A valence states approach for luminescence enhancement by low dopant concentration in Eu-doped ZnO nanoparticles

Abstract

The paper presents a simple, reproducible, controllable, and direct wet chemical synthesis method for Zn 1-x Eu x O nanoparticles. The full understanding of decomposition mechanism of the as-obtained oxalate precipitate was achieved based on the thermal analysis correlated with the evolved gas analysis and FTIR spectroscopy. The structure, morphology, and optical luminescent properties of the Zn 1-x Eu x O nanoparticles have been investigated by X-ray diffraction, Raman spectroscopy, HRTEM, SAED, XPS, and PL. The XRD studies reveal the formation of a hexagonal wurtzite-type structure. The presence of Eu 2 O 3 cubic structure can be observed up to 0.5 mol% Eu, suggesting that the solubility of the divalent or trivalent Eu into the ZnO lattice is limited. The formation of Eu 2 O 3 secondary phase at higher Eu concentration is sustained by Raman spectroscopy and XPS, as well. The TEM investigations of the Eu-doped ZnO samples illustrate the presence of aggregates with different shapes and dimensions formed by agglomerated spherical and polyhedral nanoparticles with sizes ranging from 20 to 120 nm. The effect of europium concentration on the structural and morphological characteristics, as well as on the luminescent properties was studied with special emphasis on the europium chemical states-Eu 2? and Eu 3? . The PL measurements sustain the presence of both divalent and trivalent europium ions into the ZnO host lattice and, at the same time, an increase of its defects density induced by the dopant presence.

Lanthanide (Eu, Tb, La)-Doped ZnO Nanoparticles Synthesized Using Whey as an Eco-Friendly Chelating Agent

“…coupling of Eu 3d 9 4f 6 final state configurations. The binding energies of each peak and the large spin-orbit splitting of 30.1 eV, are well in agreement with trivalent Eu previously observed in Eu-doped ZnO and with Eu bonded to oxygen in Eu2O3 [34][35][36]. Interestingly, there are two additional low-intensity peaks that appear at 10 eV lower binding energy below Eu 3+ 3d5/2 and 3d3/2 main groups, which can be assigned to divalent Eu 3d 9 4f 7 final state configurations, Eu 2+ 3d5/2 and 3d3/2 photoelectron lines.…”

Bright red luminescence emission of macroporous honeycomb-like Eu3+ ion-doped ZnO nanoparticles developed by gel-combustion technique

“…This reduction in crystallite size of doped ZnO was primarily due to the creation of Eu-O-Zn on the doped product surface, which inhibits the development of crystallite size [38]. This type of inhibitory effect has also been found with different RE ions for ZnO doped [38][39][40]. In addition, Scherer plots (SP) were built for the ZnO and Eu 3+ doped ZnO nanoparticles by placing (1/cosθ) on the x-axis and β hkl (rad) along the y-axis as shown in Fig.…”

Composition and Surface Optical Properties of GaSe:Eu Crystals before and after Heat Treatment

“…The low peak intensity of this line is probably determined by the low Eu 3+ concentration in the surface layer of the sample. In [26], the XPS spectrum of Eu 3+ ions in ZnO nanoparticles is analyzed, from which it can be clearly seen that the Eu 3+ 3d3/2 signal is ~2 times smaller compared to that of Eu 3+ 3d5/2. At the same time, the emission lines of carbon are well emphasized in the recorded XPS spectrum, which are probably caused by the sample adsorption of hydrocarbons from the atmosphere.…”

“…The ε-GaSe polytype is a typical representative of the point group D3h, displaying 12 vibration modes. The planar vibrations E ′ and E ′′ and non-planar vibrations A 1 ′ and A 2 ′′ are known to be active in Raman spectra [26,27].…”