Synthesis and Characterization of Eu2+/Nd3+ Activated CaSi2O5 Phosphor for Bioimaging Applications

Abstract

The advancement of non-invasive diagnostic tools has propelled the development of luminescent nanomaterials with enhanced imaging capabilities. In this study, Eu²⁺/Nd³⁺ codoped CaSi₂O₅ phosphors were synthesized via a conventional solid-state reaction route under a reducing environment to explore their potential for bioimaging applications. Calcium silicate, known for its intrinsic biocompatibility, served as the host matrix, whereas Eu²⁺ acted as the primary luminescent centre and Nd³⁺ was used as the near-infrared (NIR) sensitizer to support deep-tissue excitation. Structural analysis via X-ray diffraction (XRD) verified the formation of a triclinic crystal structure and the average crystallite size was validated through both Scherrer equation and Williamson–Hall analyses. Field emission gun scanning electron microscopy (FEG-SEM) images revealed flower-like microstructures with embedded fine white particles. Energy-dispersive X-ray spectroscopy (EDX) detected the existence of expected chemical components of the phosphor, whereas Fourier-transform infrared (FTIR) spectra provided evidence of successful dopant incorporation through characteristic vibrations corresponding to Ca–O, Si–O–Si, Eu–O and Nd–O bonds. Photoluminescence studies showed an excitation spectrum with distinct and intense absorption bands within the range of 700–1000 nm, attributed to the 4f–4f transitions of Nd³⁺ ions, and upon excitation at approximately 800 nm, the phosphor exhibited dual emission bands around 410 and 440 nm with optimal intensity corresponding to the characteristic 4f⁶5d¹ → 4f⁷ transitions of Eu²⁺. The afterglow decay analysis showed persistent luminescence exceeding 15 min, and CIE chromaticity analysis confirmed that the emission lies within the blue spectral range (x = 0.155, y = 0.059), indicating high potential for background-free bioimaging with high chromatic accuracy. These findings suggest that Eu²⁺/Nd³⁺ doped CaSi₂O₅ can be a promising luminescent material for advanced biomedical imaging applications.