Influence of exciton-phonon coupling on the energy position of the near-band-edge photoluminescence of ZnO nanowires

Abstract

Room-temperature near-band-edge photoluminescence of ZnO is composed of contributions from free-exciton recombination and its longitudinal-optical phonon replica. By tracking the photoluminescence of ZnO nanowires from 4K up to room temperature, the authors show that the relative contributions of these emission lines show a strong variation for samples grown under different conditions. The varying coupling strengths of the excitons and phonons thus lead to a significant shift of the energy position of the room-temperature photoluminescence. They verify that this is not caused by laser heating or stress/strain but is most probably related to crystalline imperfections in the surface region.

Growth of ZnO nanostructures on Au-coated Si: Influence of growth temperature on growth mechanism and morphology

“…Slight shifts in the UV peak position are most probably associated with surface effects which alter the relative magnitudes of the free exciton and LO phonon contributions to the room temperature emission, as discussed in Ref. 27, because we see no evidence of strain effects in our XRD data. 27 Figure 6͑b͒ shows low temperature ͑ϳ18 K͒ band-edge PL data for samples grown at 950 and 1150°C.…”

“…27, because we see no evidence of strain effects in our XRD data. 27 Figure 6͑b͒ shows low temperature ͑ϳ18 K͒ band-edge PL data for samples grown at 950 and 1150°C. The sample grown at 950°C shows a dominant bound exciton emission at ϳ3.356 eV, assigned to the I 9 line associated with In contamination of the source powder.…”

Localized versus delocalized states: Photoluminescence from electrochemically synthesized ZnO nanowires

“…13 The 1-LO-phonon replica of the FX ͑FX-1LO͒ and the B transitions ͑B-1LO͒ are visible at an energy separation of 72 meV to the lower energy side of their respective zerophonon lines. 2,10 All bands shift to lower energies as the temperature increases due to the reduction of the band gap. The intensities of the D 0 X and B bands decrease while those of the FX and FX-1LO bands increase.…”

“…[6][7][8][9] Because of the aqueous environment, the limited purity of the involved chemicals and the low growth temperatures ͑especially when compared to typical growth temperatures used for vapor-phase epitaxial methods͒ is not a priori clear how the nanowire material compares to that of nanowires synthesized by, e.g., high-temperature vaporliquid-solid processes. 10 However, a detailed knowledge of the microscopic processes governing the optical and electronic properties of chemically synthesized nanowires is mandatory to understand, tailor, and optimize any optoelectronic device based on such nanowires.…”

Photoluminescence emission at aging in ambient air of ZnO:Ag nanocrystals obtained by ultrasonic spray pyrolysis

“…The near-band-edge (NBE) emission at 3.0-3.37 eV is attributed to the free (FE) or bound (BE) excitons, their LO phonon replicas, such as FE-1LO or FE-2LO, to optical transition between the free to bound states, such as the shallow donor and valence band, or to donor-acceptor pairs [14]. However, the position of the near-band-edge emission at room temperature can vary significantly due to the variation of relative contributions of free exciton emission and phonon replicas [15].…”