Upconverting NaErF4:Yb3+,Gd3+ nanoparticles (NPs) and nanorods (NRs) with improved red emission have been successfully achieved via a facile hydrothermal route using oleic acid as the assistant surfactant. The crystalline phase, morphology even the size are simultaneously tuned by controlling the reaction temperatures and Gd3+ doping contents. The higher synthesis temperature leads to the morphology evolution from NPs to NRs. The integrated intensity ratio of red to green emissions is much improved for Gd3+ codoping nanostructures. The microstructure characterizations along with the steady and transient spectroscopy are performed to better understand the underlying mechanisms of phase evolution and emission enhancement. For the different states of Er3+, i.e. H-2(11/2) and F-4(9/2), the radiative/non-radiative transition probabilities could be affected by Gd3+ doping in different ways as for NPs and NRs, based on the lifetime and emission intensity data. NaErF4:Yb3+,Gd3+ nanosctructures are expected to have promising applications in multimodal bioimaging for deeper tissue penetration.