Color tuning and white light emission from sol-gel SiO₂ nanoparticles doped with Sr²⁺

A series of silica (SiO₂) nanoparticles doped with different concentrations of Sr²⁺ ions were successfully synthesized using the sol-gel method. The structural, morphological and optical properties of the phosphors were characterized by X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), transmission electron microscopy (TEM), ultraviolet–visible (UV–vis) diffuse reflection and photoluminescence (PL) measurements. The XRD results showed that the amorphous SiO₂ changed to crystalline orthorhombic Sr₂SiO₄ with the increase in Sr²⁺ concentration. The SEM micrographs show irregular agglomerated particles whose size decreased with an increase in the Sr²⁺ concentration. The EDS measurements confirmed the presence and uniform distribution of Si, O and Sr. TEM results confirmed that the prepared powders consisted of agglomerated crystallites. The UV–vis spectra analysis showed a red shift with an increase in the concentration of Sr²⁺. The PL results showed a change in the emission spectrum with the addition of the Sr²⁺ ions. The emission was attributed to the defects within the SiO₂ backbone of O–Si–O network. The highest emission intensity was found for the sample doped with 0.4 mol% Sr²⁺, with apparent luminescence quenching at higher concentrations. The CIE coordinates indicated that the blue color from the host defects could be tuned by varying Sr²⁺ concentration.