Phase pure hexagonal beta-NaGdF4: Eu3+, Er3+ samples of less than 10 nm in crystallite size were synthesized in anhydrous ethylene glycol within 24 hours at room temperature. The materials were characterized by powder X-ray diffraction, electron microscopy, and luminescence spectroscopy. After Gd3+ excitation at 273 nm Eu3+ luminescence from the D-5(J) states dominates over Gd3+ P-6(J) emission and only weak Er3+ emissions could be observed due to strong Gd -> Eu and weak Gd -> Er energy transfer. Excitation at 377 nm results in Er3+ H-2(9/2) and Eu3+ D-5(J) emissions. The concentration dependence of the Er3+ and Eu3+ luminescence intensities points to independent behavior of the dopant ions without Er -> Eu or Eu -> Er energy transfer. Eu3+ excitation at 394 nm results in Eu3+ D-5(J) emissions only and confirms the absence of Eu-Er energy transfer. Eu3+ luminescence from the D-5(J) states prevails for all investigated excitations. The optimum Eu3+ doping level is close to 5%. Significant Er3+ luminescence was observed for 377 nm excitation only. The strong H-2(9/2) and weak S-4(3/2) Er3+ emissions indicate small losses by multiphonon relaxation and a good quality of the nanomaterial. Er co-doping hinders the energy migration on the Gd3+ and Eu3+ sublattices which results in higher Gd3+/Eu3+ and Eu3+ D-5(1)/D-5(0) emission ratios.