Two new compounds, namely {(NMe₂H₂)}[Ln(TDA)(HCOO)] 0.5H₂O, Ln = Sm³⁺ (Sm-TDA) and Gd³⁺ (Gd-TDA), where TDA³⁻ is the anion of 1H-1,2,3-triazole-4,5-dicarboxylic acid (H₃TDA), were synthesized by the solvothermal method in a DMF:H₂O mixture. According to single-crystal X-ray diffraction data, the compounds are 3d-MOFs with an anionic lattice and dimethylammonium cations occupying part of the cavities. Based on these compounds, two series of mixed-metal complexes, [NMe₂H₂][Sm_xLn_1-x(TDA)(HCOO)], (x = 0.9 (Sm_0.9Ln_0.1-TDA), x = 0.8 (Sm_0.8-Ln_0.2-TDA)…Sm_0.02Ln_0.98-TDA, Ln = Tb, Gd), were also obtained and characterized by powder XRD. The luminescent properties of the compounds were studied and it was shown that the resulting compounds are two- or three-component emitters with the possibility of fine color tuning by changing the intensities of fluorescence and phosphorescence of the ligand, as well as the luminescence of Sm³⁺ and Tb³⁺ f-ions.