Chengkang Chang

Improved electrochemical performance of LiFe0.4Mn0.6PO4/C with Cr3+ doping

LiFe0.4Mn0.6−xCrxPO4/C (x ≤ 0.01) cathode materials with different Cr-doping were synthesized by a nano-milling assisted solid-state method. The experimental results demonstrated that Cr-doping can significantly improve the electrochemical performance of the target material. Among the samples synthesized, the LiFe0.4Mn0.595Cr0.005PO4/C (with 0.5 atm% of Cr) sample exhibited the highest specific capacity and the best rate performance. It delivered initial discharge capacities of 164.0, 156.2, 147.5 and 139.3 mA h g−1 at 0.1C, 0.5C, 2C and 5C, respectively. Moreover, it showed the best cycle stability with capacity retention of 99.2% after 50 cycles at 0.1C. Such enhancement can be ascribed to the improvements in not only the electronic conductivity, but also the Li ion diffusion coefficient. Powder conductivity tests revealed that the conductivity of the powder sample with 0.5% Cr doping presents the highest conductivity of 5.91 × 10−5 S cm−1, which is almost 5.3 times that of the pristine sample. Calculations of diffusion coefficients using the EIS data also suggested a highest Li ion diffusion coefficient of 4.36 × 10−10 cm2 s−1 for the sample with 0.5% Cr doping, which is almost 4.6 times that of the pristine sample. The synthesized LiFe0.4Mn0.595Cr0.005PO4/C with such excellent electrochemical performance showed great potential for application in high-power devices.

New synthetic method and the luminescent properties of green-emitting β-Sialon: Eu2+ phosphors

Eu2+-doped β-Sialon phosphors with a composition of EuxSi5Al1−xOz+xN8−z−x (x = 0.05, 0.06, 0.07) were synthesized in a new synthetic route using novel raw materials, such as nano-silicon dioxide (SiO2), nano-carbon (C), and aluminum (Al). This is different from the prevailing method using Si3N4, AlN, and Al2O3 to obtain β-Sialon phosphors. Compared with the conventional method, lower cost raw materials, simpler pretreatment and a relatively shorter reaction time are achieved. The phosphors show a high purity. All the phosphors exhibit green emission under ultra violet (UV) radiation. A broad band of excitation spectra implies the promising application in UV ray based green light-emitting diode (LED). Chromaticity coordinates of the β-Sialon: Eu2+ phosphors demonstrate that it is accessible to obtain different green emissions from single phase of Eu2+-doped β-Sialon through adjusting Eu2O3 concentration. Furthermore, the EuxSi5Al1−xO1 + xN7 − x (x = 0.05) shows a better thermal stability than the commercial green-emitting silicate phosphor. These results indicate a promising prospect for this efficient and economic route in preparing β-Sialon: Eu2+ phosphors, and the phosphors are a highly promising candidate for LED applications.

Preparation and characterization of a new long afterglow phosphor CaSnO3: Yb3+

A new phosphor CaSnO3: Yb3+ was synthesized by a traditional solid-state reaction and the luminescent properties were investigated. The phosphors are well crystallized at 1200 °C. The excitation and the emission spectra show the characteristic broad of the Sn2+ ion and the X-ray photoelectron spectroscopy demonstrate the existence of Sn2+ ions caused by the doping of Yb3+ ions. The CaSnO3: Yb3+ phosphor showed a typical afterglow behavior when the UV source was switched off. Thermal simulated luminescence study indicated that the persistent afterglow of CaSnO3: Yb3+ phosphor was generated by the suitable electron or hole traps which were resulted from doping the calcium stannate host with rare-earth ions (Yb3+).