Optical Studies Research Articles

Comments on “Growth, XRD, optical, thermal, mechanical, electrical and NLO studies on mixture of potassium hydrogen phthalate and l‑tartaric acid crystal for NLO applications”

Comments on “Growth, XRD, optical, thermal, mechanical, electrical and NLO studies on mixture of potassium hydrogen phthalate and l‑tartaric acid crystal for NLO applications”

Heteroatom-Promoted Polyhexagonal Saddle-Shaped Molecular Structures and their Supramolecular Coassembly with C60.

Molecules with curved architecture can exhibit unique optoelectronic properties due to the concave-convex π-surface. However, synthesizing negatively curved saddle-shaped aromatic systems has been challenging due to the internal structural strain. Herein, we report the facile synthesis of two polyhexagonal molecular systems, 1 and 2, with saddle shape geometry by judiciously varying the aromatic moiety, avoiding the harsh synthetic methods as that of heptagonal aromatic saddle systems. The unique geometry preferences of B, N, and S furnish suitable curvature to the molecules, featuring saddle shape. The saddle geometry also enables them to interact with fullerene C60 , and the supramolecular interactions of fullerene C60 with 1 and 2 modify their optoelectronic properties. Crystal structure analysis reveals that 1, with a small π-surface, forms a double columnar array of fullerenes in the solid state. In contrast, 2 with a large π-surface produces a supramolecular capsule entrapping two discrete fullerenes. The intermolecular interactions between B, N, S, and the aryl-π surface of the host and C60 guest are the stabilizing factors for creating these supramolecular structures. Comprehensive computational, optical, and Raman spectroscopic studies establish the charge transfer interactions between B-N doped heterocycle host and fullerene C60 guest.

Structural, vibrational, and optical studies of newly synthesized Yavapaiite-type phases BaSb2/3X1/3(PO4)2 (X = Mn, Co, Cu, Zn)

The synthesis and structural characterization of four newly synthesized phosphates, BaSb2/3X1/3(PO4)2 phases where X represents Mn, Co, Cu, and Zn, are presented here for the first time. These BaSb2/3X1/3(PO4)2 phases, denoted as [BaSbMn], [BaSbCo], [BaSbCu], and [BaSbZn], were prepared by a solid-state reaction at 900 °C in air atmosphere. The crystal structures of these [BaSbX] materials were investigated using Rietveld analysis based on conventional X-ray powder diffraction. The structural analysis revealed that all four compounds are isostructural, exhibiting the Yavapaiite-type structure with a monoclinic C2/m space group. Raman and infrared spectroscopy were employed to elucidate the bonding characteristics within the [BaSbX] phases. UV–vis-NIR spectroscopy provided insights into the electronic properties of the compounds, revealing charge transfer and d-d transitions in Mn2+, Co2+, and Cu2+ ions. In contrast, Zn2+ exhibited full d orbitals. The absorption spectra revealed UV bands indicative of charge transfer, with optical bandgap values spanning from 3.8 eV to 4.6 eV. This range signifies a distinctive semiconducting property inherent in the synthesized materials. Analysis of the Urbach tails revealed the presence of localized states, with lower values indicating higher crystallinity, giving valuable insights into the electronic behavior of the compounds.

Optical polarization studies of latex beads in aqueous solution: An analog for radar scattering in icy regolith

This study presents low phase angle 0°–5° measurements of polarimetric properties of icy planetary regolith analog materials acquired using the custom-built Multi-Axis- Goniometer-Instrument (MAGI). We present same sense (SC), and opposite sense (OC) backscatter circular polarization coefficients, circular polarization ratio (CPR), and degree linear polarization (DLP) of spherical latex (non-dye) beads of varying sizes and volume concentrations (v/v) in aqueous solutions (λ=0.8μm) in water. We also present measurements of alumina powder in air at λ=1.064μm. Measurements showed that at a low incidence angle (i=0°), backscatter is dominated by surface specular single-bounce scattering, that hides other scattering processes. At high (i=15°) incidence angle, surface single-bounce surface scattering becomes negligible, allowing for the detection of diffuse, dihedral (multiple bounces) scattering. We find that classical Mie alumina particles (2.1μm,4.0μm) enhance subsurface scattering due to a larger void space relative to larger Mie particles (30μm), that cause the radar signal to scatter forward off small imperfections, maintaining the polarization properties of the signal and generating high >1CPR. Latex beads, representing impurities, demonstrate the impact of isotropic and anisotropic scattering on radar signatures. This study also found that the scattering medium’s anisotropy correlates to the size of the beads, while the void space of the medium inversely correlates with the bead size and the volume concentration (v/v) of the beads. Rayleigh beads, due to isotropic scattering from the reduced scattering cross-section and higher transparency relative to larger impurities, generate subsurface single bounce scattering from the sample platform, producing OC≫SC and a low (<0.5)CPR across all v/v. Rayleigh impurities in transparent water-ice simulate single bounce scattering from underlying layers. Conversely, classical and large Mie beads generate anisotropic scattering that intensifies scattering in the forward direction with high CPR, inversely proportional to the volume concentration. This study aids in interpreting radar observations of icy bodies in the solar system, providing insights into the interplay between radar waves and icy regolith compositions.

Synthesis, optical, and spectroscopic studies of bismuth boro-tellurite glass system containing BaO and V2O5

A melt quenching technique was used for the preparation of xBaO–(30-x)TeO2–35Bi2O3–33B2O3–2V2O5 (5 ≤ x ≤ 25 mol%) glasses. The structural modifications are studied by X-ray diffraction, DSC, optical, infrared spectroscopy, and Raman as a function of BaO mol%. The progressive incorporation of BaO mol% in the BTBiBV glasses decreases the optical band gap values as the number of free electrons increases with the creation of additional NBOs. The FTIR spectra of the prepared glasses consist of BO3 trigonal and BO4 tetrahedral units while TeO2 changes to TeO3 andTeO4 structural units. The Raman spectra shows that the replacement of BaO with TeO2 decreases the concentration of Te–O–Te linkages within the volume of host glass, which increases the concentration of Ba–O–Te linkages along with BO3 units. Due to this, the overall glass formers connectivity decreases which intern to the creation of NBOs. Moreover, the research highlighted that BTBiBV-5 glasses have exceptional optical properties making them promising materials for photonics, optoelectronics, and optical communication device applications.

A Photoswitchable Metallocycle Based on Azobenzene: Synthesis, Characterization, and Ultrafast Dynamics.

The novel photoswitchable ligand 3,3'-Azobenz(metPA)2 (1) is used to prepare a [Cu2(1)2](BF4)2 metallocycle (2), whose photoisomerization was characterized using static and time-resolved spectroscopic methods. Optical studies demonstrate the highly quantitative and reproducible photoinduced cyclic E/Z switching without decay of the complex. Accordingly and best to our knowledge, [Cu2(1)2](BF4)2 constitutes the first reversibly photoswitchable (3d)‑metallocycle based on azobenzene. The photoinduced multiexponential dynamics in the sub-picosecond to few picosecond time domain of 1 and 2 have been assessed. These ultrafast dynamics as well as the yield of the respective photostationary state (PSSZ = 65%) resemble the behavior of archetypical azobenzene. Also, the innovative pump-probe laser technique of gas phase transient photodissociation (t-PD) in a mass spectrometric ion trap was used to determine the intrinsic relaxation dynamics for the isolated complex. These results are consistent with the results from femtosecond UV/Vis transient absorption (fs-TA) in solution, emphasizing the azobenzene-like dynamics of 2. This unique combination of fs-TA and t-PD enables valuable insights into the prevailing interplay of dynamics and solvation. Both analyses (in solution and gas phase) and quantum chemical calculations reveal a negligible effect of the metal coordination on the switching mechanism and electronic pathway, which suggests a non-cooperative isomerization process.

Synthesis, structure determination, molecular interaction, optical, thermal and anticancer activity studies, pharmacokinetic evaluation, and in-silico analysis of monocarbonyl curcumin derivative: An approach to drug discovery

Overseeing the diverse pharmacological traits of curcumin, a novel monocarbonyl based curcumin derivative (1-(4-ethylbenzoyl)-3, 5-bis ((E)-4-methoxybenzylidene) piperidin-4-one) [EMBP] was synthesized by Claisen-Schmidt condensation and Schotten-Baumann reaction procedures, and diffraction quality crystal was obtained by slow evaporation method. Geometrical parameters were calculated for the grown crystal by using the SCXRD technique. The non-covalent interactions like CH∙∙∙π, π∙∙∙π were visualized by Hirshfeld surfaces analysis. The contribution of various interactions towards the total Hirshfeld surface has been quantified by 2D fingerprint plot. The synthesized material is characterized for various optical and spectral properties through NMR, FT-Raman, FT-IR, UV–Vis, and PL spectra. The thermal stability and melting point of the material have been examined by TG/DTA analysis. The cytotoxic effect on the normal cell line HEK-293 was evaluated, and found that the compound is highly toxic. Anticancer activity on MCF-7 cell line of the compound was assessed and found to exhibit exceptional efficacy against cancerous cells. Results of molecular docking studies and evaluated ADMET properties clearly demonstrate that the synthesized material can be proposed as a promising medication for treating breast cancer but after an extensive biological and pharmaceutical research.

Abstract 2575: GD2 targeted dual-labeled intraoperative molecular imaging probe for neuroblastoma

Abstract Neuroblastoma (NB) is the most common pediatric extracranial solid tumor, with a 5-year survival rate under 50% for those with high-risk disease. Complete surgical resection is essential for these patients and is associated with improved outcomes. However, NB resection presents significant technical challenges due to encasement of vital structures that must be preserved, as well as remote deposits of disease. The current approach to find and safely resect tumor depends on the surgeon’s eyes and hands alone. Fluorescence tracers allow enhanced tumor visualization, but most are not molecularly targeted which leads to poor tumor to background signal. Further, fluorescent signal does not penetrate more than a few millimeters, a limitation that can be overcome by inclusion of a radiotracer. We, therefore, generated and evaluated a dual radio and fluorescent antibody-based probe targeting the GD2 tumor antigen to improve the identification of NB with widely available intraoperative handheld instruments. We generated an intraoperative probe (111In-αGD2-IRDye800CW) with retained affinity and stability. In vivo- Nu/j mice were injected with SK-N-BE(2) NB cells. After tumors grew for five weeks, mice were given tail vein injections of the probe. Gamma and optical biodistribution studies were performed to determine the specificity of binding and tumor to background signal four- and six-days post probe injection. Probe uptake was compared to an isotype. Gross dissections and surgeries aimed at improving completeness of resection were performed using a handheld fluorescent camera (SPY-PHI) and a gamma probe (Neoprobe). The handheld gamma probe detected xenografts with great sensitivity (average in vivo 818 cps of In111 in tumor region versus 34.8 cps in the tail). The fluorescent imaging showed high specific binding to the tumor region. Gamma biodistribution results indicated high accumulation within tumor (13.5 %ID/g) with lower accumulation in blood (3.49 %ID/g) and muscle (0.45 %ID/g). Uptake of the probe greatly exceeded isotype control antibody on days 4 and 6 post-agent injection, for both gamma and optical biodistributions. Initial tumor resection using 111In-DTPA-aGD2-IRDye800CW in an NB bearing mouse identified residual disease left behind when resection was performed using white light alone; the residual disease was then removed, guided by fluorescence imaging. Our dual-labeled probe demonstrated antigen specificity and allowed for the sensitive detection and visualization of NB in vivo with widely available intraoperative tools. This targeted probe could provide a means to improve surgical NB resection, by enabling localization of the all regions of tumor using radio-guidance, followed by clear definition of tumor margins with fluorescent signal, to maximize preservation of vital tissues. Ultimately, we believe this approach can improve safety, extent of NB resection, and patient outcomes. Citation Format: ReidAnn E. Sever, Lauren Taylor Rosenblum, Kayla C. Stanley, Dominic M. Menendez, W Barry Edwards, Marcus M. Malek, Gary Kohanbash. GD2 targeted dual-labeled intraoperative molecular imaging probe for neuroblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2575.

Self-Sustaining Water Microdroplet Resonators Using 3D-Printed Microfluidics.

Microdroplet resonators provide an excellent tool for optical studies of water, but water microdroplets are difficult to maintain outside a carefully controlled environment. We present a method for maintaining a water microdroplet resonator on a 3D-printed hydrophobic surface in an ambient environment. The droplet is maintained through a passive microfluidic system that supplies water to the droplet through a vertical channel at a rate equivalent to its evaporation. In this manner, we are able to create and passively maintain water microdroplet resonators with quality factors as high as 3×108.

Morphological, Optical and Voronoi Polygon Analysis of Breath Figures Prepared on Polymeric Surface

Background/ Objectives: The formation of breath figures over polymers like polystyrene has vast applications in material science for making numerous micro- and nanopatterned functional surfaces. However, the breath figures (BFs) method is a complex phenomenon as the actual formation of structures are many times unpredictable and the nature of structure depends on the type of polymer, solvent, degree of humidity and additives used. The work presented in this paper deals with the study of condensation on the surface of volatile polystyrene polymer solution and their uses for non-wetting using optical and morphological studies along with mathematical model Voronoi polygon analysis using polystyrene and solvent of benzene and chloroform. The growth dynamics of Breath-Figures (BFs) formed due to condensation is presented in brief. Method: Breath Figure (BF) patterns were prepared by two solvents: benzene and chloroform. Different representative values of relative Humidity viz. 60, 70, 80 and 90 % were employed for making BFs. Two different polymer concentrations of 5 and 10 w/v % was used in this study. Findings: The morphology has been statistically analyzed for different parameters like average diameter and their size distribution etc. In case of BFs formed on benzene surface, droplet has average diameter of about 12 µm at 90% humidity but in case of chloroform surface this diameter is about 25 µm at 90% humidity. Voronoi analysis demonstrates simplistic way to qualitatively check the six-fold order and the coordination numbers in BFs. Novelty: The work shows comparative study of BFs patterns using polystyrene on two different solvents with changing humidity. The study shows morphology of the breath patterns is mainly dependent on the polymer concentration, humidity and density of solvents which is a new observation. The study leads to the acquisition of new knowledge on BFs which provides insight important for various applications including biological fields. Keywords: Breath­figures, Voronoi polygon, Polystyrene, Contact angle, Condensation

A comparison of chemical and biogenic surfactant mediated synthesis of ZnO/CuO: Highlighting the antimicrobial activity of the bio-functionalized metal oxide nanoparticles

This study presents a comparative account on synthesis and characterization of ZnO/CuO (ZC) nanostructures by exploiting the capping, stabilizing and reducing characteristics of the biogenic green surfactants (rhamnolipid and surfactin) vis-à-vis chemical surfactant (sodium dodecyl sulfate). The ZC material is characterized by various sophisticated analytical tools such as X-ray diffraction (XRD), spectroscopic, and microscopic methods. The optical studies reveal the bandgap energy of the pristine ZC to be 3.77 eV, which varies marginally for SDS@ZnO/CuO (3.65 eV), rhamnolipd@ZnO/CuO (3.69 eV) and surfactin@ZnO/CuO (3.75 eV). In addition, antibacterial activities of the prepared samples against two pathogenic bacteria, Micrococcus luteus (ATCC 4698) and Escherichia coli DH5α (CP026085) are investigated and the mode of action is demonstrated through the destabilization and disruption of the bacterial membranes and subsequent killing.

Myosin-5 varies its step length to carry cargo straight along the irregular F-actin track

Molecular motors employ chemical energy to generate unidirectional mechanical output against a track while navigating a chaotic cellular environment, potential disorder on the track, and against Brownian motion. Nevertheless, decades of nanometer-precise optical studies suggest that myosin-5a, one of the prototypical molecular motors, takes uniform steps spanning 13 subunits (36 nm) along its F-actin track. Here, we use high-resolution interferometric scattering microscopy to reveal that myosin takes strides spanning 22 to 34 actin subunits, despite walking straight along the helical actin filament. We show that cumulative angular disorder in F-actin accounts for the observed proportion of each stride length, akin to crossing a river on variably spaced stepping stones. Electron microscopy revealed the structure of the stepping molecule. Our results indicate that both motor and track are soft materials that can adapt to function in complex cellular conditions.

Optical soliton solutions to the coupled Kaup-Newell equation in birefringent fibers

One of the fastest growing fields of study in nonlinear optics is optical solitons. This article investigates the optical soliton solutions of the coupled Kaup-Newell equation in birefringent fibers without four wave mixing. This model helps explain how modified structures, particularly Alfven waves, propagate in optical fiber and plasma physics. The results presented in this research clearly show how well the new mapping method handle nonlinear Kaup-Newell equation in coupled vector form, in birefringent fiber without four-wave mixing, to extract the analytical soliton solutions. Four-wave mixing expresses a nonlinear optical effect in which four waves interact each other as a result of the third order nonlinearity. As a valuable outcome of this article, a variety of solitons are discovered including bright, dark, periodic, singular bell-shaped, gap, flat-kink, dark-singular, and w-shaped. The existence criteria for these solitons are also obtained that are presented as constraint conditions. The constraint relations guarantee the existence of such solitons. Furthermore, graphs in 2D, 3D and contour are created to show the physical characteristics of the solutions that are produced. The new mapping method is clear and effective, and the solutions provide a wealth of avenues for additional research. The technique can also be functional to other sorts of nonlinear evolution equations in contemporary areas of research. The outcomes presented in this work are new versions which have never been observed before in existing literature.

Defect Passivation of 2D Semiconductors by Fixating Chemisorbed Oxygen Molecules via h-BN Encapsulations.

Hexagonal boron nitride (h-BN) is a key ingredient for various 2D van der Waals heterostructure devices, but the exact role of h-BN encapsulation in relation to the internal defects of 2D semiconductors remains unclear. Here, it is reported that h-BN encapsulation greatly removes the defect-related gap states by stabilizing the chemisorbed oxygen molecules onto the defects of monolayer WS2 crystals. Electron energy loss spectroscopy (EELS) combined with theoretical analysis clearly confirms that the oxygen molecules are chemisorbed onto the defects of WS2 crystals and are fixated by h-BN encapsulation, with excluding a possibility of oxygen molecules trapped in bubbles or wrinkles formed at the interface between WS2 and h-BN. Optical spectroscopic studies show that h-BN encapsulation prevents the desorption of oxygen molecules over various excitation and ambient conditions, resulting in a greatly lowered and stabilized free electron density in monolayer WS2 crystals. This suppresses the exciton annihilation processes by two orders of magnitude compared to that of bare WS2 . Furthermore, the valley polarization becomes robust against the various excitation and ambient conditions in the h-BN encapsulated WS2 crystals.

Silver nanoparticles induced enhanced stability, dielectric anisotropy, and electro-optical parameters of a nematic liquid crystalline material 4-(trans-4-n-hexylcyclohexyl) isothiocyanatobenzene

Nanocomposites of 4-(trans-4-n-hexylcyclohexyl) isothiocyanatobenzene nematic liquid crystals and silver nanoparticles have been prepared. UV absorption spectroscopy, Fourier transform infrared and Raman spectroscopies were used to characterize the morphology of silver nanoparticles (Ag-NPs). Thermodynamic, optical, and dielectric studies have been done to explore the change in the physical parameters of the composites with respect to the pure sample. Due to dispersion of silver nanoparticles, transition temperature, associated enthalpy and order parameters of the nanocomposites have increased. Dielectric study shows enhanced dielectric anisotropy for Ag-NPs dispersed nanocomposites. The relaxation frequency of an observed mode has shifted towards high frequency region for the nanocomposites. Optical band gap for pure and nanocomposites samples has been estimated from UV absorption peaks and it is found that optical properties of the nanocomposites are almost invariant. Threshold (switching) voltage, rotational viscosity and splay elastic constant for pure and dispersed samples have also been obtained from electro-optical studies.

Structural, optical, and charge carrier dynamics study of metal-doped La6MoO12- based ionic conductors

In this work, we successfully substituted Nb on the Mo site of the La6MoO12 compound by incorporating Sm2O3 through the solution combustion method and investigated their structural, optical, and electrical properties. The X-ray diffraction profile confirmed a transition from the rhombohedral R2 to the R1 phase with increasing Nb. A red shift was found in the optical bandgap energy with increasing Nb concentration. Conductivity spectra showed a negative temperature coefficient of resistance (NTCR) behaviour for the samples. Conductivity and activation energy showed opposite nature through all the compositions. The maximum conductivity value was observed for La5.4Sm0.6Mo0.94Nb0.06O12±δ compound (R2 phase), which also exhibited the highest value of Fermi density following Mott's Variable Range Hopping (VRH) model.

Optical and numerical study on the effect of wall impingement on passive jet ignition characteristics of methane/air mixture

Pre-chamber turbulent jet ignition is a promising high-efficiency combustion technique to achieve stable lean-burn operation for spark-ignition engines. Wall impingement by a high momentum turbulent jet could exert a critical influence on jet ignition behavior. In this work, the passive jet ignition characteristics of premixed methane/air mixture under wall impinging condition was investigated based on optical experiments in a constant volume chamber and numerical simulations. Two ignition modes were found for flat wall impinging cases across a range of non-dimensional impinging distances (H/D) from 5.7 to 20. In mode 1, ignition initiates from near wall region. Under lean conditions of λ = 1.3, compared with that in the free jet case, the ignition delay time characterized by a 5 % mass fraction burned (MFB-05), decreases by 3.3 ms at H = 30 mm and increases by up to 6.6 ms at H = 20 mm. In mode 2, ignition initiates from the jet root. The ignition delay times are shorter for all impinging distances (H = 20, 30, 40 mm), with MFB-05 decreasing by up to 3.4 ms. Simulations reveal that when the wall is located in the jet developing zone with H/D below 7, wall impinging deteriorates the ignition, which is attributed by higher turbulent kinetic energy (TKE) and lower Damköhler (Da) number near the stagnation zone, resulting in extended ignition delay. Conversely, as H/D increases, ignition is promoted by the stagnation effect with a shorter ignition delay. Additionally, the effect of wall shapes was analyzed. Using sharp-tip V-shaped wall, the stagnation region with high TKE is minimized. A blunt-tip V-shaped wall shows enhanced impinging but no obvious increase of Da number at stagnation point. Using M-shaped wall, the ignition mode with a “lift-off” flame was found. Besides, ignition is more favorable in the secondary jet zone with active radicals and higher Da number.

Nonlinear optical properties of zinc oxide thin films

This study reports the influence of deposition temperature (573 K-773 K) on the microstructural, linear and nonlinear optical properties of zinc oxide nano thin films synthesized using the chemical spray pyrolysis method. Synthesized films are polycrystalline, exhibiting a dominant (101) orientation, for which the crystallite size is found to increase with deposition temperature up to 723 K followed by a decrease. Concurrently, the deposit prepared at 723 K showed improved electrical properties, i.e. higher charge carrier concentration and mobility. Optical studies reveal increased transmittance in the visible region and a gradual increase of optical bandgap with deposition temperature. The photoluminescence studies show a near-white light emission for all thin films, however, the density of defect states was comparatively higher for thin films deposited at lower temperatures. A saturable absorption behaviour was observed due to the presence of defects. The thin films show a negative refractive index with self-defocusing phenomena. The total nonlinear susceptibility is found to decrease with increasing deposition temperature, and the solution-processed functional thin films thus have potential implications for nonlinear optical applications such as nonlinear optical switching, optical memory management, and saturable absorbers.

Impact of Homocyclic and Heterocyclic Rings of Chalcones on Charge Transfer Behaviour: A Nonlinear Optical Study

This paper presents the effects of incorporating thienyl and phenyl rings as the terminal ring in the cinnamoyl counterparts of chalcones with donor-acceptor-donor (D-A-D) push-pull setting, on their photophysical responses. Two fluoro-methoxy substituted chalcone derivatives with distinct cinnamoyl systems, 4-methylthiophene-2-carbaldehyde (2F4MA48) and 2,4-dimethylbenzaldehyde (2F4MA96), were synthesized. Characterization of these chalcone derivatives was performed using nuclear magnetic resonance (NMR), Fourier-transform infrared (FTIR) and single-crystal X-ray diffraction (SCXRD). Comparative studies on the linear and nonlinear optical responses were carried out through both experimental analyses and theoretical density functional theory (DFT) calculations. The electronic absorption spectra computed using DFT were compared with the UV-Vis spectra to elucidate the intramolecular charge transfer mechanism via the hole-electron distribution and interfragmentary charge transfer analyses. Molecular properties were examined through electrostatic potential (ESP) maps, π-electron localization function (ELF-π), and frontier molecular orbitals (FMOs). The incorporation of thienyl ring is found to give a stronger push-pull effect and greater electron delocalization. Experimental nonlinear optical responses were investigated using Z-scan technique with a continuous-wave incident laser at a wavelength of 532 nm. Both compounds showed two-photon-induced reverse saturation absorption (RSA) and self-defocusing responses. It was observed that the thienyl-based chalcone, exhibited greater optical nonlinearity in terms of nonlinear absorption (NLA), nonlinear refraction (NLR), and optical limiting. The experimental third-order nonlinear optical susceptibility (χ(3)) was determined to be 8.04 × 10−8 esu for 2F4MA48 and 1.08 × 10−8 esu for 2F4MA96. The onset limiting threshold (FS) was found to be 2.63 kJ cm−2 for 2F4MA48 and 5.23 kJ cm−2 for 2F4MA96. The steep optical limiting traces of 2F4MA48 show superior performance compared to 2F4MA96.

Short excitonic lifetimes of MoSe2 monolayers grown by molecular beam epitaxy on the hexagonal boron nitride

We present a time-resolved optical study of recently developed narrow-line MoSe2 monolayers grown on hexagonal boron nitride with means of molecular beam epitaxy. We find that the photoluminescence decay times are significantly shorter than in the case of the exfoliated samples, even below one picosecond. Such a short timescale requires measurements with better resolution than achievable with a streak camera. Therefore, we employ an excitation correlation spectroscopy pump-probe technique. This approach allows us to identify two distinct non-radiative recombination channels attributed to lattice imperfections. The first channel is active at helium temperatures. It reduces the lifetime of the neutral exciton to below one picosecond. The second channel becomes active at elevated temperatures, further shortening the lifetimes of both neutral and charged exciton. The high effectiveness of both radiative and non-radiative recombination makes epitaxial MoSe2 a promising material for ultrafast optoelectronics.