Optical gas sensing by micro-photoluminescence on multiple and single ZnO nanowires

Abstract

ZnO nanowires with average diameters of 50–200 nm were grown by chemical vapor deposition. Their gas sensing properties were analyzed by micro‐photoluminescence spectroscopy allowing for optical readout. The influence of O2 atmosphere on the emission intensity was investigated for ZnO nanowires with different metal cover layers and after O2 plasma pre‐treatment. Investigations of single ZnO nanowires showed an improved sensitivity towards O2. Photoresponse of a single ZnO nanowire (inset) to O2 ambient.

The Influence of Surface Doping on Adsorption Ability of Nanopowder Metal Oxides for Gas Sensors

“…ZnO nanopowders exhibit efficient photoluminescence in the visible range [2]. The photoluminescence spectra of metal oxide nanopowders is sensitive to the presence of oxidizing and reducing gases in the ambient air [3,4]. The adsorption of oxidative and reductive gases on the surface of nanopowders leads to a change in the charge density on the surface and a shift of the Fermi level.…”

Low Energy Pulsed Laser Excitation in UV Enhances the Gas Sensing Capacity of Photoluminescent ZnO Nanohybrids

“…The influence of irradiation parameters, such as excitation intensity and wavelength, on the response of the ZnO-PDMS sensor against ethanol and oxygen, have been systematically investigated in a comparative study performed employing pulsed excitation at 248 and 355 nm. This study represents the first demonstration that the sensing performance of the PL-based ZnO sensors can be optimized by tuning the excitation parameters and it particularly illustrates that maintaining a low pump energy density is crucial for enhancing the sensitivity of the sensor achieving response values approaching 100%.Monitoring the optical properties of semiconductor materials [12][13][14], such as transmittance, reflectance, or photoluminescence (PL) emission, which have also been found to undergo changes in the presence of external chemical stimuli, appears a promising alternative for gas sensing albeit such an approach is much less investigated, to date. Importantly, changes in optical properties are observable at room temperature, and their recording requires straightforward experimental equipment, while the sensing material itself does not require any elaborate preparation for a measurement to be performed.…”

“…Upon photoexcitation of the semiconductor, adsorbed O 2 molecules are reduced to O − 2 ions ( O 2 + e − → O − 2 ) [9]. The extraction of electrons from the conduction band [12] leads to the formation of an electron depleted layer, the thickness of which has been suggested to have an impact on the UV photoluminescence leading to a reduction of its intensity [21]. When ethanol is present, it interacts with the photo-generated oxygen ions (O − 2 ) [9] causing the release of trapped electrons back to ZnO [25], thereby reducing the depletion layer thickness and enhancing the ZnO PL emission over that observed in air.…”

“…Monitoring the optical properties of semiconductor materials [12][13][14], such as transmittance, reflectance, or photoluminescence (PL) emission, which have also been found to undergo changes in the presence of external chemical stimuli, appears a promising alternative for gas sensing albeit such an approach is much less investigated, to date. Importantly, changes in optical properties are observable at room temperature, and their recording requires straightforward experimental equipment, while the sensing material itself does not require any elaborate preparation for a measurement to be performed.…”

Nanopowder Metal Oxide for Photoluminescent Gas Sensing

“…The adsorption of oxidative and reductive gases on the surface of nanopowders leads to a change in the charge density on the surface and a shift of the Fermi level. This induces a change in the electron distribution in the nanomaterial [ 16 – 18 ]. A wide range of adsorption centers leads to low selectivity of material, and consequently we need to find ways of improving this.…”