Ultrathin Europium Oxide Nanoplatelets: “Hidden” Parameters and Controlled Synthesis, Unusual Crystal Structure, and Photoluminescence Properties

Abstract

A good understanding of the relationship between the atomic scale structure of ultrasmall europium oxide nanocrystals (NCs) and their photoluminescence properties is of major interest in the design and development of innovative europium-based nanophosphors. As a consequence, the preparation of reliable (controlled size and shape distributions) and structurally well characterized ultrasmall europium oxide NCs is an essential prerequisite to understand the size effects on their photoluminescence properties. First, we reveal that nonaqueous approaches used to synthesize ultrasmall europium oxide NCs are deeply affected by "hidden" parameters that are directly related to the preparation of the reactive mixture. Indeed, trace amounts of products of side reactions and byproducts, such as acetic acid and water, act as growth-directing agents. Second, the challenging problem related to the structural characterization of ultrasmall europium oxide NCs is addressed for the first time by coupling high-resolution transmission electron microscopy and X-ray atomic pair distribution function. The ultrasmall thickness of the as-prepared NCs apparently dictates the crystalline structure, which can no longer be described by the crystal phases of their bulk counterparts. The induced distortions due to the ultrasmall thickness as well as the bonding of the stabilizing organic ligand are strong enough to break down the symmetry and, hence, prevent the europium oxide NCs from accommodating the usual bulk crystal phase. Finally, the formation of such unusual polymorphs of europium oxide has a profound impact on the resulting crystal field, with direct effects on the photoluminescence properties.

Probing the Crystal Structure and Formation Mechanism of Lanthanide-Doped Upconverting Nanocrystals

“…It is important to note that the structural model obtained from the short-range order is characterized by deviations in terms of bond distances and bond angles (Figures 4a 3 to 4c 3 ) compared to the structural model derived from the long-range order. Such a phenomenon appears to be limited particularly when comparing with other systems such as ultra-small quantum dots (CdSe) 38 or ultrathin europium oxide nanoplatelets 43 . Nevertheless, it is still unclear whether such limited deviations can significantly modify the UC properties.…”

Ultrasmall Downconverting Nanoparticle for Enhanced Cerenkov Imaging

“…The uEuNPs were synthesized through thermal hydrolysis of europium(III) acetate in oleylamine and oleic acid under argon. 18 TEM images and DLS further verified the size of uEuNP to be uniformly ∼7 ± 2 nm (Figure 1b, d) with a slightly increased hydrodynamic diameter of ∼11 nm (Figure 1d). The lattice constant (d 222 = 3 Å) has been confirmed by HR-TEM (Figure 1c) and XRD spectrum (Figure S6) analyses.…”

Mechanical and Tribological Performances Enhanced by Self‐Assembled Structures

“…[ 24 ] Therefore, when an appropriate amount of oleylamine (OAm) is added to the NSt solution, oleic acid (OA) on the NSt edges may become involved in a nucleophilic attack on the carbonyl group owing to OAm molecules (Figure 2f). [ 26 ] This leads to facile exfoliation of OA on the NSt edges using ultrasound at 60 °C. [ 27 ] Infrared spectra and thermogravimetric (TGA) analysis curves show the process of the alteration of the surface state (Figure S10, Supporting Information).…”