Collective substitutions of selective rare earths (Yb3+, Dy3+, Tb3+, Gd3+, Eu3+, Nd3+) in ZrO2: an exciting prospect for biomedical applications

Abstract

The study aims to understand the significance of collective rare earth (RE³⁺) substitutions in ZrO₂ structures for biomedical applications. The RE³⁺ ions namely Yb³⁺, Dy³⁺, Tb³⁺, Gd³⁺, Eu³⁺, and Nd³⁺ were selected and their concentrations were adjusted to obtain three different combinations. The influence of RE³⁺ on the crystal structure of ZrO₂ alongside the absorption, luminescence, mechanical, magnetic, computed tomography (CT), magnetic resonance imaging (MRI) properties was explored. The concomitant effect of the average ionic size and RE³⁺ concentration determines the crystallization behavior of ZrO₂ at elevated temperatures. The collective RE³⁺ substitutions exhibit both up-conversion and down-conversion emissions with their respective excitation at 793 and 350 nm. Nevertheless, increment in the concentration of RE³⁺ is found to be detrimental to the mechanical stability of ZrO₂. The collective characteristics of multiple RE³⁺ demonstrate the potential of the investigated system in multimodal imaging applications. The unique luminescence characteristics of Eu³⁺ and Tb³⁺ are promising for fluorescence imaging while the presence of Dy³⁺, Tb³⁺, Gd³⁺ and Nd³⁺ unveils a paramagnetic response required for MRI. In addition, Dy³⁺ and Yb³⁺ contribute to the high X-ray absorption coefficient values suitable for X-ray CT imaging.