EPR and photoluminescence spectroscopy studies on the defect structure of ZnO nanocrystals

Abstract

Structural and optical properties of ZnO nanoparticles can be fine tuned by a novel variant of milling performed at cryogenic temperatures. In this study intrinsic defect centers such as oxygen and zinc vacancies are characterized using electron paramagnetic resonance (EPR) and photoluminescence (PL) spectroscopy. Three different surface defects with different g factors were identified by EPR for which the spectral intensities change upon decreasing the crystal size. EPR and PL intensities revealed a linear correlation giving detailed information about optical and electronic properties of ZnO. The core-shell model established from optical emission and EPR suggests distinguished electronic states in the band gap belonging to negatively charged Zn vacancies and positively charged oxygen vacancies. This model indicates a correlation between red emission and positively charged oxygen vacancies, which lead to a possible transition from a typical n-type to a p-type ZnO semiconductor.

Core-defect reduction in ZnO nanorods by cobalt incorporation

“…Their identification still remains controversial but two main assignments are usually made: (1) a single-ionized zinc interstitial (Zn + i ) at g ⊥ = 1.9595 and g ∥ = 1.9605 17,18 , and (2) the so-called D * center at g ⊥ = 1.9605 and g ∥ = 1.9565 19,20 . Besides, a g ∼ 1.96 signal has been proved to decrease when reducing the ZnO nanoparticles size, thus being attributed to a shallow donor CD signal [21][22][23] . However, the nanoparticles not being oriented, the information on anisotropy is lost so that the signal may arise from defects mentioned in (1), (2), or both.…”

Search for Origin of Room Temperature Ferromagnetism Properties in Ni-Doped ZnO Nanostructure

“…There is a broad and intense green emission peak E 10 is also observed in all ZnO samples (see supporting figure S2). The cause of this peak is considered as a green emission (504-524nm) is due to the recombination of photo generated hole and the electron trapped by single ionized oxygen vacancies (V o + ), this proof of presence of singly ionized oxygen vacancy states 51,52 . However oxygen vacancies, which are an important class of point defects in oxides and also known as colour centres (F centres) 53 shows three dissimilar charge states, as F 2+ (unoccupied), F + (singly occupied), and F 0 (doubly occupied), in the ZnO lattice.…”

Correlation between structural and electronic order–disorder effects and optical properties in ZnO nanocrystals

“…In addition, although it is well-known that the presence of lattice defects plays a key role in the physical and chemical properties of ZnO nanostructures, 10,11 many questions still remain due to the lack of conclusive evidence for defects responsible for luminescence properties.…”

“…Although dened ZnO nanostructures with different morphologies have been reported using a variety of procedures, [7][8][9][10][11][12]29 existing methods require either harsh conditions, complex procedures or long reaction times. In addition, although it is well-known that the presence of lattice defects plays a key role in the physical and chemical properties of ZnO nanostructures, 10,11 many questions still remain due to the lack of conclusive evidence for defects responsible for luminescence properties.…”