Determination Of Optical Band Gap Research Articles

Thermally stable luminescence and dosimetric features of Ho(III) activated tungstate double perovskite

Luminescent efficient tungstate double perovskites Ca3WO6 doped with Ho3+ were synthesized via the solid-state reaction at 1200 C°. The resulting phosphors were analyzed using Rietveld refinement of X-ray diffraction (XRD) data, confirming a monoclinic crystal structure with crystallite sizes ranging between 50 and 55 nm. Optical bandgap determination was facilitated by diffusion reflectance spectra (DRS). Fourier transform infrared (FTIR) studies were conducted to identify functional group vibrations. The optical excitation of the Ca3WO6:Ho3+ phosphors under different excitation conditions resulted in intense green photoluminescence (PL) emission at 545 nm, indicative of the 5F4–5I8 transition of Ho3+ ions. Thermal stability assessment of Ca3WO6:1 % Ho3+ phosphor under blue excitation (454 nm) revealed good thermally stable luminescence about 85.32 % at LED working temperature (150 °C). PL decay studies were conducted to analyze fluorescent behaviour, wherein by means of PL decay lifetime, the PL quantum efficiency of Ca3WO6:1 % Ho3+ phosphor is computed to be 91.1 %. The CIE color coordinates of the phosphors being investigated reside within the green spectral region, with a calculated color purity of 93.25 % observed for Ca3WO6:1%Ho3+. Furthermore, the phosphors under study exhibited high-quality thermoluminescence (TL) after beta irradiation. The detailed TL characterization conducted to assess dosimetric properties. The impact of Ho3+ concentrations and beta dose on TL intensity are two major aspects that have been investigated in detail. TL fading experiments were performed to determine dose storage capacity over a month after beta irradiation. Additionally, the various heating rate (VHR) experiments are conducted to determine the TL kinetic parameters. Besides, the glow curve deconvolution (GCD) for trap parameter determination is also applied, where the results obtained are comparable with the VHR results.

Hybridization of ellipsometry and XPS energy loss: Robust band gap and broadband optical constants determination of SiGe, HfON and MoOx thin films

In this study, we compare the robustness of optical constants and optical band gap determination of three different materials: SiGe, N-doped HfO2 and MoOx, using the combination of two techniques: spectroscopic ellipsometry, and energy loss signal (ELS) of X-ray photoelectron spectroscopy (XPS). The determination of such physical properties is achieved through the hybridization of the two techniques based on multiple Tauc-Lorentz model, applied on the whole energy range of measurement.Such use of hybridized data demonstrates a new robust method to determine the band gap of the studied materials, together with the optical indices (refractive index and extinction coefficient) on a wide energy range (up to 40 eV). This method provides an extension of determination of the relevant physical quantities compared to each technique on their own.Moreover, this algorithm is tested on limit conditions, where the energy ranges of measurement of the two respective techniques presented no overlap. Yet the use of a unique physical model still allows us to calculate the different physical quantities even on the energy range where no measurement is performed, validating the semi-predictive nature of the hybrid technique. Additional measurements under different experimental configurations validate the extended scope of such hybrid technique.

Study of Structure, Morphology and Optical Properties of Cobalt-Doped and Co/Al-co-Doped ZnO Thin Films Deposited by Electrospray Method

A versatile electrospray method was utilized for deposition of thin ZnO films doped with Co (5%) (CZO) or co-doped with Co (2.5%) and Al (2.5%) (CAZO). Thin polycrystalline films with approximate thickness of 200 nm and high transmittance (more than 80%) were obtained. No additional XRD peaks due to dopant impurities or dopant oxides were observed. The cobalt doping led to decrease in grain size and increase in crystallite size from 22 nm to 29 nm in the (101) direction. Smaller changes were observed for the CAZO films. Surface roughness of the films was measured using a 3D optical profiler. Surface roughness of the doped films was from 5 nm to 9 nm higher than that of the pure films. Refractive index, extinction coefficient and thickness of the films were calculated using ellipsometric measurements and were further used for determination of optical band gap and Urbach energy. Refractive index and optical band gap increased with doping from 1.86 and 3.29 eV for pure ZnO to 2.00 and 3.35 eV for CZO and 1.97 and 3.33 eV for CAZO films. Through calculation of Urbach energy (119 meV for pure ZnO, 236 meV for CZO and 138 meV for CAZO), it was demonstrated that doping leads to an increase in structural disorder, most pronounced in the case of Co doping.

Separation and online optical characterization of fluorescent components of pyrogenic carbons for carbon dots identification

Optical features of fluorescent components of pyrogenic carbons as flame-formed carbon particulate matter (PM) were studied by setting up a facile and fast method (SEC-Abs/Fluo) based on size exclusion chromatography (SEC) coupled with UV–Visible absorption and fluorescence spectrometers as detectors. The SEC-Abs/Fluo method simultaneously allowed the molecular weight (MW) separation and identification of blue- and green-fluorescent PM components exhibiting size and spectroscopic features typical of carbon dots (CDs). The SEC-Abs/Fluo method allowed the online determination of quantum yield (QY) and optical band gap of fluorescent components also in strongly-scattering carbon suspensions so avoiding tedious pretreatment of carbon samples. From the detailed separation and analysis of blue- and green-fluorescent PM components along with two commercial pitches, aromatic species having MW > 1000 u and band gap <1–1.5 eV resulted to be scarcely or no fluorescent indicating these are the MW and band gap thresholds for fluorescence emission. Indeed, a sharp QY decrease was for the first time noticed in a narrower band gap (1–1.5 eV) range, where carriers can more easily tunnel to defects of the carbon network reducing fluorescence emission. The exponential increase of QY as the band gap rises was found with a more regular trend for the MW-segregated components in comparison to the bulk samples. The method can support and guide the choice of the optimal operating conditions to maximize CD formation and their purification from not-fluorescing components and can also be helpful in disentangling CD fluorescence attribution.

Absorption spectrum fitting method (ASF), DASF method and structural studies of Li2O–SrO–B2O3–MnO quaternary glass system

In this paper the quaternary glass system Li2O–SrO–B2O3–MnO was prepared by traditional melt-quenching technique. Alternative methods like Absorption Spectrum Fitting method (ASF) and Derivative Absorption Spectrum Fitting method (DASF) were put forward for the determination of optical energy band gap and Urbach energy values for the manganese doped lithium strontium borate glasses. These methods require only the measurement of the glass sample absorbance instead of thickness of the glass sample. The values of the optical band gap obtained using ASF and DASF methods were compared, and a good agreement between the values and similar trend was observed. In addition to the above two methods the FT-IR and Raman techniques are also employed to scrutinize the structural details of manganese doped lithium strontium borate glasses. The fraction of N4 and N3 values are also projected to investigate the structural changes of the obtained glass system.

Precise determination of optical band gap in Cr-doped semiconductor nanowires

Pristine and chromium-doped ZnO nanowires were prepared following the traditional co-precipitation method. X-ray diffraction data identified a pure wurtzite hexagonal crystal structure characteristic for ZnO, irrespective of the doping level. The particle size, as deduced form Williamson–Hall plots, was found to be 45–55 nm for all samples. Scanning electron microscopy revealed a clear nanowires morphology for the pure and doped samples, while elemental analysis ensured the successful Cr-doping. Distinct spectroscopic signatures of Cr-doping were revealed from a detailed deconvolution process applied to optical spectra of doped samples, where Cr3+ optical transitions were unambiguously identified at ~ 420 and ~ 665 nm. Particularly relevant, is the spectral decomposition here performed for the superimposed absorption edge (~ 385 nm) and Cr3+ optical resonance at ~ 420 nm, allowing to claim practically doping-independent optical band gap behavior in the present doping regime. This is further supported by identifying the characteristic ZnO near edge photoluminescence peak (~ 392 nm) which maintains fixed wavelength after Cr-doping. These findings contrast earlier studies on Cr-doped semiconductor nanoparticles and glass systems where the optical band gap has been largely underestimated. We attribute the inconsistence band gap values reported in literature for Cr-doped semiconductors to the proximity of Cr optical transitions to the semiconductor absorption edge.

Synthesis and Characterization of MXene from MAX phase

In today’s technology advancement dictates towards finding a new element for wide applications, starting from medicine to energy storage as well as other optoelectronics. A group of transition metals and aluminium or silicon chemically combine with carbon or nitrogen is known as MAX phase. A technique has been described here to eliminate aluminium from the MAX phase to form exfoliated layered structured MXene, which may create a potential role in the above mentioned applications. After successful synthesis of MXene was characterized using XRD to determine the crystallinity, SEM analysis for morphological study, EDAX for elemental analysis, and UV-Vis spectroscopy for optical band gap determination.

High energy ion irradiation effect on electrical and optical properties of polymers

This study details the effects of ion irradiation on the polymeric target. The objective is to alter the optical and electrical properties of the conjugated organic materials and to achieve the improved optical and electrical response in view of their application in photo-electronics, micro-electronics, circuit boards, and photo-conductive electrodes. Metallic aluminum (Al) target is irradiated using Nd: YAG laser for 200 laser shots. The laser induced plasma ions (LPPI) are exposed to polymeric substrates of polyethylene terephthalate (PET), polymethyl methacrylate (PMMA) and acrylonitrile butadiene styrene (ABS) under heavy ion fluxes (2 × 109 cm−2) and vacuum conditions (10−3 Torr). The irradiated specimens are analyzed for chemical changes, optical band gap determination, and electrical properties employing the FTIR spectroscopy, UV–Visible spectroscopy and four-point probe technique, respectively. Ion irradiation of polymers significantly modified the chemical properties of polymers. The optical transmission in the IR region is increased for irradiated specimens. Optical band gap modifications indicated significant reduction in band gap. Urbach activation energies underwent an increase in their values representing an improved crystallinity for ion beam irradiated polymers. Reduction in resistivity values is observed for the ion exposed specimens.

Optical Band Gap Determination of Ni-Al Doped Polyaniline at Room Temperature and Different Annealing Temperatures

Spectroscopic techniques are very useful for characterizing semiconducting and conducting materials. The optical properties (specially reflection spectra) of polyaniline mix with metal Ni and Al with different composition in bulk form were studied. The reflection spectra of these materials are recorded by a Hitachi spectro-photometer model (330), at room temperature, in the wavelength range 300-600 nm. From the analysis of reflection spectra, polyaniline mix with metal Ni and Al have been found to have energy bandgap which decreases with increase of concentration of Al. an effort has also been made to study the structure formation using XRD techniques.

Influence of sputtered time on the structural and optical characterization of Al-doped ZnO thin films prepared by RF sputtering technique

In this project, aluminum doped zinc oxide thin films were deposited on glass substrate by the RF sputtering technique. The consequence of sputtered time on the structural and optical characteristics was evaluated. The optical parameter values were determined by ultra violet visible spectroscopy that the nature of optical transitions reveals direct allowed transition for all AZO thin films. Also, some physical quantities such as the Urbach tail energy, refractive index (n) in the edge of absorption and dielectric constant (e) were reported for the AZO thin films with various sputtered time. Derivation ineffective thickness method (DITM) was employed to the optical band gap determination and transition index without any presumption about transition natural. Time of reaction plays an essential role in controlling the physical quantities of thin films. This parameter helps to obtain the optimal thickness.

Development of an algorithm for precise and automated determination of optical band gap from Tauc analysis: case studies using alpha-irradiated CR-39 detectors

Tauc analysis is popularly used for the determination of optical band gap by extrapolating the linear portion of the Tauc’s plot and finding its intersection point at energy axis. In most of the studies, the data points in the linear portion of the Tauc’s plot are selected manually, which is time-consuming and the reproducibility in the selection process gets affected. To overcome this, an automated determination of band gap has been proposed for ensuring the reproducibility as well as for faster selection process. In this work, we report the development of an efficient algorithm which can provide the information of the optical band gap by Tauc analysis. The algorithm is based on finding the linear portion around maximum slope of the Tauc’s plot. A computer program (autoTauc) based on the algorithm was written and was validated through CR-39 irradiated to four different alpha fluences. The extrapolated linear line obtained through linear regression (using the program) was observed to pass through the linear portion of the Tauc’s plot. The optical band gap was found to be decreasing linearly with the alpha fluence for both direct and indirect transitions. Also the direct band gap was found to be higher than the indirect band gap.

Synthesis and optical band gap determination of CuO nanoparticles from salen-based infinite coordination polymer nanospheres

A symmetric bi-carboxylic acid functionalized salen-type ligand was used as organic linker to prepare a Cu-based infinite coordination polymer. The analytical data demonstrated that the proposed structure contains one bi-carboxylic acid salen type ligand and two copper cations in each monomeric unit. One of the Cu2+ cations is coordinated by N2O2 site of salen ligand and the other one acts as node to connect metal-organic linkers to each other. The reasonable formation mechanism for coordination polymer formation proposed which shows the formation of nanoparticles from intertwined oligomer chains. The prepared coordination polymer was used as a good precursor to synthesis copper oxide nanoparticles with larger band gap relative to bulk CuO.

Chemical vapor deposition growth of boron–carbon–nitrogen layers from methylamine borane thermolysis products

This work investigates the growth of B–C–N layers by chemical vapor deposition using methylamine borane (MeAB) as the single-source precursor. MeAB has been synthesized and characterized, paying particular attention to the analysis of its thermolysis products, which are the gaseous precursors for B–C–N growth. Samples have been grown on Cu foils and transferred onto different substrates for their morphological, structural, chemical, electronic and optical characterizations. The results of these characterizations indicate a segregation of h-BN and graphene-like (Gr) domains. However, there is an important presence of B and N interactions with C at the Gr borders, and of C interacting at the h-BN-edges, respectively, in the obtained nano-layers. In particular, there is a significant presence of C–N bonds, at Gr/h-BN borders and in the form of N doping of Gr domains. The overall B:C:N contents in the layers is close to 1:3:1.5. A careful analysis of the optical bandgap determination of the obtained B–C–N layers is presented, discussed and compared with previous seminal works with samples of similar composition.

Determination of optical band gap of powder-form nanomaterials with improved accuracy

Accurate determination of a material’s optical band gap lies in the precise measurement of its absorption coefficients, either from its absorbance via the Beer–Lambert law or diffuse reflectance spectrum via the Kubelka–Munk function. Absorption coefficients of powder-form nanomaterials calculated from absorbance spectrum do not match those calculated from diffuse reflectance spectrum, implying the inaccuracy of the traditional optical band gap measurement method for such samples. We have modified the Beer–Lambert law and the Kubelka–Munk function with proper approximations for powder-form nanomaterials. Applying the modified method for powder-form nanomaterial samples, both absorbance and diffuse reflectance spectra yield exactly the same absorption coefficients and therefore accurately determine the optical band gap.

Characterization of Tb-doped hydroxyapatite for biomedical applications: optical properties and energy band gap determination

In the present work, the synthesis, by means of the sol–gel method, of calcium-deficient hydroxyapatite and Tb-doped calcium-deficient hydroxyapatite with dopant content of 10 and 12 wt% is reported. The synthesized samples exhibit diffraction patterns and structural characteristics consistent with those reported in the literature for synthetic hydroxyapatite. The results of the chemical characterization show that the synthesized samples are suitable for biomedical applications, and the incorporation of Tb3+ in the host structure occurs both substitutional and by dopant insertion in calcium vacancy sites. In addition, using spectroscopic techniques, the values of the valence band, optical band gap energies, and luminescent response were determined for all samples, concluding that the increase in dopant has the consequence of decreasing the value of the optical band gap, as it was expected; However, it is also observed that the maximum luminescent emission is obtained for the sample synthesized with 10 wt% of terbium.

Structural, optical, electrical, and thermal properties of PANI/[Co(NH3)2(C2H8N2)2]Cl3 nanocomposite

The study reports successful synthesis of [Co(NH3)2(C2H8N2)2]Cl3 photoadduct and its subsequent use as a filler in polyaniline (PANI) matrix to form PANI/photoadduct nanocomposite by chemical oxidative polymerisation method. The photo-induced exchange of ligands between the hexamine metal complex and ethylenediamine solution on photo irradiation resulted in the formation of photoadduct. FTIR and UV–Vis analysis show a significant interaction developed between the photoadduct and the PANI chains and hence successful nanocomposite formation. Optical band gap determination from Tauc plot shows higher value of band gap in case of PANI/photoadduct nanocomposite than that of PANI. The structural characteristics of the PANI/photoadduct nanocomposite as observed from XRD show crystalline nature of the nanocomposite. SEM analysis shows photoadduct particles lying embedded in the polymer matrix. The porous sponge like surface morphology of the nanocomposite shows potential of material to act as a catalyst. Electrical measurement of the nanocomposite revealed its less conducting nature than PANI which is attributed to charge carrier scattering by embedded photoadduct particles. This is in consistent with the higher value of band gap energy obtained in case of PANI/photoadduct nanocomposite. The thermal analysis shows improvement in the thermal stability of PANI nanocomposite with incorporated filler photoadduct, which holds the polymer chains tightly bound to each other and hence confers some extra stability to the polymer against thermal degradation.

Spectrophotometric method for optical band gap and electronic transitions determination of semiconductor materials

The optical band gap energy and the electronic processes involved are important parameters of a semiconductor material and it is therefore important to determine their correct values. Among the possible methods, the spectrophotometric is one of the most common. Several methods can be applied to determine the optical band gap energy and still now a defined consensus on the most suitable one has not been established. A highly diffused and accurate optical method is based on Tauc relationship, however to apply this equation is necessary to know the nature of the electronic transitions involved commonly related to the coefficient n. For this purpose, a spectrophotometric technique was used and we developed a graphical method for electronic transitions and band gap energy determination for samples in powder form. In particular, the n coefficient of Tauc equation was determined thorough mathematical elaboration of experimental results on TiO2 (anatase), ZnO, and SnO2. The results were used to calculate the band gap energy values and then compared with the information obtained by Ultraviolet Photoelectron Spectroscopy (UPS). This approach provides a quick and accurate method for band gap determination through n coefficient calculation. Moreover, this simple but reliable method can be used to evaluate the nature of electronic transition that occurs in a semiconductor material in powder form.

Determination of Optical Band Gap and Germanium Content of Hydrogenated Micro-Crystalline Si1−x Gex Films by Ultraviolet-Visible and Auger Electron Spectroscopy Measurements

Determination of Optical Band Gap and Germanium Content of Hydrogenated Micro-Crystalline Si1−x Gex Films by Ultraviolet-Visible and Auger Electron Spectroscopy Measurements

Spectral and Non Radiative Decay Studies of Lead Di Bromide Single Crystals by Mode Matched Thermal Lens Technique.

In the present paper, the investigations on the non radiative decay mechanism, optical band gap determination from absorption spectroscopic studies and fluorescence emission by photo luminescence techniques using different excitation wavelengths on gel derived lead di bromide single crystals are reported. Non radiative decay of the sample is studied using high sensitive dual beam mode matched thermal lens technique. For the thermal lensing experiment the crystal in solution phase is incorporated with rhodamine 6G dye for enhancing the absorption of the crystal sample. The thermal diffusivity of lead di bromide is determined using the probe beam intensity v/s time measurements.

Derivation of ineffective thickness method for investigation of the exact behavior of the optical transitions in nanostructured thin films

Optical band gap determination in nanostructured semiconductor thin films is to some extent difficult. Procedure of the extrapolating the linear part of the graphs in optical band gap determination in Tauc’s model for nanostructures has shortage because the edges of the tail states complicate the definition of the accurate optical band gap (due to the surface atoms). A new revised method (named as DITM: Derivation of Ineffective Thickness Method) is proposed for the exact determination of the optical band gap in addition to the treatment of optical transitions in nanostructure semiconductors. In Tauc model and ineffective thickness method (ITM), one has to determine the kind of optical transition before the determination of the optical band gap, but in DITM, not any supposition of the treatment of optical transition. DITM method was employed on CdSe thin films semiconductor alloy in order to confirm the validity of this new method.