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

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.