Orange/Red Photoluminescence Enhancement Upon SF6 Plasma Treatment of Vertically Aligned ZnO Nanorods

Abstract

Although the origin and possible mechanisms for green and yellow emission from different zinc oxide (ZnO) forms have been extensively investigated, the same for red/orange PL emission from ZnO nanorods (nR) remains largely unaddressed. In this work, vertically aligned zinc oxide nanorods arrays (ZnO nR) were produced using hydrothermal process followed by plasma treatment in argon/sulfur hexafluoride (Ar/SF6) gas mixture for different time. The annealed samples were highly crystalline with ~45 nm crystallite size, (002) preferred orientation, and a relatively low strain value of 1.45 × 10−3, as determined from X-ray diffraction pattern. As compared to as-deposited ZnO nR, the plasma treatment under certain conditions demonstrated enhancement in the room temperature photoluminescence (PL) emission intensity, in the visible orange/red spectral regime, by a factor of 2. The PL intensity enhancement induced by SF6 plasma treatment may be attributed to surface chemistry modification as confirmed by X-ray photoelectron spectroscopy (XPS) studies. Several factors including presence of hydroxyl group on the ZnO surface, increased oxygen level in the ZnO lattice (OL), generation of F–OH and F–Zn bonds and passivation of surface states and bulk defects are considered to be active towards red/orange emission in the PL spectrum. The PL spectra were deconvoluted into component Gaussian sub-peaks representing transitions from conduction-band minimum (CBM) to oxygen interstitials (Oi) and CBM to oxygen vacancies (VO) with corresponding photon energies of 2.21 and 1.90 eV, respectively. The optimum plasma treatment route for ZnO nanostructures with resulting enhancement in the PL emission offers strong potential for photonic applications such as visible wavelength phosphors.

Unraveling the effect of Gd doping on the structural, optical, and magnetic properties of ZnO based diluted magnetic semiconductor nanorods

“…The orange-red PL band was earlier attributed either to oxygen interstitial atoms (O i ) due to excess oxygen on the ZnO surface or to the hydroxyl group (OH). 92 The orange emission is caused by transition from the Zn interstitial (Zn i ) to the oxygen interstitial (O i ) states. Such phenomena are generally observed in oxygen rich systems, see the results of EDX.…”

Morphology Related Defectiveness in ZnO Luminescence: From Bulk to Nano-Size

“…The ZnO defect emissions in the VIS range have been already investigated, but no consensus has been reached about their origin. The luminescence in the orange–red region of the spectrum is generally detected in oxygen-rich samples: an enhancement of the red emission at ~1.9 eV was observed in ZnO NPs after annealing in air [ 20 ] and in ZnO nanorods after SF 6 plasma treatment [ 21 ]. The yellow–green band, reported between 2.2 and 2.4 eV, is the most commonly observed [ 18 ] and the most controversial.…”

Design and Testing of Bistable Lattices with Tensegrity Architecture and Nanoscale Features Fabricated by Multiphoton Lithography

“…It is worth noting that extraordinary strength-to-weight and stiffness-to-weight ratios, frequency bandgaps, negative overall elastic moduli, negative mass density, auxeticity and solitary wave propagation represent characteristic and unconventional properties of such systems [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18], as well as a multistable mechanical response [19][20][21][22][23][24][25][26][27][28]. However, the additive manufacturing of multi-cell realizations of mechanical metamaterials remains a challenge at present, due to the difficulty of reproducing the desired behaviors at small scales [8,9,[29][30][31][32].…”