The results reported here focus on the spectroscopy and dynamics of GaSe nanoparticle aggregates, and InSe/GaSe nanoparticle heterojunctions. Nanoparticle aggregates form spontaneously and reversibly in high concentration, room temperature solutions. The high-concentration absorption spectra are semiquantitatively modeled in terms of the lowest two absorption bands of bulk GaSe, quantum confinement effects and dipolar coupling between excited state monomers. From the model, the interparticle coupling is estimated to be about -300 cm -1. Addition of InSe nanoparticles results in these particles being incorporated into the aggregates and thereby forming InSe/GaSe nanoparticle heterojunctions. This results in emission quenching, and suggest that photoinduced charge transfer takes place. Based on energetic considerations, we expect that excitation of a heterojunction will result in electron or hole transfer producing a (InSe) +(GaSe) - charge separated state. Transient absorption results support this interpretation.