Abstract
Short-wavelength luminescence is essential for high-performance optoelectronic device applications. There have been efforts to obtain intense ultraviolet (UV) emission by encapsulating ZnO one-dimensional (1D) nanostructures with materials such as ZnS. However, the encapsulation of ZnS 1D nanostructures with ZnO has not been reported. In this paper, we report ultraintense UV emission from ZnS nanorods coated with ZnO, i.e., ZnS-core/ZnO-shell nanorods. UV emission from the ZnS-core/ZnO-shell nanorods was much more intense than that obtained from the extensively studied ZnO-core/ZnS-shell nanorods. The highest intensity of the near-band-edge emission from the ZnS-core/ZnO-shell nanorods was obtained with a ZnO shell layer thickness of 35 nm, which is ∼16 times higher than that of pristine ZnS nanorods. Moreover, the deep level (DL) emission was suppressed completely. The substantial enhancement of the UV emission from the ZnS nanorods and the complete suppression of the DL emission by ZnO sheathing can be rationalized by combining the following four effects: the reinforcement of the UV emission by the overlap of the UV emissions from the ZnS core and ZnO shell, enhancement of the emission from the ZnO shell by the carrier transfer from the ZnS core to the ZnO shell, suppression of the capture of carriers by the surface states on the ZnS surface, and suppression of the visible emission and nonradiative recombination in ZnS.
Highlights
Short-wavelength luminescence is essential for high-performance optoelectronic devices such as white light emitting diodes (LED), compact disks/digital video disks with high information storage capacities, and short-wavelength laser diodes (LDs) for generation optical communication. 2–6 compound semiconductors such as ZnO, ZnS, ZnSe, and ZnTe as well as the 3–5 compound semiconductor GaN are promising short-wavelength light emitting materials[1,2]
A gold nanoparticle is observed at the tip of each nanorod, suggesting that the ZnS nanorods were grown by the vapor-liquid-solid (VLS) mechanism[22]
The NBE emission from ZnS or ZnO nanostructures is associated with the excitons bound to shallow donors, whereas the deep level (DL) emission is associated with the oxygen vacancy-related defects[24,25] such as singly-ionized oxygen vacancies, which can form recombination centers
Summary
Short-wavelength luminescence is essential for high-performance optoelectronic devices such as white light emitting diodes (LED), compact disks/digital video disks with high information storage capacities, and short-wavelength laser diodes (LDs) for generation optical communication. 2–6 compound semiconductors such as ZnO, ZnS, ZnSe, and ZnTe as well as the 3–5 compound semiconductor GaN are promising short-wavelength light emitting materials[1,2]. Various techniques, including thermal annealing, plasma treatment, doping, decoration with nanoparticles, and core-shell structure formation, have been studied for this purpose[4,5,6]. Of these techniques, encapsulation of ZnO 1D nanostructures with other materials has been studied most widely. Among these efforts, the best results were obtained by Li et al.[13] The intensity of the NBE emission of ZnO nanowires increased ~5 times, and the DL emission was suppressed completely upon sheathing them with ZnS thin films.
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