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In this article, the thermoelectric properties of five different polymorphs of gallium phosphide (GaP) such zinc-blende (zb-GaP), wurtzite (wz-GaP), sphalerite (sp-GaP), Beryllium oxide (β-BeO-GaP), and Silicon carbide (SiC-GaP) have been reported in detail. In this regard, the prerequisite electronic structure calculations have been performed in the framework of density functional theory (DFT), whereas the results for thermoelectric properties have been obtained via Boltzmann transport theory (BTT). We found that these GaP polymorphs exhibit relatively higher electrical conductivity corresponding to holes as a result larger power factors (PFs) have been realized for n-type doping than p-type. The highest values of PF corresponding to n-type doping have been recorded as 27.492 × 1010 W/mK2s, 27.999 × 1010 W/mK2s, 29.491 × 1010 W/mK2s, 15.706 × 1010 W/mK2s, and 26.557 × 1010 W/mK2s respectively, for zb-GaP, wz-GaP, sp-GaP, β-BeO- GaP, and SiC-GaP. Moreover, their PF has been further enhanced by the increase in temperature. In contrast, the Seebeck coefficients (thermopowers) have been found relatively larger for p-type doping than n-type. The relatively large thermopowers and lower thermal conductivity for p-type doping have resulted in the enhancement of Figure-of-merit (zT) by holes rather than electrons. The highest zT values have been recorded as 0.997, 1.004, 0.998, 1.001, and 1.010 in the case of zb-GaP, wz-GaP, sp-GaP, β-BeO-GaP, and SiC-GaP respectively. Our study indicates the adequate potential of these different polymorphs of GaP for thermoelectric applications.

A successful flash combustion synthesis of NiO spherical nanoparticles with various contents of lanthanum (La) doping (La@NiO SNPs) with remarkably enhanced dielectric and electrical properties are reported. Single phase has been confirmed through X-ray diffraction and FT-Raman spectroscopic analysis. Increasing La content in NiO reduced the crystallite size by 341% to 6.65 nm from 22.70 nm. The composition of elements in the final product was assessed via EDX analysis. Moreover, monophasic La@NiO SNPs synthesis with size reduction was observed using field emission scanning electron microscopy (FESEM). A red shift in optical energy gaps (3.52–3.26 eV) was observed with increasing La contents from pure to 10 wt%. Capacitance (109–964 PF), impedance (9.41 × 104–1.67 × 104 kΩ), dielectric constant (100–967), dielectric loss (335–10666), and electrical conductivity (4–5 S/m) values were remarkably improved with La doping. The current (I)–voltage (V) characteristics of pure and La@NiO NPs were performed under the biased voltage of ±20 V. Current was noticed in the range of (3.81 × 10−4–9.91 × 10−3 amp) at pure, 1.0, 3.0, 5.0, and 10 wt% of La@NiO NPs. Enhancements in the dielectric and electrical properties of as-synthesized NPs make them suitable for optoelectronics uses.

The authors report on the synthesis of Fe–NiO nanoparticles (Fe–NiO NPs) with a spherical shape via facile flash combustion synthesis. A structural test shows cubic formations of Fe–NiO NPs in all Fe concentrations. A reduction in crystallite size was observed with increasing Fe content from 27 nm to 12 nm. A vibrational study also indicates a cubic Fe–NiO NPs structure. However, slight shifts in peak positions were observed during Fe doping in NiO. The existence of Fe in NiO product was confirmed using energy dispersive X-ray (EDX) analysis, and its homogeneity in the final products was observed in scanning electron microscopy (SEM) e-mapping images. An X‐ray photoelectron spectroscopy (XPS) study was also carried out to confirm the incorporation of Fe in NiO matrix. A field-emission scanning electron microscopy (FESEM) study showed the formation of spherical nanoparticles in all Fe–NiO NPs samples. However, it was noted that the grain size reduced with increasing Fe content, which is in agreement with the X-ray diffraction (XRD) results. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) with a selected area electron diffraction (SAED) curve indicate very low-dimension NP formation from NiO. An optical test was performed based on the Kubelka-Munk theory along with an estimation of energy gas, which showed an increase of 3.5–3.75 eV with Fe content doping in NiO. Furthermore, the possibility of applying spherical Fe–NiO NPs as an electrode material was also assessed in a three-electrode assembly cell, and the results show that the NiO doped with 5% of Fe exhibited superior capacitance performance (F4, 297.67 F g-1) compared to the other samples.

The development of materials in two-dimensions has been established as an effective approach to improve their thermoelectric performance for renewable energy production. In this article, we generated monolayers of the orthorhombic structured lead-chalcogenides PbX (X = S, Se, and Te) for room-temperature thermoelectric applications. The Density functional theory and semiclassical Boltzmann transport theory-based computational approaches have been adopted to carry out this study. The band structures of PbX monolayers exhibited narrow indirect bandgaps with a large density of states corresponding to their bandgap edges. Accordingly, substantial electrical conductivities and Seebeck coefficients have been obtained at moderate level doping that has caused significant thermoelectric power factors (PFs) and figures-of-merit (zT) ~1. The single-layered PbX showed anisotropic dispersion of electronic states in the band structure. A relatively lighter effective mass of charge carriers has been extrapolated from the bands oriented in the y-direction than that of the x-direction. As a result, the electrical conductivities and PFs have been observed larger in the y-direction. The optimum PFs recorded for single-layered PbS, PbSe, and PbTe in y-direction amounts to 9.90 × 1010 W/mK2s at 1.0 eV, 10.40 × 1010 W/mK2s at 0.82 eV, and 10.80 × 1010 W/mK2s 0.66 eV respectively. Moreover, a slight increase in p-type doping is found to improve the x-component of the PF, whereas n-type doping has led to improvement in the y-component of PF. Our results show an improved thermoelectric response of PbX monolayer (PbTe in particular) than their bulk counterparts reported in the literature, which indicates the promise of PbX monolayers for nanoscale thermoelectric applications at room temperature.

The narrow bandgap PbSe has attracted a remarkable interest from the researchers in recent years for their potential optoelectronics and photovoltaic applications. In this article, we report the optoelectronic properties of cubic (NaCl-type) and orthorhombic (Cmcm- and Pnma-type) polymorphs of PbSe using the density functional theory based first-principles approaches. In accordance with the available literature, the NaCl–PbSe has been found stable in the ground state, whereas the Cmcm-, Pnma-types of PbSe have been realized at intermediate pressure of ~4.5 GPa. The electronic structures and optical spectra of these polymorphs have been determined using the Tran-Blaha modified Becke-Johnson exchange potential with and without spin-orbit coupling (SOC) effects. The inclusion of SOC has shown important effects on the electronic structures and consequently on the optical spectra. Despite SOC driven energy gap narrowing of these polymorphs, the direct bandgap nature of Cmcm-PbSe calculated with TB-mBJ has changed to indirect nature with the inclusion of SOC. Moreover, our results of the optical spectra of NaCl–PbSe have shown that this phase is isotropic, whereas a sufficiently high degree of anisotropy in the optical spectra has been recorded for Cmcm-, Pnma-types of PbSe. These PbSe polymorphs exhibited a high optical absorption that approaches as large as 106 cm−1. Moreover, our study provides comprehensive details of exciton binding energies and plasmon energies. This work is believed to provide a strong foundation to exploit the optoelectronic character of the studied phases of PbSe for next-generation optoelectronic and photovoltaic applications.

Nickel oxide has tremendous applications in the field of biomedicine. In this study, NiO nanoparticles were synthesized with different Bi contents (NiO@Bi; 0.0–7.5 wt%), and multifunctional usages were investigated. Structural confirmation was conducted through XRD and Raman studies, which revealed a monophasic cubic system. With increasing Bi content, broadening of the XRD and Raman peaks were observed, indicating a reduction in particle size. The crystallite size was found to be in the range of 10–26 nm. The decrease in particle size was confirmed through dynamic light scattering measurement. The homogeneous distribution of all elements and the presence of Bi were detected by an EDX/SEM e-mapping study. Field emission electron microscopy confirmed the formation of spherical shape nanoparticles. The grain size was reduced from 30 nm to 10 nm with Bi content, in accordance with XRD and Raman results. The Kubelka-Munk method was employed to determine the effect of Bi content on the optical band gap of NiO. The energy gap was reduced with Bi content in the range of 3.32–3.50 eV. Antimicrobial and in vitro cytotoxic characteristics of the prepared NPs were also studied. The results revealed that all NiO@Bi NPs had negligible antimicrobial activity and no cytotoxic effects on both normal and activated splenic cells. The in vivo acute cytotoxicity study indicated no cytotoxic effects on liver and kidney functions. The prepared NiO@Bi NPs were implanted in living organisms without hepatic/renal toxicity, demonstrating excellent biocompatibility, cell viability, and superior quality of nanocrystals, suggesting that the prepared NPs are ideal candidates for antibacterial and biomedical applications.

Herein, we report a novel method for the synthesis of pure and Tb-doped NiO nanocomposites with homogeneity using a non-toxic material, citric acid, via one-step flash combustion at 550 °C. The single cubic phase was determined by X-ray diffraction (XRD) analysis, confirming the high purity of the synthesized products. A systematic reduction and broadening of the XRD peaks was seen with increasing incorporation of Tb, indicating a decreasing particle size from 26 to 7 nm. The zeta potential was approximately −6.7 mV for pure NiO and 19 mV for 20% Tb-doped NiO NPs. The higher value of zeta potential indicates that the doped samples are more stable in aqueous media than undoped samples. FT-Raman spectra revealed the absence of impurity peaks and peak broadening with increasing Tb concentrations. All Raman modes were red shifted in comparison to bulk NiO. EDX/SEM mapping revealed the presence of Tb and its homogeneous distribution within NiO. FE-SEM and TEM confirmed the spherical morphology of NiO when doped with Tb. The surface area and pore volume of 5 wt% Tb-doped NiO NPs was determined to be 18.5 m2/g and 8.34 × 10−2 cm3/g, respectively. The energy gap varied with Tb-doping and noticed in the range of 3.5–3.6 eV. An intense single emission peak at 396 ± 5 nm for all Tb-doped NiO NPs was observed. Tb-doped NiO NPs demonstrated e r ′ values in range of 30–77 at 4 kHz and 20 to 41 at 6 MHz. Dark and photo current-voltage investigations revealed that Tb-doping significantly enhanced the electrical properties of NiO, making them highly applicable for optoelectronic devices.

High-quality thin film-based photodetectors containing praseodymium doped cadmium sulfide (Pr:CdS) were fabricated through spray pyrolysis and studied for various opto-electrical applications. Field emission electron microscopy (FE-SEM) revealed that the prepared films were highly compacted with an extremely fine nanostructure without any pinhole or crack. X-ray diffraction and FT-Raman spectroscopy studies confirmed the single hexagonal phase of all the films. The crystallite size was found to lie between 19 and 32 nm. Optical spectroscopy revealed that the fabricated films have low absorbance and high transmittance (in range of 70–80%). The energy gap was found to lie in the range of 2.40–2.44 eV. The PL spectra contained an intense green emission band at ~531 ± 5 nm (2.33 eV), and its intensity was enhanced by increasing the Pr doping content in CdS. The dark and photo currents of CdS increased by approximately 950 and 42 times, respectively with the addition of 5.0 wt% Pr. The responsivity (R) and specific detectivity (D*) were remarkably enhanced to 2.71 AW-1 and 6.9 × 1011 Jones, respectively, for the 5.0 wt% Pr:CdS film. The external quantum efficiency (EQE) of 5 wt% Pr:CdS films was 43 times that of pure CdS films, and the on/off ratio was 3.95 × 102 for 5.0 wt% Pr:CdS film. Its high R, D*, and EQE values, and photo-switching behavior make Pr:CdS a good contender for high quality photodetector applications.

Herein, novel Ag-doped PbS (Ag:PbS) nanoparticles (NPs) were synthesized via a facile and rapid microwave route. Field emission scanning electron microscopy (FESEM)/energy-dispersive X-ray (EDX) spectroscopy were employed to confirm the homogeneous doping of Ag in PbS. The transmission electron microscopy (TEM) exposed that the PbS NPs were fully encapsulated with Ag. X-ray diffraction (XRD) analysis revealed that all the samples possessed cubic crystal structures whereas the peak positions for the Ag:PbS were slightly shifted towards lower angle compared to pure PbS, further confirm the Ag doping in NPs. Fourier-transform Raman (FT-Raman) spectra also confirmed the phase and doping of Ag in PbS NPs. The grain sizes of the synthesized NPs were found to be in the range of 15–40 nm while calculated crystallite sizes of these samples were in the range of 18–26 nm. The zeta potential for 5.0 wt% Ag:PbS NPs was found to be approximately 10 times higher than that for pure PbS NPs, signifying the high stability of the doped NPs in aqueous media. The optical band gap of Ag:PbS NPs were evaluated from diffused reflectance spectra and found to be in range of 1.95–2.51 eV; increases with Ag doping. The quenching in photoluminescence (PL) intensity was observed with the increase of Ag doping concentration attributed to the charge transfer between Ag and PbS. Moreover, Ag doping also improve the electrical and dielectric properties of PbS NPs. Finally, optoelectrical properties of synthesized materials were investigated under 633 nm laser-light illumination to determine their applicability as visible-light photodetectors. It was found that the Ag doped PbS NPs exhibited enhanced photodetector figures of merit compared to the pure PbS NPs.

The single-layered Germanium sulfide exhibits interesting optoelectronic properties however the indirect bandgap hinders its practical applications for nanoscale optoelectronic and photovoltaic devices. Herein, we report two direct bandgap polymorphs of single-layered GeS (δ-GeS and e-GeS) and explore their optoelectronic properties using the density functional theory based computational approaches. The indirect bandgap of the intrinsic GeS monolayer (α-GeS) calculated in present study amounts to 0.76 eV, whereas the direct bandgap energies for δ- and e-derivatives of GeS have been recorded as 1.93 and 2.10 eV respectively. The optical spectra of these monolayers demonstrated a high degree of anisotropy and significantly different optical absorption, reflection, and refraction coefficients were seen in the x- and y-directions. They exhibited different plasmons energies along x- and y-directions which reveal the GeS monolayers as potential polarizers of electromagnetic radiations. Moreover, these monolayers demonstrated exceptionally large optical absorption spanning over a wide range of electromagnetic spectrum. The absorption coefficients were recorded typically larger along y-axis than x-axis. The designed direct bandgap monolayers are believed to overcome the major hurdles of single-layered GeS for nanoscale optoelectronic applications.

Dimensionality reduction has been proved as a feasible route to enhance the performance of thermoelectric materials for renewable energy applications. In this article, we investigate the effect of dimensions reduction on thermoelectric properties of GeSe using the density functional theory and Boltzmann transport theory based first-principles approaches. These investigations have been carried out for bulk (3D) and three polymorphs of single-layered (2D) GeSe (such as α-GeSe, β-GeSe, and γ-GeSe). Calculations of energetic stability demonstrated the 2D-GeSe as stable as the 3D-GeSe. The arrangement of bands within the electronic band structures of 3D and 2D GeSe showed them as indirect bandgap semiconductors. The β-GeSe and γ-GeSe exhibited wider energy bandgap and consequently large Seebeck coefficients than the 3D-GeSe and α-GeSe. The reduction in structural dimensions stimulated a sharp increase in electrical conductivity and Seebeck coefficient (particularly for β-GeSe and γ-GeSe) which has resulted in large power factor. The room-temperature thermoelectric figure of merit (ZT) of 3D-GeSe, α-GeSe, β-GeSe, and γ-GeSe of magnitude 1.02, 0.83, 1.00, and 1.10 respectively have typically broken the benchmark value of ZT ≈ 1. The ZT of these materials is sensitive to change in temperature and has been recorded as large as 1.72 for γ-GeSe at a low temperature of 150 K. The large power factors and ZT of single-layered GeSe reveal the dimensionality reduction as a feasible approach for enhancing the performance of thermoelectric materials for renewable energy applications.

Synthesis of pure and 0.1 to 5 wt.% Gd-doped CdS nanoparticles (NPs) was achieved through a modified domestic microwave-assisted route in a short timespan at 700 W power. The formation of hexagonal CdS NPs was verified via X-ray diffraction analysis, and no structural variation was observed except for lattice variation. The size of the crystallites (D), dislocation concentration, and lattice strain were calculated, and the D was in the range of 3–6 nm. Fourier transform-Raman analysis confirmed the presence of 1LO, 2LO, and 3LO modes at 294.76, 590, and 890 cm−1, respectively, in all the synthesized nanostructures, with minute variations in their positions due to doping; however, no new mode was observed. The position of the vibration modes was red shifted compared to that of the bulk material, indicating a confinement effect. Scanning electron microscopy (SEM) mapping/energy-dispersive X-ray spectroscopy revealed homogeneous doping of Gd and the presence of all the constituents in the final products. The morphology of the synthesized materials was tested via field-emission SEM, which revealed spherical NPs with small dimensions. Additionally, high-resolution transmission electron microscopy was performed to visualize the shape and size of the prepared 0.1% Gd:CdS NPs. The energy gap was calculated using the Kubelka–Munk theory and found to be in the range of 2.31–2.41 eV. The photoluminescence emission spectra exhibited two green emission peaks at 516 ± 2 nm and 555 ± 2 nm and showed the reduction of defects with Gd doping in terms of intensity quenching. The dielectric constant ( e ' ), loss, and alternating-current electrical properties were studied in the high-frequency range. The values of e ' were in the range of 17–27. An enhancement of these values was observed for CdS when it was doped with Gd. The electrical conductivity exhibited frequency power law behavior.

Pure and potassium iodide (KI) doped hydroxyapatite (HAp) nanostructures were prepared through a facile microwave route. Field emission - SEM (FESEM) confirm low dimension nanorods (NRs) morphology of final products. The average dimension of NRs is may be in the range of 10–20 nm. Predominant single segment was approved by XRD and EDX analyses. Lattice constants, crystallite size, density of dislocations, strain and % of crystallinity were determined and the average crystallite size is observed in 9–16 nm range and degree of crystallinity is observed to be high viz. ~ 59% for 30% KI doped HAp. Vibrational studies were done through FT-IR and FT-Raman spectroscopy and confirm the phase of HAp. The catalytic activity of all samples is done in bioremediation of methylene blue using Stenotrophomonas maltophilia strain Kilany_MB. These results suggested that HAp and KI-HAp as a promising nano-catalyst in bioremediation of water from methylene blue.

Samarium and aluminium co-doped ZnO (Sm:AZO) thin films were deposited on glass substrate by nebulizer spray pyrolysis technique with different Sm doping concentrations (0 at%, 0.5 at%, 1 at% and 1.5 at%). X-ray diffraction patterns confirm the polycrystalline nature of prepared films with hexagonal crystal structure. The average crystallite size was found to be reduced with Sm doping due to increased lattice defects. The Raman spectra exhibited characteristic ZnO wurtzite structure confirmed through the presence of E2-high mode peak at 438 cm−1. The surface topology analysis revealed uniformly distributed wheat shaped particles without any pinholes for 1 at% Sm doped ZnO film. Sm:AZO films displayed high transparency which is around 90% and the energy gap of ~ 3.30 eV. Photoluminescence spectra of the thin films showed an UV emission peak at ~ 386 nm corresponds to near band edge (NBE) emission of bulk ZnO. Room temperature Hall Effect measurement showed that all the prepared films possess n-type conducting nature with low electrical resistivity (ρ) 4.31 × 10−4 Ω cm for 1 at% Sm doped film. High figure of merit (ф) value of ~ 11.9 × 10−3 (Ω/cm)−1 was observed which indicates that the deposited films are highly suitable for opto-electronic device applications.