Size-induced variations in bulk/surface structures and their impact on photoluminescence properties of GdVO4:Eu3+ nanoparticles

Abstract

This work explores the size-induced lattice modification and its relevance to photoluminescence properties of tetragonal zircon-type GdVO(4):Eu(3+) nanostructures. GdVO(4):Eu(3+) nanoparticles with crystallite sizes ranging from 14.4 to 24.7 nm were synthesized by a hydrothermal method using sodium citrate as a capping agent. Regardless of the reaction temperatures, all samples retained an ellipsoidal-like morphology. Nevertheless, as the crystallite size reduces, there appears a tensile strain and lattice distortion, which is accompanied by a lattice expansion and a decreased symmetry of structural units. These lattice modifications could be associated with the changes in the interior chemical bonding due to the interactions of surface defect dipoles that have imposed an increased negative pressure with crystallite size reduction. Furthermore, crystallite size reduction also led to a significant increase in the amounts of surface hydroxyl groups and citric species, as well as the concentration of the surface Eu(3+) ions. When Eu(3+) was taken as a structural probe, it was found that the asymmetric ratio (I(02)/I(01)) of Eu(3+) gradually declined to show a remarkable decrease in color chromaticity as crystallite size reduces, which could be interpreted as due to the change of local environments of Eu(3+) ions from the interior to the surface of the nanoparticles.

Structural, Spectroscopic, and Magnetic Properties of Eu3+-Doped GdVO4 Nanocrystals Synthesized by a Hydrothermal Method

“…32−35 On the basis of the VO 4 3− transition bands, the maximum at ∼305 nm is associated with the symmetryallowed 1 A 1 → 1 T 2 (t 1 → 2e) absorption and that at ∼336 nm with the symmetry-forbidden 1 A 1 → 1 T 1 (t 1 → 2e) absorption of the VO 4 3− unit. 14,36,37 This intense wide peak is an evidence of effectively activated emission of Eu 3+ ions through energy transfer between VO 4 3− groups and Eu 3+ ions preceded by CT between V 5+ and O 2− . 38,39 The energy migration in Ln 3+ -containing systems due to CT was carefully investigated by Faustino et al 40 The presented excitation spectra change with increasing concentration of Eu 3+ .…”

Study of the high pressure effect on nanoparticles GdVO4: Eu3+optical properties

“…Unanimous opinion about the reasons of the mentioned effect of high pressure on fluorescence lifetime does not exist. Some authors concluded that decreasing τ for the Eu 3+ fluorescence lifetime in nanoparticle may be due to the change of nanoparticle size under pressure (36). Others concluded that the decrease in the lifetime under pressure is caused by an increase in the electronic transition probabilities, which is a result of the enhanced crystal field strength around the Tb 3+ ions (27).…”

Multifunctional Eu3+- and Er3+/Yb3+-doped GdVO4 nanoparticles synthesized by reverse micelle method

“…The overall structure is composed of alternating edge-sharing GdO 8 dodecahedra and VO 4 tetrahedra, forming chains parallel to the c -axis24. The local symmetry (the first coordination sphere) around the lanthanide ions shows the highest effect on their luminescence properties.…”

“…Previous reports on the structure of GdVO 4 NPs (see for example Refs. 11 and 24) have demonstrated the particle-size-dependent lattice expansion or contraction. In the present study, no significant changes were observed in the lattice parameters between bulk particles and NPs.…”