. . . . . "The concentration-dependent spectroscopic characteristics of GaSe nanoparticles are interpreted in terms ofthe particles forming strongly interacting aggregates in high-concentration, room-temperature solutions. Thehigh-concentration absorption spectra are semiquantitatively modeled in terms of the lowest two absorptionbands of bulk GaSe, quantum confinement effects, and dipolar coupling between excited state monomers.The model predicts that the lowest energy absorption band shifts slightly to the red and sharpens, while thenext band shifts to the blue as the concentration is increased. This correctly explains the observed absorptionspectra and their reversible changes with concentrations. Static emission data and initial anisotropies of time-resolved emission may also be qualitatively understood on the basis of this simple model. From the model,the interparticle coupling is estimated to be about \u2212300 cm-1. This is less than the energy differences betweenadjacent particles in the aggregates but much greater than what is observed between other types ofsemiconductor nanoparticles. Polydisperse samples have larger energy differences but comparable couplingsbetween adjacent particles. As a result, the spectroscopic effects of aggregation are less pronounced. Thenanoparticle aggregate spectra are reminiscent of J-aggregate spectra of organic dyes." . "Spectroscopy of GaSe Nanoparticle Aggregates" . . . . . . . . . . . .