Structure and photoluminescence properties of Dy3+ doping in Sr-Si-O-N frameworks for highly efficient white light and optical information storage applications

A series of Dy3+ doped Sr-Si-O-N frameworks with single phase were successfully developed by a two-step synthetic method. Under excitation of NUV light, Dy3+ singly-doped SrSi2O2N2 (a typical Sr-Si-O-N framework) phosphors exhibited two emission peaks at 478 nm and 571 nm, corresponding to blue (F-4(9).2 -> H-6(15)-2) and yellow (F-4(9)-2 -> H-6(13).2) emissions of Dy3+ ions. Compared with the traditional solid state reaction, the two-step method facilitated the formation of SrSi2O2N2: Dy3+ phosphor with pure phase and greatly enhanced the photoluminescence emission intensity (similar to 4 times). The emission intensities of SrSi2O2N2: Dy3+ phosphors reached the maximum when x = 0.06 due to the concentration quenching, which was confirmed to be electric dipole-electric dipole interaction. The SrSi2O2N2: Dy3+ phosphors with an excellent thermal stability can be regarded as the potential single phase white-light phosphors when excited by NUV light. The optimal chromaticity coordinate of white light is (0.3347, 0.3966) for SrSi2O2N2: 0.06Dy(3+) phosphor. Interestingly, the single green emission band at 525 nm was observed and a unique thermo-stimulated luminescence property was demonstrated for Dy3+/Eu2+ co-doped SrSi2O2N2 phosphors. A specific photographic pattern (for example pentagon pattern) was obtained by covered the mask on the surface of SrSi2O2N2: Eu2+, Dy3+ pellets under excitation of UV light. After UV lights turn off, the pentagon patterns were reproduced by heating the SrSi2O2N2: Eu2+, Dy3+ pellets. It was validated from the decrease of PL emission intensity and decay time with the increasing Dy3+ content that Dy3+ ions were acted as the deep trap centers. Similar thermal-stimulated luminescence was also found for Eu2+ singly-doped SrSi2O2 N-2 phosphor due to the oxygen vacancy in host lattice. Furthermore, the mechanism of thermal-stimulated luminescence has been proposed and Dy3+/Eu2+ co-doped SrSi2O2N2 phosphors with deep traps are suitable to be the good candidates for optical information storage applications.