• Energy Research

Abstract Although aluminate phosphors have attracted great interest for applications in lamps, cathode ray tubes and plasma display panels, there still remain issues affecting operational parameters such as luminescence efficiency, stability against temperature, high color purity and perfect decay time. In addition, issues involving important aspects of the monoclinic↔hexagonal phase transition temperature still exist. In this work, SrAl x O y :Eu 2+ ,Dy 3+ phosphor powders were prepared by the sol–gel method. X-ray diffraction (XRD) has shown that both crystallinity and crystallite sizes increased as the temperature increased. Both SrAl 2 O 4 and Sr 2 Al 3 O 6 phases were observed. Photoluminescence (PL) characterization shows temperature-dependence, which indicates emission at low and high annealing temperatures originating from Eu 2+ and Eu 3+ ions. Thermoluminescence glow and decay measurements provided useful insight on the influence of traps on luminescence behavior. Differential scanning calorimetry (DSC) and thermogravimetric studies (TGA) on composites of the phosphor in low density polyethylene (LDPE) demonstrated the varied influence of annealing temperature on some luminescence and thermal properties.

Electrochemical deposition and characterization of nanocrystallite-CdS thin films for thin film solar cell application are reported. The two-electrode system used provides a relatively simple and cost-effective approach for large-scale deposition of semiconductors for solar cell and other optoelectronic device application. Five CdS thin films were deposited for 45 minutes each at different cathodic deposition voltages in order to study their properties. X-ray diffraction study reveals that the as-deposited films contain mixed phases of hexagonal and cubic CdS crystallites with large amounts of internal strain and dislocation density. Postdeposition annealing results in phase transformation which leaves the films with only the hexagonal crystal phase and reduced strain and dislocation density while increasing the crystallite sizes from 21.0–42.0 nm to 31.2–63.0 nm. Photoelectrochemical cell study shows that all the CdS films have n-type electrical conductivity. Optical characterization reveals that all samples show similar transmittance and absorbance responses with the transmittance slightly increasing towards higher growth voltages. All the annealed films show energy bandgap of 2.42 eV. Scanning electron microscopy and energy dispersive X-ray analyses show that grains on the surface of the films tend to get cemented together after annealing with prior CdCl2 treatment while all the films are S-rich.

CuInse 2 films and related alloys were prepared by thermal evaporation of Cu, InSe and GaSe compounds instead of elemental sources. Band gap tailoring in Cu(In,Ga)Se 2 based solar cells is an interesting path to improve their performance. In order to get comparable results solar cells with Ga/(In+Ga) ratios x =0 and 0.3 were prepared, all with a simple two-step sequential evaporation process. The morphology of the resulting films grown at 550°C was characterized by the presence of large facetted chalcopyrite grains, which are typical for device quality material. It is important to note that absorber films with elemental gallium resulted in a significant decrease in the average grain size of the film. The XRD diffraction pattern of a single-phase Cu(In,Ga)Se 2 films depicts diffraction peaks shift to higher 2θ values compared to that of pure CuInSe 2 . The PL spectrum of Cu(In,Ga)Se 2 thin films also depicts the presence of the peak at higher energy that is attributed to the incorporation of gallium into the chalcopyrite lattice. As the band gap of CIGS increases with gallium content, desirable effects of producing higher open-circuit voltage and low-current density devices were achieved. A corresponding increase in device efficiency with gallium content caused by a higher fill factor was observed. The best results show passive area efficiencies of up to 10.2% and open circuit voltage (V oc ) up to 519 mV at a minimum band gap of 1.18eV.

Abstract Electrodeposition of CdTeSe thin films with two-electrode electrodeposition method in potentiostatic mode was performed at different TeO2 concentrations of 0.075, 0.150, 0.225, 0.30, and 0.375 mM. The structural, optical, surface morphology, surface roughness, and compositional properties of as-deposited (AD) and annealed (HT) CdTeSe thin film samples were investigated by using x-ray diffraction (XRD), ultraviolet-visible (UV-Vis) spectrophotometry, scanning electron microscopy, scanning probe microscopy and energy-dispersive x-ray spectroscopy, respectively. The XRD results confirmed that CdSe thin films are of hexagonal structure. After TeO2 was added, the CdTeSe films were found to have mixed hexagonal and cubic phases. The UV-Vis spectrophotometry results confirmed that the absorbance and band gap of the materials varied as the TeO2 concentration changed. For AD samples, the energy band gap was found to be (1.45–1.75) eV; for HT samples, it varied from (1.53–1.86) eV with TeO2 concentration. The average surface roughness was 93.17 nm and 79.59 nm for the AD and HT un-doped CdSe films, respectively. The average surface roughness values for the AD TeO2 doped (CdTeSe) samples were observed to be 23.00, 162.29, and 26.90 nm, and for the HT samples, they were 25.80, 153.10, and 19.35 nm for TeO2-concentrations of 0.075,0.150, and 0.375 mM respectively. Compositional analysis verified the presence of Cd, Te, and Se in the films. The results show that CdSeTe thin films have potential applications in thin-film solar cell device technology.

In this work, a density functional theory (DFT) with Hubbard correction (U) approaches implemented through the Quantum ESPRESSO code is utilized to investigate the effects of fluorine (F) doping on the structural, electronic, and optical properties of rutile TiO2. Rutile TiO2 is a promising material for renewable energy production and environmental remediation, but its wide bandgap limits its application to the UV spectrum, which is narrow and expensive. To extend the absorption edge of TiO2 into the visible light range, different concentrations of F were substituted at oxygen atom sites. The structural analysis reveals that the lattice constants and bond lengths of TiO2 increased with F concentrations. Ab initio molecular dynamics simulations (AIMD) at 1000 K confirm that both pristine and F-doped rutile TiO2 maintains structural integrity, indicating excellent thermal stability essential for high-temperature photocatalytic applications. Band structure calculations show that pure rutile TiO2 has a bandgap of 3.0 eV, which increases as the F concentration rises, with the 0.25 F-doped structures exhibiting an even larger bandgap, preventing it from responding to visible light. The absorption edge of doped TiO2 shifts towards the visible region, as shown by the imaginary part of the dielectric function. This research provides valuable insights for experimentalists, helping them understand how varying F concentrations influence the properties of rutile TiO2 for photocatalytic applications.

Mg1.5Al2O4.5: x% Eu3+ (0 ≤ x ≤ 2) nanopowders were successfully synthesized via sol–gel method. The X-ray diffraction (XRD) spectrum revealed that the Mg1.5Al2O4.5: x% Eu3+ matches the single phase of face-centred cubic MgAl2O4. The estimated average crystallite sizes calculated using the XRD spectra were found to be in the order of 4 nm. The estimated crystal size was confirmed by the high-resolution transmission electron microscopy. The energy dispersive X-ray spectroscopy confirmed the presence of all expected elementary composition (Mg, Al, O and Eu). The field emission gun scanning electron microscope showed that varying the Eu3+ concentration influence the morphology of the prepared nanophosphor. The photoluminescence results showed that the host emits the violet colour at around 382 nm, which was attributed to the defects within the band gap ( Eg) of host material. The Eu3+-doped samples showed the emission at around 560, 580, 593, 618, 655 and 704 nm which are, respectively, attributed to the 5D1 → 7F3, 5D0 → 7F0, 5D0 → 7F1, 5D0 → 7F2, 5D0 → 7F3 and 5D0 → 7F4 characteristic transitions in Eu3+. The International Commission on Illumination colour chromaticity showed that the Eu3+ doping influences the emission colour.