Luminescent properties of Eu2+-activated (Sr1−z, Caz)(Al1−y, By)2O4 phosphors for UV LEDs

A series of (Sr1−z, Caz)(Al1−y, By)2O4:xEu2+ phosphors were synthesized by the sol-gel process and were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), and photoluminescence (PL) excitation and emission spectra. The experiment results revealed that the highest intensity of Sr(Al1.98, B0.02)O4:Eu2+ phosphor with pure monoclinic SrAl2O4 was achieved by annealing at the temperature of 1200 °C and the Eu2+ content of 8 mol%. However, when the post-treatment temperature for Sr(Al1.98, B0.02)O4: Eu2+ was over 1200 °C, the Sr4Al14O25 phase appeared as a minor phase, inducing small blue-shift in the emission peak (520-509 nm). Doping higher content of B3+ (y = 0.02-0.40) into SrAl2O4:Eu2+ at 1200 °C resulted in the transformation of phase from SrAl2O4 to Sr4Al14O25 as well as to SrB2Al2O7, which made the emission intensity enhance and the emission shift to a much shorter wavelength region (λp = 467 nm). It was found that, instead of purely using Sr atoms, Ca atoms with content of 20-40% could induce the crystal structure of (Sr1−z, Caz)(Al1−y, By)2O4:xEu2+, which led to SrAl2O4 from monoclinic to hexagonal phase. As a result, SrAl2O4 solid solution was obtained and then SrAl2O4:Eu2+ to emit 518 nm green light. At higher Ca content (z > 40%), a new CaAl2O4 solid solution was formed and a blue emission of CaAl2O4:Eu2+ was obtained.