Ln(SePh)(3) (Ln = Ce, Pr, Nd) reacts with elemental Se in the presence of Na ions to give (py)(16)Ln(17)NaSe(18)(SePh)(16), a spherical cluster with a 1 nm diameter. All three rare-earth metals form isostructural products. The molecular structure contains a central Ln ion surrounded by eight five-coordinate Se2- that are then surrounded by a group of 16 Ln that define the cluster surface, with additional mu(3) and mu(5) Se2-, mu(3) and mu(4) SePh-, and pyridine donors saturating the vacant coordination sites of the surface Ln, and a Na ion coordinating to selenolates, a selenido, and pyridine ligands. NIR emission studies of the Nd compound reveal that this material has a 35% quantum efficiency, with four transitions from the excited state F-4(3/2) ion to I-4(9/2), I-4(11/2), I-4(13/2), and I-4(15/2) states clearly evident. The presence of Na+ is key to the formation of these larger clusters, where reactions using identical concentrations of Nd(SePh)(3) and Se with either Li or K led only to the isolation of (py)(8)Nd8Se6(SePh)(12).