Morphology control and enhancement of 1.5 μm emission in Ca2+/Ce3+ codoped NaGdF4:Yb3+, Er3+ submicrorods

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.