Decoration of ZnO Nanorods with Coral Reefs like NiO Nanostructures by the Hydrothermal Growth Method and Their Luminescence Study

Composite nanostructures of coral reefs like p-type NiO/n-type ZnO were synthesized on fluorine-doped tin oxide glass substrates by hydrothermal growth. Structural characterization was performed by field emission scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray diffraction techniques. This investigation shows that the adopted synthesis leads to high crystalline quality nanostructures. The morphological study shows that the coral reefs like nanostructures are densely packed on the ZnO nanorods. Cathodoluminescence (CL) spectra for the synthesized composite nanostructures are dominated mainly by a broad interstitial defect related luminescence centered at ~630 nm. Spatially resolved CL images reveal that the luminescence of the decorated ZnO nanostructures is enhanced by the presence of the NiO.     

Structural and Luminescence Behavior of Nanocrystalline Orthophosphate KMeY(PO4)2: Eu3+ (Me = Ca,Sr) Synthesized by Hydrothermal Method

KMeY(PO₄)₂:5% Eu³⁺ phosphates have been synthesized by a novel hydrothermal method. Spectroscopic, structural, and morphological properties of the obtained samples were investigated by X-ray, TEM, Raman, infrared, absorption, and luminescence studies. The microscopic analysis of the obtained samples showed that the mean diameter of synthesized crystals was about 15 nm. The KCaY(PO₄)₂ and KSrY(PO₄)₂ compounds were isostructural and they crystallized in a rhabdophane-type hexagonal structure with the unit-cell parameters a = b ≈ 6.90 Å, c ≈ 6.34 Å, and a = b ≈ 7.00 Å, c ≈ 6.42 Å for the Ca and Sr compound, respectively. Spectroscopic investigations showed intense ⁵D₀ → ⁷F₄ transitions connected with D₂ site symmetry of Eu³⁺ ions. Furthermore, for the sample annealed at 500 °C, europium ions were located in two optical sites, on the surface of grains and in the bulk. Thermal treatment of powders at high temperature provided better grain crystallinity and only one position of dopant in the crystalline structure. The most intense emission was possessed by the KSrY(PO₄)₂:5% Eu³⁺ sample calcinated at 500 °C.