Electron spin resonance properties of ZnO microcrystallites

Oxygen‐deficient BaAl2O4, with strong optical absorption in the spectra range from 200 to 2500 nm, was prepared by a simple and economic thermal treatment of BaAl2O4 in a H2 gas flow. Further studies found that a molar ratio of oxygen vacancies of about 0.4 % existed in the prepared oxygen‐deficient BaAl2O4 sample. The influence of oxygen vacancies on the electronic band structures and optical absorption of BaAl2O4 are elucidated via first principle calculations. Oxygen vacancies introduce impurity states above the valence band; these impurities expand and enhance the optical absorption of BaAl2O4. This approach is proposed to develop a new type of optical materials and to be applicable to many wide bandgap materials.

Section: Full Papermentioning

confidence: 97%

“…An explanation could be that the existence of complex defect structures (such as neighboring vacancies) might form in R-BaAl 2 O 4 because of the reduction in the H 2 flow, while no such process was performed in the cases where a small g-shift was observed. [28][29][30][31] Further tests need to be done to allow us to draw further conclusions.…”

Section: +mentioning

confidence: 99%

Synthesis and Performance of BaAl₂O₄ with a Wide Spectral Range of Optical Absorption

Zhang

Wang

Zhu

2007

“…6). The low-field signal with g-factor close to the free-electron value (g = 2.0023) is generally attributed to an unpaired electron trapped on an oxygen vacancy site (g = 1.9965, 1.9948; [39] 2.0190; [40] 2.0106 [41] ). The other, highfield signal at g » 1.96, which was sometimes also attributed to unpaired electrons trapped on oxygen vacancies, has been reported to result from shallow donor centers such as ionized impurity atoms in the crystal lattice of ZnO.…”

Section: Impurities and Oxygen Vacanciesmentioning

confidence: 99%

Zinc Oxide Nanoparticles with Defects

Ischenko

Polarz

Grote

et al. 2005

537

360

Zinc oxide in the form of nanoscale materials can be regarded as one of the most important semiconductor oxides at present. However, the question of how chemical defects influence the properties of nanoscale zinc oxide materials has seldom been addressed. In this paper, we report on the introduction of defects into nanoscale ZnO, their comprehensive analysis using a combination of techniques (powder X‐ray diffraction (PXRD), X‐ray absorption spectroscopy/extended X‐ray absorption fine structure (XAS/EXAFS), electron paramagnetic resonance (EPR), magic‐angle spinning nuclear magnetic resonance (MAS‐NMR), Fourier‐transform infrared (FTIR), UV‐vis, and photoluminescence (PL) spectroscopies coupled with ab‐initio calculations), and the investigation of correlations between the different types of defects. It is seen that defect‐rich zinc oxide can be obtained under kinetically controlled conditions of ZnO formation. This is realized by the thermolysis of molecular, organometallic precursors in which ZnO is pre‐organized on a molecular scale. It is seen that these precursors form ZnO at low temperatures far from thermodynamic equilibrium. The resulting nanocrystalline ZnO is rich in defects. Depending on conditions, ZnO of high microstructural strain, high content of oxygen vacancies, and particular content of heteroatom impurities can be obtained. It is shown how the mentioned defects influence the electronic properties of the semiconductor nanoparticles.

“…[13] A signal with g = 2.003 was attributed to chemisorbed O 2 ± . [11,13] Two EPR studies on ZnO nanocrystallites found signals with g = 2.0190 [12] and g = 2.0106 [10] which was attributed to O 2± vacancies located at the surface of nanocrystallites. The location of defects at the surface was confirmed by reduction of EPR signal intensity by coating the particles with a layer of surfactant.…”

Section: Introductionmentioning

confidence: 99%

“…The location of defects at the surface was confirmed by reduction of EPR signal intensity by coating the particles with a layer of surfactant. [12] However, many EPR studies attribute the commonly observed signal g = 1.96 to the singly ionized oxygen vacancy V + o . [1,4±6,11,16,18] Based on the correlation between the intensity of this EPR signal and the green PL intensity, green emission has been explained as the transition between a singly charged oxygen vacancy and a photoexcited hole.…”

Section: Introductionmentioning

confidence: 99%

Photoluminescence and Electron Paramagnetic Resonance of ZnO Tetrapod Structures

Djurišić¹,

Choy

Roy

et al. 2004

600

351

ZnO tetrapod nanostructures have been prepared by the evaporation of Zn in air (no flow), dry and humid argon flow, and dry and humid nitrogen flow. Their properties have been investigated using scanning electron microscopy (SEM), X‐ray diffraction (XRD), photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies (at different temperatures), and electron paramagnetic resonance (EPR) spectroscopy at –160 °C and room temperature. It is found that the fabrication conditions significantly influence the EPR and PL spectra obtained. While a g = 1.96 EPR signal is present in some of the samples, green PL emission can be observed from all the samples. Therefore, the green emission in our samples does not originate from the commonly assumed transition between a singly charged oxygen vacancy and a photoexcited hole [K. Vanheusden, C. H. Seager, W. L. Warren, D. R. Tallant, J. A. Voigt, Appl. Phys. Lett. 1996, 68, 403]. However, the green emission can be suppressed by coating the nanostructures with a surfactant for all fabrication conditions, which indicates that this emission originates from surface defects.