Cosubstitution of Lanthanides (Gd3+/Dy3+/Yb3+) in β-Ca3(PO4)2 for Upconversion Luminescence, CT/MRI Multimodal Imaging

Multifunctional Gd3+, Dy3+ and Yb3+ cosubstitutions in beta-Ca-3(PO4)(2) were achieved through a facile synthetic technique. Gd3+ and Dy3+ prefer to occupy the 7-fold coordinated Ca2+(1), 6- or 8-fold coordinated Ca2+(2), and 8-fold coordinated Ca2+(3) sites of the beta-Ca-3(PO4)(2) structure. The shortest Ca(5)-O bond length of to Ca2+(5) site with 6-fold co-ordination favors Yb3+ accommodation. The substitution limit of each dopant to attain beta-Ca-3(PO4)(2) solid solution is determined as, similar to 1.25 mol %. The combined substitutions displayed upconversion emission in blue, yellow and red regions on excitation at 980 nm via the energy transfer mechanism from Yb3+ to Dy3+. Yb3+ and Dy3+ combination induces a high X-ray absorption ability for computed tomography (CT). The materials also displayed paramagnetic behavior and exhibited high longitudinal (r(1) = 48.71 mM(-1) s(-1)) and transverse relaxivity (r(2) = 61.79 mM(-1) s(-1)) indicating their potential as T-1 and T-2 contrast agents in magnetic resonance imaging (MRI). The negligible toxicity of Gd3+/Dy3+/Yb3+ cosubstitutions in beta-Ca-3(PO4)(2) is also demonstrated. The overall results justify the potential of the developed material as possible contrast agent for T-1 and T-2 MRI/CT/upconversion luminescence.