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ZnGa2O4 hollow nanostructures were synthesized by a two step hydrothermal and calcination process using carbon spheres as a template. We observed that the carbon@Ga(OH)CO3 core–shell nanostructures were covered by a uniform shell of Zn(OH)2 nanoparticles when prepared using 2.5 mmol of ZnAc, and ZnGa2O4 hollow nanostructures with diameters of approximately 200 nm and shell thicknesses of around 15 nm could then be obtained. After calcination at 900 °C for 1 h, the amorphous core–shell–shell nanostructures yielded highly crystalline ZnGa2O4 hollow nanostructures. The shell possesses a single-crystal structure and a lattice spacing of around 0.253 nm which corresponds to the d spacing of (311) crystal planes of cubic ZnGa2O4. The composition and surface electron state of the ZnGa2O4 hollow nanostructures prepared at 900 °C were confirmed by X-ray photoelectron spectroscopy. UV and blue emissions of the ZnGa2O4 hollow nanostructures were found to result from self-activation centers of the octahedral Ga–O groups in the spinel structures and symmetry distortion of the octahedral sites by oxygen vacancies, respectively. [ABSTRACT FROM AUTHOR]

Abstract: The pure β-Ga2O3 and Tb3+ doped β-Ga2O3 hollow nanostructures with various Tb3+ concentrations were prepared by hydrothermal and cacination processes. The X-ray diffraction patterns indicate that the core-shell structures are amorphous phase before calcination and perfectly crystallized β-Ga2O3 hollow nanostructures were obtained at 800°C. The sharp and intense band absorption at 1384cm−1, which was attributed to the Ga(OH)CO3 shell, was observed by Fourier transform infrared. Field-emission scanning electron microscopy and high-resolution transmission electron microscopy investigations showed β-Ga2O3 hollow nanostructures with diameters of about 200nm and thicknesses of about 20~30nm. The green emission spectra of Tb3+ doped β-Ga2O3 hollow nanostructures as a function of Tb3+ ions were observed due to the 5 D 4→7 F J transition. The Tb3+-doped β-Ga2O3 hollow nanostructures showed the highest green emission intensity at 7mol% of Tb3+ ions. [Copyright &y& Elsevier]

Abstract: The enhancement of the red emission of Eu3+-doped β-Ga2O3 nanoparticles using Eu2O3@B2O3 core–shell structure as an activator were prepared as a function of the firing temperatures. The transmittance eletron microscope image and electron energy loss spectrum of the B2O3-coated Eu2O3 particles shows that the B2O3 coating is uniform, with a thickness of around 10nm, and that the core–shell structure consisted of Eu and B elements. The X-ray diffraction patterns indicate that the Eu2O3@B2O3 (3mol%)-doped β-Ga2O3 nanoparticles were indexed to the monoclinic crystalline β-Ga2O3. The broad absorption peaks at 1300cm−1 (B–O bonds) disappeared in the patterns of the Eu2O3@B2O3 (3mol%)-doped β-Ga2O3 nanoparticles prepared at 800°C for 5h, because of the evaporation of B2O3. The highest emission peaks of Eu2O3@B2O3 (3mol%)-doped β-Ga2O3 nanoparticles were observed when prepared at 800°C for 5h. The Eu2O3@B2O3 core–shell structure used as an activator significantly enhanced the emission intensity compared with non-coated Eu2O3 doped β-Ga2O3 nanoparticles. [Copyright &y& Elsevier]