X-ray absorption spectroscopy and Eu3+-emission characteristics in GaAs/SnO2 heterostructure

Abstract

X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) data are used for investigating heterostructure samples of GaAs/SnO 2. XANES data are used for analyzing the local organization around Eu in the heterostructure formed by GaAs and Eu-doped SnO 2. The differences between the XANES data for these samples and data obtained for Eu-doped SnO 2 thin films, deposited on glass substrate, are assumed as responsible for the differences in the photoluminescence (PL) spectra concerning the Eu 3+ emission, since films deposited on glass substrate do not present Eu 3+ PL transitions until the annealing temperature is rather high. Eu 3+ emission is explored using two different excitation sources: 350 nm from a Kr + laser (above SnO 2 energy bandgap) and 488 nm from an Ar + laser (below SnO 2 bandgap energy). The existence of more organized regions around the Eu 3+ site observed for the heterostructure surface may be associated with the Eu 3+ luminescent emission. The main and secondary features in the XANES show that there are differences in the average local Eu environment for the SnO 2 :Eu isolated thin films and heterostructures, being more organized in the latter. Electrical characterization evidences that the portion of the resistivity reduction that corresponds to photo-ionized intrabandgap states is responsible for the persistent photoconductivity phenomenon in the heterostructures.

Strategy to Probe the Local Atomic Structure of Luminescent Rare Earth Complexes by X-ray Absorption Near-Edge Spectroscopy Simulation Using a Machine Learning-Based PyFitIt Approach

“…The normalized Eu L 3 -absorption edge (2p 3/2 initial state) XANES spectrum of the Eu 3+ complexes displays the prominent rising edge peak at ∼6982.8 eV, assigned to the 2 p 3/2 → 5d electronic transition of the Eu 3+ ion (see the Supporting Information, Figure S1a). The similar energy position of the white line peak for both the [C 4 mim]­[Eu­(dbm) 4 ] and [Eu­(tta) 3 (H 2 O) 2 ] complexes when compared to the hydrated Eu­(III) chloride starting material manifested the trivalent oxidation state of the Eu ion, as reported earlier in the literature . The total area under the white line peak of the Eu L 3 -edge spectrum for the Eu 3+ compounds is usually related to the number of empty 5d states .…”

“…The similar energy position of the white line peak for both the [C 4 mim]­[Eu­(dbm) 4 ] and [Eu­(tta) 3 (H 2 O) 2 ] complexes when compared to the hydrated Eu­(III) chloride starting material manifested the trivalent oxidation state of the Eu ion, as reported earlier in the literature . The total area under the white line peak of the Eu L 3 -edge spectrum for the Eu 3+ compounds is usually related to the number of empty 5d states . Thus, the comparable area suggests a similar electronic configuration and subsequent empty 5d levels of Eu for both the Eu 3+ complexes and EuCl 3 ·6H 2 O starting material (Supporting Information, Figure S1a).…”

“…36 The total area under the white line peak of the Eu L 3 -edge spectrum for the Eu 3+ compounds is usually related to the number of empty 5d states. 36 Thus, the comparable area suggests a similar electronic configuration and subsequent empty 5d levels of Eu for both the Eu 3+ complexes and EuCl 3 •6H 2 O starting material (Supporting Information, Figure S1a). The Gd L 3edge XANES spectra of the [Gd(tta) 3 (H 2 O) 2 ] and reference Gd 2 O 3 are similar to each other with white line peak at 7249 eV ( 2 p 3/2 → 5d transition), characteristic of the Gd in the +3 oxidation state.…”