A Comprehensive Study on the Upconversion Dynamics of Red-Emitting Er3+/Yb3+ Co-doped Gd3TaO7 Nanoparticles for Deep-Tissue Optical and Multimodal Imaging

Multimodal imaging is a very attractive emerging field, in which the main challenge is to achieve high contrast across different imaging modalities with a single probe. Gadolinium tantalates (Gd3TaO7) have been shown to be suitable candidates for this application, and the polyol method has been proven effective for obtaining RE3TaO7 with size and shape control. Er3+/Yb3+ co-doped Gd3TaO7 particles with a diameter of around 170 nm after annealing at 1000 °C for 2 h were observed by transmission electron microscopy. X-ray diffraction analysis confirmed the nanoparticles’ crystallization as a pure Gd3TaO7 defective-fluorite cubic structure. Upconversion luminescence with intense red emission bands was observed for the samples with different Er3+/Yb3+ concentrations under 980 nm excitation, which can be explored for deep tissue imaging. A comprehensive study of the Yb3+ → Er3+ energy transfer mechanisms within the host lattice was carried out using the Inokuti−Hirayama and Yokota−Tanimoto models. Moreover, in addition to the application of this material as a probe for optical imaging, their potential application as a multimodal imaging probe was investigated, and magnetic resonance and computed tomography studies were also conducted. These results show that these compounds exhibit interesting luminescent properties and are suitable for application as multimodal imaging probes.