A series of NaBiF₄:Er³⁺/Yb³⁺ micro-/nanocrystals were synthesized via the low-temperature molten-salt method in NH₄NO₃ flux. The influences of the amount of NaF and NH₄NO₃ flux used, the reaction time and reaction temperature on the crystal phase structure, morphology and size of the resultant samples were systematically investigated. The morphology, size, doped concentrations of Er³⁺ and Yb³⁺, pumping power, and temperature dependences of UC emissions were studied in detail under 980 nm irradiation. The NaBiF₄:3 mol% Er³⁺/20 mol% Yb³⁺ crystal exhibits the strongest green UC emission, which was observed under several mW 980 nm excitation at room temperature. The energy transfer between Bi³⁺ and Er³⁺ during UC emission process was also discussed at length.