Rare earth-doped Y₂O₃ phosphors represent a class of fluorescent materials that have unique optical characteristics and properties, which are reflected in high color purity and long lifetime, with the possibility of covering the entire electromagnetic spectrum, along with low cytotoxicity. In this paper, we propose the synthesis of crystalline Nd³⁺-doped Y₂O₃ nanoparticles for the development of fluorescent labels with applicability in imaging. The nitrates of the two main cations, urea as a precipitating agent, and sea buckthorn (Hippophae rhamnoides) extract are the raw materials used in the precipitation procedure to obtain the oxide precursor. Thermal decomposition of the precursor occurs at 600°C in the presence of glycerin used as a combustion agent. By controlling the parameters, we oriented the process towards obtaining sufficiently small dimensions for efficient visualization of the distributions of target molecules in imaging, but no smaller than 10 nm to avoid the problem of cytotoxicity. SEM analysis shows well-defined particles with a spherical shape, smooth surface, no defects, and an average size of 50 nm. Analysis by X-ray diffraction, FTIR and EDX spectroscopy demonstrates the purity and high degree of crystallinity of the developed fluorescent labels and the possibility of using these types of materials in the field of biotechnology, as a result of meeting structural requirements. The study of the optical properties of doped phosphor shows red-shifted absorption spectra relative to Y₂O₃, and by excitation at 980 nm, multiple emission peaks in the NIR region were observed. The synthesis of NIR-emitting phosphors for biomedical applications is the main objective of this work, as they are less absorbed and scattered by tissue structures, and can achieve high penetration efficiency.

Acknowledgements: This work was supported by a grant of the Ministry of Research, Innovation and Digitization, CNCS-UEFISCDI, project number PN-IV-P2-2.1-TE-2023-0417, within PNCDI IV.