No abstract

In this study, we report the first preparation of phase-pure Co9S8 yolk–shell microspheres in a facile two-step process and their improved electrochemical properties. Yolk–shell Co3O4 precursor microspheres are initially obtained by spray pyrolysis and are subsequently transformed into Co9S8 yolk–shell microspheres by simple sulfidation in the presence of thiourea as a sulfur source at 350 °C under a reducing atmosphere. For comparison, filled Co9S8 microspheres were also prepared using the same procedure but in the absence of sucrose during the spray pyrolysis. The prepared yolk–shell Co9S8 microspheres exhibited a Brunauer–Emmett–Teller (BET) specific surface area of 18 m(2) g(−1) with a mean pore size of 16 nm. The yolk–shell Co9S8 microspheres have initial discharge and charge capacities of 1008 and 767 mA h g(−1) at a current density of 1000 mA g(−1), respectively, while the filled Co9S8 microspheres have initial discharge and charge capacities of 838 and 638 mA h g(−1), respectively. After 100 cycles, the discharge capacities of the yolk–shell and filled microspheres are 634 and 434 mA h g(−1), respectively, and the corresponding capacity retentions after the first cycle are 82% and 66%.

BaMgAl 10 O 17 :Mn phosphor particles with a spherical shape and fine size of less than 1 µm were prepared by spray pyrolysis, and their luminescence properties under vacuum ultraviolet (VUV) excitation were investigated by changing the concentration of activators and the composition of host matrix. It was found that by substituting Sr for Ba sites in the conduction layers the excitation efficiency at wavelengths shorter than 160 nm is enhanced. As a result, the photoluminescence intensity of BaMgAl 10 O 17 :Mn phosphor increases under VUV excitation (147 nm) without any shift in the peak position of the emission spectrum. The photoluminescence intensity of (Ba,Sr)MgAl 10 O 17 :Mn phosphor was also additionally improved by codoping Eu 2+ ions as a consequence of the energy transfer from Eu 2+ in the conduction layer to Mn 2+ in the spinel block. Finally, the highest photoluminescence intensity achieved when 40 at. % of Ba was replaced with Sr and 0.1 at. % Eu was codoped was about 20% higher than that of commercial BaMgAl 10 O 17 :Mn phosphor prepared by a conventional solid-state route.