Double emitting phosphor NaSr 4(BO 3) 3:Ce 3+, Tb 3+ for near-UV light-emitting diodes

Abstract

Blue and green double emitting phosphor, Ce 3+ and Tb 3+ co-doped NaSr 4(BO 3) 3, was synthesized in a weak reducing atmosphere by a conventional high temperature solid-state reaction technique. For comparison, Ce 3+ or Tb 3+ singly doped NaSr 4(BO 3) 3 was also prepared. The emission and excitation spectra of all samples have been investigated. NaSr 4(BO 3) 3:Tb 3+ excitation includes a strong absorption at about 240 nm and some weak sharp lines in near-ultraviolet (n-UV) spectral region. The excitation of Ce 3+ and Tb 3+ co-doped NaSr 4(BO 3) 3 shows a strong broad band absorption in the n-UV region from the contribution of Ce 3+, which makes it suitable for excitation by a n-UV LED chip. The emission of NaSr 4(BO 3) 3:Ce 3+,Tb 3+ consists of a blue emission band from Ce 3+ and a green emission from Tb 3+ under the excitation of n-UV light. Energy transfer between Ce 3+ and Tb 3+ is also discussed, and the relative intensity of blue emission and green emission could be tuned by adjusting the concentration of Ce 3+ and Tb 3+. The phosphor NaSr 4(BO 3) 3:Ce 3+,Tb 3+ could be considered as a double emission phosphor for n-UV excited white light-emitting diodes.