Near-infrared luminescent rare-earth organic complexes have attracted intensive attention in the field of optical waveguide amplification. However, their optical gains were commonly less than 4 dB/cm due to limited doping concentrations. Herein, two one-dimensional (1D) Nd 3+ coordination chains, namely, [Nd(TTA) 3 (DBTDPO)] n ( Nd1 ) and [Nd(TTA) 3 (DPEPO)] n ( Nd2 ), bridged by phosphine oxide ligands were developed for the neodymium-doped waveguide amplifier. Despite its P-P distance being similar to DBTDPO, the different P═O orientation of DPEPO renders markedly shorter intra- and interchain Nd-Nd distances for Nd2 in comparison to Nd1 . Furthermore, the weaker intermolecular interactions alleviate the quenching effect for Nd2 . Therefore, Nd2 can provide more locally concentrated and radiative Nd 3+ ions, leading to a larger Nd 3+ -characteristic 1.06 μm emission intensity and duration than Nd1 . Based on embedded and evanescent-field waveguide structures, Nd2 achieves state-of-the-art gain maxima of 5.7 and 4.9 dB/cm as well as outstanding gain stability. These results indicate that controllable coordination assembly of lanthanide ions in multidimension provides a flexible approach to combine local high-density outputs and effective suppression of quenching.