The photophysics of mixed aggregates of GaSe/InSe nanoparticles have been studied using static and timeresolved absorption and emission spectroscopies. The results indicate that the GaSe/InSe interfaces form heterojunctions and exhibit photoinduced direct charge transfer from the GaSe valence band to the InSe conduction band. This results in the electrons and holes being localized separately in these two types of nanoparticles. The energy diagram of the nanoparticle heterojunction can be constructed from the static spectra, known bulk band offsets, and quantum confinement effects. These considerations accurately predict the energy of the observed charge-transfer band. Photoexcitation also produces excitons in the aggregates, away from the heterojunctions. These excitons can undergo diffusion and quench upon reaching a heterojunction. Timeresolved fluorescence kinetics can be modeled to extract an exciton diffusion coefficient. A value of 2.0 nm(2)/ns is obtained, which is in good agreement with values obtained from previous fluorescence anisotropy decay measurements.