Photoluminescence investigation of the carrier recombination processes in ZnO quantum dots and nanocrystals

Abstract

The carrier recombination processes in ZnO quantum dots ͑ϳ4 nm in diameter͒, ZnO nanocrystals ͑ϳ20 nm in diameter͒ and bulk ZnO crystal have been studied using photoluminescence ͑PL͒ spectroscopy in the temperature range from 8.5 to 300 K. The obtained experimental data suggest that the ultraviolet PL in ZnO quantum dots originates from recombination of the acceptor-bound excitons for all temperatures. In the larger size ZnO nanocrystals, the recombination of the acceptor-bound excitons is the dominant contribution to PL only at low temperature ͑T Ͻ 150 K͒. For higher temperatures ͑T Ͼ 150 K͒, PL is mostly due to recombination of the donor-bound excitons. Recombination processes in ZnO quantum dots and nanocrystals differ from those in bulk ZnO mainly because of the large surface-to-volume ratio in both types of nanoparticles and, consequently, a large number of acceptor defects near the surface. No strong inhomogeneous broadening has been observed in ultraviolet PL from ZnO quantum dots. Our results shed light on the carrier-recombination processes in ZnO quantum dots and nanocrystals, and can be used for the ZnO nanostructure optimization for the proposed optoelectronic and spintronic applications.

Deep level related photoluminescence in ZnMgO

“…where L is the excitation intensity and k is the power factor [49]. The underlying recombination process for 1 < k < 2 is known to be excitonic, whereas for k < 1 either a donor state (D-h), an acceptor state (e-A) or both states (donor-acceptor pair transition) are involved.…”

Synthesis, luminescence properties and EPR investigation of hydrothermally derived uniform ZnO hexagonal rods

“…Several emission bands, including band edge UV emission at 400 nm ($3.10 eV) and defect related violet emission at 420 nm ($2.95 eV), blue-green emission at 482 nm ($2.57 eV) and green emission at 524 nm ($2.36 eV) were observed. In PL spectrum of ZnO band at 400 nm, could be attributed to free exciton recombination through exciton-exciton collisions, [23] corresponding to the near-band-gap emission (NBE), which corresponds to an energy gap of 3.10 eV.…”

Multicolor Luminescence from Semiconductor Nanocrystal Composites Tunable in an Electric Field

“…The origin of the A-line emission is currently under discussion. Possible assignments of the A-line include: neutral excitons bound to nitrogen impurities (Look et al, 2002;Yang et al, 2006), donor-acceptor pair recombination , free-to neutral-acceptor transitions (Cao et al, 2007), two-electron transition of exciton bound to neutral donor (Studenikin et al, 2000), the first longitudinal optical (LO) phonon replica of free excitons (Hirai et al, 2008) or excitons bound to surface or structural defects ( Fallert et al, 2007;Fonoberov et al, 2006;He et al, 2007;Meyer et al, 2004;Teke et al, 2004). Recently, on a basis of cathodoluminescence measurements, it was suggested that this line is composed of two overlapped bands related to point defects and the first LO phonon replica of the free exciton (Mass et al, 2008).…”