Applications In Optical Devices Research Articles

Nonlinear Optical Saturable Absorption Properties of 2D VP Nanosheets and Application as SA in a Passively Q-Switched Nd:YVO4 Laser

Two-dimensional (2D) violet phosphorus (VP) plays a significant role in the applications of photonic and optoelectronic devices due to its unique optical and electrical properties. The ultrafast carrier dynamics and nonlinear optical absorption properties were systematically investigated here. The intra- and inter-band ultrafast relaxation times of 2D VP nanosheets were measured to be ~6.83 ps and ~62.91 ps using the pump–probe method with a probe laser operating at 1.03 μm. The nonlinear absorption coefficient βeff, the saturation intensity Is, the modulation depth ΔR, and the nonsaturable loss were determined to be −2.18 × 104 cm/MW, 329 kW/cm2, 6.3%, and 9.8%, respectively, by using the Z-scan and I-scan methods, indicating the tremendous saturable absorption property of 2D VP nanosheets. Furthermore, the passively Q-switched Nd:YVO4 laser was realized with the 2D VP nanosheet-based SA, in which the average output power of 700 mW and the pulse duration of 478 ns were obtained. These results effectively reveal the nonlinear optical absorption characteristics of VP nanosheets, demonstrating their outstanding light-manipulating capabilities and providing a basis for the applications of ultrafast optical devices. Our results verify the excellent saturable absorption properties of 2D VP, paving the way for its applications in pulsed laser generation.

Fabrication, surface characterization and effect of oxygen irradiation on polymeric nanocomposite films

This study addressed the preparation of nanocomposites consisting of polyvinyl alcohol (PVA) and titanium oxide (TiO2) for utilization in optoelectronics technologies. PVA/10%TiO2 nanocomposite samples with a mean thickness of 0.1[Formula: see text]mm were created using the solution casting method. The PVA/TiO2 films are irradiated with oxygen fluences of [Formula: see text], [Formula: see text] and [Formula: see text] ions/cm2. The X-ray diffraction (XRD) and FTIR methodologies were employed to investigate the impact of ion bombardment on the structural characteristics and functional groups of PVA/TiO2 substrates. Diffraction peaks are 20.1° for PVA and 25.4° for TiO2, indicating the successful PVA/TiO2 nanocomposite construction. The absorbance (A) of unirradiated and irradiated samples was measured using UV–Vis spectroscopy within a wavelength range of 200–1100[Formula: see text]nm. Band gaps ([Formula: see text]) were calculated using Tauc’s formula for PVA/TiO2 films, exhibiting a decrease from 4.56[Formula: see text]eV for unirradiated PVA/TiO2 film to 4.16, 3.95 and 3.88[Formula: see text]eV at ion fluences of [Formula: see text], [Formula: see text] and [Formula: see text] ions/cm2, respectively. Furthermore, the Ubrach tail has a rise of 1.23[Formula: see text]eV for unirradiated PVA/TiO2 to 1.28[Formula: see text]eV, 1.4[Formula: see text]eV and 1.77[Formula: see text]eV for irradiated films with ion fluences of [Formula: see text], [Formula: see text] and [Formula: see text] ions/cm2, respectively. Additionally, following ion irradiation, the PVA/TiO2 absorption edge [Formula: see text], which was 3.56[Formula: see text]eV, decreased to 3.48, 3.37 and 3.23[Formula: see text]eV, with increasing ion beam fluences. This study demonstrated that the optical behaviors of the PVA/TiO2 films were altered under bombardment, suggesting their potential applicability in optical devices.

Fabrication of pbs films for air mass filter of solar simulator

The production of solar panels is continuously increasing due to increasing demands at industrial and residential levels. This also leads to an increasing demand for solar simulator testing tools. A solar simulator is a tool to assess a solar panel's performance in lab and industry scales. One of the main components of the solar simulator is the Air Mass Filter (AMF). The primary function of AMF is to remove unwanted wave bands from the solar simulator light source (e.g., Xe arc lamp) so that the filtered spectrum is commensurate to that of solar irradiation. An AMF can be produced by fabricating a thin material layer on a transparent substrate like glass. The film would absorb certain wave bands in different ways. This paper reports the fabrication of the chalcogenide PbS thin films for applying AMF. The thermal evaporation technique is used for the film fabrication. PbS is known for its versatility for applications in different optical devices due to its tailorable optical properties. Different amounts (in grams) of PbS source powders are used to deposit the PbS thin films. The optical properties of the films are then examined using UV-Vis spectroscopy. The distributions of the transmittance intensity of the Xe-arc-lamp light with and without the use of the films as an optical filter are then examined using a solar simulator. From the experiments, the film deposited using a 0.012 g PbS powder source is regarded as the optimum one regarding the transmittance intensity distribution.

Ab initio calculation of electronic and optical properties of vdWHs HfX2/BSb(X = Se,S) using density functional theory

Recently, another series of two-dimensional (2D) materials called van der Waals heterostructures (vdWhs) have attracted a lot of attention due to their outstanding properties and wide application in electronic and optical devices. Based on density functional theory (DFT) calculations, the properties of heterostructures were investigated with two different vertical arrangements, formed by two isolated sheets of HfX2(X = Se,S) and Boron antimonide(BSb) monolayer. In particular, vdW interactions are present in all these heterostructures rather than covalent bonding. All thevdWHsare semiconductor with indirect k-M band gap, for which the HSE06 functional exhibit a larger gap, but the electronic gap of all heterostructures is smaller than the electronic gap of their constituent sheets. In addition, all vdWHs show excellent optical absorption in the visible, near-infrared, and ultraviolet regions in the x direction, while the absorption peaks for all vdWHs are higher in the z direction. By fabricating heterostructures from isolated plates, their absorption power increases. The present review demonstrates an effective method for the design of novel vdWHs, and it explores their applications for photocatalytic, photovoltaic, and optical devices.

Fundamentals and emerging optical applications of hexagonal boron nitride: a tutorial

Hexagonal boron nitride (hBN), also known as white graphite, is a transparent layered crystal with a wide bandgap. Its crystal structure resembles graphite, featuring layers composed of honeycomb lattices held together through van der Waals forces. The layered crystal structure of hBN facilitates exfoliation into thinner flakes and makes it highly anisotropic in in-plane and out-of-plane directions. Unlike graphite, hBN is both insulating and transparent, making it an ideal material for isolating devices from the environment and acting as a waveguide. As a result, hBN has found extensive applications in optical devices, electronic devices, and quantum photonic devices. This comprehensive tutorial aims to provide readers with a thorough understanding of hBN, covering its synthesis, lattice and spectroscopic characterization, and various applications in optoelectronic and quantum photonic devices. This tutorial is designed for both readers without prior experience in hBN and those with expertise in specific fields seeking to understand its relevance and connections to others.

Investigation of structural, electronic, optical and thermoelectric properties of hallide double perovskite Rb2AlAgX6 (X = Cl, I): A first-principles DFT study

In order to meet the demands of the energy consumption, double perovskites (DP) are a dependable green energy source. Consequently, there is a great deal of promise for thermoelectric and optoelectronic device applications when studying these perovskite halides. Our work examined the thermoelectric and optoelectronic properties of Rb2AlAgCl6 and Rb2AlAgI6 halides using Density Functional Theory (DFT). The tolerance factor and energy of formation for the halides that were examined show that they are stable in the cubic phase, structurally and thermodynamically. We calculated the bandgaps for Rb2AlAgCl6 (Eg = 3.82 eV) and Rb2AlAgI6 (Eg = 1.321 eV) using mBJ potentials, and compared them to the reported values. The optical characteristics of the materials under investigation were revealed through the use of a complicated dielectric function. The computed optical findings show that the materials are suitable for optoelectronic applications, with maximal light absorption occurring in the ultraviolet (UV) and infrared (IR) ranges. Optical parameters obtained includes large values of absorption coefficients (∼105cm−1), low reflectivity (∼1–15 %), and high optical conductivity (∼1015 sec−1). Thermoelectric properties revealed enhanced power factor for Rb2AlAgI6 as compared to Rb2AlAgCl6. These results imply that these materials are appropriate for application in optical and thermoelectric devices.

A Tunable Hydrophilic-Hydrophobic, Stimulus Responsive, and Robust Iridescent Structural Color Bionic Film with Chiral Photonic Crystal Nanointerface.

Bio-inspired in nature, using nanomaterials to fabricate the vivid bionic structural color and intelligent stimulus responsive interface as smart skin or optical devices are widely concerned and remain a huge challenge. Here, the bionic flexible film is designed and fabricated with chiral nanointerface and tunable hydrophilic-hydrophobic by the ultrasonic energy perturbation strategy and crosslinking of the cellulose nanocrystals (CNC). An intelligent nanointerface with adjustable hydrophilic and hydrophobic properties is constructed by the supramolecular assembly using a smart ionic liquid molecule. The bionic flexible film possessed the variable hydrophilic-hydrophobic, stimulus responsive, and robust iridescent structural color. The reflective wavelength and the helical pitch of the film can be easily modulated through the ultrasonic energy perturbation strategy. The bionic flexible film by covalent cross-linking has excellent robustness, good elasticity and flexibility. The tunable brilliant structural color of the chiral nanointerface is attributed to the surface charge change of the CNC photonic crystal, which is disturbed by ultrasonic energy perturbation. The bionic flexible film with tunable structure color has intelligent hydrophilic and hydrophobic stimulus response properties. The chiral bionic materials have potential applications in smart skin, optical devices, bionic materials, robots, anti-counterfeiting, colorful displays, and stealth materials.

Incorporation of neodymium, holmium, erbium, and samarium (oxides) in zinc-borotellurite glass: Physical and optical comparative analysis

Investigating the effect of different types of rare-earth oxides on zinc borotellurite glass is important to determine the potential application in optical devices. The addition of rare-earth oxides in zinc borotellurite glass is well-known to enhance the optical properties due to the effects of 4f-4f transitions. In this work, we aim to compare the effect of different rare-earth oxides on zinc borotellurite glass denoted as ZBTNd, ZBTHo, ZBTEr and ZBTSm. The glass samples were successfully fabricated via the melt-quenched technique. The physical investigation of the glasses has been done by measuring the density and molar volume. It was found that ZBTNd glass has the lowest density than the other glasses due to the small atomic radius in neodymium oxide. High-density value for ZBTHo glass shows potential to be used as radiation shielding properties. The high value of molar volume for ZBTNd glass is advantageous for fiber optics as ZBTNd glass has good performance in elasticity. It was found that ZBTEr has a lower refractive index than the other glasses due to low dispersion characteristics. However, ZBTEr glass has good performance to be used in optical communication applications. It was found that the optical absorption shifts to a longer wavelength beginning from ZBTEr > ZBTHo > ZBTNd > ZBTSm. The optical band gap energy for ZBTEr glass is higher than the other glasses due to the Coulomb repulsion energy for erbium which is greater than neodymium and samarium and slightly higher than holmium. The pattern of electronic polarizability for all glasses was found as follows ZBTSm>ZBTNd>ZBTEr>ZBTHo. The optical basicity for ZBTEr was found highest which indicates a higher acidity, meanwhile, the ZBTNd glass has the lowest value which corresponds to a higher basicity.

Controlled growth of 3R phase niobium diselenide and its properties

Inversion symmetry broken 3R phase transition metal dichalcogenides (TMDs) show fascinating prospects in spintronics, valleytronics, and nonlinear optics. However, the controlled synthesis of 3R phase TMDs is still a great challenge. In this work, two-dimensional 3R-NbSe2 single crystals up to 0.2 mm were synthesized for the first time through chemical vapor deposition method by designing a space-confined system. The crystal size and morphology can be controlled by the location of the stacked substrates and the amount of the Nb2O5 precursor. Scanning transmission electron microscopy and Raman measurements reveal the NbSe2 exhibits a pure 3R stacking mode with relatively weak interlayer van der Waals interactions. Importantly, 3R-NbSe2 shows obvious second harmonic generation signal which intensity intensified as thickness increases. Density functional theory calculations and optical absorption demonstrate the coexistence of metallic and semiconducting optical properties of 3R-NbSe2. We designed a NbSe2/WS2/NbSe2 photodetector utilizing the metallicity of 3R-NbSe2, which shows good performance especially an ultrafast response (6–7 μs, 0.5 ms–7.9 s for Au electrodes in literature). The proposed strategy and findings are of great significance for the growth of many other 3R-TMDs and applications of nonlinear optical and ultrafast devices.

Studies on the synthesis, growth, and characterization of 2-cyanopyridinium salicylate single crystals for nonlinear optical applications

By employing methanol as the solvent in slow solvent evaporation method, a new nonlinear optical organic single crystal of 2-cyanopyridinium salicylate (2-CPSC) was grown. The lattice parameters of the 2-CPSC crystals were found out to be a = 7.7764(9) Å, b = 12.3938(17) Å, c = 12.3685(18) Å, and β = 94.44º using single crystal X-ray diffraction (SCXRD) analysis. The confirmation of crystalline nature was done by powder XRD analysis. The 2-CPSC crystal's chemical composition and functional groups were confirmed by Fourier transform infrared (FTIR) spectral analysis. The optical study was done by ultraviolet-visible-near infrared (UV–Vis-NIR) spectral analysis showing a cutoff wavelength of 338 nm. Studies on the grown 2-CPSC crystal's dielectric and Vicker's microhardness were also conducted. The linear dependence of photocurrent with the applied electric field was revealed for the grown crystals. The 2-CPSC crystal's third-order nonlinearity was investigated by the single-beam Z-scan technique using a continuous He-Ne laser. The open aperture Z-scan reveals the two-photo absorption mechanism and the closed aperture Z-scan study reveals the positive nonlinearity of the 2-CPSC crystals with third order susceptibility value of χ3=2.6763×10−6(esu). The density functional theory (DFT) method of B3LYP level with the 6–31++G(d,p) basis set was used for different quantum chemical calculations like geometry optimization, natural bond orbital (NBO) analysis, mulliken atomic charge, and molecular electrostatic potential (MEP). The higher nonlinearity of the 2-CPSC can be a potential alternative for commercially available potassium dihydrogen phosphate (KDP) and candidate for its application in nonlinear optical devices like optical limiting and optical switching.

Theoretical investigation of bidirectional and unidirectional dual-band absorption in one dimensional Octonacci sequences controlled by Dirac semimetal and Vanadium dioxide

The dual-band absorption properties of one-dimensional ternary Octonacci sequences, comprising dielectric, Dirac semimetal (DS), and Vanadium dioxide (VO2), are investigated theoretically and numerically using transfer matrix method, full-wave simulations, and impedance match theory. The photonic quasi-periodic multilayers exhibit bidirectional dual-band high absorption properties, attributed to strong electric field localization. Interestingly, this dual-band absorption can be spectrally tuned to the desired frequencies by adjusting the Fermi energy of the DS, changing the structure's parameters, the choice of dielectric, and the angle of incidence. Furthermore, the addition of a VO2 layer at the bottom of the Octonacci sequence enables the realization of dynamically tunable bidirectional and unidirectional dual-band absorption by modulating the conductivity of VO2. Remarkably, the absorption response remains insensitive to the polarization of the incident wave. These unique properties, together with the ease of manufacturing, make our proposed structures a promising candidate for wide applications in tunable optical devices.

Optical Phenomena in Molecule-Based Magnetic Materials.

Since the last century, we have witnessed the development of molecular magnetism which deals with magnetic materials based on molecular species, i.e., organic radicals and metal complexes. Among them, the broadest attention was devoted to molecule-based ferro-/ferrimagnets, spin transition materials, including those exploring electron transfer, molecular nanomagnets, such as single-molecule magnets (SMMs), molecular qubits, and stimuli-responsive magnetic materials. Their physical properties open the application horizons in sensors, data storage, spintronics, and quantum computation. It was found that various optical phenomena, such as thermochromism, photoswitching of magnetic and optical characteristics, luminescence, nonlinear optical and chiroptical effects, as well as optical responsivity to external stimuli, can be implemented into molecule-based magnetic materials. Moreover, the fruitful interactions of these optical effects with magnetism in molecule-based materials can provide new physical cross-effects and multifunctionality, enriching the applications in optical, electronic, and magnetic devices. This Review aims to show the scope of optical phenomena generated in molecule-based magnetic materials, including the recent advances in such areas as high-temperature photomagnetism, optical thermometry utilizing SMMs, optical addressability of molecular qubits, magneto-chiral dichroism, and opto-magneto-electric multifunctionality. These findings are discussed in the context of the types of optical phenomena accessible for various classes of molecule-based magnetic materials.

Modulation of Second-Order Sideband Efficiency in an Atom-Assisted Optomechanical System

We propose an efficient scheme to enhance the generation of optical second-order sidebands (OSSs) in an atom-assisted optomechanical system. The cavity field is coupled with a strong driving field and a weak probe field, and a control field is applied to the atom. We use the steady-state method to analyze the nonlinear interaction in the system, which is different from the traditional linear analysis method. The existence of an auxiliary three-level atom driven by the control field significantly enhances the generation of an OSS. It is found that the efficiency of the OSS can be effectively modulated by adjusting the Rabi frequency of the control field, optomechanical cooperativity and atomic coupling strength. Our scheme provides a promising solution for controlling light propagation and has potential application in quantum optical devices and quantum information networks.

Prolonged Exciton Lifetime Is Achieved in Porphyrin Nanoring by Template Engineering: A Nonadiabatic Tight Binding Approach.

Porphyrin nanoring has been attracting immense attention due to its light harvesting capacity and potential applications in optical, catalysis, sensor, and electronic devices. We demonstrate by nonadiabatic quantum dynamics simulations that the photovoltaic efficiency can be enhanced by template engineering. Altering the hexadentate template (T6) with two tridentate templates (2T3) within the porphyrin ring (P6) cavity accelerated the electron transfer twice and suppressed the electron-hole recombination by nearly three times. The atomistic tight-binding simulation rationalized the dynamics by different localizations of charge of the band edge states, changes in nonadiabatic coupling, alteration in quantum coherence, and involvement of diverse electron-phonon vibrational modes. Further 2T3 templates more strongly hold the P6 ring than T6, reducing the structural fluctuation. As a result, the nonadiabatic coupling becomes weaker and suppresses the carrier recombination. Current atomistic simulation presents a template engineering strategy to enhance the exciton lifetime along with ultrafast charge separation, crucial factors for photovoltaic applications.

The growth aspects and experimental techniques for the characterization of amino acid L-histidine hybrid crystals for nonlinear optical device applications

The development of crystal growth and measurement methods opens new possibilities for studying materials with remarkable nonlinear optical features. The development of bulk crystals is a constant concern to be beneficial for device applications. This study focuses on the development of nonlinear optical crystals of l-histidine complexes, characterization approaches, and prospective applications. The solution growth approach, a straightforward, inexpensive, and low-temperature growth technique, was adopted broadly. Recent studies show that l-histidine derivatives have potential optical, SHG, thermal, dielectric, and mechanical properties, making them an excellent choice for nonlinear optical devices. In this work, structural, spectroscopic, chemical composition, linear and nonlinear optical analyses, thermal, and dielectric characterizations of l-histidine derivatives were conducted. Most of the l-histidine complexes were found to be crystallized in orthorhombic and monoclinic crystal systems with P212121 and P21 space groups. The crystalline perfections of the samples were analyzed by the HR-XRD method. The energy-dispersive X-ray (EDX) spectroscopic technique was applied to evaluate the chemical content of the compounds. FT-IR and FT-Raman techniques were used to recognize the molecular vibrations and functional groups of the l-histidine derivatives. The UV-visible and photoconductivity studies were done to examine the optical behaviors of the developed crystals. Most of the crystals were found to have excellent optical transparency and wide bandgaps. It has been observed that l-histidine hydro-fluoride dehydrate and l-histidine tetrafluoroborate are found to have the highest second harmonic generation (SHG) efficiencies. The dielectric analyses were utilized to study the dielectric constant and dielectric loss variations with the applied frequency. According to the thermal analyses, most of the crystals were found to have substantial thermal stabilities suitable for device applications.

Novel third order nonlinear optical stilbazolium crystal replaced with 3-methoxy benzaldehyde as donor for optical device applications

A novel organic nonlinear optical stilbazolium group single crystal of 1-methyl-2-[2-(3-methoxystyryl)]-pyridinium iodide (subsequently referred to as MSMI) was grown by the solution growth technique using the method of slow evaporation at ambient temperature. The Single-crystal XRD investigation indicates that the MSMI crystal belongs to a monoclinic crystal system with a centrosymmetric space group. CHN elemental analyser confirms the weight percentage of carbon (C = 51.00 %) hydrogen (H = 4.55 %) and nitrogen (N = 3.94 %) in the MSMI crystal structure. The presence of 16 hydrogen atoms and 15 carbon atoms in the MSMI was affirmed by the Nuclear Magnetic Resonance (NMR) spectroscopic analysis. Fourier Transform Infrared (FTIR) studies confirmed the fundamental vibrations for different functional groups found in the MSMI crystal. The Hirsfeld surface analysis figured out the hydrogen bond interaction and π…π interaction which supports the stability of the crystal structure. The crystal is found to exhibit transmittance of wavelength above 400 nm and has a band gap of 3.05 eV ascertained from UV–Vis-NIR spectroscopic analysis. Photoluminescence (PL) studies reveal that the title crystal has an emission wavelength of 572 nm. The surface characteristics of the title crystal were examined by Atomic Force Microscopy (AFM), and etching studies. The value of Meyer's number is n = 1.8 which is determined by the Vickers microhardness studies. The value of the third-order nonlinear refractive index (n2) is 4.662×10−8 cm2/W, the nonlinear absorption coefficient (β) is 1.305×10−3 cm/W, nonlinear susceptibility (χ(3)) is 9.297×10−5 esu and the optical limiting threshold is 11.43 J/cm2 was ascertained form the Z-scan technique. The results indicate that the MSMI crystal is a potential optical limiter and has promising applications in nonlinear optical devices.

Giant Faraday rotation in atomically thin semiconductors

Faraday rotation is a fundamental effect in the magneto-optical response of solids, liquids and gases. Materials with a large Verdet constant find applications in optical modulators, sensors and non-reciprocal devices, such as optical isolators. Here, we demonstrate that the plane of polarization of light exhibits a giant Faraday rotation of several degrees around the A exciton transition in hBN-encapsulated monolayers of WSe2 and MoSe2 under moderate magnetic fields. This results in the highest known Verdet constant of -1.9 × 107 deg T−1 cm−1 for any material in the visible regime. Additionally, interlayer excitons in hBN-encapsulated bilayer MoS2 exhibit a large Verdet constant (VIL ≈ +2 × 105 deg T−1 cm−2) of opposite sign compared to A excitons in monolayers. The giant Faraday rotation is due to the giant oscillator strength and high g-factor of the excitons in atomically thin semiconducting transition metal dichalcogenides. We deduce the complete in-plane complex dielectric tensor of hBN-encapsulated WSe2 and MoSe2 monolayers, which is vital for the prediction of Kerr, Faraday and magneto-circular dichroism spectra of 2D heterostructures. Our results pose a crucial advance in the potential usage of two-dimensional materials in ultrathin optical polarization devices.

Cr2AlB2/PbS heterostructure as saturable absorber for ultrashort pulse generation

Rapid progress has been realized in the nonlinear optical device applications of 2D materials. 2D materials are attractive due to their characteristics optical nonlinearities and distinctive light-matter interactions, which assure them promising nonlinear optical devices for ultrashort pulses generating. Cr2AlB2, a member of the new series of 2D materials known as MBenes, has been predicted to have potential saturable absorption properties. In this study, the saturable absorption properties of Cr2AlB2 and Cr2AlB2/PbS vdW heterostructure SAs are investigated. In comparison with Cr2AlB2, the Cr2AlB2/PbS vdW heterostructure exhibits better saturable absorption. The enhancements of nonlinear optical properties can be attributed to the carrier migration between heterostructure. The simulation results based on the Ginzburg-Landu equation are employed to predict the laser performances of Cr2AlB2 and Cr2AlB2/PbS heterostructure SA. By incorporating SAs in the cavity, highly stable conventional solitons were observed. Both simulation and experimental results demonstrate that Cr2AlB2/PbS vdW heterostructure has superior pulse performance compared to the Cr2AlB2 SA. These results demonstrate that Cr2AlB2/PbS vdW heterostructure processes better saturable absorption properties and serves as a promising SA in ultrashort pulse generation.

Azobenzene-Based Conjugated Polymers: Synthesis, Properties, and Biological Applications.

Conjugated polymers (CPs) have been developed quickly as an emerging functional material with applications in optical and electronic devices, owing to their highly electron-delocalized backbones and versatile side groups for facile processibility, high mechanical strength, and environmental stability. CPs exhibit multistimuli responsive behavior and fluorescence quenching properties by incorporating azobenzene functionality into their molecular structures. Over the past few decades, significant progress has been made in developing functional azobenzene-based conjugated polymers (azo-CPs), utilizing diverse molecular design strategies and synthetic pathways. This article comprehensively reviews the rapidly evolving research field of azo-CPs, focusing on the structural characteristics and synthesis methods of general azo-CPs, as well as the applications of charged azo-CPs, specifically azobenzene-based conjugated polyelectrolytes (azo-CPEs). Based on their molecular structures, azo-CPs can be broadly categorized into three primary types: linear CPs with azobenzene incorporated into the side chain, linear CPs with azobenzene integrated into the main chain, and branched CPs containing azobenzene moieties. These systems are promising for biomedical applications in biosensing, bioimaging, targeted protein degradation, and cellular apoptosis.

Synthesis, structural, optical, dielectric, magnetic and magneto-dielectric properties of CoFe2O4 and Graphene Quantum Dots (GQDs) decorated CoFe2O4 hybrid nanocomposite

A sol-gel synthesis method was used for the synthesis of pure CoFe2O4 (CFO) as well as Graphene Quantum Dots (GQDs) decorated CoFe2O4 Hybrid Nanocomposite (GCHN). From X-ray diffraction (XRD) data it was analyzed that both these samples have a cubic structure with Fd-3m space group. Using Debye-Scherer's equation, the average sizes were determined to be 24.48 and 13.74 nm, respectively. FTIR spectra revealed details about vibration bands and functional groups present. Raman spectra confirmed existence of GQDs in GCHN with an ID/IG ratio of ∼0.8. The results of Field emission scanning electron microscopy (FESEM) analysis exhibited microstructural morphological details having shapes of grains to be non-uniform in shape. UV–visible data was used to calculate band gap (Eg) energy by using Tauc plot method and found to be 2.52 eV and 2.99 eV respectively for CFO and GCHN. Urbach energy (EU) was found to be 1.03 and 1.19 eV for CFO and GCHN respectively. The dielectric properties of GCHN were analyzed for dependence on frequency and temperature and explained by Maxwell-Wagner-type polarization. The frequency-dependent ac conductivity (σac) followed Jonscher's power law and investigated dynamics of ion hopping. Impedance spectroscopy was used to further evaluate Nyquist plots with respect to temperature as well as magnetic fields to estimate grain and grain boundary contributions. This was further used to evaluate electrical characteristics such as relaxation time (τ). Activation energies (Ea) calculated using relaxation times were found to be 0.48 eV for CFO while 0.22 and 0.92 eV for GCHN respectively. At room temperature, CFO and GCHN exhibited a strong magneto-dielectric coupling (MD) and showed negative magneto-dielectric properties in low-frequency regions. At room temperature (RT), magnetization values of CFO and GCHN displayed were 38.48 and 7.52 emu/g respectively. The lower magnetization value was possibly due to shielding by GQDs in GCHN. These properties enable it to be used as a potential application in microelectronic systems, spintronics, optical and optoelectronic devices, magnetic resonance imaging (MRI) and memory devices.