Kubelka-Munk Method Research Articles

The Influence of Cuprum (II) Acetate (Cu (CH3COO)2) Dopant and Heating Temperature in The Fabrication of Thin Films of Barium Strontium Titanate (Ba0.4Sr0.6TiO3)

Abstract Barium Strontium Titanate (BST), or BaxSr1-xTiO3, is an excellent ferroelectric material that is widely used on thin film applications in microelectronic devices, making BST very essential to the tech industries. This research aims to fabricate Cuprum doped BST thin films at low temperature using the Chemical Solution Deposition (CSD) and spin coating technique, and then to analyze the thin film’s band gap energy from the UV-Vis curve, XRD Spectral and EDAX. The advantage lies in the use of low temperatures in which it allows a significant energy savings compared to other studies. Using the Kubelka-Munk method with the Tauc Plot relation, the bandgap energy values for each BST substrates were obtained. Without Cuprum (II) Acetate dopant, the Band Gap values of the thin film samples are 3.84 eV and 3.77 eV. With 3% concentration of Cuprum (II) Acetate dopant, we obtained smaller Band Gap values, which are 3.74 eV and 3.71 eV. Based on the XRD spectral analysis, the lattice parameters were determined with a tetragonal crystal structure. However, according to the EDAX analysis, the elemental composition obtained is not yet stoichiometric. This research is important to serve as a reference for other researchers and manufacturers to opt into fabrication of thin films with lower energy cost, provide guidance for researchers to have more flexibility in their own thin film fabrication.

Investigating the Structural, Linear/Nonlinear Optical, and Photoluminescence Characteristics of CuO/ZnMn2O4 Nanocomposite for Physicochemical Applications

The structural, optical, and photoluminescence performance of CuO/ZnMn2O4 nanocomposites was investigated for optical applications. Nanocomposites of xCuO/(1-x)ZnMn2O4 (x; 0 to 0.7) were equipped using the sol-gel route. Synchrotron X-ray diffraction data were collected to examine the structural parameters. Rietveld refinement analysis reveals that the crystallite size decreases upon raising x from 0 to 0.7. High-resolution transmission electron microscopy revealed that the distribution of particle sizes demonstrates a relatively broad spectrum within the nanometer range. Raman spectroscopy investigations were applied to examine the structure’s vibrations. Scanning electron microscopy was used to examine the morphology of the formed samples. UV–vis spectrophotometry was applied to collect optical absorbance and reflectance measurements of the samples. Optical energy gap E g was determined utilizing the Kubelka-Munk method. The refractive index investigations were explored based on seven empirical formulas. The nonlinear optical parameters were explored as a function of CuO contents. The influence of CuO amount on the photoluminescence spectra was investigated. CIE chromaticity diagrams showed that all samples have various degrees of blue-violet colors. A significant improvement was achieved in the linear/nonlinear optical performance of nano ZnMn2O4 by forming CuO/ZnMn2O4 heterojunction, supporting the possible use of CuO/ZnMn2O4 nanocomposites in various optical applications.

Production of GeOx Films at Different Oxygen Flow Rates and Different Annealing Temperatures and Examination of Energy Band Gaps using Kubelka Munk Method

In this study, GeOx films were grown on silicon substrates using the Radio Frequency (RF) Magnetron Sputtering method at different oxygen flow rates and annealing temperatures. The films were produced at a substrate temperature of 250°C and a working pressure of 13 mTorr. Subsequently, the films were annealed at temperatures of 300°C, 500°C, 600°C, 700°C, 900°C, and 1000°C. Total and diffuse reflection measurements were performed to investigate the optical properties of the films. Energy band gaps were determined using diffuse reflection measurements and they were calculated using the Kubelka-Munk method. It was observed that the energy band gap increased with increasing oxygen ratio. Additionally, annealing temperatures were found to cause changes in the energy band gaps.

Exploring the optical behavior and relative translucency parameter of CAD-CAM resin-based composites, polymer-infiltrated ceramic network, and feldspar porcelain

ObjectivesTo evaluate and compare the optical properties and relative translucency parameter of CAD-CAM restorative materials. MethodsFour CAD-CAM materials were evaluated: Lava Ultimate (LU), Grandio Blocs (GB), VITA Enamic (VE), and VITA Mark II (VM). Disk-shaped samples in shade A2-HT were prepared (n = 10) and polished to 1.00 ± 0.01 mm of thickness. Scattering (S), absorption (K), albedo (a) coefficient, transmittance (T%), light reflectivity (RI), infinite optical thickness (X∞), and radiative transfer coefficients (μa, and μ′S) were calculated using Kubelka-Munk method and Thennadil's semi-empirical approach. Root Mean Square Error (RMSE) and Goodness of Fit (GFC) were used as performance optical behavior. Translucency differences were evaluated using the relative translucency parameter (RTP00) and 50:50 % translucency perceptibility and acceptability thresholds (TPT00 and TAT00). ResultsThe spectral distribution of S, K, T%, RI, and X∞ was wavelength-dependent. GFC and RMSE values indicated good spectral behavior matches and good comparative spectral values for RI in LU-GB, LU-VE, and GB-VE, and for K in VE-VM. VM displayed the highest scattering values across the wavelengths, while VE and VM showed lower absorption at shorter wavelengths. LU and GB had the highest transmittance. The X∞ values indicated that all 1.0 mm thick materials could be influenced by the background. No good spectral match and no good comparative spectral values were found between CAD-CAM materials and anterior bovine maxillary specimens. VM had the lowest RTP00 values with perceptible and unacceptable differences compared to CAD-CAM materials evaluated. SignificanceUnderstanding the optical behavior of different CAD-CAM materials was essential for guiding clinicians in material selection and optimizing their clinical performance. The findings confirm that the different compositions and microstructure impact the optical properties and translucency of CAD-CAM restorative materials.

Structural and optical properties of mesoporous akermanite derived from industrial waste for multifunctional applications

The present study focuses on the synthesis of akermanite by chemical free hydrothermal route using two major industrial waste ground granulated blast furnace slag (GGBS) and coal fly ash (FA) as the initial precursors. Further, leaf extract and Cetyltrimethyl ammonium bromide (CTAB) have been used as stabilizing and chelating agent to observe their effect on the structural, optical and morphological properties of the nanoparticles. The synthesized powders were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), ultraviolet visible (UV–visible) spectroscopy, Brunauer-Emmett-Teller (BET) analyser techniques. The detailed structural studies implied that the fabricated powders are akermanite and the average crystallite size was calculated to be in the range 23–27 nm. Field emission scanning electron microscopy analysis showed that the samples synthesized using water and leaf extract adopt rod like morphology while the sample fabricated using CTAB are seed shaped. The calculated bandgap of the developed powders from the UV-Visible reflectance spectra using Kubelka-Munk method lie in the range 3.1–3.26 eV. BET analysis revealed all the samples are mesoporous in nature and their specific surface area were estimated.

Exploring the Structural, Optical and Photoluminescence Performances of CuCo2O4 and ZnMn2O4 Alloying

The performance of the structural, linear/ nonlinear optical and photoluminescent properties of CuCo2O4 and ZnMn2O4 alloying was investigated. (1−x)CuCo2O4/(x)ZnMn2O4 (x = 0, 0.10, 0.15, 0.2) samples were prepared by the sol-gel and hydrothermal procedures. Synchrotron X-ray diffraction measurements were employed to investigate the structural and microstructural properties applying the Rietveld refinement method. Fourier transform infraed and Raman techniques were applied to explore the structures’ variation and chemical bonding of the obtained phases. Ultraviolet–visible diffuse reflectance spectroscopy measurements were collected to explore the optical properties. The optical band gap values were determined using the Kubelka-Munk method. All samples exhibited two band gaps in the visible-NIR regions. Upon composing with ZnMn2O4, the band gaps of CuCo2O4 declined for x = 0.1 and 0.15, followed by an increase at x = 0.2. The possible electronic band structure of the samples and the photoluminescent performance of the prepared samples was investigated. The observed PL patterns manifest wide and asymmetrical emissions. The CIE chromaticity diagram for all samples was plotted. The obtained findings of (1−x)CuCo2O4/(x)ZnMn2O4 nominate their efficient role in optical device fabrication and photocatalyst applications.

Concentration-dependent luminescence characterization of terbium-doped strontium aluminate nanophosphors.

The present investigation describes the synthesis of luminescent terbium-doped strontium aluminate nanoparticles emitting bright green light, which were synthesized through a solid-state reaction method assisted by microwave radiation. Various samples containing different concentrations of Tb were synthesized, and an analysis of their structural and morphological features was conducted using powder x-ray diffraction, Fourier transform infrared spectroscopy and field emission scanning electron microscopy. The band gaps of the samples were determined utilizing the Kubelka-Munk method. The quenching mechanism observed was identified to be due to dipole-dipole interaction using the Dexter theory. The optimized sample with a terbium concentration of 4at.% has a luminescence lifetime of 1.05 ms with 20.62% quantum efficiency. The results of this study indicate that the terbium-doped strontium aluminate fluorescent nanoparticles exhibit promising potential for a wide range of applications, including bioimaging, sensing and solid-state lighting.

Optoelectronic properties of BiCuOSe p-type oxychalcogenides

BiCuOSe systems are proposed as candidates to develop transparent p-type semiconductors in the visible region. This work reports the characterization results obtained for the BiCuOSe powders, synthesized by the solid-state reaction (SSR) method through mechanical milling, and nanostructured thin films deposited from the same processed powders using the pulsed laser deposition (PLD) technique. Structural characterization through X-ray diffraction (XRD) showed that the material presents a tetragonal structure with an average crystallite size of 21 nm and a preferential orientation in the (1 0 2) plane. The morphological and particle size evolution of BiCuOSe powders is presented as a function of the milling time. Transmission and scanning electron microscopies confirmed the spherical geometry of the particles in the powders and nanosheets like structure for the films. Particle sizes were also estimated, ranging from 10 to 100 nm for powders and 60 to 70 nm for films. The bandgap values, EG, for BiCuOSe powders were estimated from diffuse reflectance spectra using the Kubelka–Munk method, yielding values close to 0.7 eV. For thin films, EG values were estimated using the Tauc method, obtaining values in the range of 0.8–3.5 eV, depending on the annealing treatment. Additionally, electrical properties were measured in all deposited thin films, confirming the p-type conductivity, a minimal resistivity of 0.0735 Ω cm, hole mobility on the order of 88 cm2/Vs, and carrier concentration of 9.7 × 1018 cm−3.

Ni-doped ZnO nanoparticles derived by the sol–gel method: structural, optical, and magnetic characteristics

A simple sol–gel route was used for preparation of Ni doped ZnO nanoparticles (Ni:ZnO) with 0, 3, 5, 7 and 9 wt% of Ni to Zn precursor salts. Structural, optical and room temperature magnetic properties were studied. The prevailing structural arrangement that observed in all the examined samples is the wurtzite structure of ZnO. Nevertheless. The orderly development of NiO rock-salt phase on at the surfaces of ZnO nanoparticles upon Ni doping is confirmed by Rietveld refinements. The ZnO wurtzite structure is dominant in all the samples as confirmed by both XRD and Raman results. The average crystallite size showed almost no change upon Ni doping. RTFM behavior is being exhibited for all Ni:ZnO nanoparticles that is demonstrating using of ZnO as the host structure allowed for the efficient formation of DMS. The Near-infrared solar reflectance (RNIR) and the visible solar reflectance (RVis) values reduced with increasing of the Ni content as a result of the rising in density of trap states upon Ni doping of the samples. Kubelka-Munk method was used to determine the energy band gap (Eg) and band Urbach energy (EU) tails from diffused reflectance (DRS) results. The obtained energy gap values were very close in all studied samples with an average value of energy gap is 3.164 eV. The EU values raise from 123 to 173 meV upon increasing of Ni content in the samples in agreement with lower values of RNIR and RVis and their effect on optical performance of the investigated samples in applications.

Structural, Optical, Electrical, and Magnetic Characterization of PC/PEO Blend Incorporated with ZnFe2O4 Nanoparticles

In this study, zinc ferrite nanoparticles (ZnFe2O4 NPs) were incorporated into a polycarbonate/polyethylene oxide (PC/PEO) blend using the casting method. The resulting blends were subjected to comprehensive analysis using various techniques. X‐ray diffraction (XRD) analysis revealed that the presence of ZnFe2O4 nanoparticles had a significant impact on the crystal structure of the PC/PEO blend, leading to a reduction in crystallinity. Fourier‐transform infrared (FT‐IR) measurements further confirmed the uniform distribution and compatibility of PC and PEO as polymer components, as well as their compatibility with the blend containing ZnFe2O4 NPs. The optical properties of the PC/PEO blend, including band gap and Urbach energy, were quantified using the Kubelka–Munk method. The incorporation of ZnFe2O4 NPs resulted in the formation of sub‐band states between the valence and conduction bands, leading to a decrease in the band gap values. Field emission scanning electron microscopy (FESEM) analysis revealed a noticeable modification in the surface roughness, with the addition of ZnFe2O4 NPs resulting in a smoother surface texture. The electrical properties of the blends, including dielectric constant, dielectric loss, and AC conductivity, were measured. The addition of ZnFe2O4 NPs increased the dielectric constant (ε′) at lower frequencies, while it remained relatively stable at higher frequencies due to the localized charge carriers within the polymer blend. The higher values of ε’ observed at lower frequencies can be attributed to the movement of ions, which contributes to enhanced ionic conductivity. The magnetic properties of the blends were evaluated, demonstrating an increase in magnetic saturation upon the addition of ZnFe2O4 NPs. These findings provide valuable insights into the structural, optical, electrical, and magnetic characteristics of PC/PEO blends incorporated with ZnFe2O4 nanoparticles, thereby highlighting their potential for a wide range of technological applications.

Comparative characteristic of Bi- and La- doped (Ca/Sr)MoO4 -based materials with a defect scheelite-type structure

CaMoO4- and SrMoO4-based scheelite-type phases are noteworthy functional materials, whose properties strongly correlate with their structure. This work is devoted to La- or Bi-doped scheelite-type molybdates. The purpose of the present study is to quantify the effect of isolated electron pairs of bismuth on the distortion of the structure and related properties. Conventional solid-state technology was used for the synthesis of (Ca/Sr)1–3xLa2xФxMoO4 and Sr1–3xBi2xФxMoO4, (0.025≤ x ≤ 0.275). The structure was investigated by X-ray powder diffraction and Raman spectroscopy. Rates of structure distortion were characterised by the analysis of the autocorrelation function (AAF) of Raman spectra. Energy gaps were calculated by the Kubelka-Munk method. The conductivity was studied with a.c. impedance spectroscopy. For (Ca/Sr)1−3x(Bi/La)2xФxMoO4 series 0.025 ≤ x ≤ 0.15 compositions show a basic defect scheelite structure, while 0.15 x ≤ 0.225 compositions of Bi-doped samples exhibit tetragonal supercells. The chemical compression of unit cell is more evident in the case of Bi-doping, indicating the preferred orientation of the isolated electron pairs. The distortion of MoO4 polyhedra showed by AAF was more significant for Sr1−3xBi2xФxMoO4 than for Sr1−3xLa2xФxMoO4, the Δcorr parameters for Bi-doped compositions were almost double in comparison with La-doped one in the range of 50–600 cm–1 of the Raman shift. The «critical» x = 0.15 point was also clearly indicated by Δcorr parameter. The AAF of the Raman spectra of solid oxides was shown to be a good tool for prediction of properties and points of phase transitions in solid oxides.

Green method for preparation ZnO nanoparticles using red peony leaves extracts

The source of clean, dry red peony leaves has been carefully packaged and preserved. Then the red peony leaves were extracted to get the extracts solution at the optimum extraction temperature, extraction time and leaves sample weight. The precursor material used to prepare ZnO nanoparticles with spherical wurtzite structure was zinc acetate dihydrate salt (Zn(O2CCH3)2.2H2O) with the reducing and stabilized agent being flavonoid extraction from red peony leaves. The structure and characterizations of the fabricated ZnO nanoparticles were studied by measurement methods such as XRD, SEM, EDX, reflectance spectra. The study results showed that the extraction parameters of peony leaves to obtain the optimal flavonoid extraction yield were red peony leaves weight of 20 grams extracted in 100 ml of distilled water, extraction time of 60 minutes and extraction temperature of 70 °C. ZnO spherical wurtzite nanoparticles were prepared by wet chemical method at low temperature of 110 oC, with particle size according to SEM were about of 200-400 nm. The band gap was determined by the Kubelka-Munk method to achieve Eg» 3.05-3.17 eV. The ZnO spherical wurtzite nanoparticles were prepared in this our study with further purposes will be modified to reduce the Eg bandgap energy for applications as highly effective absorbents, photocatalysts in the visible light region.

Solution combustion synthesis of Dy-doped ZnO nanoparticles: An investigation of their structural, optical and photoluminescence characteristics

Undoped and Dy-doped ZnO nanoparticles were synthesized by solution combustion technique using urea as fuel. The synthesized nanoparticles were examined by various characterization tools for their structural, optical and photoluminescence properties. All the nanoparticles are found to possess the hexagonal wurtzite structure of ZnO with crystallite sizes in the range of 16–23 nm. The structural parameters viz. lattice constants, bond lengths, bond angles, and lattice strain of the nanoparticles have been evaluated. The high-resolution transmission electron micrographs and selected area electron diffraction patterns confirm the high crystallinity of the nanoparticles. The optical bandgap estimated from the diffuse reflectance spectra using the Kubelka-Munk method is found to be 2.90 eV for the undoped ZnO. A sharp narrow UV emission peak at ∼396 nm originating from the excitonic recombination is observed in the PL spectra of all the nanoparticles. The visible emission peaks in the PL spectra of undoped ZnO are attributed to different native defects, whereas in Dy-doped ZnO nanoparticles, the visible emissions (blue, yellow and red) are assigned to the 4f intrashell transitions in Dy3+ ions. It has been concluded that the solution combustion synthesized 5 mol% Dy-doped ZnO can be a promising material for white luminescence applications.

Polypropylene film surface modification for improving its hydrophilicity for innovative applications

Organic polymeric materials, especially polyolefins, contain mainly C and H atoms and thus present serious surface problems due to low surface energy and reactive inertness. Using method developed in this work it is possible to convert the H atoms of the polypropylene (PP) film surface into polar groups by treatment with a mixture of chromic, sulphuric, and phosphoric acids in a short time at elevated temperature. Hydroxyl and carboxyl groups on the surface of materials not only determine their chemical and physical properties, but also provide reactive centers for various applications. Optical microscopy (OM) and atomic force microscopy (AFM) analyses have shown that induced surface modification of the PP film causes mainly physical changes, creating microcraters and surface roughness and hence increasing surface tension, while X-ray diffraction (XRD) analysis has confirmed the absence of phase changes. The attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy analysis has confirmed the grafting of polar groups, such as hydroxyl, carboxyl, and carbonyl onto the surface of the PP. This indicates that used mixture destroyed or at least broke down to some extent the covalent bonds of the main carbon skeletons, which were present on PP substrate surfaces and improved surface wettability and zeta potential. The simultaneous thermal analysis (thermogravimetry (TG) and differential scanning calorimetry (DSC)) results have shown that the presence of polar groups in the PP-[O] film samples affects the melting and decomposition temperatures; they are higher than those of PP film. The change in the enthalpy of melting indicated a change in the surface energy. The band gap (Eg) determined from diffuse reflectance spectra in the UV-visible region by the Kubelka-Munk method has decreased for modified PP films, and they have become more suitable for optoelectronics.

Effect of metal ions on structural, morphological and optical properties of nano-crystallite spinel cobalt-aluminate (CoAl2O4)

The bright blue nano crystallite cobalt aluminate (CoAl2O4) was synthesized by sol–gel method using a mixture of chelating agent of glycerol and citric acid. The effects of changing (0.05, 0.075, 0.10, 0.25, 0.50, and 0.75 mol/L) metal ion concentration on the structural, morphological and color properties of synthesized CoAl2O4 were characterized by using X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), Nanoparticle size analyzer, Simultaneous Thermal Analyzer (STA), UV–vis absorption spectroscopy, and CIE-LAB colorimetric analysis. From the X-ray peak profile analysis, the crystallite size was measured by Debye-Scherrer (D-S) equation, and three different models presenting average crystallite sizes between 88.3 and 125.4 nm.The average lattice strain, dislocation density, lattice constant, cell volume, and zeta potential were between 0.00021 and 0.0058, (1.73 to 12.8) × 1014 (lines/m2), 8.10658 to 8.11181 Å, 533.60 to 533.81 Å3, −56.4 to − 63.5 mV, respectively. Using UV–vis absorption spectroscopy, the band gap was calculated from Kubelka-Munk method, and the values of band gap increasing from 1.82 to 1.84 eV, respectively. The reflectance spectra and the CIE-L*a*b* values of cobalt aluminate is also measured which confirmed the formation of blue nano crystallite cobalt aluminate.

Photocatalytic Efficiency of TiO2/Fe2O3 and TiO2/WO3 Nanocomposites

The photocatalytic proprieties of TiO2/FeO3 and TiO2/WO3 nanocomposites have been investigated using methylene blue as a pollutant. We propose a non-conventional approach for material preparation, i.e., the Doctor Blade technique, which is an easy and inexpensive method for coating materials. Several drawbacks related to the use of powders can be alleviated by using solid substrates, and this deposition method allows us to take advantage of the high surface area of nanoparticles, avoiding dispersion in the solution. The possibility of coating a material with a photoactive molecule with an easy and inexpensive method leads to the use of photocatalysis in the real world. The structural, optical, and textural characterizations of these materials were carried out using UV-vis. Diffuse Reflectance Spectroscopy (DRS) was used to calculate the energy band gap with the Kubelka-Munk method, and N2 absorption-desorption measurements were used to study the exposed surface area (SBET). The photocatalytic activity was evaluated in nanocomposites containing 0.1/0.2/0.3/0.5 wt.% of Fe2O3 or WO3 or both Fe2O3 and WO3. An enhancement of about 60% was achieved by adding 0.2% wt. of WO3 after 2 h of exposure to UV light. The TiO2@Fe2O3 and TiO2@WO3/Fe2O3 mixtures showed the same behavior as the TiO2@WO3 mixture. Therefore, the photoactivity of these photocatalysts is not related to the oxide itself. These solid results are due to the energy band structure of the materials. In fact, there is an important band matching among TiO2, WO3, and Fe2O3, which gives these nanocomposites a substantial improvement in photodegradation. The pH evaluated was neutral pH both at the beginning and at the end of the experiment, which is consistent with the well-known photodegradation pathway of methylene blue.

Effect of the zinc substitution on the physical and optical properties of tellurium vanadate glasses

In this communication, we report the physical and optical properties of xZnO-(60-x)TeO2-40V2O5 (x = 20, 25, 30, 35, and 40 mol%) glass systems. The glasses were prepared using the melt-quenching method. The amorphous nature of the glass systems was confirmed using powder X-ray diffraction. We have elucidated the changes in the rigidity and elastic moduli of the glass system as a function of composition. These changes were measured in terms of changes in the physical parameters like density, molar volume, and packing density of the glasses. The elastic moduli of the glass systems, like Young's modulus, bulk modulus, shear modulus, longitudinal modulus, and Poisson's ratio, were estimated using Makishima-Mackenzie's theory. The changes in the elasticity of the present system were correlated with the structural changes occurring in the glasses by adding ZnO at the expense of TeO2. The optical properties of the glass system were found by means of diffuse reflectance spectroscopy. Using Kubelka Munk method, the corresponding band gap energy and Urbach energy of the glass system were estimated. The present investigation sheds light on understanding the concentration effect of ZnO in the glass network.

Highly Selective Photocatalytic Conversion of Glucose on Holo-Symmetrically Spherical Three-Dimensionally Ordered Macroporous Heterojunction Photonic Crystal

Highly Selective Photocatalytic Conversion of Glucose on Holo-Symmetrically Spherical Three-Dimensionally Ordered Macroporous Heterojunction Photonic Crystal

Structures and optical properties of CdSe nano flakes synthesized by an elemental direct reaction method

CdSe nano flakes have been synthesized through using the selenium powder and cadmium foil in the ethylenediamine by an elemental direct reaction method. These high-quality CdSe nano flakes, being approximately perpendicular to the cadmium foil substrate, show the hexagonal structure and are characterized with the networking structures. According to Kubelka-Munk method, band gap of CdSe nano flakes can be estimated to be ∼2.44 eV. Multi-peak emissions under the excitation of 325 nm can be observed at room temperature. From green to red, four emissions can be fitted and attributed to the transition of band gap, selenium vacancies, interstitial cadmium, and the surface defects associated with oxygen, respectively. Investigation of multi-peak emission origins as well as understanding and regulating of defect states are helpful for CdSe nano flakes to apply in the field of the optoelectronic devices.

Structure and microwave dielectric properties of Bi- and Ge-doped calcium molybdate

The powders of Ca1–2xBi2xMo1–xGexO4 solid solutions weresynthesized by the conventional solid state method and investigated by X–ray powder diffraction and Raman spectroscopy. The Ca1–2xBi2xMo1–xGexO4 compositions crystallize in scheelite structure (sp. gr. I41/a) at 0 x 0.4, but traces of bismuth germanates are detected by scanning electron microscopy. The x = 0.5 composition contains several phases with BiVO4- type structures. Raman spectroscopy detected the deformation of [BO4]2– polyhedra and changes in B–O bond length (B = Mo, Ge). The energy gaps were calculated from the diffuse scattering spectra by the Kubelka-Munk method. Energy gap (Eg) values decrease with x from 3.29 eV to 2.91 eV, probably due to 6s2 electrons of bismuth in the valence band and changes of the conductivity band by electrons of germanium. Such values of Eg can provide photocatalytical activity of powders under UV and visible light. The electrodynamic parameters of the ceramic sample of Ca1–2xBi2xMo1–xGexO4 were measured by the transmission line method. The average permittivity increases with x from ~10 to ~18 which correlates with theoretical ε, Vmol and total polarizability of samples. An increase in the concentration of bismuth and germanium leads to the additional resonant peaks in the spectra of ε, S11 and S21. These resonant peaks can be probably caused by the appearance of irregular structural domains of Bi atoms or induced by the increased size of grains in the ceramic samples.