Sol-gel-nitridation preparation and photoluminescence properties of Dy3+-doped M2Si5N8 (M=Ca, Sr, Ba) phosphors for white light emitting diodes

M2Si5N8:Dy3+(M=Ca, Sr, Ba) nitride phosphors with different Dy3+ ion concentrations were prepared via a novel sol-gel-nitridation method involving an annealing step at 1300 or 1400 °C. The X-ray diffraction patterns indicate that the structure of these phosphors is in good agreement with the standard M2Si5N8 crystal structure. The photoluminescence spectra recorded for the prepared phosphors exhibited an intense white emission consisting of a blue emission peak (485 nm) and a yellow emission peak (582 nm), which are attributed to the characteristic 4F9/2→6H15/2 and 4F9/2→6H13/2 transitions of the Dy3+ ions, respectively. When using a different alkaline earth metal, the structure of the resulting M2Si5N8 phosphors changed and the luminescence was also affected. The chromaticity coordinates of the prepared Sr2Si5N8:Dy3+, Ca2Si5N8:Dy3+, Ba2Si5N8:Dy3+ phosphors with blue and yellow emission peaks were (x=0.391, y=0.397), (x=0.448, y=0.433) and, (x=0.42, y=0.414), respectively, which are all close to the standard white light coordinates (0.33, 0.33). The lifetime values of the obtained Ca2Si5N8:Dy3+, Sr2Si5N8:Dy3+ and Ba2Si5N8:Dy3+ phosphors were determined to be 0.028, 0.0167 and 0.0113 ms, respectively.