Cubic nano-spherical and hexagonal microprismatic NaY F 4 : Yb, Er up-conversion (UC) phosphors have successfully been synthesized separately through a mild hydrothermal method. The morphology of the NaY F 4 : Yb, Er crystals can be controlled by adjusting the Ln 3+ /F − ratio in the reaction solution. The efficient UC luminescence can be detected under excitation at 980 nm. Red and green emissions originate from a two-photon mechanism. Factors affecting the phase and morphology of the samples, and their UC luminescence properties are investigated using microscopic and spectroscopic techniques.