The successful synthesis of rare earth doped nano/microcrystals with the desired morphology, uniform monodispersity, and intense infrared emission is of fundamental significance, and would facilitate their application in infrared emission-related miniaturization and integration in optoelectronics. However, simultaneously controlling the morphology and enhancing the infrared emission through simple and effective methods has not been well explored. In this study, via Ca2+ doping with an optimized concentration of 25 mol% in the hydrothermal solution, irregular NaGdF4:Yb/Er submicrocrystals converted into highly uniform submicrorods. Meanwhile, an obvious enhancement of visible upconversion (UC) and near-infrared (NIR) downconversion (DC) emission were obtained, probably due to the improved morphology and lowering the local crystal field symmetry around the rare earth ions induced by Ca2+ doping. Furthermore, Ce3+ ions with an optimized concentration of 2 mol% were codoped to intentionally tailor the branching ratio through efficient energy transfer from Er3+ to Ce3+. As a result, the ∼1530 nm emission intensity of the NaGdF4: 25Ca/2Ce/20Yb/2Er submicrorods increased by about 6.4 times in comparison with the NaGdF4:20Yb/2Er counterpart.
The three-dimensional (3D) graphene aerogel (GA)-wrapped LiFePO 4 submicron-rod composite (LFP@GA) has been prepared successfully through a solvothermal method followed with rapid freeze-drying. Monodispersed LiFePO 4 submicron-rods are well-enwrapped with the graphene sheets and which further form a highly porous and conductive 3D structure, leading to the overall rapid electron transport of the composite electrode and affording many interwoven pores for fast supply of Li + and storage of electrolyte. Moreover, the combination of the rod-shaped LFP and porous 3D structure can effectively relieve the stress resulted from the structural change during the insertion/deinsertion of Li + . Owing to these particular structure and characteristics, the LFP@GA composite presents a high discharge capacity (162.7 mAh g −1 at 0.1 C), a remarkable rate capacity (119.9 mAh g −1 at 5 C) and an excellent long-term cycle stability after 1000 cycles at 1 C (86.5% capacity retention), which is potential for use in Li-ion batteries.
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