Isostructural lanthanide metal organic frameworks (MOFs) are synthesized through the spontaneous self-assembly of H(3)BTPCA (1,1',1 ''-(benzene-1,3,5-triyl)tripiperidine-4-carboxylic acid) ligands and lanthanide ions (we term these MOFs Ln-BTPCA, Ln = La3+, Tb3+, Sm3+, etc.). Prompted by the observation that the different lanthanide ions have identical coordination environment in these MOFs, we explored and succeeded in the preparation of mixed-lanthanide analogues of the single-lanthanide MOFs by way of in situ doping using a mixture of lanthanide salts. With careful adjustment of the relative concentration of the lanthanide ions, the color of the luminescence can be modulated, and white light-emission can indeed be achieved. The mechanisms possibly responsible for the observed photophysical properties of these mixed-lanthanide MOFs are also discussed.