The near-IR luminescence properties of two ErIII-containing coordination polymers, namely, [Er(btc)(H2O)5·3.5H2O] [(btc)3– = 1,3,5-benzenetricarboxylate] and [Er2(bdc)3- (H2O)4] [(bdc)2– = 1,4-benzenedicarboxylate] were investigated with the aim of testing their potential use as optical materials. Because both present relatively small quantum yields and short excited-state lifetimes, factors influencing their luminescent properties were deciphered in an effort to improve their luminescent properties. Thus, three other families of compounds were also investigated: (i) the two corre- sponding dehydrated compounds with respective chemical formula [Er(btc)] and [Er2(bdc)3] for evaluating the importance of O–H vibrators, (ii) the heterodinuclear compounds [Er2–2xY2x(bdc)3(H2O)4] (x = 0.2, 0.5, 0.8 and 0.9) for estimating the role of intermetallic quenching and (iii) the heterodinuclear compounds [Er2–2xYb2x(bdc)3(H2O)4] (x = 0.2 and 0.5) for checking whether YbIII-sensitized up-conversion can be induced or not.