Luminescence and Resonance Raman Spectroscopy of Indirect Excitons in AgBr Nanocrystals

Abstract

ABSTRACTAgBr nanocrystals with radii R ≈ 2.5 to 5 nm comparable with the exciton Bohr radius are produced in inverse micelles. As compared with bulk AgBr, the exciton emission exhibits a substantial blue shift and enhanced intensity due to the spatial confinement. Besides luminescence, first- and second-order resonance Raman scattering is discovered the occurrence of a zero-phonon process clearly revealing mixing of L with Г point states. From time-resolved measurements, exciton lifetimes of the order of 500 μs are found. They are close to the radiative lifetime in the bulk demonstrating that nonradiative processes are negligible in these nanocrystals. In agreement with state mixing, the total decay rate is found proportional to R−2. A small shift of the TO(L) Raman line with excitation photon energy is analyzed in terms of the wavevector dependent interaction of the quantized exciton states with the dispersive phonon.