We have studied the mechanism of visible photoluminescence (PL) in GaAs nanocrystals in ${\mathrm{SiO}}_2$ matrices formed by sequential ion implantation and thermal annealing. GaAs nanocrystal samples with the average diameter of ∼6 nm show a broad PL in the red spectral region. The PL peak energy of GaAs nanocrystals is blueshifted from that of the bulk GaAs crystal. Under resonant excitation at energies within the red PL band, the fine structures related to the LO phonon of the GaAs crystal are clearly observed in the PL spectrum at low temperatures. The excitation energy dependence of resonantly excited PL spectra shows that there are two different components of GaAs-related luminescence. In addition, in persistent luminescence hole-burning spectra, a pronounced hole is observed at the energy of the burning laser. The hole burnt in the luminescence spectrum has two structures related to the zero-phonon-line emission and the one-LO-phonon-assisted emission of delocalized excitons in GaAs nanocrystals. From resonantly excited PL spectra and luminescence hole-burning spectra, it is concluded that visible luminescence comes from both delocalized excitons and excitons bound to impurities in quantum-confined GaAs nanocrystals.

• Received 15 February 2000

DOI:https://doi.org/10.1103/PhysRevB.62.5100