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This research article reveals the effect of Dy +3 substitution on ?-ferrites KFe 11-x Dy x O 17 with composition (x=0.00, 0.25, 0.50, 0.75 and 1.0). The samples were synthesized by sol-gel auto- combustion method, sintered at 950 o C temperature. The XRD patterns confirmed the single phase of the synthesized samples. The crystallite size varied in the range of 21.49 nm to 25.24 nm for all samples. The polarization verses electric field (P-E) loops indicated the loosy behavior in all samples. The lossy behavior of the samples was seemed to be increased up to x=0.5 and then decreased. The theoretical expression was used to fit an upper branch of P-E loops. FT-IR spectra showed absorption bands at different wavenumbers due to M-O-M stretching vibrations, H-O-H stretching, and C-O-C stretching vibrations, which also confirmed the formation of the single-phase in the samples. Electrochemical measurements of synthesized nano ferrites were carried out by using cyclic voltammetry in a 3.0 M KOH solution. Electrochemical impedance spectroscopy (EIS) has been described by Nyquist plots.

A series of divalent Zn substituted T-type hexagonal ferrite material having the composition (x= 0.0, 0.02, 0.06, 0.1) was synthesized by using the sol-gel auto combustion method. Structural, morphological, optical, and electrical properties of T-type hexagonal ferrite were explored by using an X-ray diffractometer, scanning electron microscopy, Fourier transform infrared spectroscopy and Precision multiferroic II. The X-ray diffraction (XRD) patterns showed the single hexagonal phase ferrites for all the samples. With the substitution of the ions, the change in the values of lattice constants ‘a’, ‘c’ and unit cell volume was observed. The Debye Scherrer formula was used to calculate the crystallite size which was determined to be varied in the range of 26.3nm to 28.3nm. FTIR spectra also indicated that the present synthesized material had single-phase hexagonal structure. SEM micrographs revealed the agglomeration of small grains. The average grain size was found to be 0.331um which might be suitable for microwave absorption applications. The Polarization verse Electric field (P-E) loops unveiled the increase in saturation and remnant polarization. The P-E loops also exhibited the lossy behavior after substitution and the increase in lossy behavior with substitution results in an increase in conductivity of the material.

In present work, an investigation was carried out about the various important properties of Yb 3+ substituted Potassium based ?-hexaferrite KFe 11-x Yb x O 17 (x= 0.0, 0.02, 0.06, 0.1). The Sol-gel auto combustion technique was used to synthesize all the samples. The X-ray diffraction (XRD) patterns confirmed the single hexagonal phase for all prepared samples. The Scanning Electron Microscopy (SEM) confirmed the agglomeration of small particles into big grains. The DC electrical resistivity, measured in the voltage range of (-200V) to (200V), was observed to vary with Yb 3+ contents. The Polarization versus electric field loops revealed the lossy behaviour of pure and substitute samples which indicated the resistive nature of the samples. The saturation and remanence polarization first decreased and then increased with Yb 3+ substitution due to ferric ions distribution between octahedral sites and resistive nature of the samples, respectively. The samples exhibited peculiar magnetic behaviour with the substitution of Yb 3+ ions. The saturation magnetization was increased up to concentration x = 0.06 and then decreased with further substitution of Yb 3+ contents. The coercivity values varied in the range of 141.43 to 279.26 Oe for all the samples which confirmed the soft magnetic nature of present synthesized material. The real part (µ’) and imaginary part (µ’’) of permeability exhibited the high values at low frequencies and these values decreased with the increase of frequency. The prepared samples were supposed to be used as core material of transformer and in high frequency applications due to high resistivity value and low eddy current losses.

In this research work the substitutional effect of Mg2+ on Structural, Electrical Polarization, FTIR, SEM and magnetic properties of Sr1-xMgx Mn2 Fe4 O11 R-type hexaferrite nanoparticles with compositions (x= 0, 0.25, 0.75,1.0) were investigated. The sol-gel auto-combustion method was adopted to synthesize the samples, and the powder was sintered at 800°C for 4 hours to achieve the stable hexagonal phase. XRD pattern showed that all the prepared samples have a single phase R-type hexagonal structure. The lattice parameter a, c, and unit cell volume V decreased with Mg substitution. The dislocation density increased with Mg substitution, while crystalline size varied with Mg doping. The Fourier transform infrared spectroscopy (FTIR) spectra further verified the single hexagonal phase of the produced samples. The saturation and remanent polarization increased with Mg substitution in the polarization versus electric field loops. The P-E loops also indicate the lossy behavior decreased with Mg substitution. By substituting Mg+2, the saturation magnetization, retentivity, and coercivity increased initially, then decreased. VSM measurements reveal ferrimagnetic and paramagnetic nature for all the samples.

The rare-earth element Yb3+-substituted β-ferrites KFe11−xYbxO17 with composition (x = 0, 0.02, 0.06 and 0.1) have been synthesized by sol–gel auto combustion method and sintered at 950 °C. X-ray diffraction (XRD) analysis divulged the formation of single phase β-hexagonal ferrites structure for the whole series. The crystallite size varied in the range of 26–43 nm for all samples. FTIR spectra showed absorption bands at different wave numbers which also confirmed the single phase of the samples. The samples had high dielectric constant, dielectric loss, and tangent loss values at lower frequencies while these values declined with increase in frequency. This dielectric behavior of the samples had been explained on the basis of Maxwell–Wagner and Koop’s model. The dielectric constant results were fitted theoretically by using Debye function which indicated the involvement of more than one ion in dielectric relaxation process. The AC conductivity increased with the increase of frequency and the nonlinear fitting of AC conductivity was obtained through Jonscher’s power law that followed conduction model exactly. The semicircle of cole–cole plots adumbrated the contribution of both grains and grain boundaries to the resistive and capacitive behavior of the material.

In this article, Pr–Mn substituted X-type hexagonal ferrite Sr1–xPrxCu2MnyFe28–yO46 with concentrations of $x =0$ , 0.02, 0.06, 0.1 and $y =0$ , 0.1, 0.3, 0.5 were prepared by using cotton soaked method. The main intention of this article was to explain the microwave absorption phenomenon theoretically and to perceive the effect of Pr–Mn substitution on structural, magnetic, thermal, and microwave absorption properties of X-type hexagonal ferrites. Moreover, the fabrication of material suitable for microwave absorption devices, permanent magnets, and for recording media applications was also aimed in present investigation. The XRD patterns reveal that all the prepared samples possess X-type hexagonal structure. A gradual and slight increase in both lattice parameters “ $a$ ” and “ $c$ ” values was observed with Pr–Mn substitution. The metal–oxygen stretching (M–O) vibrations in the FTIR spectrum at a low frequency indicates the presence of single phase in synthesized material. The enhancement in magnetic properties (saturation magnetization, retentivity, and coercivity) has been observed with the substitution of Pr–Mn contents in pure ferrites. A maximum reflection loss (RL) of −27.21 dB at 11.891 GHz was attained by Pr–Mn-substituted ferrites and reflectivity results agree well with RL results. Microwave absorption property of this substituted material made it a potential candidate to be used in super high frequency (SHF) devices.

Triplet-triplet annihilation (TTA) upconversion, a photophysical phenomenon of conversion of low-energy photon into high-energy photon, is a promising approach due to its low excitation power requirement and high upconversion quantum yields. Most of the triplet photosensitizers (PSs) used for TTA upconversion are based on transition metal complexes and organic chromophores containing heavy atom. Recently TTA upconversion with heavy atom-free PSs has gained much attention due to its minimal detrimental effects. In this chapter we summarize organic triplet PSs with different intersystem crossing (ISC) mechanism used in TTA upconversion. We briefly describe different types of triplet PSs for TTA upconversion such as heavy atom-containing organic chromophores, BODIPY dimers involving exciton coupling, and electron spin convertor-bearing dyes. Recently new triplet PSs involving charge recombination (CR)-induced ISC and thermally activated delayed fluorescence (TADF) have been used in the TTA upconversion. We discuss the benefits of these PSs for TTA upconversion. This book chapter provides current progress in the field of TTA upconversion and designing new efficient triplet PSs.

A series of rare earth elements (RE = Ce, Dy, Yb, La and Pr) substituted Sr0.9RE0.1Mn2Fe4O11 R-type hexagonal ferrites has been prepared by using the Sol–gel technique. The effect of RE substitution on its structural, electric polarization, dielectric and microwave absorption properties was studied. XRD patterns showed that all the prepared samples possess R-type hexagonal structure. The lattice parameters and unit cell volume varied with the substitution of RE contents. The average crystallite size, measured by Scherer formula, varied in the range of 6–15 nm for all samples. These results make this material suitable for being used in multilayer chip inductors (MLCI’s). The dielectric constant was found to decrease at high frequencies. This behavior has been explained on the basis of Maxwell–Wagner’s and Koop’s theory. An increase in AC conductivity was observed with increase in frequency. The decrease in lossy behavior with RE substitution in pure sample indicated the increase in the resistive nature of samples as observed from the electric polarization analysis. The Yb substituted sample exhibited highest value of microwave absorption − 40.5 dB at 11.4 GHz frequency among all the substituted samples.

Road accident is a widespread problem in many urban areas nowadays. Reckless Driving (Over-Speed) is one of the attributes leading to the enormous destruction of pedestrian life. Autonomous vehicle speed control is an important research area in the Intelligent Transportation System (ITS) to mitigate road accidents in densely populated areas. Many existed works utilized Reinforcement Learning (RL) to control the vehicle speed intelligently. However, controlling the over-speed of the vehicle using RL under the speed limit of the different zones (i.e., Town, Rural Main Road, Highways, and so forth) is also another demanding task because of the speed limit variation. Therefore, we propose a Deep-Q-Network (DQN) based Deep Reinforcement Learning (Deep RL) method to overcome the over-speed problem in various speed limit areas. In this paper, the proposed system will reduce the vehicle speed intelligently if the driver passes over the speed limit in a particular zone. The simulation results show that our proposed solution can successfully reduce the vehicle speed under various zone-based speed limits.

Different perylene-3,4:9,10-bis(dicarboximide) (abbreviated as perylenebisimides, or simply PBI) compounds (MT-PBI, DT-PBI, MP-PBI and DP-PBI) with thienyl and phenyl substituents at the bay position were prepared to study the effect of substitution on the photophysical properties, especially the intersystem crossing (ISC) efficacy. We found that the derivative with a monothienyl substituent (MT-PBI) shows efficient ISC (singlet oxygen quantum yield ΦΔ = 72%) and longer triplet state lifetime (τT = 64.4 μs) as compared to reference compounds (derivative with monophenyl substituent at bay position, MP-PBI, ΦΔ = 23% and τT = 48.5 μs). Theoretical computations reveal that the ISC efficiency is dependent on the magnitude of the spin orbit couplings (SOC) between the singlet and triplet excited states, and the SOC matrix element is up to 2 cm−1 for compound showing the highest ISC efficiency. Femtosecond transient absorption spectra show the ISC rate constant of 8 × 109 s−1 for MT-PBI, and no charge transfer exists. Photo-driven electron transfer was observed with the PBI derivatives in the presence of sacrificial electron donor triethanolamine (TEOA), and reversible formation of PBI radical anion (PBI−•) was observed, which shows absorption in the range of 600 nm–800 nm and 900 nm–1000 nm. Delayed fluorescence (P-type) in MT-PBI was also observed (τT = 31.0 μs). These finding are useful for the design of PBI-derived heavy atom-free compounds to be used as triplet photosensitizers.

This research project was designed to understand the synergistic effect of Mg2+ and Yb3+ ions substitution on structural, dielectric, electrical resistivity and electrical polarization properties of Sr1-xMgxFe4-yYbyMn2O11 (x = 0, 0.1, 0.2, 0.3 and y = 0, 0.02, 0.06, 0.1) R-type hexagonal ferrites prepared via sol–gel auto combustion method. The XRD graphs revealed that the present synthesized material exhibited the single phase. The Rietveld refinement was also carried out to fit XRD patterns which confirmed the single phase for all samples. The SEM micrographs indicate the platelet like structure for the grains. The curve fitting of real and imaginary part of permittivity results was done by using the modified Debye function. The ac conductivity enhanced with frequency. The electrical resistivity, calculated in the voltage range of (-200 V to 0 V) and (0 V to 200 V) was found to vary with Mg-Yb substitution. The P-E loops for each concentration unveiled the loosy behavior.

Spin-orbit charge transfer-induced intersystem crossing (SOCT-ISC) is of particular interest for preparation of heavy atom-free triplet photosensitizers. Up to now, examples for SOCT-ISC dyads are limited and electron donor/acceptor SOCT-ISC dyads showing strong visible-light harvesting are rare. Herein, we studied the photophysics of a series of Bodipy-anthracene (BDP-An) compact dyads, especially the triplet state electron spin dynamics with the time-resolved electron paramagnetic resonance (TREPR) spectroscopy. The electronic coupling matrix elements (VDA*) between the 1CT (charge transfer) state and 1LE (locally excited) state are in the range 773–1545 cm–1. For one dyad, we observed three triplet states simultaneously with TREPR, that is triplet states confined on the anthracene (3An) and the Bodipy (3BDP) moieties as well as a 3CT state. Based on the electron spin polarization of these three triplet states and the optical experiments, the SOCT-ISC mechanism is confirmed and the radical pair-ISC mech...

In the present investigation, the divalent basic element “Sr2+” was replaced with another divalent element “Mg2+” to understand the influential effect of Mg2+ on structural, electrical, dielectric and FTIR properties of Sr2+ based R-type hexagonal ferrites Sr1-xMgxFe4Sn2O11 with composition (x = 0.0, 0.1, 0.2, 0.3). The material was synthesized by sol-gel auto combustion method and sintered at 800 °C temperature for development of the required phase. The XRD and FTIR analysis revealed the formation of single-phase R-type hexagonal ferrites. It was observed that the values of lattice parameters a (A), c (A), crystallite size (nm), X-ray density (g/cm3) and unit cell volume V (A) 3 changed with Mg2+ substitution. The Scherer formula was used to find the crystallite size which varied in the range from 11 to 13 nm for all synthesized samples. The FTIR spectra also indicated the presence of negligible amount of moisture and Nitrogen in sample, absorbed from the atmosphere. The dielectric constant results showed the higher values for Mg2+ substituted samples than the pure sample. Furthermore, Debye function was used for the fitting of the dielectric constant results which indicated the participation of more than one ion in the increment of dielectric constant. The AC conductivity increased with the increase of frequency, consequently the experimental result was compared with theoretical results by Jonscher's power law which elicited the conduction mechanism. The P-E (polarization vs. electric field) loops substantiated the decrease in saturation and remnant polarization with Mg+2 content. The electrical resistivity of synthesized sample unveiled the resistive nature of sample significantly. It is suggested that the present R-type ferrites are useful in microwave absorption devices and in transformer to reduce the eddy current losses.

This research article reports the exploration of structural, dielectric, optical and electrical polarization properties of β-type hexagonal ferrite KLaxFe11-xO17 upon the substitution of rare earth element La3+ with compositions (x = 0, 0.02, 0.06 and 0.1). The samples were synthesized by adopting the sol-gel auto-combustion technique and the sintering temperature was 950 °C. The XRD patterns revealed the single hexagonal phase for all the samples. The lattice parameters a (A), c (A), crystallite size (nm), X-ray density (g/cm3) and unit cell volume V (A) 3 changed with La3+ substitution. The crystallite size was found to be varied in the range from 24 to 27 nm for all samples as calculated from Scherer formula. Fourier transform infrared spectroscopy (FTIR) spectra also confirmed the single phase for the synthesized samples. The dielectric constant exhibited the higher values than the pure sample with substitution. The dielectric constant results were fitted with the Debye function which indicated the participation of more than one ion in the increment of dielectric constant. The real (M′) and imaginary (M″) part of complex modulus graphs delineated the peaks shifting towards high and low frequency region which confirmed the occurrence of relaxation phenomenon in material. The polarization verses electric field loops corroborated the decrease in saturation and remnant polarization with La3+ contents. The P-E loops also showed the lossy behavior and the increment in lossy behavior with substitution pointed out the increase in resistivity of the samples. From aforementioned evidences, it is confirmed that the present synthesized beta ferrites are useful in the fabrication of humidity sensors and to reduce the eddy current losses.

A series of rare earth Pr3+ element substituted, Sr1-xPrxMn2Fe4O11 (x = 0, 0.02, 0.06, 0.1) R-type hexagonal ferrites has been synthesized by adopting the Sol-gel method. The influence of Pr-substitution on its structural, electrical, dielectric and magnetic behavior was examined. XRD patterns indicate the single phase for all the samples. The lattice parameters and unit cell volume changed with the substitution of Pr3+ contents. The electrical resistivity of the sample significantly varied with the substitution of Pr3+ ions. The sample with the Pr3+ concentration x = 0.1 was observed to have highest resistivity among the others. The dielectric constant was found to decrease at high frequencies for all samples. The tangent loss revealed the hopping type conduction between Fe3+ and Fe2+ sites. The increase in AC conductivity was observed as a function of frequency. The sample with concentration x = 0.1 revealed the maximum value of polarization. A peculiar magnetic trend was observed for all samples upon the substitution of Pr-contents. The unsubstituted sample exhibited the soft ferrimagnetic properties while the paramagnetic behavior was observed for Pr concentration x = 0.02 and last two concentrations (x = 0.06 and 0.1) unveiled the superparamagnetic nature.