Coexistence phenomenon of Ce-Ce and Eu-Eu in Ce/Eu co-doped LiBaBO phosphor: luminescence and energy transfer.

Ce/Eu-doped LiBaBO (LBB) samples were prepared via conventional high temperature solid state reactions. The XRD patterns, crystal structures, luminescence properties, and decay times were investigated systematically. Ce ions exist in LBB:xCe that were synthesized in a reducing atmosphere and in an air atmosphere. However, we observed Eu ions in LBB:yEu in a reducing atmosphere and Eu ions in LBB:zEu in an air atmosphere. LBB:0.05Ce,yEu phosphors synthesized in a reducing atmosphere only possess Ce and Eu and exhibit a broad excitation band ranging from 350 to 425 nm. A reduction phenomenon of Eu → Eu and coexistence of Ce, Ce, Eu and Eu were observed when LBB:0.05Ce,wEu phosphors were synthesized in an air atmosphere. There are three processes in LBB:0.05Ce,wEu, i.e., energy transfers from Ce to Eu and from Eu to Eu, and metal-metal charge transfer (MMCT) between Ce and Eu. Moreover, the MMCT process is dominant in LBB:0.05Ce,wEu due to less efficient energy transfer from Ce to Eu. Moreover, the CIE coordinates of LBB:0.05Ce,wEu vary systematically from light blue (0.313, 0.129) to red (0.589, 0.315) for LBB:0.05Ce,wEu synthesized in air with the changes in Eu ion concentration. Thus, we can control the color by controlling the synthesis atmospheres.