Synthesis and luminescence properties of highly uniform spherical SiO2@SrSi2O2N2:Eu2+ core–shell structured phosphors

Abstract

The novel SiO₂@SrSi₂O₂N₂:Eu²⁺ core–shell structured oxynitride phosphors were synthesized by an interfacial reaction mechanism for the first time. First, SrCO₃:Eu³⁺ layers were deposited on monodispersed and spherical SiO₂ templates through the urea homogeneous precipitation methods to fabricate the SiO₂@SrCO₃:Eu³⁺ precursor particles; then the precursor particles were coated with H₃BO₃, which will be transformed to a protective h-BN film to prevent the agglomeration of the SiO₂ templates at high temperature; at last, the SiO₂@SrSi₂O₂N₂:Eu²⁺ core–shell structured phosphors were synthesized through a gas reduction and nitridation method at 1350 °C under a NH₃ gas flow. A uniform dense shell composed of nano-sized (∼20 nm) SrSi₂O₂N₂:Eu²⁺ grains tightly adhered to the surface of the SiO₂ cores. X-Ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FE-SEM), high resolution transition electron microscopy (HR-TEM) as well as photoluminescence (PL) spectra were used to characterize the samples. The results indicate that the obtained submicron SiO₂@SrSi₂O₂N₂:Eu²⁺ phosphors consist of the outer h-BN film, the middle SrSi₂O₂N₂:Eu²⁺ shell, and amorphous SiO₂ cores and exhibit narrow particle size distribution, perfectly spherical morphology and non-aggregation. Under the excitation of UV and blue light, the phosphors show strong green emission due to the 4f⁶5d–4f⁷ transition of Eu²⁺. This study opens new possibilities to facilely synthesize highly stable spherical (oxo)nitridosilicate phosphors with monodispersity and improved luminescence properties for display and lighting devices.