Increase In Cr3 Research Articles

Highly uniform microspheres of broadband near-infrared-emitting Ba(Hf1-xCrx)O3 perovskite phosphor

Chromium activated BaHfO3 (BHOC) perovskite phosphor with varying amount of Cr3+ ion (1–10 %) was prepared by hydrothermal synthesis and was characterized systematically using x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), positron annhilation lifetime spectroscopy (PALS) and time resolved photoluminescence (TRPL). FESEM show the formation of highly uniform microsphere of BHOC with very smooth surface texture. XPS showed the stabilization of chromium in +3 oxidation states, formation of oxygen vacancies and improved crystallinity in 6 % doped in BHOC sample. Under 500 nm excitation, BHOC perovskite demonstrated a very broad near infrared (NIR) emission band (700–1050 nm) centered at 815 nm with a full width at half-maximum (FWHM) of ∼150 nm and a wide absorption band, suggesting its potential application as NIR phosphor. The fraction of positrons getting trapped in the defects and vacancy clusters decreased with increase in Cr3+ doping and showed minima at 6.0 % doping and this sample also showed highest NIR light emission.

Influential trivalent ion (Cr3+) substitution in mixed Ni–Zn nanoferrites: Cation distribution, magnetic, Mossbauer, electric, and dielectric studies

Herein, we report the influence of trivalent chromium (Cr3+) ion substitution on the electric, dielectric, and hyperfine interaction properties of a mixed Ni–Zn nanoferrite system synthesized by an auto combustion solution-gelation route. The XRD analysis verified the monophase nanocrystalline formation of prepared ferrites belonging to the spinel group with a cubic structure. TEM images displayed the sphere-like morphologies of the typical nanoferrite sample. FT-IR spectra uncover the occurrence of two absorption frequency bands in the desired region belonging to spinel ferrite. The magnetic parameters decreased significantly with increasing Cr3+ concentration. Mossbauer parameters, such as the hyperfine field, line-width, isomer shift and quadrupole splitting, were deduced for all the samples. DCR studies confirmed the semiconducting behavior of all the samples with an increasing resistivity trend after Cr3+ substitution. The dielectric study showed a decreasing trend with an increase in Cr3+ concentration. All the results display the influential substitution of Cr3+ ions in the Ni–Zn ferrite system, which shows the usability of the prepared samples in higher frequency ranging systems.

FTIR and Electrical Properties of Cr Substituted Li0.5Fe2.5−xO4 Synthesized Using Sol-Gel Auto Combustion

The highly desirable properties of lithium ferrite and various metal ion substituted lithium ferrite make it a useful material for many electronic and magnetic applications. This research used a simple sol-gel auto-combustion method for the synthesis of Cr substituted Li0.5Fe2.5O4 ferrite. Here, in the B-site, Fe3+ ions were swapped by non-magnetic Cr3+ ions at different concentrations. All the samples of Cr substituted Li0.5Fe2.5O4 were confirmed through X-ray diffraction patterns to have a single-phase spinel-type structure with cubic symmetry, which was thereafter confirmed by its refinement through Rietveld. An increase in the substitution of Cr3+ instead of Fe3+ ions in the spinel ferrite system results in an increased nanocrystalline size. The average crystallite size decreased from 30 nm to 10 nm with an increase in Cr3+ content. Analogous particle size was evaluated through transmission electron microscopy (TEM) analysis. Fourier transform infrared spectroscopy (FTIR) provides an overview of the structural distortion of the lithium ferrite lattice with the substitution of Cr3+ ions. The Semiconducting (NTCR) nature of the Cr substituted Li0.5Fe2.5O4 nanoparticles was confirmed through the temperature-dependent DC resistivity. The evaluated trend of the dielectric properties (ε′, ε″, and tan δ) strengthens the facts observed in the electrical conduction mechanism.

Structure and optical, magnetic and photocatalytic properties of Cr3+ substituted zinc nano-ferrites

In this paper, the Cr3+ substituted zinc ferrite (ZnCrxFe2-xO4 with x = 0, 0.15 and 0.25) nanoparticles with single cubic spinel structure (Fd-3 m space group) were prepared by chemical co-precipitation method, and their structure and optical, magnetic and photocatalytic performaces were investigated. With Cr added, the lattice parameter and average grain size of the ferrites remarkably changed. High-quality nanostructured ferrite with an average particle size of 22–31 nm are revealed by TEM and SEM. The vibrational stretching modes of tetrahedral and octahedral sites were confirmed by FTIR. The optical studies proved a gradual decrease in the optical band gap which indicated the emergence of sub-band-gap energy levels by the chromium content. The magnetic properties were investigated through magnetization technique. The saturation magnetization measured from M-H hysteresis plot show decreasing trend with increase in Cr3+ content. The photocatalytic degradation of aqueous solution of Methyl Orange (MO) in the presence of prepared nano-ferrite under visible-light irradiation has been studied and discussed. The photodegradation efficiency of MO over ZnCrxFe2-xO4 photocatalysts is enhanced; (69%, 74% and 82% with increasing Cr3+content, respectively) compared with its modest value 12% without addition.

Cr3+ doped Al2O3 nanoparticles: Effect of Cr3+ content in intensifying red emission

Cr3+-doped α-Al2O3 nanoparticles (Al2−xCrxO3, 0.005 ≤ x ≤ 0.05) were synthesized by co-precipitation method. X-ray diffraction (XRD) patterns of Cr3+:Al2O3 nanoparticles revealed the crystallite size of ∼53 nm and electron microscopy (SEM & TEM) confirmed the spherical nanoparticle formation. Diffuse reflectance spectra (DRS) displayed peaks at 406 and 558 nm corresponding to the Cr3+ transitions which became prominent with the increase in Cr3+ concentration which was also evidenced by the gradually increasing pink coloration of the samples. Photoluminescence (PL) studies showed the sharp red emission at 694 nm (ruby line) which was observed for all samples. The Dq/B value for all samples was found to be greater than 2.3 confirming the presence of Cr3+ ions in the octahedral sites. Chromaticity diagrams displayed the maximum red appearance for the sample with x = 0.01 and a lifetime of 4 ms. The synthesized Cr3+:Al2O3 nanoparticles with smaller crystallite sizes and narrow near monochromatic emission can be used in various applications including sensing, lasing, and bioimaging applications.

Correlation between electrical conductivity and luminescence properties in β-Ga2O3:Cr3+ and β-Ga2O3:Cr,Mg single crystals

The photoluminescence, excitation, and absorption spectra as well as the electrical conductivity of β-Ga2O3:Cr and β-Ga2O3:Cr,Mg single crystals were studied. The as-grown β-Ga2O3:Cr crystals had a green color, the conductivity at about 10−2–10−3 Ω−1 cm−1, and a low yield of Cr3+ impurity luminescence. Annealing in oxygen atmosphere led to a strong increase in Cr3+ red luminescence yield, increase in the resistivity, and changes in the absorption and excitation spectra. Similarly, increases in the Cr3+ luminescence yield and resistivity were observed after codoping of β-Ga2O3:Cr crystals with magnesium (Mg2+). The registered changes in the Cr3+ luminescence yield, electrical conductivity, and in the absorption and excitation spectra are considered to be due to the shift in the Fermi level. In the as-grown β-Ga2O3:Cr crystals, the Fermi level is located near the bottom of the conduction band, and most chromium ions are in the Cr2+ charge state. Annealing in an oxygen atmosphere as well as codoping of the crystals with chromium and magnesium impurities moves the Fermi level toward the middle of the bandgap and recharges the chromium ions to the Cr3+ state.

Concentration-dependent fluorescence decay and energy transfer in Cr3+ and Nd3+ co-doped Y3Al5O12 ceramic powder

Energy transfer from Cr3+ to Nd3+ in Cr3+ and Nd3+ co-doped Y3Al5O12 (Nd/Cr:YAG) was investigated by measuring the decay curves of Nd3+ and Cr3+ fluorescence for Cr:YAG and Nd/Cr:YAG ceramic powder samples that were produced by the sol–gel method in a Cr3+ concentration range of 0.1–6.0 mol%. The energy transfer processes in Nd/Cr:YAG could be explained based on dipole–dipole interactions even when the concentration quenching of Cr3+ was included, and the experimental fluorescence decay characteristics of Nd3+ excited through Cr3+ were consistent with the theoretical predictions based on dipole–dipole interactions. For a high-quality Nd/Cr:YAG ceramic with negligible concentration quenching, the energy transfer efficiency from Cr3+ to Nd3+ increased with an increase in Cr3+ concentration.

Ferrimagnetic to antiferromagnetic transition and complex impedance analysis of Cr-doped magnesium ferrite nanoparticles

The chromium-doped magnesium ferrite (MgCrxFe2−xO4, x = 0.0, 0.4, 0.8, 1.2, 1.6, and 2.0) were prepared using sol–gel technique. X-ray diffraction scans confirmed the cubic spinel structure for all the nanoparticles samples. Reduction in lattice parameter and average crystallite size with increasing Cr3+ concentration was observed due to smaller ionic radii of Cr3+ (0.67 A) ions as compared to Fe3+ (0.63 A) ions. In FTIR vibrational studies, the addition of Cr3+ shows the splitting of ν1 band into two sub-bands due to variation of bond strength between same cations present at tetrahedral and octahedral lattice sites. With increasing Cr3+ concentration, the ZFC–FC magnetic curves revealed a ferrimagnetic (FiM) to antiferromagnetic (AFM) transition as compound transformed from MgFe2O4 to MgCr2O4. The M–H loops revealed decrease in saturation magnetization with increase in Cr3+ concentration which is attributed to FiM to AFM transition. The coercivity showed a non-monotonic behavior and has maximum value of 750 Oe for x = 1.2 due to overlapping of blocking and Neel transition temperatures. The dielectric properties showed a decreasing trend with increasing Cr3+ concentration. The room temperature impedance spectroscopy (Nyquist plots) was simulated using equivalent RC circuit model and an appearance of second semi-circle in the Nyquist plot with increasing Cr3+ concentration is observed which can be attributed to the contribution of grains in the hooping mechanism.

Competition of magnetic ordering and spin-phonon coupling in multiferroic hexagonal YMn1−xCrxO3

Hexagonal yttrium manganite (YMnO3) and chromium doped yttrium manganite (YMn1 – xCrxO3) were prepared by the solid-state method. X-ray diffraction and Raman scattering were combined to explore the structural characterization. Structural analysis illustrates that the lattice is compressed and the tilt of the MO5 (M = Cr or Mn) bipyramid is decreased with an increase in Cr3+ concentration, leading to declining frustration. Magnetic measurement suggests both weak ferromagnetic (FM) and antiferromagnetic (AFM) orderings enhanced with the growth of doping concentration. Enhanced weak FM ordering may arise from breaking of the superexchange interaction and introduction of the double-exchange interaction inside the layers, and the increased AFM ordering is attributed to the improved coupling between neighboring planes that resulted from the structural distortion. Spin-phonon coupling is discussed to confirm the enhanced coupling between interplane Mn3+ moments.

Optical and Conductivity Studies of Cr3+ Doped Polyvinyl Pyrrolidone Polymer Electrolytes

Polymer electrolyte films of polyvinyl pyrrolidone (PVP) embedded with various concentrations of Cr3+ ions were prepared by a solution casting technique. The complexation between the Cr3+ ions and the polymer was confirmed by Fourier transform infrared (FTIR) spectroscopy and UV–vis spectroscopy. The electrical conductivity of the films was measured using an impedence analyzer in the frequency range of 42 Hz to 5 MHz at ambient temperature. It was observed that the conductivity increased with the increase in the Cr3+ ion concentration. UV–visible absorption spectra in the wavelength range of 200–800 nm were used to determine the direct and indirect optical energy band gaps and optical absorption edge. Both of the optical band gaps decreased with the increase in Cr3+ ion concentration. FTIR studies on pure and Cr3+ doped PVP polymer films revealed the vibrational changes that occurred due to the effect of the dopant Cr3+ ions in the polymer. Our results suggested that Cr3+, as a dopant, is a good choice to improve the electrical properties of PVP polymer electrolytes.

Effect of Cr3+ doping on structural and optical property of ZnGa2O4 synthesized by sol gel method

Zinc gallate host and chromium ions doped ZnGa2O4 nano-powders was synthesized by citric acid assisted sol-gel method. The dopant molar percentage were varied between (0–2.5 mol. %). The x-ray diffraction (XRD) patterns shown that all synthesized nano powders are cubic structured and doping of Cr3+ ions did not affect the structure at all. The scanning electron microscope micrographs show small particles in nano range that are uniformly distributed, but became agglomerated with high doping of chromium concentrations. The high-resolution transmission electron microscope (HR-TEM) image shows the formation of several agglomerated particles with clear grain boundary and different sizes. Energy dispersive x-ray spectroscopy measurements confirm the presence of the expected elements. Ultraviolet–visible spectrophotometer measurement shows the % reflectance in the UV–vis region to be dependents on Cr3+ ions and the estimated band gap was found to vary between 4.46 and 4.80 eV. Un-doped ZnGa2O4 nano powder displays a broad blue emission but doping with Cr3+ ions caused the emission to occur in the near infrared region. An increase in Cr3+ ions up to 2.0 mol% lead to significantly enhancement in the near infra-red (NIR) emission but decrease thereafter. The CIE color coordinates values located in blue and NIR of the spectrum for undoped and Cr3+ doped samples, respectively. The photoluminescence emission intensity was also observed to be dependent on the excitation wavelength and the emission PL spectrum perfectly match the transparency window of living tissues and can effectively be used for bio imaging application.

Structural, Optical, Magnetic, and Dielectric Properties of Cr3+ Substituted Cobalt Aluminate Nanoparticles

The present study investigates the influence of Cr3+ substitution on structural, optical, dielectric, and magnetic properties of cobalt aluminates in the aluminates series CoAl2-xCrxO4, 0.00 ≤ x ≤ 0.20. These series of nanoparticles are effectively synthesized using the co-precipitation method. The cubic spinel aluminate structure is confirmed by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopic measurements. Transmission electron microscopy (TEM) analysis shows the formation of spherical nanoparticles, which are homogeneous in shape and size. The optical properties of the prepared samples have been investigated by means of optical absorbance spectra. The optical band gap $$ \kern0.5em {E}_{\mathrm{opt}}^i $$ and Urbach energy Eu are estimated. At room temperature, the magnetization of undoped CoAl2O4 reveals a weak ferromagnetic behavior. This ferromagnetism is increased for the sample with x = 0.05, and the samples with higher Cr3+ content have a tendency to be superparamagnetic on account of the formation of single-domain particles as a consequence of small particle size. Real part of dielectric constant (e′), dielectric loss (tanδ), ac conductivity (σac), real part of impedance (Z′), and imaginary part of impedance (Z″) are analyzed as a function of frequency and Cr3+ content. The results show that the dielectric loss (tanδ), dielectric permittivity (e′), and ac conductivity (σac) decrease with the increase in Cr3+ content, x = 0.05, and then increase with a further increase in Cr3+ content. The increase in these parameters has been explained on the basis of the hopping mechanism. From the Cole–Cole diagram, the value of the relaxation time τ can be calculated and it has been found to increase with increasing the Cr3+ content. Actually, a high dielectric constant makes these materials good for energy storage at high frequencies.

Strain induced magnetism and superexchange interaction in Cr substituted nanocrystalline cobalt ferrite

Distribution of magnetic relaxation time using Mössbauer spectroscopy has been observed for CoFe2-xCrxO4 (0.1 ≤ x ≤ 0.4) annealed at lower temperature (≤400 °C). The estimated cation distribution over A and B sites observed by Mössbauer spectroscopy is consistent with that obtained by the Rietveld analysis of the X-ray diffraction patterns. Saturation magnetization and magnetocrystalline anisotropy constant increase up to 20% of Cr (x = 0.2) substitution and, decrease with further increase of x. However, the coercive field as well as the Néel temperature decreases with increase in Cr3+ concentration, i.e., a crossover from the hard magnetic to soft magnetic nature by Cr substitution at the Fe site of CoFe2O4 has been observed. This behavior is attributed to the competition between strain induced magnetism and superexchange interaction between cations.

Preparation and Characterization of Chromium Doped Ni-Cu-Zn Nano Ferrites.

Chromium doped Ni-Cu-Zn nano ferrites with chemical formula Ni0.2Cu0.2Zn0.6Fe2-xCrxO4 (x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) were prepared by using sol-gel auto combustion method. The prepared precursors of Chromium substituted Ni-Cu-Zn ferrites were sintered at 500 °C for 4h. Compositional stoichiometry were confirmed from EDAX patterns. The XRD data revealed that the all samples possess a single phase cubic spinel structure. The Lattice constant, X-ray density, hopping lengths and crystallite size determined from XRD data decreases with increase in Cr3+ concentration. The IR spectra show two major absorption bands, high frequency band ν1 ≈ 600 cm-1 and low frequency band ν2 ≈ 450 cm-1 attributed to the stretching vibration of tetrahedral and octahedral sites respectively. The surface morphology of the prepared samples was studied by Scanning Electron Microscopy and Transmission Electron Morphology.

Spectroscopic Study of the Reversible Chemical Reduction and Reoxidation of Substitutional Cr Ions in Sr2TiO4.

The solid-state synthesis and controllable speciation of Cr dopants in the layered perovskite Sr2TiO4 is reported. We employed a chemical reduction procedure with NaBH4 at relatively mild temperatures (<450 °C) to impart sensitive control over the relative concentration of Cr3+ dopants, the charge-state of oxygen-vacancy defects, and presence of Ti3+ defects in highly reduced Cr-doped Sr2TiO4. The electron paramagnetic resonance (EPR) spectra of the reduced powder samples reveal a 12-fold increase in the Cr3+ concentration within the axially compressed Ti4+-site of the Sr2TiO4 host. The increase in Cr3+ content is achieved through the reduction of higher-valence Cr ions that are either EPR silent or diamagnetic. The spin-Hamiltonian parameters for Cr3+ substituted at the B-site of Sr2TiO4 were refined to D = -201 × 10-4 cm-1, g⊥ = 1.980, and g∥ = 1.978. In addition, the Cr3+ ion exhibits a temperature-dependent axial component to the zero-field splitting of the 4A2 ground term that is accounted for by ligand field theory and an isotropic contraction of the Sr2TiO4 lattice with decreasing temperature. The observed changes to the electronic structure upon reduction are quantitatively reversible upon reoxidation of the sample under aerobic annealing at the same temperature and duration as the reduction conditions. This temperature dependence of the Cr3+ content in the Cr-doped Sr2TiO4 powders is discussed and contrasted to our recent study on Cr-doped SrTiO3.

Study of the Structural and Electrical Properties of Cr-Doped BiFeO&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt; Ceramic

Multiferroic BiFe1-xCrxO3 (x = 0.2 and 0.4) ceramics were synthesized in a single phase. The effects of Cr3+ substitution on the crystal structure, dielectric permittivity and leakage current were investigated. Preliminary X-ray structural studies revealed that the samples had a rhombohedral perovskite crystal structure. The dielectric constant e' significantly increased while the dielectric loss tanδ was substantially decreased with the increase in Cr3+ substitution. The temperature effect on the dielectric properties exhibited an anomaly corresponding to magneto-electric coupling in the samples and was shifted to lower temperatures with the increase in Cr3+ substitution. The leakage current density also reduced in magnitude with the increase in the Cr3+ substitution.

Microwave absorption studies of Cr-doped Co–U type hexaferrites over 2–18 GHz frequency range

The effect of Cr3+ ions doping on the electromagnetic (EM) properties of polycrystalline U-type hexaferrite samples: Ba4Co2-3xCr2xFe36O60 (0.0≤x≤0.60, in steps of 0.15) have been studied. The X-ray diffraction (XRD) studies confirmed the formation of single U-type hexaferrite phase in all the prepared samples. Le Bail refinement of XRD patterns was used to calculate the lattice parameters ‘a’ and ‘c’. The room temperature M–H studies indicate that the saturation magnetization (Ms) decreases and coercivity (Hc) increases with increasing Cr3+ ions concentration. The complex permittivity (ε*=ε′−iε″) and permeability (μ*=μ′−iμ″) measurement were carried out using vector network analyser (VNA) over 2–18GHz frequency range. The complex permeability (μ*=μ′−μ″) spectra clearly observed the ferromagnetic resonance (FMR) phenomenon in all the prepared samples. The maximum microwave absorption (MWA) of 99.97% (or minimum reflection loss RLmin=−34.90dB) was observed for Ba4Co1.1Cr0.6Fe36O60 sample at 8.2GHz frequency with 1.7mm absorber thickness. The RLmin peak was found to shift towards higher microwave (MW) frequency with increase in Cr3+ ions concentration.

Synthesis and Evaluation of Microstructural and Magnetic Properties of Cr3+ Substitution Barium Hexaferrite Nanoparticles (BaFe10.5−x Al1.5Cr x O19)

Pure barium ferrite and BaFe10.5−x Al1.5Cr x O19 (x = 0, 0.5, 1.0, 1.5, 2.0) nanoparticles were synthesized by auto-combustion sol–gel method. The effect of substituting Fe3+ ions by Al3+ and Cr3+ ions on the structural, chemical composition, morphology and magnetic properties of BaFe12O19 and BaFe10.5−x Al1.5Cr x O19 hexaferrites have been investigated using X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy and vibrating sample magnetometer (VSM), respectively. The results confirmed that the hexagonal phase has been formed in all of nanoparticles and the value of lattice parameter (c) decreased, while the value of lattice parameter (a) remained nearly constant with the increase in Cr3+ ions contents in comparison to pure barium ferrite. The crystallite size and mean particle size of the nanoparticles lie in the ranges 33–42 and 35–70 nm, respectively. The VSM measurements show that with substituting Al and Cr cations in the hexagonal structure of barium ferrite, the saturation magnetization (M s ) and remanence magnetization (M r ) of the nanoparticles reduce, while coercive field (H c ) increased from 4.45 kOe for pure barium ferrite to 6.9 kOe for BaFe10.5Al1.5O19 (x = 0) due to the increase in the magnetocrystalline anisotropy and the decrease of the particle size.

Spectroscopic and photoluminescence properties of MgO:Cr3+ nanosheets for WLEDs

This work explores the synthesis of nanocrystalline MgO:Cr3+ (1–9mol%) nanophosphors via solution combustion route at 400°C. The nanophosphors were well characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infra-Red (FTIR) spectroscopy. PXRD results confirm cubic phase and SEM micrographs indicate that the particles are highly porous and agglomerated. The TEM images show that the powder consists of spherical particles of size ∼5–15nm. Upon 356nm excitation the emission profile of MgO:Cr3+ exhibits an emission peak at 677nm due to 2Eg→4A2g transition. It was observed that PL intensity increases with increase in Cr3+ concentration and highest PL intensity was observed for 3mol% doped sample and afterward it decreases, attributed to concentration quenching. The resultant CIE chromaticity co-ordinates in the white region make the present phosphor highly useful for display applications and also for white light-emitting diodes (WLEDs).

Incorporation of Cr 3+ ions in tuning the magnetic and transport properties of nano zinc ferrite

Cost effective and low temperature synthesis methods namely solution combustion and hydrothermal methods were used to prepare chromium incorporated nanocrystalline zinc ferrites. The effect of incorporation of low concentration Cr3+ ions on the structural, morphological, magnetic and transport properties of the zinc ferrite compounds were investigated. The crystalline nature and size variation with chromium content were valid from powder x-ray diffraction. Particles size and crystallite size variation were valid from scanning electron microscopy and transmission electron microscopy respectively. With the increase in chromium incorporation, the crystallite and particles sizes were decreased. Fourier transform infrared spectroscopy (FTIR) studies confirmed the presence of strong metal-oxygen bonds. The elastic properties of the materials in both the methods were estimated by FTIR studies. Magnetic properties namely saturation magentization, remanent magnetization and coercivity values were decreased with increase in Cr3+ ions concentration. The dielectric properties of the samples decreased with increase in the Cr3+ ions. The dielectric constant was observed to be of the order of 106 at low frequency and almost 1 at higher frequency range. The activation energy estimated using Arrhenius plots was of the order of 0.182 eV and 0.368 eV respectively for the compounds prepared by solution combustion and hydrothermal methods. The emission spectra of the samples excited at 344 nm were reported using photoluminescence (PL) spectroscopy. Further, the approximate energy band gap(Eg) was estimated from PL studies. The Eg of the materials were lie in the range of 2.11–1.98 eV.