Influence of synthesis methods on the structural and luminescent properties of Ca2SiO4:Eu phosphors

Eu-doped Ca 2 SiO 4 phosphors have attracted considerable attention due to their potential applications in solid-state lighting, particularly in white light-emitting diodes (W-LED). In this work, Eu-doped Ca 2 SiO 4 phosphors were synthesized via conventional sol–gel and modified sol–gel combustion routes to investigate how different synthesis conditions influence the structural, morphological, compositional, textural, and optical properties of the material. Structural characterization by X-ray diffraction (XRD) revealed that the sol–gel-derived sample crystallizes predominantly in the β -Ca 2 SiO 4 phase, whereas the combustion-derived sample exhibits reduced crystallinity and features indicative of structural disorder. Electron microscopy analyses, including high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED), confirmed the predominance of the β phase while revealing reduced long-range order and nanocrystalline domains in the combustion-derived sample. Scanning electron microscopy (SEM) and N 2 adsorption–desorption measurements showed that the combustion-derived material presents a more coalesced and compact microstructure, forming dense nanocrystalline aggregates with a lower specific surface area compared to the sol–gel sample. Optical properties were investigated by UV–Vis diffuse reflectance spectroscopy, photoluminescence (PL), and X-ray excited optical luminescence (XEOL), revealing differences in band gap energies associated with variations in structural and electronic disorder induced by the synthesis routes. Urbach energy analysis indicated a significantly higher degree of band-tail disorder in the combustion-derived sample. X-ray absorption near-edge structure (XANES) spectroscopy confirmed the coexistence of Eu 2 + and Eu 3 + oxidation states in the sol–gel sample, while only Eu 3 + was detected in the modified combustion-derived material. Furthermore, XEOL mapping revealed radiative recombination associated with F-centers in the sol–gel sample, with specific regions exhibiting a higher concentration of F-centers relative to Eu-related luminescent centers. Overall, the results demonstrate that the synthesis route plays a key role in controlling the structural, morphological, and optical properties of Eu-doped Ca 2 SiO 4 phosphors.