Optical Characterization of Strong UV Luminescence Emitted from the Excitonic Edge of Nickel Oxide Nanotowers.

Ching-Hwa Ho,Ching-Hsiang Chan,Yuan-Ron Ma,Yi-Ming Kuo

doi:10.1038/srep15856

Abstract

NiO had been claimed to have the potential for application in transparent conducting oxide, electrochromic device for light control, and nonvolatile memory device. However, the detailed study of excitonic transition and light-emission property of NiO has rarely been explored to date. In this work, we demonstrate strong exciton-complex emission of high-quality NiO nanotowers grown by hot-filament metal-oxide vapor deposition with photoluminescence as an evaluation tool. Fine and clear emission features coming from the excitonic edge of the NiO are obviously observed in the photoluminescence spectra. A main excitonic emission of ~3.25 eV at 300 K can be decomposed into free exciton, bound excitons, and donor-acceptor-pair irradiations at lowered temperatures down to 10 K. The band-edge excitonic structure for the NiO nanocrystals has been evaluated and analyzed by transmission and thermoreflectacne measurements herein. All the experimental results demonstrate the cubic NiO thin-film nanotower is an applicable direct-band-gap material appropriate for UV luminescence and transparent-conducting-oxide applications.

Highlights

The iron Trial group (Fe, Co, Ni) monoxides have received more attentions on various branches of magnetic study owing to the large magnetic pole created by unpaired electrons
The experimental results of NiO nanostructures show a prominent excitonic emission at ~3.25 eV and a direct gap larger than 3.51 eV, which can act as an UV luminescence material as well as a transparent conducting oxide (TCO) constituent by the iron-Trial transition element Ni
The transmittance spectra at 30 and 300 K simultaneously show two dips that matched well with the two excitonic transitions measured by TR measurements with EX = 3.35 and B = 3.61 eV at 30 K and EX = 3.25 and B = 3.51 eV at 300 K, respectively

Summary

Introduction

The iron Trial group (Fe, Co, Ni) monoxides have received more attentions on various branches of magnetic study owing to the large magnetic pole created by unpaired electrons. The NiO thin-film nanostructures own some specific electronic and structural properties to lend itself a promising candidate for applications in hydrogen and glucose sensor[6,7], resistive switching memory[8,9], electrochemical electrode for battery and supercapacitor use[10], electrochromic device[11], and dye-sensitized and hybrid thin-film solar cells[12,13,14,15]. The behaviors of electrochromic and resistive switching in the NiO can be attributed to the mobile ions (Ni2+, OH−, etc.) and defects (vacancy, interstitial, or hole) migrated in the nickel oxide under different electric fields for changing the electronic structure or band-gap state. The experimental results of NiO nanostructures show a prominent excitonic emission at ~3.25 eV and a direct gap larger than 3.51 eV, which can act as an UV (or white-light) luminescence material as well as a transparent conducting oxide (TCO) constituent by the iron-Trial transition element Ni

Methods

Results

Conclusion