The luminescent properties of two families of heteronuclear lanthanide-containing coordination polymers are compared. These families have general chemical formulas [Ln(2-2x)Ln(2x)'(ip)(3)(H2O)(9)center dot 6H(2)O](infinity) and [Ln(2-2x)Ln(2x)'(aip)(2)(H2O)(10)center dot(aip)center dot 4H(2)O](infinity) where H(2)ip and H(2)aip stand for isophthalic acid and 5-amino-isophthalic acid, respectively, and where Ln and Ln' are one of the lanthanide ions between Sm3+ and Dy3+. Heteronuclear compounds that belong to each family are isostructural to the already reported homonuclear compounds [Gd-2(ip)(3)(H2O)(9)center dot 6H(2)O](infinity) and [Eu-2(aip)(2)(H2O)(10)center dot(aip)center dot 4H(2)O](infinity), respectively. These two crystal structures are very similar. However, despite similar chemical formulas, similar crystal structures, and similar hydration rates, these two families of compounds present very different luminescent properties that have thus been deeply investigated. This study demonstrates that these different optical behaviors can be attributed to the presence of a PET (photoinduced electron transfer) mechanism that is only present in the amino-isophthalate-containing coordination polymers.