Photoluminescence of Bi3+ in LiCaY5(BO3)6 and color-tunable emission through energy transfer to Eu3+/Tb3+

Abstract

Bi3+ has an outer shell lone pair electrons and the energy of 6p orbitals are also sensible to the coordination environment, therefore its typical wide band excitation and emission spectra are highly dependent on the host structure. The recently reported LiCaY5(BO3)6 has multiple sites suitable for cationic doping. In this work, Bi3+ singly doped phosphors and Bi3+/Eu3+ and Bi3+/Tb3+ co-doped phosphors were prepared by high temperature solid state reactions. Careful Rietveld refinements on powder X-ray diffraction suggest the site-preferential doping of Bi3+ into M3 site, which has an octahedral cavity. By 1 atom% doping, Bi3+ exhibits a broad emission band centered at 364 nm with an internal quantum efficiency of 39.8%. The energy transfer to Eu3+/Tb3+ are firmly proved by both the emission intensity change and the decay curves, which is likely through the dipole-dipole interactions. Color-tunable emissions from blue to red, or from blue to green have been realized and the combination with 275 nm LED chip gives the bright blue, red and green emission for LiCa(Y0.99Bi0.01)5(BO3)6, LiCa(Y0.69Bi0.01Eu0.3)5(BO3)6, and LiCa(Y0.69Bi0.01Tb0.3)5(BO3)6, respectively.