Excitonic properties of ZnO nanocrystalline films prepared by oxidation of zinc-implanted silica

Abstract

Zinc oxide nanocrystalline films with (002) preferred orientation and intense ultravoilet (UV) emission were prepared by oxidation of zinc-implanted silica at 700°C for 2 h in oxygen ambient. A TEM micrograph showed that ZnO nanocrystalline films with a thickness of about 90 nm were formed on the surface of the Zn-implanted silica substrate. The quality and excitonic properties of the ZnO nanocrystalline films were studied through absorption spectra at room temperature and photoluminescence (PL) spectra in the temperature range from 79 to 300 K. At room temperature, a strong free excitonic emission peak at 377 nm with a very weak deep-level emission can be observed. The intensity ratio of the UV near-band-edge emission to the deep-level emission can reach up to 40. The temperature-dependent PL indicated that the UV near-band-edge emission in the temperature range 79–187 K can be attributed to a free exciton (FE), a bound exciton and the one longitudinal-optical phonon replica of FE lines. The presence of a strong emission of FE lines at 79 K suggested that high-purity ZnO nanocrystalline films have been obtained.

Intense near-infrared emission from ZnO-LiYbO_2 hybrid phosphors through efficient energy transfer from ZnO to Yb^3+

“…This result also explained the red shift of the SA emission in ZnO-LiYbO 2 hybrid phosphors compared to that in the pure ZnO. The SA emission in the pure ZnO is due to the radiative recombination of electrons from a level close to the conduction band edge and deeply trapped holes [14,15], whereas in the ZnO-LiYbO 2 hybrid phosphors, the SA emission is due to the radiative recombination of the electrons trapped by the Yb 3+ related defect energy levels that somewhat deeper into the forbidden band and the deeply trapped holes. …”

“…3(c). It is seen that there are two excitation bands for the SA emission in pure ZnO, a broad one peaked at 350 nm and a narrow one located at 390 nm, corresponding to the band-band excitation and excitation absorption of ZnO, respectively [15]. In the Li 2 O-doped ZnO, the narrow excitation band for the SA emission is remarkable decreased.…”

Up-conversion effect of Er- and Yb-doped ZnO thin films

“…As far as the annealed samples are concerned, the intensity of the emission at 375 nm, related to the excitonic band-to-band recombination (BBR) of ZnO (usually observed in the nanostructured material) [32], increased with the crystalline domain size, obtaining higher intensity for the sample deposited under O 2 atmosphere (see experimental results of XRD data). On the other hand, the broad visible emission (BVE) that these samples presented is due to the radiative recombination in deep-level defects such as oxygen vacancies and/or Zn atoms in interstitial position inside the ZnO lattice [33].…”

Activation of visible up-conversion luminescence in transparent and conducting ZnO:Er:Yb films by laser annealing

“…The UV emission peak for the air-and vacuum-annealed samples at 372−375 nm corresponds to the band-to-band excitonic recombination, and the broad band centered around 660 nm is attributed to deep intra-band gap energy states generated by defects within the ZnO matrix [17]. The shape and position of this visible band depend on the defect state populations.…”