The [RE(NTA)(H₂O)₂]⋅(H₂O) rare-earth complexes (RE³⁺: Eu, Gd, Tb and NTA: nitrilotriacetate) were synthesized and characterized by elemental analysis, thermogravimetry, X-ray diffraction, and infrared spectroscopy. The complexes show high crystallinity and thermostability. The photoluminescence behavior was studied based on the excitation and emission spectra, and luminescence decay curves. The compounds exhibit red (Eu³⁺), green (Tb³⁺) and UV (Gd³⁺) monochromatic emissions under UV excitation. The NTA ligand acts as luminescence sensitizer in the ligand-to- RE³⁺ intramolecular energy transfer process, owing to the fact that the first excited triplet state (T1: 29 000 cm⁻¹) is located above of the ⁵D₀ (Eu³⁺) and ⁵D₄ (Tb³⁺) emitting levels. The experimental intensity parameters Ωλ (λ: 2 and 4) for the Eu³⁺ NTA complex were calculated, and the results are discussed. The Gd³⁺-NTA complex exhibits a high-intensity emission band in the UV region (32 000 cm⁻¹) assigned to the ⁶P_7/2→⁸S_7/2 intraconfigurational transition.