Determination of the microstructure of Eu-treated ZnO nanowires by x-ray absorption

Abstract

X-ray absorption near-edge structure ͑XANES͒, extended x-ray absorption fine structures ͑EXAFS͒, and photoluminescence measurements were used to elucidate the microstructural and photoluminescence properties of ZnO nanowires ͑ZnO-NWs͒ that had been treated with Eu by thermal diffusion. The O K-and Eu L 3-edge XANES and EXAFS spectra at the Zn K-and Eu L 3-edge verified the formation of Eu 2 O 3-like layer on the surface of ZnO-NWs. X-ray diffraction, XANES and EXAFS measurements consistently suggest the lack of substitutional doping of Eu ions at the Zn ion sites in the interior of ZnO-NWs. The clear sharp and intense emission bands in the range 610-630 nm of Eu-treated ZnO-NWs originated from the intra-4f transition of Eu ions in the Eu 2 O 3-like surface layer.

Investigation of the Emission Mechanism in Milled SrAl2O4:Eu, Dy Using Optical and Synchrotron X-ray Spectroscopy

“…The O K-edge X-ray spectra for the as purchased and dry milled samples, in general, look similar, suggesting the local oxygen environment is not strongly affected with milling. The spectral features resemble those found in strontium oxide based materials and do not agree with published O K-edge SXANES data for aluminum oxide, europium oxide, or lanthanum oxide . Interestingly, however, we observe a shift in the pre-edge peak of ∼0.4 eV with milling.…”

Origin of magnetic properties in carbon implanted ZnO nanowires

“…2(a) , the angles θ between the surface normal and the direction of incident X-ray are selected to obtain the local atomic structure in particular regions, with θ = 80 0 and 0 0 , which are typically used for probing surface and bulk regions (upper insets), respectively. The Zn K -edge FT spectra include two main features at ~1.8 and 3.1 Å, corresponding to the NN Zn-O and Zn-Zn bond distances (without phase correction) in ZnO nanostructures 48 , 49 . The general line-shape and radial distribution of the FT spectra of the surface and bulk regions of ZnO-C:NW and ZnO-NW are very similar to each other, with no clear broadened or split features associated with the NN Zn-O and Zn-Zn bond distances in the FT spectra of ZnO-C:NW, relative to those in the FT spectra of ZnO-NW.…”

Correlation among photoluminescence and the electronic and atomic structures of Sr2SiO4:xEu3+ phosphors: X-ray absorption and emission studies

“…However, their presence or absence depends principally on the host lattice. 9 Nevertheless, in this study of the origin of the Eu 3+ luminescence of SSO:xEu 3+ phosphors, the emission features mostly correspond to transitions from the excited 5 D 0 level to the 7 F J levels in the Eu 4 f 6 configuration and are affected strongly by the CT band and/or the local electronic/atomic structures of the Eu 3+ ions in the formation of the Eu 3+ –O 2− associations and the host lattice. Principally, the PL is a three-step process: (1) absorption of a UV photon, (2) transfer of the excitation energy (or electrons) to the luminescent centers, and (3) radiative emission from the luminescent centers.…”

“…These materials, when excited by light of a suitable wavelength/energy, provide a high PL yield and favorable chromaticity owing to the intra-4 f –4 f parity-forbidden transitions of the Eu 3+ activators or the 4 f– 5 d transitions of the Eu 2+ rare-earth ions, whose intensity depends on the site symmetry and the nature of the host matrix 4 . Eu 3+ dopants typically exhibit orange-red ( 5 D 0 → 7 F J ), green ( 5 D 1 → 7 F 1 ) or blue ( 5 D 2 → 7 F 0 ) luminescence as a result of intra 4 f –4 f transitions 5 , 6 . Furthermore, the emission of the Eu 2+ dopant originates from the 4 f– 5 d transition, the color of which varies from ultraviolet (UV) to red, depending on the crystal symmetry and the effect of the crystal field on the excited 5 d states 7 , 8 .…”

“…Furthermore, the emission of the Eu 2+ dopant originates from the 4 f– 5 d transition, the color of which varies from ultraviolet (UV) to red, depending on the crystal symmetry and the effect of the crystal field on the excited 5 d states 7 , 8 . Notably, in Eu 3+ emission, the resonant excitation cross-section of 4 f –4 f transitions is normally small 1 , 6 , so emission occurs upon transition to the ground 7 F J state from 5 D J states, presumably involving the O 2− → Eu 3+ charge-transfer (CT) band 7 , 8 . The replacement of divalent ions in the host lattice with trivalent ions requires charge compensation to maintain electrical neutrality and plays a critical role in the excitation of Eu 3+ -activators in which nonradiative relaxation to 5 D J states is followed by radiative emission 9 , 10 .…”