Bulk Yttria as a Host for Lanthanides in Biomedical Applications: Influence of Concentration Gradients on Structural, Mechanical, Optical, and in Vitro Imaging Behavior.

The biomedical application of yttria (Y 2 O 3 ) as a bulk material to host a series of rare earth elements (RE 3+ ) has been explored in the current investigation. Dy 3+ , Gd 3+ , Tb 3+ , Yb 3+ , Eu 3+ , and Nd 3+ were chosen for this purpose, and their corresponding concentrations in Y 2 O 3 have been varied to obtain five different combinations. The results ascertain the potential of Y 2 O 3 to host different RE 3+ to retain a discrete cubic yttria ( c -Y 2 O 3 ) devoid of significant structural distortion until 1400 °C. Depending upon the size of RE 3+ , either a contracted or expanded cubic Y 2 O 3 unit cell has been determined from the XRD and Raman analyses. Other than the typical vibrational modes of c -Y 2 O 3 , Raman spectra also unveiled characteristic emission features of RE 3+ that were dependent on the excitation laser used to record the spectra. The characteristic absorption and emission characteristics depending on the type of RE 3+ substitutions were determined from the optical measurements. Pore free microstructures determined from the morphological analysis are reflected in the enhanced mechanical behavior of RE 3+ doped Y 2 O 3 specimens. Dy 3+ and Yb 3+ substituted Y 2 O 3 unveiled computed tomography (CT) imaging features. Dy 3+ , Tb 3+ , and Nd 3+ dopant compositions delivered T 2 magnetic resonance imaging (MRI) contrast features, while the specimen comprising Gd 3+ revealed both T 1 and T 2 MRI characteristics.