Jia-Ye Tang

Color tunable Sr2SiO4:Eu2+ phosphors through the modification of crystal structure

Eu2+ doped Sr2SiO4 phosphors were prepared through a solid-state reaction method. The phase-composition and photoluminescence of the obtained phosphors were systematically studied in terms of calcination temperature, Eu and Ba doping. High calcination temperature promoted the phase transformation from α′–Sr2SiO4 (orthorhombic) to β–Sr2SiO4 (monoclinic), while the doping of Eu or Ba ions could stabilize α′–Sr2SiO4 phase due to their long bond length with oxygen. Small amount of Eu/Ba doping prefers to occupy Sr(I) sites in the crystal lattice of Sr2SiO4, acting as nucleation sites for both α′– and β–Sr2SiO4 phases. After nucleation, Eu2+ ions distribute equally in the two sites. Through structural modification, the Sr2SiO4:Eu2+ phosphors could be controlled to emit different colors in a wide range, from blue to yellow, making them good candidates for tuning the chromaticity in application.

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.

Enhancement of emission intensity of Sr2Si5N8:Eu2+ red-emitting phosphor by localized surface plasmon resonance of Ag nanoparticles with different morphologies

The emission intensity of commercial red Sr2Si5N8:Eu2+ phosphor, which is used in white light-emitting diodes (LEDs), was enhanced by coupling with the localized surface plasmon (LSP) oscillation of nano-structured (nano-spheres and nano-rods) Ag particles produced by a seed growth method. Coatings of Ag nanoparticles mixed with phosphors on an epoxy substrate were prepared. The experimental results showed that spectral overlap occurs between the LSP resonance band of Ag nanoparticles and the excitation and emission spectra of the phosphor. The emission intensity was enhanced (∼25%) by the synergistic effect of Ag nano-spheres and nano-rods mixed in optimal proportions. The produced phosphors improved the quantum efficiency of red phosphors, which is a very important feature in white LED systems.