Strong Deep-Level-Emission Photoluminescence in NiO Nanoparticles

Abstract

Nickel oxide is one of the highly promising semiconducting materials, but its large band gap (3.7 to 4 eV) limits its use in practical applications. Here we report the effect of nickel/oxygen vacancies and interstitial defects on the near-band-edge (NBE) and deep-level-emission (DLE) in various sizes of nickel oxide (NiO) nanoparticles. The ultraviolet (UV) emission originated from excitonic recombination corresponding near-band-edge (NBE) transition of NiO, while deep-level-emission (DLE) in the visible region due to various structural defects such as oxygen vacancies and interstitial defects. We found that the NiO nanoparticles exhibit a strong green band emission around ~2.37 eV in all samples, covering 80% integrated intensity of PL spectra. This apparently anomalous phenomenon is attributed to photogenerated holes trapped in the deep level oxygen vacancy recombining with the electrons trapped in a shallow level located just below the conducting band.

Structural and Enhanced Optical Properties of Stabilized γ‒Bi2O3 Nanoparticles: Effect of Oxygen Ion Vacancies

“…It is also utilized in analyzing point defects such as cation and anion vacancies [35]. Similarly, PL spectroscopies can be used as a powerful tool in identifying defects, particularly for V O in metal oxides [26,36]. Our experimental results indicate the formation of vacancies at B(1) and O(2) sites during annealing, of which the former could be intrinsic and later play a decisive role in the RT stabilization of γ-Bi 2 O 3 .…”

Structure of Ni(OH)2 intermediates determines the efficiency of NiO-based photocathodes – a case study using novel mesoporous NiO nanostars

“…3.83 eV, is consistent within the range of NiO optical band gaps reported in literature. [51][52][53] The emission of NiO shows near band edge (NBE) UV emission and deep level (DL) defect related emission in the visible range (inset of Fig. 4a).…”

“…, l em z 460 nm) or between an electron in conduction band and a photo-generated trapped hole occupying oxygen vacancy (V O 2+ , l em z 527 nm) and interstitial (O i , l em z 585 nm). [53][54][55] The O i and V O 2+ defects are thus considered shallow and deep trap states, respectively. These traps determine the charge transport in NiO and act as recombination centers.…”

“…3a), the positive charge density of NiO NS is mainly localized on either the O or Ni atom and hence, it is advantageous since binding modes of phosphonic and carboxylic acid anchoring group toward NiO surface are determined by the formation of strong P-O-Ni and C-O-Ni covalent bonds, respectively. [52][53][54] Electrostatic interaction between pyridine anchoring moiety and non-polar plane (100) of NiO may occur for sensitization although the binding strength is lower than the interaction between either carboxylic or phosphonic acid and NiO, and hence, it results in a lower dye-loading compared with other complexes. 60,61 NiO NS-based dye-sensitized solar cells…”

Room Temperature Magnetic Memory Effect in Cluster-Glassy Fe-Doped NiO Nanoparticles

“…Among the various AF materials, nickel oxide (NiO) is one of the few p -type semiconductors (acceptor state induced by the nickel vacancy (V Ni ) with a wide-bandgap E g = 4 eV) having face-centered-cubic ( fcc ) crystal symmetry. In the bulk form, NiO possesses AF ordering with the Neel transition temperature T N of 523 K [ 2 ]. However, NiO nanostructure exhibits anomalous magnetic properties that are very sensitive to size, Ni vacancy defects, morphology, and crystal structure, thus showing a wide variety of intriguing phenomena.…”