Co-doped CdS Research Articles

Experimental and DFT studies of structural and optoelectronic properties of CdS, Zn doped CdS, and (Zn-Ni) co-doping CdS nanomaterials

Abstract This paper presents experimental and theoretical studies of binary semiconductor CdS, Zn:CdS, and (Zn-Ni) co-doped CdS. Thin films of pure CdS, Cd35ZnS36, and Cd34ZnNiS36 alloys grown by sol-gel spin coating were analyzed using X-ray diffraction, EDX, and UV-vis spectroscopy. The experimental results show the success of growing nanomaterials in hexagonal structures with crystallite sizes ranging from 1.6 to 2.11 nm and possessing band gaps in the region 2.30 -2.49 eV. Additionally, we investigate the structural and optoelectronic properties of these materials in the ground state using the density functional theory implemented in the WIEN2k software. The first principles calculations confirmed that the structural and optical properties of CdS align with the experimental results. For nanostructure Cd35ZnS36, the lattice parameters decrease, and the band gap increases to 2.85 eV with Zn doping. The (Zn-Ni) co-doped CdS structure optimization shows that the ferromagnetic configuration is more stable than the non-magnetic structure. The spin-polarized band structure investigations reveal that the majority spin-up channel is about 2.79 eV while the minority spin-down channel is around 2.19 eV. These results increase the importance of Zn:CdS and CdZnNiS alloys for optoelectronic and spintronic applications. The calculated optical properties of CdS, Zn:CdS, and (Zn-Ni) co-doped CdS show slight changes in refractive index and extinction coefficient with the doping and a quantitative agreement with the experimental findings.

Introduction of Co atoms into CdS thin films for improving photovoltaic properties

This paper represents a systematic work on the fabrication of chemical bath-grown CdS films with and without Co atoms and their photovoltaic performances in hybrid solar cells. Structural properties showed 1% Co-doping promoted crystal quality of CdS films. However, a poor crystal quality was developed above 3% Co concentrations. A reduction in sphere size of CdS samples was observed for 1% Co-doping which was ascribed to slow growth of film. Optical examination demonstrated CdS films with 1% Co-doping displayed the highest transparency of 85% in the visible and near-infrared regions, which were explained by the improvement of crystal quality. A maximum band gap of 2.43 eV was found for 1% Co-doped CdS films, whereas an increase in Co concentration to 7% led to a decline in the band gap of CdS that was attributed to sp-d exchange interaction. Photoluminescence data showed Co-doped CdS films had lower PL peak intensity than that of CdS, demonstrating a decrease in the number of intrinsic defects. Photovoltaic measurements displayed that the best efficiency of 0.488% was achieved for CdS-based device including 1% Co atoms, which were almost a seven-fold boost in overall efficiency compared to bare CdS-based device. The enhancement in power conversion efficiency originated from an increase in short-circuit current density of 1% Co-doped CdS-based photovoltaic cell.

Investigation of Optical Characteristics and Synthesis of Cobalt-Doped Cds (Cds: Co) Using Simple and Rapid Microwave Activated Method

Cobalt-doped cadmium sulphide semiconductor nanoparticles (CdS: Co NPs) were made using a microwave-assisted method with different cobalt concentrations. Chemicals like sodium sulphide, cobalt chloride, and cadmium acetate were used. The Debye-Scherer equation helped find the nanoparticles' size, revealing a 2 to 4 nm range. X-ray diffraction showed a zinc-blend structure. The optical bandgap energies were found to be undoped and doped are 2.44eV and 2.58eV, respectively. For pure CdS, the XRD spectra display three main peaks at 2θ = 26.68°, 44.16°, and 52.32°. Modest alterations have been noted in 2θ for Co doping levels of 3% in CdS NPs. The peaks point to the samples' cubic structure and correlate to the (1 1 1), (2 2 0), and (3 1 1) planes. The sizes of the nanoparticles, which are 2.29 nm, 3.64 nm, for pure and Co (3%) doped CdS, were determined using the FWHM and Debye Scherer equation. The substitution of Co2+ion for Cd2+ion may be the cause of the decrease in nanoparticle size observed in the Co-doped CdS sample as concentration rises. The difference in the ionic radii of Cd2+ (0.98 Å) and Co2+ (0.72 Å) shows that when the concentration of Co-doped CdS increases, the lattice constant falls. The peak at 3646 cm-1 in the higher energy area of the 400–4000 cm–1 FTIR spectra is attributed to the O–H stretching of absorbed water on the surface of CdS. Its bending vibration confirms the existence of water. Using HRTEM, the size of the produced nanoparticles was examined. Additionally, it confirms the sample's nanocrystalline structure. For 3% Co-doped CdS, the average size of randomly chosen nanoparticles is determined.

Enhanced electrochemical and thermal stability of CdS:Pb2+, Cu2+ co-doped nanoparticles on energy storage applications

For the first time, we prepared the Pb2+, Cu2+ co-doped CdS nanoparticles that were prepared by a simple chemical precipitated method. Structural and lattice parameters were determined by XRD. It was found that mixed cubic-hexagonal crystal structure for the co-doped nanoparticles. Polyvinylpyrrolidone (PVP) was used as a surfactant to control particle size. The organic functional group's presence in the surfactant was identified by FT-IR. Two distinct morphologies were found for the co-doped sample that was studied by TEM. TG–DTA was used to study thermal stability and phase transition of the sample. CV analysis was used to determine the potential window of oxidation and reduction of the sample. In addition, VSM exhibits diamagnetic behavior for CdS:Pb:Cu nanoparticles. We found that the excellent electrochemical, thermal and magnetic properties of the co-doped CdS nanoparticles can be used for electrochemical energy storage applications.

Architecture design of TiO2 with Co-doped CdS quantum dots photoelectrode for water splitting.

Photoelectrochemical hydrogen production is a critical key to solving the carbon-zero goal of countries due to renewable sources of solar light and combustion products of hydrogen-only water. Here, an architecture design for an n-type nano rosettes-rod TiO2 (RT) surface using CdS and Co-doped CdS quantum dots (QDs) is carried out utilizing the SILAR (simple ionic layer adsorption and reaction) method. Furthermore, the photocatalytic behaviour of Co-doped CdS QDs SILAR cycles deposition is investigated in various cycles, including 5, 8, 10, and 12. The FESEM, Raman XRD, Uv-Vis spectrometer, and vibration modes are used to evaluate the photoelectrode surface structure, crystal structure, and solar light absorption, respectively. FESEM images and XRD pattern revealed successive CdS QDS and Co-doped CdS QDs deposition on the RT boundary and rising SILAR cycles of Co-doped CdS QDs lead to further coverage of RT surface. UV-vis spectrometer indicated shifting solar light absorption to the visible region by applying more SILAR cycles of Co-doped CdS QDs deposition. The electrochemical parameters obtained from EIS showed total polarization resistance (Rp) of the RT electrode dramatically decreased with 10 SILAR cycle Co-doped CdS QDs deposition (5093 Ω cm2 and 617 Ω cm2). Linear sweep voltammetry (LSV) and chronoamperometric photocatalytic performance measurements indicated Co-doped CdS QDs on RT extremely enhanced photoresponse under solar irradiation and 10 SILAR cycle Co-doped CdS QDs improved photocurrent density about fourfold according to blank RT electrode.

Ferromagnetism of Ni and I co-doped CdS: A first-principles study

This study provides insight into understanding the electronic and magnetic properties of Ni-doped and (Ni, I) co-doped CdS, which are systematically investigated by adopting the first principles approach. The findings reveal that Ni doping at the Cd site in CdS crystal modifies its ground state of non-magnetic to half-metallic ferromagnet, whereas the introduction of I as a co-doping at the S site changes the ground state of Ni-doped CdS system from half-metallic to magnetic metal. More importantly, it is found that the magnetic moment of Ni-dopant is reduced and the magnetic exchange coupling between Ni sites is enhanced after I co-doping. The estimated Curie temperature of (Ni, I) co-doped CdS is above room temperature. These findings highlight that the co-doped (Ni, I) CdS sample is a promising potential candidate for spintronics applications in future.

Half-Metallic Ferromagnetism in the Co-Doped CdS Diluted Magnetic Semiconductor

Half-Metallic Ferromagnetism in the Co-Doped CdS Diluted Magnetic Semiconductor

First principles calculations of structural, electronic, magnetic and optical properties of Gd doped and Gd, Mn co-doped zinc blende CdS

In this work, we studied the magnetic stability, electronic and optical properties of Gd doped CdS and (Gd, Mn) co-doped CdS, in a zinc blend structure, using first-principles calculations based on the full-potential linearized augmented plane wave method (FP-LAPW) with the GGA + U approximation. The lattice parameter increases by Gd doping and decreases by (Gd, Mn) co-doping. The calculations of the differences in total energies ΔE prove that the CdS: Gd is stable in the antiferromagnetic state (AFM). While, the co-doped system CdS: (Gd, Mn) is stable in the ferromagnetic states (FM). The CdS: (Gd, Mn) has an interesting magnetic moment compared to the CdS: Gd. The total densities of states show the metallic character of the CdS: Gd and the half-metallic character of CdS: (Gd, Mn). The real and imaginary parts of the dielectric function, the absorption coefficient, and the refractive index are calculated. Both systems have a significant redshift and have a strong light absorption in the visible and UV regions. Co-doping CdS by Gd and Mn gives interesting results compared to the CdS: Gd. These make CdS: (Gd, Mn) an important material for different applications. This work provides the possibility to fabricate new optoelectronic and spintronic devices.

Carbon nitride derived carbon and nitrogen Co-doped CdS for stable photocatalytic hydrogen evolution

The narrow band-gap and long life-time of photo-generated charges endow CdS with much higher photocatalytic hydrogen evolution (PHE) activity over other photocatalysts. Thus, CdS based materials are considered to be most promising photocatalysts for PHE activity and stability. In this work, graphitic carbon nitride (GCN) is used as sacrifice agent to synthesize is nitrogen and carbon co-doped CdS nanoparticles with of uniform small size and higher specific surface area via hydrothermal reaction. Besides, co-doping of nitrogen and especially carbon leads to electron penetration to CdS results in tuned band structure of doped CdS with down-shifted conducting band and valance band positions. Moreover, the doped heteroatoms act as charge trapping centers that enhance charge separation within CdS particles endowing their photo-generated charges with longer life-time in compared with that of bare CdS. Benefited from non-metallic heteroatoms doping, obviously increased PHE activity and stability of CdS under visible light irradiation are achieved.

Role of Cobalt Doping in CdS Quantum Dots for Potential Application in Thin Film Optoelectronic Devices

Colloidal quantum dots (QDs) are promising materials for optoelectronic devices. In this paper, monodispersed and environment stable cobalt (Co)-doped CdS QDs have been synthesized and characterized for potential application in thin film optoelectronic devices. The Rietveld refinement profiles of X-ray diffraction data reveal that both undoped and Co-doped CdS QDs exhibit a zinc blende structure without any impurity phase. X-ray photoemission spectroscopy has been used for electronic structure and valence state analysis. The detailed information about the doping, coordination number, and local geometry has been studied with XANES and EXAFS measurements. Analysis of Raman spectra reveals that the intensity of longitudinal optical (LO) modes varies considerably due to short-range structural disorder. Absorption spectra also show the creation of a new doping band (DB) near the NIR region in Co-doped CdS QDs which is not observed for doping of many other transition metals. The width of this DB increases with an increase in the doping concentration, and enhancement of photoconductivity of the thin film heterojunction of the samples has been obtained. Evolution of the new DB and enhancement of the photocurrent upon Co doping make the prepared quantum dots very promising materials to exploit for fabricating UV–vis/NIR thin film optoelectronic devices.

Efficient red photoluminescence from Al3+ and Cu+ co-doped CdS QDs embedded silicate glasses

Embedding CdS QDs into glasses can improve the thermal and chemical stability of QDs, which facilitates their wide and endurable applications such as nonlinear optical devices, optical filters, LED color converter and other optical emitters. Unlike colloid CdS QDs, it is difficult to modify surface states of CdS QDs in glasses by constructing ZnS or Cd1-xZnxS shell. In this work, Cu+ ions doped CdS QDs were precipitated in silicate glasses. It was found that Al3+ ions were simultaneously incorporated into CdS QDs along with Cu+ ions. Incorporation of Al3+ ions into CdS QDs not only lead to well dispersion of Cu+ ions, but also created sulfur vacancies and formed one electron trapping level below the conduction band of CdS QDs, leading to the donor–acceptor photoluminescence with improved photoluminescence quantum yields and thermal stability. Results reported provides an effective method to alleviate the surface defects and improve the photoluminescence quantum yields, promoting their potential applications as color-converting materials for light-emitting diodes.

Polyoxometalate Template-Based Synthetic Strategy to Prepare Ni, Mo Co-Doped CdS for Efficient Photocatalytic Hydrogen Evolution from Water Splitting

In this work, a novel polyoxometalate template-based strategy was applied to construct the bi-metal-doped CdS photocatalysts. NiMo6 polyoxometalate template precursor was applied for the preparation of Ni, Mo co-doped CdS photocatalysts (NiMo-CdS). The structures of the materials were explored by XRD, SEM, HRTEM, HAADF, element mapping, XPS, Raman spectrum and UV-vis DRS. Moreover, the results of the UV-vis spectrum showed that NiMo-CdS exhibited an enhanced performance on light absorption. The results of photocatalytic hydrogen evolution from water splitting demonstrated that the NiMo-CdS showed higher efficiency on hydrogen evolution than noble-metal Pt-doped CdS. The reason could be ascribed to the enhanced light absorption ability and charge separation after Ni and Mo were introduced, which could also act as co-catalysts. The apparent quantum yield (AQY) efficiency could reach 42% at 365 nm. This work proposed a novel and inexpensive method to synthesize the bi-metal (Ni, Mo) decorated CdS photocatalysts for efficient hydrogen evolution from water splitting.

Copper dopants impact enhanced behavior of Mn:Cu co-doped CdS nanocrystals (quantum dots) and their characteristics for optoelectronic applications

Mn and Cu:Mn co-doped CdS nanostructures were chemically prepared and deposited as thin films on glass slides by PLD technique. XRD peaks showed hexagonal nanostructure (Greenockite) phase. The studied parameters are as follows: strain, particle size, bond length, and stress to get more information about crystal structures. The analysis confirmed that the Cu/Mn ratio co-doping remarkably influenced the surface morphologies of the (CuxMn1−x) co-doped CdS (QDs) at (x = 0, 1, 2 and 3) at.%. The chemical composition analysis EDX announced that the Cu/Mn is present in the doped films. Two luminescence peaks appeared in the photoluminescence (PL) spectrum for all samples of the compounds referring recombination of the defect sates of Mn:CdS. The energy gap values of all deposited films were observed to be in the range of (2.97‒2.74) eV, optical absorbance has two absorption peaks, and shifted to higher wavelengths, UV–Vis particle size was in the range (2.47‒3.10 nm) and was estimated using Brus equation.

Activation of infrared emission in (iodine, nickel) Co-Doped CdS nanobelts for solar cells and optoelectronic applications

Achieving tunable emission in semiconductors over a wide-spectral range has always remained a challenge for its potential applications. For this purpose, transition metals (TMs) have been widely doped into II-VI semiconductors, however, least efforts have been made on adding non-metals. Here, we co-doped non-metal and TM, i.e. iodine + nickel (I + Ni) into CdS 1D nanostructures and explored optical properties for the first time. FESEM shows that among CdS: (F + Ni, Cl + Ni, Br + Ni, I + Ni), I + Ni-doped CdS nanobelts (NBs) were thinner and have high crystallinity confirmed by XRD and Raman spectroscopy. Successful incorporation of iodine into CdS NBs was confirmed by EDX. Low temperature (80 K) photoluminescence (PL) of I + Ni doped CdS shows multiple emission centred at 525, 583, 758, and 916 nm, respectively. The first emission corresponds to exciton magnetic polaron (EMP) and the next two emissions correspond to d-d transition (3A2g → 1Eg) and (3T1P → 3T1F) of Ni ions, respectively. The last emission (916 nm) originated only in the I + Ni co-doped CdS NB which may correspond to the iodine incorporated into belts. According to the best knowledge, iodine related emission was detected for the first time. This work will promote their future applications in solar cells and optoelectronic devices.

Tuning Paramagnetic effect of Co-Doped CdS diluted magnetic semiconductor quantum dots

Abstract Diluted magnetic semiconductor quantum dots (DMS-QDs) are known for their outstanding optical and magnetic properties. II–VI DMS-QDs, in particular, are interesting for spintronics, nonvolatile memory, and magneto-optical devices. Therefore, studying the optical and magnetic properties of different II-VI semiconductors doped with transition metal atoms is of great importance. Tuning II-VI QDs optical properties can be mastered by changing the QDs particle size and/or structure. However tuning the magnetic properties of DMS-QDs is still within trial and error verification, although it is crucial in targeting different applications in spintronics. We hereby demonstrate, the ability to tune the paramagnetic effect of homogeneous Co-doped CdS QDs following a co-precipitation synthesis route with different Co2+ concentrations. The structural, optical and magnetic properties have been comprehensively studied. The dopant cobalt atoms concentration and chemical-configuration were precisely tracked by x-ray photoemission spectroscopy. Excitingly, the different Co-concentrations of 2, 5 and 10% significantly improve the magnetic properties of the CdS QDs, which exhibit a paramagnetic concentration-dependent effect. With 10% of Co atoms, we were able to achieve ∼ 200 × 10 − 6 molar susceptibility, that is, the same value to that of pure CoS. Thus we could obtain the highest possible paramagnetic effect in the CdS semiconducting matrix exhibiting 2.76 eV band gap, i.e. in the visible range. This efficacious result encourages the use of the present method in preparing DMS-QDs materials targeting various spintronics applications.

Structural, optical and magnetic behaviors of Fe/Mn-doped and co-doped CdS thin films prepared by spray pyrolysis method

CdS thin films doped and co-doped with Fe and Mn were prepared by spray pyrolysis technique and the films were portrayed by X-ray diffraction, laser Raman, XPS, FESEM with EDAX, UV–Vis, PL, and VSM analyses. The structural parameters were identified and the crystalline nature of the films was confirmed by X-ray diffraction patterns. The different optical phonon modes of vibrations present in the films were studied using laser Raman analysis. XPS analysis was used to study the binding states of electrons at various energy levels and the binding energy shift due to doping in the thin films under study was also determined. The morphology of the thin films was studied using FESEM technique and the change in the morphologies due to doping is evident from the images. To resolve the band gap of the material of the thin films before and after doping, UV–Vis absorption spectra have been recorded using UV–Vis spectrophotometer. It is found that the band gap has been tuned due to doping. PL spectral studies and VSM studies have been employed to study the luminescence and magnetic properties, respectively, with respect to the doping elements. The presence of weak ferromagnetic nature of the doped films indicates that the defects created by the doped elements induced ferromagnetic property even in the CdS thin film.

Characterization of CBD–CdS nanocrystals doped with Co2+

Co-doped CdS nanofilms are synthesised by chemical bath deposition growth technique at the temperature of 60 ± 2 °C. The cobalt molar fraction was ranged from 0 ≤ x ≤ 5.47, which was determined by energy-dispersive X-ray spectroscopy. The X-ray diffraction shows that the nanofilms are of CoS–CdS nanocomposites with individual CdS and CoS crystalline planes. The Co-doped CdS crystalline phase was zinc-blende that was determined by X-ray diffraction and confirmed by Raman spectroscopy. The average grain size of the CdS films was ranged from 2.56 to 1.67 nm that was determined by Debye–Scherrer equation from ZB (111) direction and it was confirmed by Wang equation and high resolution transmission electron microscopy (HRTEM). Raman scattering shows that the CdS lattice dynamics is characteristic of a bimodal behaviour, in which the first optical longitudinal mode denotes the characteristic peak at 305 cm−1 of the CdS nanocrystals that is associated with the cobalt incorporation. Nanofilms present two main bandgaps at ~ 2.56 and 3.80 eV, which are attributed to single CdS and quantum-confinement due to nanocrystals size. The increase in band gap with increase in cobalt concentration suggests intermetallic compound of CoS (Eg = 1.60 eV) with CdS (Eg = 2.44 eV). The CdS nanocrystals size was ranged from 2.46 to 1.81 nm that was determined from ZB (111) direction by Debye–Scherrer equation and confirmed by the Wang equation. The room-temperature photoluminescence of the Co-doped CdS presents well-resolved radiative bands associated to structural defects and with the quantum-confinement. For the Co-doped CdS the photoluminescence intensity increases indicate a high-passivation of the nanocrystals.

High-performance visible light photocatalytic activity of cobalt (Co) doped CdS nanoparticles by wet chemical route

The role of cobalt (Co) dopant on structural, morphological, optical and photocatalytic properties of CdS nanoparticles were methodically reported. XRD analysis confirms that both pure and Co-doped CdS samples have cubic structure with no impurity phases detected and the results are good in agreement with the standard JCPDS value (Card No. 80-0019). TEM images reveal the spherical morphology with an average diameter of around 15–35 nm. A noticeable red-shift of absorption edge and bandgap narrowing can be attributed to the inclusion of cobalt ions and creation of defect levels in the bandgap, which is confirmed by UV analysis. Photoluminescence spectra show defects-free nature of synthesized nanoparticles. The functional groups and chemical interaction were determined by FTIR spectra. The photodegradation of MB dye with Co-doped CdS is more efficient under visible light compared to pure CdS. The 15 mol% Co-doped CdS acts as an efficient photocatalyst. The presence of Co2+ generated electron and holes and prolonged the recombination rate by introducing the temporary trapping sites, which essentially causes to improve the photocatalytic efficiency of the synthesized samples. The possible photocatalytic mechanism by Co doping is also discussed in detail.

Studies on Dilute Magnetic Semiconducting Co-Doped CdS Thin Films Prepared by Chemical Bath Deposition method

The Co-doped CdS polycrystalline thin films were deposited onto the glass substrates by chemical bath deposition method. All the deposited films were characterized for structural, surface morphology, elemental, optical and magnetic properties using X-ray diffractometer, scanning electron microscopy (SEM), energy dispersive X-ray, UV–Vis. NIR spectrometer and Vibrating sample magnetometer before and after doping. The thin films exhibit hexagonal wurtizite structure with (0 0 2) preferential orientation and the calculated crystallite size is 29 and 18 nm for pristine and Co-doped CdS films respectively. X-ray photoelectron spectroscopy (XPS) analysis showed the presence of Cd, S and Co peaks along with O 1s peak. The studies revealed that the surface Cd atoms of films are found to be bound either to S atoms or O atoms. SEM images showed grainy surface for pristine which gets modified under Co doping. Energy dispersive analysis using X-rays confirmed the presence of Cd, S and Co in the films. From optical transmittance spectra, the bandgap was estimated and found to be varying from 2.4 to 2.27 eV with the increase of Co concentrations. The room-temperature ferromagnetic behavior was exhibited by Co-doped CdS films.

The possible doping of Al3+ and F− modification onto CdS in montmorillonite

The doping of aluminum (Al3+) and the co-doping of aluminum (Al3+)/fluoride (F−) into cadmium sulfide-montmorillonite were investigated. The Al3+ doping was achieved by the reactions between Al3+/Cd2+-montmorillonite and an aqueous solution of sulfide (S2−). The doping of F− was conducted by the reactions between the Al3+ doped sample and an aqueous solution of sodium fluoride (NaF) at room temperature. The products were characterized by powder X-ray diffraction, transmission electron microscopy, as well as Raman, UV–visible and photoluminescence spectroscopies. The blue-shift of the absorption onset and the emission band, as well as the increase in the photoluminescence intensity of the Al3+ doped and Al3+/F− co-doped CdS in montmorillonite if compared with pure CdS and CdS in montmorillonite were ascribed to quantum size effect and Burstein–Moss effect.