Structure and visible light luminescence of 3D flower-like Co3O4 hierarchical microstructures assembled by hexagonal...

A two-step strategy has been developed to fabricate 3D flower-like Co3O4 hierarchical microstructures assembled by hexagonal porous nanoplates. The synthetic procedure was described as (1) 3D flower-like α-Co(OH)2 microstructures were prepared by a facile surfactant-free low-temperature hydrothermal process; (2) 3D flower-like Co3O4 hierarchical microstructures were fabricated by annealing the obtained 3D flower-like α-Co(OH)2 microstructures. X-ray diffraction and Raman spectrum analyses demonstrate that the hierarchical microstructures formed from 3D flower-like α-Co(OH)2 microstructures are composed of pure cubic phase Co3O4. Scanning electronic microscopy demonstrates that the as-prepared Co3O4 microstructures exhibit 3D flower-like hierarchical structures assembled by hexagonal porous nanoplates. Photoluminescence demonstrates that these novel 3D flower-like Co3O4 hierarchical microstructures display a broad strong emission in the visible range of 650 to 800 nm with a peak at around 710 nm (1.75 eV), which is very close to the indirect optical band gap of 1.60 eV for Co3O4 thin film. The result indicates that the photoluminescence emission likely originates from the indirect optical band gap emission. The broad photoluminescence emission may be resulted from a wide size distribution of porous nanoplates in 3D hierarchical microstructures. These 3D flower-like Co3O4 hierarchical microstructures with unique optical properties may find new potential applications in visible light emitting materials.