RESUMO
We describe the transformation of a colloidal photonic crystal into a photonic crystal heterostructure. It was achieved by annealing a polystyrene multilayer colloidal photonic crystal partially immersed in water using a solvent vapor. The floating polystyrene colloidal photonic crystal was divided into two parts by the liquid level, which can be manipulated by the addition of ethanol into the water. The top part protruding out of the water experienced a uniform lattice stretching upon exposure to the solvent vapor. The bottom part that stayed immersed in the water remained unaffected due to the protection by the water. The inconsistent behaviors of the two parts resulted in the formation of a colloidal photonic crystal heterostructure. Such a heterostructure was free of interface imperfection since it was a direct descendant of the original colloidal crystal. Meanwhile, optical measurements demonstrated the presence of a wider photonic band gap along the crystallographic [111] direction in these photonic crystal heterostructures compared with the original colloidal photonic crystals.
RESUMO
Hexagonal crown-capped ZnO micro rods were successfully prepared by a facile low-temperature hydrothermal method. The as-prepared ZnO micro rods are 4.4-5.2 µm in length and 2.4-3.6 µm in diameter, possessing a single-crystal hexagonal structure. The morphology evolution and structure changes were tracked during hydrothermal growth by field-emission scanning electron microscopy and X-ray diffraction, respectively. A three-stage growth mechanism of the hexagonal crown-capped ZnO micro rods was proposed and further verified by a growth solution renewal experiment. The room-temperature photoluminescence (PL) spectrum of the hexagonal crowns exhibits a strong UV emission at about 382 nm. The temperature dependent PL results indicate that the UV emission originates from the radiative free-exciton recombination.
