Synthesis of Eu3+-doped Gd2O3 in hollow nanoparticle structures by controlled chemical etching with poly(acrylic acid)

Abstract

Hollow Eu³⁺:Gd₂O₃ nanoparticles were easily prepared, without employing templates, from spherical crystalline Eu³⁺:Gd₂O₃ nanoparticles (NPs) via the simple etching process induced by the acidic moieties in the sodium salt solution of poly(acrylic acid), PAA-Na. Some portion of carboxylate units in PAA-Na could bind to the surface of Eu³⁺:Gd₂O₃ NPs and control the etching rate of Eu³⁺:Gd₂O₃ in acidic conditions such that the rate becomes comparable to the cation migration rate within the crystalline NPs, generating hollow Eu³⁺:Gd₂O₃ NPs. This controlled etching process in the presence of additional acid after surface treatment of Eu³⁺:Gd₂O₃ NPs with PAA-Na, varied the resulting structures from solid NPs to core-shell, core-void-shell, yolk-shell, and finally, hollow NPs. Based on the low r₂/r₁ value obtained from the relaxation times measured by time-domain nuclear magnetic resonance (TD-NMR) spectrometry and the good photoluminescent properties of hollow Eu³⁺:Gd₂O₃ NPs, accelerated development of multimodal nanoprobes and drug delivery vessels is expected, using the various morphological novelties of synthesized Eu-doped Gd₂O₃ nanoparticles.