Strong visible and near infrared photoluminescence from ZnO nanorods/nanowires grown on single layer graphene studied using sub-band gap excitation

Abstract

Fabrication and optoelectronic applications of graphene based hybrid 2D-1D semiconductor nanostructures have gained tremendous research interest in recent times. Herein, we present a systematic study on the origin and evolution of strong broad band visible and near infrared (NIR) photoluminescence (PL) from vertical ZnO nanorods (NRs) and nanowires (NWs) grown on single layer graphene using both above band gap and sub-band gap optical excitations. High resolution field emission scanning electron microscopy and X-ray diffraction studies are carried out to reveal the morphology and crystalline quality of as-grown and annealed ZnO NRs/NWs on graphene. Room temperature PL studies reveal that besides the UV and visible PL bands, a new near-infrared (NIR) PL emission band appears in the range between 815 nm and 886 nm (1.40-1.52 eV). X-ray photoelectron spectroscopy studies revealed excess oxygen content and unreacted metallic Zn in the asgrown ZnO nanostructures, owing to the low temperature growth by a physical vapor deposition method. Post-growth annealing at 700 C in the Ar gas ambient results in the enhanced intensity of both visible and NIR PL bands. On the other hand, subsequent high vacuum annealing at 700 C results in a drastic reduction in the visible PL band and complete suppression of the NIR PL band. PL decay dynamics of green emission in Ar annealed samples show tri-exponential decay on the nanosecond timescale including a very slow decay component (time constant $604.5 ns). Based on these results, the NIR PL band comprising two peaks centered at $820 nm and $860 nm is tentatively assigned to neutral and negatively charged oxygen interstitial (O i) defects in ZnO, detected experimentally for the first time. The evidence for oxygen induced trap states on the ZnO NW surface is further substantiated by the slow photocurrent response of graphene-ZnO NRs/NWs. These results are important for tunable light emission, photodetection, and other cutting edge applications of graphene-ZnO based 2D-1D hybrid nanostructures. Published by AIP Publishing.

In Situ Growth of ZnO inside a Porous Silicon Matrix Obtained by Electrochemical Etching with a Hydrofluoric Acid-Formaldehyde Solution

“…As discussed above, the origin of these bands is due to quantum confinement in PS [22]. Similarly, for the ZnO/PS shown in Figure 2(c), the presence of three well-determined luminescence bands was observed: two at 698 nm and 712 nm corresponding to the quantum confinement of electrons in the nanocrystals of silicon in PS [22] and another centered at 774 nm that has been related to oxygen defects such as O i and O Zn [25][26][27]. These defects O i and O Zn are formed during the growth process due to the oxygen-rich conditions [26].…”

Assessment of synthesis approaches for tuning the photocatalytic property of ZnO nanoparticles

“…This indicates that relatively more oxygen interstitials are present in Z-01 than Z-02 [50]. A small hump in the green emission region observed in both the samples represent recombination of a shallowly trapped electron with a deeply trapped hole at valence band of Zn and oxygen interstitials [51]. The blue-emissions occurring at 453 nm and 471 nm, as shown in Fig.…”

Mapping the structural, electrical, and optical properties of hydrothermally grown phosphorus-doped ZnO nanorods for optoelectronic device applications

“…The enhanced length and diameter of the nanorods till 0.1% of NH 4 H 2 (PO 4 ) 2 M ratio is attributed to the larger size of the phosphorus compared to oxygen atoms in the ZnO [12, 13, 25]. Beyond 0.1% M ratio, the nature of length and diameter variation can be understood on the basis of saturation of solubility limit of the incorporating phosphorus into ZnO matrix [26]. Though all the other parameters kept constant or slowed down to increase or decrease except the doping concentration, the length and diameter of the nanorods were still found to be increased, which indicates the successful incorporation of phosphorus into the ZnO nanorods [12, 25].…”