DSSCs have garnered significant attention as a promising technology for renewable energy generation. The carrier kinetics, or the dynamics of charge carriers, play a vital role in the efficiency of DSSC. However, numerous of its optoelectronics characteristics at low frequencies are highly contested. Here, we thoroughly investigated the carrier dynamics of curcumin-based sensitized cell using impedance spectroscopy and modulus spectroscopy under illumination and dark condition. It is revealed that the dielectric relaxation in curcumin-based DSSC follows the interfacial (Maxwell-Wagner type) polarization probably ascribed to the grain boundary effect. Moreover, the comparative evaluation of impedance and modulus spectra at lower frequencies demonstrates the localized type of charge-carrier relaxation in this curcumin-based sensitized cell, which has been related with the conductivity hopping phenomena. These results illustrate the potential of curcumin as a promising new sensitizer for DSSCs and highlight the importance of continued research into new and innovative materials for sustainable energy technology.

We explored the impact of Gd doping on the structural, electronic and optical characteristics of the ZnO powder. The Gd-doped ZnO (0, 2% and 5%) powder samples have been synthesized using the conventional solid-state reaction process with varied Gd concentrations. The XRD pattern confirmed that all the studied samples are in the hexagonal wurtzite crystalline structure. The morphology has been explored using SEM images, which exhibited an agglomerated rod-like particle structure. The XPS results indicate the presence of oxygen vacancies (Vo) in the Gd-doped ZnO samples and the Vo’s are found to increase with increasing Gd amount. According to PL findings, the intensity ratio of the green and ultra-violet emission peaks is found to increase from 0.090 to 0.418 with increasing Gd-doping concentrations, confirming that Vo’s are increasing with Gd-doping. The UV-visible spectroscopy results reveal that the energy band gap (Eg) decreased from 3.31 eV to 3.23 eV with increasing Gd-doping concentration. Bangladesh J. Sci. Ind. Res. 58(1), 53-64, 2023

Zinc oxide is a multifunctional material with important applications in areas like electronics, optoelectronics, sensors and photocatalysis. In the present work, the Cu-doped ZnO (Cu = 0%, 2% and 5%) nanoparticles have been synthesized and investigated using various techniques like XRD, SEM, XPS, PL and UV spectroscopic measurements. The study is aimed at exploring the mechanism of room-temperature ferromagnetism in these dilute magnetic semiconductors, which has been a mystery for a long time. The X-ray diffraction patterns revealed the hexagonal wurtzite crystal structure of the P6 3 mc space group and an average crystalline size of 26 nm to 32 nm. The morphology has been analyzed using SEM images, which depict irregular grain size distribution and agglomerated spheroid-like particle structure. The X-ray photoelectron spectroscopy (XPS) findings exhibited the inducement of remarkable oxygen vacancies (V o ) with Cu doping. The 2% Cu-doped sample shows the maximum value of the oxygen vacancies. The magnetization measurements reveal weak ferromagnetism in the pure ZnO sample, whereas the Cu-doped ZnO nanocrystalline samples show remarkable room temperature ferromagnetism (RTFM). The 2% Cu-doped sample depicts the highest value of saturation magnetization. The UV spectroscopy indicates that the band gap is reduced upon Cu doping; the value of E g is found to be the lowest (2.96 eV) for the 2% Cu-doped sample. The Photoluminescence (PL) spectroscopy indicates the presence of defect-related states, which are found to be the maximum for the 2% Cu-doped sample, in good agreement with the XPS results. The induced magnetization in the Cu-doped nano-crystalline samples is found to show a direct relationship with the oxygen vacancies and is proposed to be caused by the exchange interactions between the Cu 2+ ions and the oxygen vacancies. The inducement of ferromagnetism in ZnO renders it a potential system for spintronic devices. The key benefits of spintronic devices are their compact size, excellent luminous efficiency, ecologically benign composition, long persistence and potential energy savings.

The present work focuses on developing Gd-doped Mn spinel nanoferrites and their potential application in the photodegradation of water pollutants. The impact of Gd3+ ion substitution on structural, electronic, and magnetic characteristics of manganese ferrites has been studied. Nanocrystalline samples of MnGdxFe2-xO4 (x = 0.0 to 0.10, in step size of 0.02) ferrites were prepared via sol–gel self-ignition route. The Rietveld, XPS, HRTEM, and SAED characterization methods confirmed the formation of phase pure ferrite nanoparticles ( 8–22 nm) in the cubic spinel structure. The Gd3+ content in these nanoferrites responded to a systematic reduction in the size of nanocrystallites and an upsurge in the density of nanoferrites. The XPS study revealed fine assimilation of constituent elements in the fcc lattice and ruled out impurities in the nanoferrites. The Fe and the Gd ions were found to be in Fe3+ and Gd3+ states, respectively. While a major fraction of the Mn ions were found to be in the Mn2+ state, a small fraction of Mn4+ ions was observed on the surface of nanoparticles. The nanoferrites were found to exhibit a soft ferromagnetic state from 300 to 20 K limits. The highest saturation magnetization was observed for x = 0.02 (MS = 66.6 emu/g at 20 K). The observed magnetic properties can be understood with the competing (Fe3+ and Mn2+)A–O2−–[Fe3+, Mn2+, and Gd3+]B superexchange interactions and magnetocrystalline anisotropy. Due to the small band gap energy of Gd-doped Mn ferrites than that of the pure Mn ferrite, they have demonstrated excellent photocatalytic activity for the degradation of methylene blue (MB) dye under visible light illumination. As much as 96.35

Polycrystalline Zn1−xCuxO (x = 0.0, 0.02, and 0.05) samples have been prepared using the solid-state reaction procedure. The X-ray diffraction (XRD) patterns of the samples confirm that Cu ions are successfully included in the ZnO hexagonal wurtzite structure. Rietveld analysis of the XRD patterns confirms the phase purity of the synthesized samples and a slight variation in their lattice parameter upon Cu doping. The morphology study by scanning electron microscopy (SEM) depicts transfiguration with Cu doping. The existence of oxygen vacancies (Vo) in the Cu-doped samples is indicated by X-ray photoelectron spectroscopy (XPS). The magnetization measurements reveal the diamagnetic nature of pure ZnO while the Cu-doped samples depict a room-temperature ferromagnetic (RTFM) behavior. The 2

Dye-sensitized solar cell (DSSC) has demonstrated promising photovoltaic performance with several photo-sensitizers. N719 dye, is a popular sensitizer used in DSSC due to its ability to absorb light in the visible region and its unique characteristics such as ultrafast electron injection and stable anchoring to the TiO2 surface. However, many of its intriguing optoelectronic properties and charge carrier relaxation at low frequency are contested. Here impedance and modulus spectroscopy were employed to extensively explore the charge carrier dynamics under both light-off and illumination conditions, and it was found that there is a significant change observed in the low-frequency regime in both cases. The fabricated N719 dye based DSSC exhibit the highest JSC of 10.89 mA/cm2, a highest VOC of 0.672 V, a fill-factor of 0.65 and photoconversion efficiency of 4.81%. The Nyquist plot of N719 DSSC under light-off and illumination conditions demonstrates that at higher frequency, a small arc is observed, and at a lower value, a large arc is observed. Moreover, the Nyquist plots exhibit depressed semicircles due to deviation from ideal Debye relaxation nature. The dielectric relaxation is found to follow the interfacial polarization of Maxwell-Wagner type probably attributed to the grain boundary effects. Furthermore, the comparative analysis of modulus and impedance spectra at low frequency reveals the localized carrier relaxation in this N719 DSSC which has been correlated with conductivity hopping process.

The lead (Pb)-based halide perovskites have been reported to be promising materials for photovoltaic applications; however, the presence of toxic lead in them concerns the environmental and health issues. In this work, we have, therefore, studied the lead-free and non-toxic tin-based halide perovskite, CsSnI 3 , which is an eco-friendly material with high power conversion efficiency, thus, being a potential candidate for photovoltaic applications. We have investigated the influence of CsI and SnI 2 -terminated (001) surfaces on structural, electronic and optical properties of lead-free tin-based halide perovskite CsSnI 3 from the first principal calculations, based on density functional theory (DFT). The calculations of electronic and optical parameters are performed under the parameterisation of PBE_Sol for exchange–correlation functions conjugated with modified- Beche-Johnshon (mBJ) exchange potential. The optimised lattice constant, the energy band structure and the density of states (DOS) have been calculated for the bulk and different terminated surface structures. The optical properties of CsSnI 3 are computed in terms of the real and imaginary part of absorption coefficient, dielectric function, refractive index, conductivity, reflectivity, extinction coefficient and electron energy loss. The photovoltaic characteristics for the CsI-termination are found to be better than the bulk and SnI 2 -terminated surfaces. This study reveals that optical and electronic properties can be tuned by selecting proper surface termination in halide perovskite CsSnI 3 . The CsSnI 3 surfaces exhibit semiconductor behaviour with a direct energy band gap and a high value of absorption power in the ultraviolet and visible region, rendering these inorganic halide perovskite materials important for the eco-friendly and efficient optoelectronic devices.

Objective: To gain better insight into the extent of secondary bacterial and fungal infections in hospitalized patients in India, and to assess how these alter the course of coronavirus disease 2019 (COVID-19) so that control measures can be suggested. Methods: In this retrospective, multicentre study, the data of all patients who tested positive for severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) on reverse transcriptase polymerase chain reaction (RT-PCR), admitted to hospital between March 2020 and July 2021, were accessed from the electronic health records of a network of 10 hospitals across five states in North India. Results: Of 19,852 patients testing positive for SARS-CoV-2 on RT-PCR and admitted to the study hospitals during the study period, 1940 (9.8%) patients developed secondary infections (SIs). Patients with SIs were, on average, 8 years older than patients without SIs (median age 62.6 vs 54.3 years; P <0.001). The risk of SIs was significantly (P <0.001) associated with age, severity of disease at admission, diabetes, admission to the intensive care unit (ICU), and ventilator use. The most common site of infection was urine (41.7%), followed by blood (30.8%) and sputum/bronchoalveolar lavage/endotracheal fluid (24.8%); the least common was pus/wound discharge (2.6%). Gram-negative bacilli (GNB) were the most common organisms (63.2%), followed by Gram-positive cocci (GPC) (19.6%) and fungi (17.3%). Most patients with SIs were on multiple antimicrobials. The most commonly used antibiotics against GNB were beta-lactam/beta-lactamase inhibitors (76.9%), carbapenems (57.7%), cephalosporins (53.9%), and antibiotics against carbapenem-resistant Enterobacteriaceae (47.1%). Empirical use of antibiotics against GPC was seen in 58.9% of patients with SIs, and empirical use of antifungals was observed in 56.9% of patients with SIs. The average length of hospital stay for patients with SIs was almost twice as long as that of patients without SIs (median 13 vs 7 days). Overall mortality among patients with SIs (40.3%) was more than eight times higher than that among patients without SIs (4.6%). Only 1.2% of patients with SIs with mild COVID-19 at admission died, compared with 17.5% of those with moderate COVID-19 at admission and 58.5% of those with severe COVID-19 at admission (P <0.001). The mortality rate was highest in patients with bloodstream infections (49.8%), followed by those with hospital-acquired pneumonia (47.9%), urinary tract infections (29.4%), and skin and soft tissue infections (29.4%). The mortality rate in patients with diabetes with SIs was 45.2%, compared with 34.3% in those without diabetes (P < 0.001). Conclusions: SIs complicate the course of patients hospitalized with COVID-19. These patients tend to have a much longer hospital stay, a higher requirement for oxygen and ICU care, and a significantly higher mortality rate compared with those without SIs. The groups most vulnerable to SIs are patients with more severe COVID-19, elderly patients and patients with diabetes. Judicious empirical use of combination antimicrobials in these groups of vulnerable patients can save lives. It is desirable to have region- or country-specific guidelines for appropriate use of antibiotics and antifungals to prevent their overuse.

The current article explores the dielectric and electronic properties of cobalt ferrite nanoparticles with Gd substitution in a series CoGd x Fe 2-x O 4 (0 ≤ x ≤ 0.1, in step x = 0.02) synthesized by the sol–gel self-combustion way. All the samples were studied with Fourier transform infra-red (FTIR) spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and impedance (dielectric) analyzer. One absorption band (υ 1 ) was observed in FTIR measurements, which is the characteristic feature of spinel nanoferrites in fcc type structure. The presence of active Raman modes in Raman spectra at room temperature demonstrated single phase formation of cobalt nanoferrites with metallic–metallic and metallic–oxygen bonding vibrations in the tetrahedral and octahedral sites. XPS data analysis confirmed phase purity and revealed incorporation of Gd ion in the spinel fcc lattice. The valence states of Fe, Co & Gd atoms in all these nanoparticles are found as Fe 3+ , Co 2+ , & Gd 3+ . The dielectric constant and dielectric loss are measured in a broad frequency range of 100 Hz to 120 MHz. The dielectric constant reduces with a rise in Gd concentration and frequency. This study reveals that electronic and dielectric properties could be effectively tuned by varying concentrations of gadolinium in cobalt ferrite nanoparticles.

X-ray photoelectron spectroscopy (XPS) has been employed to explore the electronic structure of Zn0.3Mn0.7+xSixFe2-2xO4 (x = 0.0-0.3) ferrite series. The Si2p XPS spectra insinuated the presence of Si ions in the +4 valence state. The elemental Si-0 and suboxide SiOx are present in the system, the former showing an increase and the latter a decrease in atomic percentage upon Mn-Si substitution. It is also inferred that a fraction of Si-0 might be residing at the grain boundaries; however, more studies are required to substantiate this. The Fe2p XPS spectra stipulate that ferrous and ferric ions co-occur in the system. The ferrous ions occupy the octahedral sites while the ferric ions dwell on both the octahedral and the tetrahedral sites. The O1s spectra indicate a remarkable increase in the oxygen defects with increasing Mn-Si substitution (x). The Mn2p XPS data indicate that the Mn+2 states show an overall increasing tendency with increasing Mn-Si concentration. Also, the Mn+4/Mn+3 ratio shows an increment with an increase in Mn-Si substitution.

A detailed electronic structure study of quadruple perovskite series, Ca1+xCu3-xTi4O12 (for x = 0.0, 0.1, 0.2, 0.5, 1.0), using electron spectroscopy for chemical analysis (ESCA) has been carriedout. The Ti2p ESCA spectra imply that Ti ions remain in the tetravalent state and show the presence of Ti clusters, TiO6 and TiO5. The Culp spectra indicate the dominance of the divalent state of Cu ions. The Ca2p spectra show that Ca atoms are divalent but spectral features are suggestive of the presence of Ca superficial atoms in the system which is possibly due to the precipitation of Ca atoms in the grain boundary regions. The Ca2p in conjunction with O1s spectra shows that there is a strong possibility of hybridization of Ca2p states with the O1s and/or the Cu3d orbitals. The remarkable shift in O1s spectra towards the lower energy side for the samples with x >= 0.5 is mainly due to the substitution of large cation Ca2+ (1.0 angstrom), for small cation Cu2+ (0.73 angstrom) in the series. That results in bond length enhancement and weakening of the bond strength. It is proposed that the shift of O1s peaks can also be partially caused by oxygen vacancies; nevertheless, more experiments are required to substantiate this.

Here, we report a detailed study on electronic structure of quadruple perovskite system, CaCu3Ti4O12 (x = 0.0, 0.1, 0.3, 0.5 and 0.7), using the powerful X-ray photoelectron spectroscopy (XPS). The Ca2p and Ti2p XPS spectra indicate that Ca and Ti ions exist in the divalent and tetravalent state, respectively, and no visible change is observed in their valence states on Fe3+-substitution (x). The asymmetrically shaped peaks of Ti(2)p(3/2) infer the significant orbital hybridization of Ti atoms with other metallic cations like Cu and Fe, i.e. the Ti2p-Cu3d-Fe3d mixed states, which shows an increment with the Fe3+-content. The spectra also indicate that the Fesubstitution causes an increase in the strength of CuFe3d-O2p hybridization while weakening the strength of TiFe3d-O2p orbital hybridization. The Cu2p spectra suggest that Cu ions exist in two valence states i.e. the Cu2+ and Cu3+ out of which Cu2+ is dominant. The XPS results show clear evidence of charge transfer amongst Ti-Cu ions and evolution of n-type charge carriers. The O1s XPS spectra indicate anti-bonding states of t(2g) and e(g) type molecular orbitals separated by an energy separation of similar to 1.6 eV. A systematic relative change in the intensity of t(2g) and e(g) peaks with Fe-substitution point towards a clear transformation of symmetry of the system from TiO6 octahedral to the square-planar.

We present a case report of a 17-year-old obese female with one-week onset of progressive confusion and double vision, associated with 50-pound weight loss in five months. On fundus examination, retinal hemorrhages and abnormalities of eye movements were seen. MRI showed abnormalities that were consistent with diagnosis of Wernicke encephalopathy (WE). Thiamine replacement caused gradual improvement in patient's symptoms. Peripapillary hemorrhages on fundus examination, as seen in our patient, have been rarely seen in WE. Obesity with retinal hemorrhages, diplopia, etc. can be misleading due to idiopathic intracranial hypertension being the most common presentation in this subset. Thus, fundoscopy should be part of routine examination in WE-suspected patients.

Ca1+xCu3-xTi4O12, x = 0.0, 0.1, 0.2, quadruple pemvskite system has been investigated by means of energy dispersive analysis of X-rays, powder X-ray diffractometry, scanning electron microscopy, de magnetization in zero-field and field-cooled modes (M(T) curves) and isothermal magnetization against magnetic field (M(H) loop) plots. The stoichiometric samples possess a single-phase crystal structure and coarse-grained microstructure. The cation distributions reveal that substituted Ca2+ ions have a strong preference for A '' - site. The M(T) curves of pristine composition exhibit reversible thermomagnetic characteristic with classic antiferromagnetic transition at T-N similar to 25K. On Ca2+ substitution, the compositions (x = 0.1 and 0.2) show coexistence of weak ferromagnetism and antiferromagnetism for T < T-N and soft ferromagnetism and paramagnetism for T >> T-N, clearly reflected in M(H) loop characteristics. The origin of ferromagnetism lies on Cu-Cu bond distance and partial occupancy of magnetic Cu2+ ion on the B-site of the system.

The electronic structures of stoichiometric, single phase, coarse-grained CaCu3-x,Ti4-x,Fe-2x,O-12 (x = 0.0, 0.1, 0.3, 0.5 and 0.7) polycrystalline ceramics have been investigated using powerful X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopic measurements, performed near Ti L-3,L-2 and Ti K- edges, registered at 300 K. The absence of pre-edge structures in Ti L-3,L-2 edge are indicative of a departure from octahedral cubic symmetry, while the observed small increase in the intensity of absorption peaks has been attributed to increasing spin-orbital coupling with increasing Fe-content (x) in the system. The presence of a pre-edge feature in Ti K- edge spectra confirms the presence of octahedrally coordinated Ti4+ ions in the system. The EXAFS spectra measured at Ti K- edge indicate the first shell Ti-O bond distances to be nearly 1.56 angstrom in the sample without Fe. With the increase in the Fe- concentration (x), the Ti-O distance shows a slight reduction. The second shell Ti-Ca bond distance comes out to be nearly 2.6 angstrom which decreases with an increase in the Fe - concentration.

In this work, we report the Doppler broadening Positron Annihilation Spectroscopy (PAS) studies of the as- synthesized and neutron irradiated Mn and Li co-doped ZnO nanocrystals (Zn 0.96-x Mn 0.04 Li x O for x =3D 0.00, 0.02, 0.03, 0.04), synthesized by low-temperature co-precipitation method. Samples were characterised by X-ray diffraction and the XRD patterns confirmed single phase Wurtzite hexagonal structure of all the samples. The samples were irradiated by neutrons obtained from a 5.0 Ci AmBe neutron source with a flux ~ 3.3×10 5 n/cm 2 -sec at irradiation position. Positron annihilation Doppler broadening spectroscopic measurements were carried out and calculated S and W parameters were plotted against Li doping concentration for the as-synthesized and the neutron irradiated samples and the findings have been discussed in terms of magnitude and nature of the defects induced.

The as-synthesized 5% Ni-doped single phase ZnO powder sample (Zn0.95Ni0.05O), prepared by solid state reaction method, shows a paramagnetic ground state at room temperature. However, when annealed under hydrogen atmosphere it shows a remarkable ferromagnetic state at 300 K. The hydrogen induced ferromagnetism is found to be reversible with regard to its re-heating in air. To investigate the electronic properties of this Ni-doped ZnO sample, we have carried out the element-sensitive X-ray-absorption spectroscopic measurements, using synchrotron radiation, in the vicinity of the Ni 2p edge, the O K edge, and at the Zn 2p edge. The spectroscopic measurements show substantial changes in the near edge spectra of H-annealed samples with respect to the as-synthesized sample. The observed spectral changes may derive from both the Ni 3d-O 2p hybridization and also from lattice defects such as oxygen vacancies. The spectral changes have been correlated with the room temperature ferromagnetism observed in this system which is very promising candidate for the future spintronic applications.

Understanding of origin of ferromagnetism in dilute magnetic oxides (DMO's) has become one of the most challenging research problems in condensed matter physics. Here we are reporting a detailed study of magnetic properties and electronic structure of two 5% Co-doped ZnO samples (the as-prepared sample Zn0.95Co0.05O and the hydrogenated sample Zn0.95Co0.05O:H). The as-prepared sample is found to be paramagnetic while through hydrogenation, we observed inducement of remarkable ferromagnetism in it. The H-mediated magnetic transition is accompanied by electronic structure modifications with no structural deviations. To get in-depth information into electronic structure correlations of the observed ferromagnetism, we have investigated their electronic properties in detail. For this purpose, we have employed the site-selective and element-sensitive X-ray-absorption spectroscopy (XAS) in the vicinity of the Cobalt L2,3 edge, the oxygen K edge, and the Zinc L3 edge using synchrotron radiation. The Co L2,3 edge spectra clearly show that Co dopants reside at the Zn sites for both these samples and that they are tetrahedrally coordinated with the ligand O atoms. Very minor changes are observed in the Zn L3 edge spectra. However, the O 1s edge spectra display dominant additional components in the ferromagnetic hydrogenated sample Zn0.95Co0.05O:H, not observed in the as-prepared non-magnetic sample Zn0.95Co0.05O. We conclude that the observed spectral features can be attributed to the presence of O vacancies and the hybridization of Co 3d states with O 2p vacancy states. These two factors together are likely to play important role in inducement of ferromagnetic ordering in this Co-doped ZnO system. However, which of these two weighs more in this mechanism, cannot be pinpointed and more studies are required in this regard.