Controlled synthesis of luminescent Gd2O3:Eu3+ nanoparticles by alkali ion doping

Abstract

The influence of mono-positive alkali ions (Li⁺, Na⁺ and K⁺) on the growth processes, crystal structure and spectroscopic properties of Gd₂O₃ colloidal nanoparticles doped with Eu³⁺ ions was investigated. The size of an alkali dopant ionic radius, with respect to that of Gd³⁺ ions, and the relative concentrations of the alkali ions against that of Gd³⁺ were found to have a significant impact on the morphology of the obtained Gd₂O₃ nanoparticles which could be tuned from ~10 nm nanospheres, through ~40 nm nanotripods and nanotriangles, leading to over 50 nm sized, square-like shaped nanoparticles. The observed evolution of the Gd₂O₃ crystal structure upon alkali ion doping allowed finding of the maxima of the impurity ion concentration inside the Gd₂O₃ crystal lattice. The distortion of the crystal structure of Gd₂O₃ introduced by Li⁺, Na⁺ or K⁺ doping was also related to the ratio of electric to magnetic dipole transitions in Eu³⁺ ions, the shape of the ⁵D₀ → ⁷F₀ transition, and the ⁵D₀ energy level luminescence lifetime values. The obtained results show the possibility of using intentional impurities to tune the morphology of colloidal Gd₂O₃ NPs, and simultaneously of using the luminescence of Eu³⁺ ions for sensing the changes in local surroundings.