Tailored TiO2 Nanorod Arrays for Dye Sensitized Solar Cell Applications

A TiO2 layer using titanium (IV) butoxide on fluorine doped tin oxide (FTO) substrate is used as a seed layer for the growth of 2D-TiO2 arrays (TRA). TRAs with length of ~1 to 2 µm were grown on seed layer (SL) by two step method. In the first step TiO2 SLs were deposited by sol-gel assisted spin coating method and the second step involved the typical hydrothermal technique to grow rutile TRAs. Most of the TRAs grown on FTO substrate without SL were randomly oriented and TRAs with 0.025M SL was oriented vertically from the substrate. Whereas TRAs grown on 0.05M SL showed hierarchical nanoflower clusters composed of a bunch of TRAs as petals blooming to all directions from the core. The XRD pattern showed all the three TRAs to be crystallized in a tetragonal rutile phase. Photo Luminescence spectra revealed that the TRAs on 0.05M SL have comparatively low intense blue emission band, predicting the suppressed electron-hole recombination rate. The power conversion efficiency of the dye sensitized solar cell (DSSC) with TRAs grown on 0.05M SL was recorded as 3%, which is 3 times greater than that without SL and 1.6 times greater than that with 0.025M SL in our observations.

Corollary of Energy Transfer On Luminescence From Ce3+ / Eu3+ Co-Activated Glasses For White Light-Emitting Diodes

A series of singly and doubly Ce3+ / Eu3+ doped lithium borate (LBZ) glasses have been synthesized via melt quenching. XRD and SEM analysis confirmed the non-crystalline nature of glasses. The emission spectrum of Ce3+: LBZ glass reveals an extensive blue emission band at 447 nm (5d→4f) by exciting with 350 nm. An intense excitation band noticed at 393 nm (7F0→5L6) of Eu3+ in Eu3+: LBZ glass, which is associated with the excitation wavelength of near-ultraviolet LED chip. The luminescence spectra of Eu3+ disclose a strong red emission at 612 nm (5D0→7F2) excited with 393 nm. By raising the content of Eu3+ ions, the luminescence features were embellished remarkably. However, the dazzling red emission intensity of Eu3+ was ameliorated by the insertion of Ce3+ ions in co-activated glass due to energy transmission. Spectral overlap, fluorescence studies, decay dynamics, CIE coordinates and color purity corroborated the transfer of energy from Ce3+ to Eu3+. The CIE color coordinates of the optimized (1.0 Ce3+ + 1.0 Eu3+) co-doped glass has been shifted to the white light region. In view of these spectral features, 1.0 mol % Ce3+ + 1.0 mol % Eu3+: LBZ glass could be suggested as a promising candidate for the white light applications.

Synthesis of silicon quantum dots using chitosan as a novel reductor agent

In the present paper we report a novel synthesis method of silicon quantum dots (SiQDs) using 3-Aminopropyltriethoxysilane (APTES) as silicon precursor and low molecular weight chitosan (CS) as reducing agent. The obtained SiQDs have a hydrodynamic diameter of 2.3 nm, water dispersible, presents blue emission band at 434.5 nm (2.85 eV) with a Commission Internationale de l’Eclairage 1931 (CIE1931) chromaticity coordinates (x = 0.1665, y = 0.1222), the experimental absorbance of the SiQDS was measured and the band gap (Eg) was estimated through PerkinElmer’s method, the obtained value was 3.1 eV and a positive ζ-potential of + 35 mV, resulting in photonics, microelectronics, and biotechnological potential applications.

Preparation and characterization of a gadolinium compound with high thermal stability

A new lanthanide compound [Gd(2,5-HPA)(2,5-PA)]n (1; 2,5-H2PA = 2,5-pyridinedicarboxylic acid) was obtained through hydrothermal reactions and structurally characterized by single-crystal X-ray diffraction. It possesses a three-dimensional (3-D) framework structure. Solid-state photoluminescence experiment revealed that it shows dark blue emission band, which can be assigned to the characteristic emission of the 4f electron intrashell transition of 6P7/2 → 8S7/2 (Gd3+). The energy transfer mechanism was explained by an energy level diagram of the gadolinium ion and 2,5-pyridinedicarboxylic acid ligand. It displayed remarkable CIE chromaticity coordinates of 0.1346 and 0.0678. The solid-state UV/Vis diffuse reflectance spectra unveiled that it possesses a wide optical band gap of 3.52 eV. Thermogravimetry (TG) measurements revealed that this compound is highly thermal stable up to around 500 °C. KEY WORDS: CIE, Energy transfer, Lanthanide, Photoluminescence, Thermal stability Bull. Chem. Soc. Ethiop. 2020, 34(3), 479-488. DOI: https://dx.doi.org/10.4314/bcse.v34i3.5

Seed-Mediated Synthesis and Photoelectric Properties of Selenium Doped Zinc Oxide Nanorods

Pristine ZnO and selenium doped ZnO (Se-ZnO) nanorods were successfully synthesized using seed-mediated hydrothermal method. The growth solution of both pure and Se-doped ZnO nanorods employed zinc nitrate hexahydrate (ZNH) and hexamethylenetetramine (HMT) as a precursor and surfactant, respectively. As a dopant source, selenium salt solution was obtained by reacting selenium powder with sodium borohydride at low temperature. The as-prepared pure ZnO and Se-doped ZnO nanorods were characterized using field effect scanning electron microscopy (FESEM), X-ray diffraction (XRD), UV-Visible spectroscopy (UV-Vis), and Photoluminescence (PL) spectroscopy. FESEM images show that the geometric shape of Se-ZnO nanoparticles is nanorods with a hexagonal cross-section. The XRD pattern shows the diffraction peak of the sample at the angles of 2θ: 34.44°, 36.25° and 47.54° which represents the hkl plane of (002), (101) and (102), respectively. The crystalline size calculated from XRD data is found to be in the range of 35-42 nm. The UV-Vis spectrum shows that Se-ZnO nanorods strong absorption peaks appeared in the range of 300-380 nm for all samples. Se doping has slightly altered the band gap energy of pure ZnO nanorods around 0.01 eV. The peak of the photoluminescence spectra of the sample at 470 nm indicates the blue emission band.

A new langbeinite-type phosphate K2GdHf(PO4)3: synthesis, crystal structure, band structure and luminescence properties

Langbeinite-type compounds are a large family that include phosphates, sulfates and arsenates, and which are accompanied by interesting physical properties. This work reports a new disordered langbeinite-type compound, K2GdHf(PO4)3 [dipotassium gadolinium hafnium tris(phosphate)], and its structure as determined by single-crystal X-ray diffraction. Theoretical studies reveal that K2GdHf(PO4)3 is an insulator with a direct band gap of 4.600 eV and that the optical transition originates from the O-2p→Hf-5d transition. A Ce3+-doped phosphor, K2Gd0.99Ce0.01Hf(PO4)3, was prepared and its luminescence properties studied. With 324 nm light excitation, a blue emission band was observed due to the 5d 1→4f 1 transition of Ce3+. The average luminescence lifetime was calculated to be 5.437 µs and the CIE chromaticity coordinates were (0.162, 0.035). One may expect that K2Gd0.99Ce0.01Hf(PO4)3 can be used as a good blue phosphor for three-colour white-light-emitting diodes (WLEDs).

A New Salt-Inclusion Single-Phased White Phosphor Ba7B3SiO13Br:Dy3+ for White Light-Emitting Diodes

A series of Ba7B3SiO13Br:Dy3+ phosphors were synthesized by a conventional solid-state reaction method for the first time. The X-ray diffraction patterns confirmed that the samples were pure phase and crystallized in a hexagonal phase with a space group of the P63mc (186). The luminescence spectrum exhibited a strong blue emission band peaked at 478 nm, a strong yellow emission band at 575 nm and a weak emission band at 665 nm, corresponding to the transitions from 4F9/2 to 6H15/2, 6H13/2 and 6H13/2 of Dy3+, respectively. According to the emission spectrum of Ba6.92B3SiO13Br:0.08Dy3+ excited at 349 nm, the chromaticity coordinate was calculated to be (0.317, 0.358) located on the white light region. The concentration quenching mechanism of Dy3+ in Ba7B3SiO13Br was ascribed to the multipolar-multipolar interaction. The current researches suggested that the phosphor can be used as a white phosphor suitable for white light-emitting diodes.

Observation of a red Ce3+ center in SrLu2O4:Ce3+ phosphor and its potential application in temperature sensing

In Ce3+ activated SrLn2O4 type phosphors (Ln = Y, Lu, Sc, etc.) only one Ce3+ center was previously reported to show a blue emission band.

Photoluminescence behavior and thermal stability of Eu-doped SiAlON thin films prepared by RF magnetron co-sputtering of SiAlON and Eu2O3 targets

Eu-doped SiAlON thin films were successfully prepared by co-sputtering method using [Formula: see text]-SiAlON and Eu2O3 ceramic target. The photoluminescence behaviors of the films are investigated as a function of Eu ions concentration and temperature. The doping concentration of Eu ions in films can be effectively controlled by adjusting the sputtering power of Eu2O3 target. XRD analysis and SEM morphology images illustrate that the Eu-doped SiAlON thin films are amorphous, dense, and smooth, no matter they experienced high temperature heat-treatment or not after co-sputtering deposition. An intense and broad blue emission band peaking at 416–450[Formula: see text]nm was exhibited when the films upon excitation at 275[Formula: see text]nm, proving a typical Eu[Formula: see text] emission. The divalent state of Eu ions in films was further identified. As the sputtering power of Eu2O3 target increases, the emission peak of Eu[Formula: see text] shows a red-shift. The prepared thin films possess a better resistant property of thermal quenching and the relative fluorescence intensity at 100∘C can remain about 86% of its initial value at room temperature.

Luminescent Properties of SiC Thin Film Deposited by VHF-PECVD: Effect of Methane Flow Rate

Bulk silicon carbide (SiC) as light emitter is less efficient due to its indirect bandgap. Therefore, nanosized SiC thin film fabrication approach enable emission wavelength shifts due to spatial confinement. The result of luminescent study of SiC thin film deposited via very high frequency plasma-enhanced chemical vapour deposition (VHF-PECVD) are presented. Precursor gasses used were silane and methane. Methane flow rate was varied from 8 sccm to 20 sccm while other parameters were maintained. Raman spectral analysis denotes the quantum confinement effect occurrence in proportion to the methane flow rate increment. The luminescence properties of the deposited SiC thin film ranging from highly green emission (~518 nm) to highly UVB emission (~294 nm) dominant luminescence. Broad blue emission band shifted toward higher wavelength with smaller FWHM as methane flow rate is increased. This results enable the possibility of luminescent SiC thin film applications in photonics and electronic integration as blue light sources.