Enhancing the UV Emission in ZnO-CNT Hybrid Nanostructures via the Surface Plasmon Resonance of Ag Nanoparticles.

Protima Rauwel,Augustinas Galeckas,Erwan Rauwel

doi:10.3390/nano11020452

Abstract

The crystal quality and surface states are two major factors that determine optical properties of ZnO nanoparticles (NPs) synthesized through nonaqueous sol–gel routes, and both are strongly dependent on the growth conditions. In this work, we investigate the influence of the different growth temperatures (240 and 300 °C) on the morphology, structural and crystal properties of ZnO NP. The effects of conjoining ZnO NP with carbon nanotubes (CNT) and the role of surface states in such a hybrid nanostructure are studied by optical emission and absorption spectroscopy. We demonstrate that depending on the synthesis conditions, activation or passivation of certain surface states may occur. Next, silver nanoparticles are incorporated into ZnO–CNT nanostructures to explore the plasmon–exciton coupling effect. The observed enhanced excitonic and suppressed defect-related emissions along with blue-shifted optical band gap suggest an intricate interaction of Burstein–Moss, surface plasmon resonance and surface band-bending effects behind the optical phenomena in hybrid ZnO–CNT–Ag nanocomposites.

Highlights

IntroductionZnO is a well-acknowledged efficient semiconductor phosphor with a wide direct band gap (~3.3 eV), high electron mobility (155 cm−2 V−1 s−1 ) and large exciton binding energy (60 meV) that ensures effective luminescence at room temperature (RT) [1]
We address the effects of synthesis conditions and the plasmonic enhancement on the UV emission in ZnO–carbon nanotubes (CNT)–Ag nanohybrids
We demonstrate that depending upon the synthesis temperature and the nature of the surface defects in ZnO, the enhancement of PL emission is possible with the addition of Ag NP [25]

Summary

Introduction

ZnO is a well-acknowledged efficient semiconductor phosphor with a wide direct band gap (~3.3 eV), high electron mobility (155 cm−2 V−1 s−1 ) and large exciton binding energy (60 meV) that ensures effective luminescence at room temperature (RT) [1] These attractive optoelectronic properties make ZnO a promising multifunctional material for a variety of short-wavelength, light-emitting and detection applications, such as ultraviolet (UV) light emitting diodes (LED), UV lasers and tunable UV photodetectors [2]. The luminescent deep states in ZnO are mostly of intrinsic origin, i.e., involving oxygen and zinc vacancies (VO , VZn ), interstitials (Zni , Oi ) and related complexes Such point defects may be represented differently at the surface and in the bulk of the crystal; they manifest different charge states and act as donors or acceptors contributing to the visible emission in ZnO [4]. In an attempt to extend the absorption into the visible range, several techniques, such as ion implantation and metal or nonmetal doping, have

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