Double emitting phosphor NaSr4(BO3)3:Ce3+, Tb3+ for near-UV light-emitting diodes

Blue and green double emitting phosphor, Ce3+ and Tb3+ co-doped NaSr4(BO3)3, was synthesized in a weak reducing atmosphere by a conventional high temperature solid-state reaction technique. For comparison, Ce3+ or Tb3+ singly doped NaSr4(BO3)3 was also prepared. The emission and excitation spectra of all samples have been investigated. NaSr4(BO3)3:Tb3+ excitation includes a strong absorption at about 240 nm and some weak sharp lines in near-ultraviolet (n-UV) spectral region. The excitation of Ce3+ and Tb3+ co-doped NaSr4(BO3)3 shows a strong broad band absorption in the n-UV region from the contribution of Ce3+, which makes it suitable for excitation by a n-UV LED chip. The emission of NaSr4(BO3)3:Ce3+,Tb3+ consists of a blue emission band from Ce3+ and a green emission from Tb3+ under the excitation of n-UV light. Energy transfer between Ce3+ and Tb3+ is also discussed, and the relative intensity of blue emission and green emission could be tuned by adjusting the concentration of Ce3+ and Tb3+. The phosphor NaSr4(BO3)3:Ce3+,Tb3+ could be considered as a double emission phosphor for n-UV excited white light-emitting diodes.