RESUMO
In this paper, Mn2+/Ln3+-doped hexagonal phase (ß-) NaGdF4:Ce (Ln = Tb, Dy, Eu) nanomaterials with subtly tuned multicolor output have been successfully synthesized by a typical simple hydrothermal method using polyethylene glycol (PEG) as a surface modifying agent. The crystal structures, morphology, luminescence performance, and energy transfer (ET) mechanism of the synthesized NaGdF4 nanoparticles (NPs) were investigated in detail. It is found that due to the effective ET between Ce3+ and Mn2+/Ln3+, the multicolor down-conversion (DC) emission phosphors can yield three major emission bands in the visible region including blue, green and red. Moreover, the white emission could be realized through manipulating the doping ratio of Ce3+, Dy3+ and Eu3+ with suitable concentration in ß-NaGdF4 NPs through effective resonance-type ET under the irradiation of 273 nm. And the corresponding CIE1931 coordinates were calculated to be (0.31, 0.32), which is near the normative white emission (0.33, 0.33). All the multicolor tuning and white emission results evidently suggest that the present Ce3+ and Mn2+/Ln3+-doped ß-NaGdF4 NPs are feasible phosphors for potential applications in white-light emitters, full-color displays and photonic devices.
RESUMO
An efficient carbon-polyaniline (PANI)-coated method was applied for perovskite-type oxide LaFeO3 to enhance its high-temperature electrochemical performance. Transmission electron microscopy (TEM) results reveal that LaFeO3 particles are evenly coated with carbon and PANI hybrid layers after carbon-PANI treatment. The carbon layers prevent the nanosized LaFeO3 particles from aggregation and allow the electrolyte to penetrate in every direction inside the particles. The PANI layers also enhance the electrocatalytic activity, facilitating hydrogen protons transferring from the electrolyte to the electrode interface. The cooperation of carbon and PANI hybrid layers results in a significant enhancement of the electrochemical performance at high temperatures. At an elevated temperature (60 °C), the maximum discharge capacity of the LaFeO3 electrodes remarkably increases from 231 mA h g(-1) to 402 mA h g(-1) and the high rate dischargeability at a discharge current density of 1500 mA g(-1) (HRD1500) increases from 22.7% to 44.3%. Moreover, the hybrid layers mitigate the corrosion of LaFeO3 electrodes by reducing the loss of active materials in the alkaline electrolyte, leading to increase in the capacity retention rate from 67.1% to 77.6% after 100 cycles (S100).
