified, and they are all ductile materials. The accurate electronic structure calculations suggest that the predicted direct bandgap of YbMSe₃ (M = Zr, Hf) is within 1.3–1.7 eV. Additionally, the small effective mass and low exciton binding energy of YbMSe₃ (M = Zr, Hf) are favorable for their photovoltaic applications. However, YbZrS₃ and YbHfS₃ show larger direct band gaps with a change from 1.92 to 2.27 eV. The optical and photovoltaic properties of these compounds are thoroughly studied. In accordance with their band gaps, YbZrSe₃ and YbHfSe₃ are discovered to exhibit high visible-light absorption coefficients. The maximum conversion efficiency analysis shows that YbMSe₃ (M = Zr, Hf) can achieve an excellent efficiency, especially for YbZrSe₃, whose efficiency can reach ~32% in a film thickness of 1 μm. Overall, our study uncovers that YbZrSe₃ is an ideal stable photovoltaic material with a high efficiency comparable to those of lead-based halide perovskites. Full article

An ultrathin film capable of exhibiting material properties across and around two different dimensions by bridging two-dimensionality frameworks, called a trans-dimensional (TD) material, can be an exceptional tool to tune various electronic and optoplasmonic properties of a system that are unattainable from either dimension. Taking an example of the planar periodic arrangement of single-walled carbon nanotube (SWCNT) TD films, we semi-analytically calculated their dynamical conductivities and dielectric responses as a function of the incident photon frequency and the SWCNT’s radius using the many-particles Green’s function formalism within the Matsubara frequency technique. The periodic array of SWCNTs has an anisotropic dielectric response, which is almost a constant and the same as that of the host dielectric medium in the perpendicular direction of the alignment of the SWCNT array due to the depolarization effect that SWCNTs have. However, the dielectric response functions depend on the incident photon energy in addition to the film’s thickness, the SWCNT’s sparseness, inhomogeneity, and the SWCNT’s diameter. The energy difference between the resonant absorption peak and the plasmonic peak varies with the thickness of the film. Varying the length of the CNTs, we also observed that the exciton–plasmon coupling strength increases with the increase in length of the SWCNTs. The metallic SWCNT-containing films have comparatively pronounced plasmon resonance peaks at low photon energy than semiconducting SWCNT-containing films. Both metallic and semiconducting SWCNT-consisting films have negative refraction for a wide range of energy, making them good candidates for metamaterials. Full article

Three-dimensional (3D) hybrid organic–inorganic perovskites (HOIPs) have attracted tremendous interest due to strong excitonic effects and large optical nonlinearities. Taking the advantages, 3D HOIPs show great potential for applications in excitonic and nonlinear devices. However, understanding the relevant mechanisms of exciton-associated nonlinear optical phenomena in 3D perovskites is still challenging. Here, we apply the quantum perturbation theory to calculate the exciton-associated degenerate 2PA spectra of 3D HOIPs. The calculated 2PA spectra of twelve 3D HOIPs are predicted to exhibit resonance peaks at both the sub-band and band edges. The exciton-resonance-associated 2PA coefficients are at least one order of magnitude larger than those of band-to-band transitions and are comparable to those of low-dimensional perovskites. To validate our model, we carried out measurements of the static light-intensity-dependent transmission on MAPbBr₃ single crystals. Enhancements of 2PA coefficients are predicted theoretically and observed experimentally with a resonant peak at 1100 nm, indicating intrinsic two-photon transitions to excitonic states in MAPbBr₃ single crystals. Full article

Perovskite materials, as emerging semiconductors, have attracted significant attention for their exceptional optoelectronic properties, tunable bandgaps, ease of fabrication, and cost-effectiveness, making them promising candidates for next-generation optoelectronic devices. The all-inorganic perovskite Cs₂AgBiBr₆ distinguishes itself from other perovskite materials due to its remarkable optical absorption and emission properties, excellent stability, prolonged carrier recombination lifetime, and nontoxic characteristics. However, a deeper understanding of its unique luminescent properties and a further optimization of its structure and performance are still necessary. This study systematically investigates the optimization of Cs₂AgBiBr₆ double perovskite films through A-site Na⁺ doping. At an optimal Na⁺ doping concentration of 3.5% (Na_0.07Cs_1.93AgBiBr₆), the film shows 1.4 times and 2.7 times enhancement in light absorption and photoluminescence intensity, compared to the undoped film. Low-temperature spectroscopy measurements indicate that Na_0.07Cs_1.93AgBiBr₆ exhibits higher exciton binding energy and phonon energy. Based on Na_0.07Cs_1.93AgBiBr₆, the photodetectors demonstrate significant performance improvements, with a high photocurrent response of 10⁻² A, a photo-to-dark current ratio (PDCR) of 7.57 × 10⁴, a responsivity (R) of 16.23 A/W, a detectivity (D*) of 2.92 × 10¹² Jones, a linear dynamic range (LDR) of 98.75 dB, and a fast response time of 943 ms. This work provides a promising strategy for optimizing all-inorganic perovskite materials through doping and offers guidance for enhancing high-performance photodetectors. Full article

Optical filters are essential components for a variety of applicative fields, such as communications, chemical analysis and optical signal processing. This article describes the preparation and characterization of a new optical filter made of polyvinyl alcohol and incremental amounts of crystal violet. By using distinct solvents (H₂O, dimethyl sulfoxide (DMSO) and H₂O₂) to obtain the dyed polymer films, new insights were gained into the pathway that underlies the possibility of tailoring the material’s optical performance. The effect of the dye content on the sample’s main properties was inspected via UV–VIS spectroscopy analysis combined with colorimetry, refractometry and atomic force microscopy experiments. The results revealed that the colorimetric parameters are affected by the dye amount and are dramatically changed when the solvent used for film preparation is different. The rise in the refractive index upon polymer dyeing was due to the synergistic effect of the larger polarizability of the dye and the occurrence of hydrogen bonds among the system components. Spectral data evidenced that samples prepared in H₂O and DMSO preserve the absorption characteristics of the added dye, whereas H₂O₂ acts as an oxidizing agent and enhances transparency. Also, for the first two solvents, multiple absorption edges were noted as a result of dye incorporation, which was responsible for the occurrence of new exciton-like states, hence the band gap reduction. The films processed in H₂O were able to block radiations in the 506–633 nm range while allowing other wavelengths to pass with a transmittance above 90%. The samples attained in DMSO presented similar properties, with the difference that the domain of light attenuation was shifted towards higher wavelengths. Atomic force microscopy showed the dye’s effect on the level of surface roughness uniformity and morphology isotropy. The dyed polymer foils in non-oxidizing agents have suitable features for use as band-pass filters. Full article

One of the key parameters characterizing the microstructure of a layer is its degree of order. It can be determined from optical studies or X-ray diffraction. However, both of these methods applied to the same layer may give different results because, for example, aggregates may contribute to the amorphous background in XRD studies, while in optical studies, they may already show order. Because we are usually interested in the optical and/or electrical properties of the layers, which in turn are closely related to their dielectric properties, determining the optical order of the layers is particularly important. In this work, the microstructure, optical properties and electrical conductivity of poly(3-hexyl)thiophene layers were investigated, and a model describing the electrical conductivity of these layers was proposed. The model is based on the generalized theory of the effective medium and uses the equation from the percolation theory of electrical conductivity for the effective medium of a mixture of two materials. The results indicate a key role of the aggregate size and limited conductivity of charge carriers, mainly due to structural imperfections that manifest themselves as an increase in the number of localized states visible in the subgap absorption near the optical absorption edge. The critical value of the order parameter and the corresponding values of the Urbach energy, excitonic linewidth and band gap energy are determined. Full article

Colloidal quasi-two-dimensional cadmium chalcogenide nanoplatelets have attracted considerable interest due to their narrow excitonic emission and absorption bands, making them promising candidates for advanced optical applications. In this study, the synthesis of quasi-two-dimensional CdSe NPLs with a thickness of 3.5 monolayers was investigated to understand the effects of synthesis temperature on their stoichiometry, morphology, and optical properties. The NPLs were synthesized using a colloidal method with temperatures ranging from 170 °C to 210 °C and optimized precursor ratios. Total reflection X-ray fluorescence (TXRF) analysis was employed to determine stoichiometry, while high-resolution transmission electron microscopy (HRTEM) and UV-Vis spectroscopy and photoluminescence spectroscopy were used to analyze the structural and optical characteristics. The results showed a strong correlation between increasing synthesis temperature and the enlargement of nanoscroll diameters, indicating dynamic growth. The best results in terms of uniformity, stoichiometry, and optical properties were achieved at a growth temperature of 200 °C. At this temperature, no additional optical bands associated with secondary populations or hetero-confinement were observed, indicating the high purity of the sample. Samples synthesized at lower temperatures exhibited deviations in stoichiometry and optical performance, suggesting the presence of residual organic compounds. Full article

We have collected theoretical arguments supporting the functional role of nano-metallic coatings of solar cells, which enhance solar cell efficiency via by plasmon-strengthening the absorption of sun-light photons and reducing the binding energy of photoexcitons. The quantum character of the plasmonic effect related to the absorption of photons (called the optical plasmonic effect) is described in terms of the Fermi golden rule for the quantum transitions of semiconductor-band electrons induced by plasmons from a nano-metallic coating. The plasmonic effect related to the lowering of the exciton binding energy (called the electrical plasmonic effect) is of particular significance for metalized perovskite solar cells and is also characterized in quantum mechanics terms. The coupling between plasmons in nanoparticles from a coating with band electrons in a semiconductor substrate significantly modifies material properties (dielectric functions) both of the particles and the semiconductor, beyond the ability of the classical electrodynamics to describe. Full article

We conducted experiments utilizing the scattering effect of zinc oxide (ZnO) to enhance the photoluminescence (PL) intensity of cesium lead bromide (CsPbBr₃) perovskite quantum dots (QDs). This study involved investigating the method for creating a CsPbBr₃ and ZnO mixture and determining the optimal mixing ratio. A mixture dispersion of CsPbBr₃ and ZnO, prepared at a 1:0.015 weight ratio through shaking, was fabricated into a film using the spin coating method. The PL intensity of this film showed a relative increase of 20% compared to the original CsPbBr₃ QD film without ZnO. The scattering effect of ZnO was confirmed through ultraviolet-visible (UV-Vis) absorption and transient PL experiments, and a long-delayed exciton lifetime was observed in the optimized mixture dispersion thin film. The morphology of the fabricated film was characterized using field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM). For the CsPbBr₃-ZnO mixture (1:0.0015) film, crystal domains of approximately 10 nm were observed using TEM. Through AFM analysis, an excellent film roughness of 4.6 nm was observed, further confirming the potential of perovskite QD/ZnO composite films as promising materials for enhanced photoconversion intensity. In future studies, applying this method to other perovskite materials and metal oxides for the optimization of photoconversion composite materials is expected to enable the fabrication of highly efficient perovskite QD/metal oxide composite films. Full article

The size-dependent photoluminescence (PL) blue shift in organometal halide perovskite nanoparticles has traditionally been attributed to quantum confinement effects (QCEs), irrespective of nanoparticle size. However, this interpretation lacks rigor for nanoparticles with diameters exceeding the exciton Bohr radius ($r_B$). To address this, we investigated the PL of MAPbBr₃ nanoparticles (MNPs) with diameters ranging from ~2 to 20 nm. By applying the Brus equation and Burstein–Moss theory to fit the PL and absorption blue shifts, we found that for MNPs larger than $r_B$, the blue shift is not predominantly governed by QCEs but aligns closely with the band filling effect. This was further corroborated by a pronounced excitation-density-dependent PL blue shift (Burstein−Moss shift) at high photoexcitation densities. Additionally, trap-state filling was also found to be not a negligible origin of the PL blue shift, especially for the smaller MNPs. The time-resolved PL spectra (TRPL) and excitation-density-dependent TRPL are collected to support the coexistence of both filling effects by the high initial carrier density (~10¹⁷–10¹⁸ cm⁻³) and the recombination dynamics of localized excitons and free carriers in the excited state. These findings underscore the combined role of the band filling and trap-state filling effects in the size-dependent PL blue shift for solution-prepared MNPs with diameters larger than $r_B$, offering new insights into the intrinsic PL blue shift in organometal halide perovskite nanoparticles. Full article

While the photophysics of closed-shell organic molecules is well established, much less is known about open-shell systems containing interacting radical pairs. In this work, we investigate the ultrafast excited state dynamics of a singlet verdazyl diradical system in solution using transient absorption (TA) spectroscopy for the first time. Following 510 nm excitation of the excitonic S₀ → S₁ transition, we detected TA signals in the 530–950 nm region from the S₁ population that decayed exponentially within a few picoseconds to form a vibrationally hot S₀* population via internal conversion. The dependence of the S₁ decay rate on solvent and radical–radical distance revealed that the excited state possesses charge-transfer character and likely accesses the S₀ state via torsional motion. The ultrafast internal conversion decay mechanism at play in our open-shell verdazyl diradicals is in stark contrast with other closed-shell, carbonyl-containing organic chromophores, which exhibit ultrafast intersystem crossing to produce long-lived triplet states as the major S₁ decay pathway. Full article