Increase In Optical Band Gap Energy Research Articles

Enhanced photocatalytic performance of novel S2− doped MIL-53(Fe) under visible light

This work highlights a systematic investigation on doping (S2−) on photoactive MIL-53(Fe) and its performance evaluation. Doping (structural/interstitial), leading to tailoring of optical band-gap energies of the parent materials to maximize their performances is well known. However, alteration or tuning of band-gap energy may not essentially always lead to a better performance in photocatalytic reactions and this aspect becomes more pertinent for hybrid materials like Metal Organic Frameworks (MOFs). Since, doping might lead to wider variations in structural conformations in a hybrid MOF like material, underlines the importance of the extent. A microwave synthesis route was proposed to effectively synthesize the products where dopant (S2−) percentages were varied from 1 to 10% stoichiometrically in the reaction mixture. Different spectroscopic techniques like UV–vis DRS, FT-IR, micro Raman, Photoluminescence (PL), Electrochemical Impedance Spectroscopy (EIS) and Electron Spin Resonance spectroscopy (ESR) were used to understand the extent of doping on structural conformations of MIL-53(Fe). The influence of doping showed an increase in optical-band gap energy w.r.t to parent MIL-53(Fe) (1.996 eV): 1% S (2.224 eV); 4% S (2.376 eV), 7% S (2.448 eV) and 10% S (2.579 eV). The coordination of metal oxo cluster from calculated Nephelauxetic factor values in synthesized materials showed electron cloud expansion from 6.51% (1% S) to 16.36% (10% S). The IVCT band intensity was highest for 1%S and accordingly Methylene blue (MB) degradation yielded best performance for 1%S doped MIL-53(Fe) (ca. 97.14%) and repeatability study showed the material to be stable even after 5 cycles. The overall reaction mechanism was hypothesized based on DPBF assay and standard reaction kinetic trap analyses.

Microwave-assisted solvothermal synthesis and optoelectronic properties of γ-MnS nanoparticles

Manganese sulfide (MnS) nanoparticles (NPs) were synthesized using a solvothermal-microwave method to evaluate the effect of growth temperature on their structural, morphological, optical and electrical properties. The obtained MnS NPs were studied using X-ray diffraction (XRD), field emission scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray (EDX) spectroscopy, photoluminescence, UV–Vis absorption spectroscopy and electrical measurements. The XRD patterns and EDX spectra confirmed the formation of MnS and the existence of the desired elements, respectively. The electron microscopy images unraveled that the obtained nanostructures are consisted of adherent spherical particles. It was observed that optical band gap energy increases and relative absorbance intensity decreases by increasing the growth temperature. Finally, the J–V and Mott–Schottky plots confirmed the p-type conductivity of the MnS NPs and the photocurrent measurements demonstrated that the increase of synthesis temperature can enhance the current density and photoresponse of the NPs.

Role of lithium ions on the physical, structural and optical properties of zinc boro tellurite glasses

Lithium zinc boro tellurite glasses with compositions xLi2O-(100-x) [0.25ZnO–0.15B2O3–0.60TeO2] [where x = 0, 5, 10, 15 and 20 mol%] have been prepared by melt-quench technique. The amorphous nature of the prepared system is ascertained by X-ray diffraction. The density and molar volume are found to decrease with the increase in concentration of Li2O. The differential scanning calorimetry is used to calculate the glass transition temperature (Tg) and the observed values are found to be decreased. The IR and Raman spectra indicate that Li2O acts as a network modifier in the glass matrix. In the present system, tellurium exists as TeO4 and TeO3, B2O3 in the form of BO4 and BO3 and zinc oxide exists as ZnO4 structural units. The values of the optical band gap are estimated from the fitting of Mott and Davis’s and model. A better convergence is achieved between experimental observed spectra of absorption coefficient and hydrogenic excitonic model. The optical band gap energy increases, whereas refractive index and molar refractivity follow the reverse trend with Li2O. The range of metallization criterion suggests that these glasses may be a potential candidate for nonlinear optical materials.

Effect of Al doping concentration on the electrical and optical properties of sol–gel derived Zn0.87Mg0.13O thin film

Zn0.87Mg0.13O thin film was developed by the sol–gel process. The effect of the Al doping concentration on the electrical and optical properties of Zn0.87Mg0.13O thin film was investigated. The lowest resistivity of 7.96 × 10−3 Ω·cm with an optical bandgap energy of 3.64 eV was achieved at a doping concentration of 0.8 mol % in solution (0.6 at. % in film). Al doping contributes to the decrease of resistivity and the increase of optical bandgap energy, whereas heavy doping of greater than 0.8 mol % shows detrimental effects on the resistivity and film crystallinity. The mobility is dominated by grain boundary scattering.

Defect-induced optical and electrical property modification in amorphous InGaZnO4 films

We report the physical characteristics of InGaZnO4 films deposited at various temperatures. The films were deposited on Al2O3(0001) substrates using pulsed laser deposition technique. Based on X-ray diffraction and field emission scanning electron microscopy measurements, the crystal structure changed from amorphous to polycrystalline as deposition temperature increased to 550°C. Furthermore, UV–vis measurements revealed a decrease in tail state i.e. improvement of local ordering, resulting in an increase of optical band-gap energy as deposition temperature increased. The core-level X-ray photoelectron spectra also showed an increase (decrease) in metal-oxide (oxygen deficiency) bond as the deposition temperature increased. The carrier concentration, Hall mobility and conductivity variation with deposition temperature are related to the competition between oxygen deficiency and grain boundary formation.

Structural and optical properties of the gadolinium–lead–germanate glasses

Glasses in the system xGd 2O 3(100 − x)[7GeO 2·3PbO] with 0 ≤ x ≤ 40 mol% have been prepared from melt quenching method. The influence of gadolinium ions on structural behavior in lead–germanate glasses has been investigated using FTIR, UV-VIS and EPR spectroscopy. The structural changes have been analyzed with increasing rare earth concentration. FTIR data suggest that the glass network modifications has taken place mainly in the germanate part whereas the lead part remained unmodified and its network consists mainly from the [GeO 4], [GeO 6], [Ge 2O 7] structural units and with interconnected through Ge–O–Ge bridges in [GeO 4] structural units. The changes in amplitude and bandwidth of the UV-VIS bands ranging from 200 nm to 350 nm depend on the content of Gd 2O 3. By increasing the Gd 2O 3 content in the glass matrix, the optical band gap energy increases, indicating changes of the lattice parameters and that no non-bridging-oxygens form upon the addition of gadolinium oxide. The decreasing trend has been observed both in optical gap band energy and refractive index of oxide glasses at x = 10 mol% Gd 2O 3 indicating breaks up the [GeO 4] tetrahedral units bonds and create of non-bridging oxygen atoms. For sample with x ≥ 20 mol%, the gadolinium ions having a behavior of network formers ( g ≈ 4.8) will coordinate more with the excess of oxygen. Accordingly, the gadolinium ions are generally suspected to improve their environment of network formers.