Luminescence optimization of Eu-doped LnAl3(BO3)4 (Ln=Y, Gd) red phosphor using spray pyrolysis

LnAl3(BO3)4:Eu3+ (Ln=Y, Gd) red phosphor particles were prepared by spray pyrolysis and the luminescent intensity under vacuum ultraviolet (VUV) excitation was investigated by changing Eu3+ content, Y/Gd molar ratio, and boron content. The concentration quenching for Eu3+ activator was observed at 5 at%. The highest luminescent intensity at 615 nm due to the 5D0→7F2 transitions of Eu3+ was achieved when the ratio of Gd to Y was 0.55. The R/O ratio (obtained by dividing the red emission intensity at 615 nm with the orange one at 592 nm), however, was not influenced by the G/Y ratio. Using excess boron, up to 135% of the stoichiometric quantity, improved the emission intensity of LnAl3(BO3)4:Eu3+ red phosphor. According to XRD analysis, the sample prepared using boron of a stoichiometric quantity had YBO3 phase as a minor phase. Such YBO3 phase progressively disappeared with an increase in the excess quantity of boron, which was responsible for the enhancement of emission intensity. In addition, the R/O ratio became larger and larger by increasing the excess content of boron due to a reduction in the symmetry of Y site. Consequently, both the emission intensity and the color coordinate of LnAl3(BO3)4:Eu3+ red phosphors were successfully optimized in terms of the Y/Gd ratio and the excess quantity of boron in spray pyrolysis.