Xiufang Yang

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

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.

Optimization mechanism of CaSi2O2N2 : Eu2+ phosphor by La3+ ion doping

La3+(lanthanide 3+) ion doping may significantly improve the photoluminescence properties of CaSi2O2N2 : Eu2+, a potential yellow–green phosphor for ultraviolet or blue light-emitting diodes. The optimization mechanism was studied in detail by the case of La3+ doping. The La3+ ions could stabilize Ca2+ vacancies, inhibit the oxidization of Eu2+ to Eu3+, based on x-ray photoelectron spectroscopy, x-ray absorption near-edge structure measurements and first-principles calculations. Consequently, not only could the total number of activators be increased, but also the non-radiative transition probability between Eu2+ and Eu3+ could be reduced as a result of La3+ doping. It was also observed that the photoluminescence of CaSi2O2N2 : Eu2+ phosphors could be enhanced by the addition of many La3+ ions, but not Sm3+ and Yb3+ ions, which confirmed the mechanism.