Correlation of native point defects and photocatalytic activity of annealed ZnO nanoparticle studied by electron spin resonance and photoluminescence emission

Abstract

In this paper, we investigate the origin of point defects revealed by electron spin resonance (ESR) and photoluminescence (PL) emission in correlation with the photocatalytic activity of ZnO nanocrystals subjected to thermal annealing at various temperatures. Two ESR signals at g ∼ 1.96 and ∼2.003 were consistently observed in all annealed ZnO samples. However, their relative intensities have changed, indicating that the point defect densities were influenced by the annealing temperature. Interestingly, when doping nanoZnO with Cr 3+ , the Q-band ESR measurements at T = 100 K did show that the g ∼ 1.96 signal was completely passivated, suggesting that the origin of the signal lies in the electrons located near the conduction band, i.e. at a shallow-donor level. The intensity of the g ∼ 2.003 signal decreased by rising the annealing temperature, and this is attributed to the depopulation of zinc interstitials through the thermally induced migration process and/or recombination with the zinc vacancies. The green PL emission line at ∼520 nm, which is dominant in the 700 • C annealed ZnO sample, shows a correlation with the ESR signal at g ∼ 1.96, whose origin is attributed to the radiative transition of the electron from the shallow donor level to the singly ionized zinc vacancy. Furthermore, the high density of the shallow donor electron states was found to be primarily responsible for the high photocatalytic activity in the degradation of methylene blue.

Steering the reaction pathway of syngas-to-light olefins with coordination unsaturated sites of ZnGaOx spinel

“…Upon H 2 reduction, a signal at g = 2.004 appears and no other signals are observed over nanoflakes. g = 2.004 signal was frequently reported to be related to the presence of a free electron in the conduction band 37 , 38 , or defect sites over singly ionized zinc vacancy of zinc-based oxides 32 , 39 – 42 . However, it was also assigned to unpaired electron trapped at an oxygen vacancy site of oxides such as ZnO 35 , 41 , 43 , Zn x Ga y O z 37 , 44 , 45 , or TiO 2 38 , 46 .…”

“…However, it was also assigned to unpaired electron trapped at an oxygen vacancy site of oxides such as ZnO 35 , 41 , 43 , Zn x Ga y O z 37 , 44 , 45 , or TiO 2 38 , 46 . The assignment of g = 1.97 also remains controversial in different studies, e.g., singly ionized oxygen vacancies with one trapped electron 33 , 47 , zinc vacancies 42 , 48 , 49 , or donor centers such as ionized impurity atoms in the crystal lattice of ZnO oxide 50 , 51 . Volatility of zinc species has been frequently reported for ZnO and Zn-based oxides, which is facilitated in vacuum and hydrogen atmosphere 52 – 55 .…”

ON THE CONTRIBUTION FACTORS OF ENHANCED PHOTOCATALYTIC ACTIVITY OF DOPED SEMICONDUCTORS: STRUCTURAL AND OPTICAL INTVESTIGATION OF CU2+ DOPED ZnO NANOPARTICLE

“…The Zn1-xCuxO samples with x = 0.0 and 0.01 were prepared by sol-gel method similar to previous reports [10,11]. Typically, the zincnitratehexahydrate -Zn(NO3)2.6H2O (Sigma-Aldrich) and copper(II) nitrate trihydrate -Cu(NO 3 )2.3H2O (Sigma-Aldrich) were mixed with citric acid -C6H8O7.H2O 1M (Sigma-Aldrich) with a molar ratio of metal ions : acid = 1:3.…”

Local Surface Plasmonic Resonance, Surface-Enhanced Raman Scattering, Photoluminescence, and Photocatalytic Activity of Hydrothermal Titanate Nanotubes Coated with Ag Nanoparticles

“…The fitting decay curves of timeresolved PL spectra shown in the subfigure of Figure 6(b) indicated that the photoelectron lifetime of TNT/Ag of ~4.26 ns was significantly longer than that of TNT, which was ~1.68 ns. Hence, the recombination rate of the composite sample was about 2.75-fold longer than that of TNT; thus, photoexcited carriers would have more time in the solution vicinity to promote highly oxidative and reductive radicals to decompose the organic dye [49,50].…”