Er coordination in Y2O3 thin films studied by extended x-ray absorption fine structure

Abstract

Extended x-ray absorption fine structure (EXAFS) spectroscopy was employed to study the Er coordination in polycrystalline Y2O3 thin films, which was found to dictate their photoluminescence (PL) properties. Incorporation of Er with concentrations varying from 6to14at.% was achieved by radical-enhanced atomic layer deposition at 350°C. In all samples, Er was found to be in the optically active trivalent state, confirmed by their x-ray absorption near-edge spectroscopy spectra. Modeling of the EXAFS data revealed that the local structure of Er3+ is similar to that of Er3+ in Er2O3. Specifically, Er3+ is coordinated with six O at 2.24 and 2.32Å. Excellent fits to the EXAFS for samples with Er3+ concentration less than 8at.% were achieved when the second coordination shell was modeled as a mixture of Y3+ and Er3+, indicating a complete miscibility of Er3+ in the Y2O3 matrix under these experimental conditions. This behavior is attributed to the almost perfect ionic size match between Y3+ and Er3+, having identical valence state and coordination characteristics. For thin films with higher Er concentrations, the EXAFS analysis revealed an exsolution with Er2O3 domain. Since there is no indication of Er clustering, it is concluded that the PL quenching observed in samples with the Er doping level exceeding 8at.% is likely due to Er ion-ion interaction but not Er immiscibility in Y2O3. Specifically, an increase in the Er3+ concentration implied an increase in the average number of Er3+ in the second coordination shell, thus making ion-ion interaction possible. The critical interionic distance between two Er3+ was determined to be ∼4Å, thus setting an upper limit on the Er3+ concentration in Y2O3 at ∼6×1021cm−3, at least three orders of magnitude higher than the Er3+ solubility limit in the conventional SiO2 host (<1018cm−3).

Plasma-Assisted Atomic Layer Deposition: Basics, Opportunities, and Challenges

“…A classic example is the ALD of metal oxides from b-diketonate precursors, such as those with acac (acetylacetonate), [97][98][99][100] hfac (1,1,1,5,5,5-hexafluoroacetylacetonate), 101,161,162 and thd (2,2,6,6,-tetramethyl-3,5-heptanedionato) 102,104,[275][276][277][278][279] ligands. Such precursors require more reactive co-reactants as they show no or low reactivity with H 2 O (in essence, they do not readily undergo hydrolysis reactions).…”

Correlation between luminescent properties and local coordination environment for erbium dopant in yttrium oxide nanotubes

“…1,8 First, the selection of a favorable host material is critical. 1,9 In this work, Y 2 O 3 is selected as a favorable host material for erbium ion substitution due to the following reasons: ͑1͒ Er 2 O 3 and Y 2 O 3 have identical cubic bixbyite crystal structures with very similar lattice constants and Y 3+ and Er 3+ ions have nearly the same ionic radii; ͑2͒ Y 2 O 3 is a refractory oxide that has a high melting point ͑ϳ2400°C͒, a very high thermal conductivity ͑ Y 2 O 3 =27 W/ mK͒, chemical stability, optical isotropicity with a refractive index of 1.91, and low phonon energies ͑380 cm −1 ͒, 4 which translate to lower nonradiative transition rates and, thus, higher quantum efficiencies of their optical transitions. Second, the design of a desirable preparation procedure is crucial, as it determines the charge state of the RE ions and local coordination environments around the dopants.…”

“…This provides insight into the local coordination environments and the origins of the PL spectral features of these nanostructured samples, from the long-range order down to the local environment of the trivalent erbium cations. 9,11,[24][25][26] Although these types of experiments have been previously conducted on bulk, thin film, and nanoparticle systems of some RE ion doped oxide materials, only a few studies using synchrotronbased analysis of RE-doped NT oxides have been reported. 5,[12][13][14][15]…”

Concentration dependence of the Er3+ visible and infrared luminescence in Y2−xErxO3 thin films on Si

“…Such a compound could be yttrium oxide ͑Y 2 O 3 ͒, in fact, both Y 2 O 3 and Er 2 O 3 have the same bodycentered cubic ͑bcc͒ crystalline structure with a lattice parameter mismatch lower than 1%; 9,10 therefore, the Er atoms can be placed in the substitutional sites of Y ions. 11 In particular, both metal ions can occupy two different sixfold coordinated cationic sites, with a C 2 or a C 3i point group symmetry, having a population ratio of 3:1.…”