A Strategy to enhance Eu(3+) emission from LiYF(4):Eu nanophosphors and green-to-orange multicolor tunable, transparent nanophosphor-polymer composites

LiYF(4):Eu nanophosphors with a single tetragonal phase are synthesized, and various strategies to enhance the Eu(3+) emission from the nanophosphors are investigated. The optimized Eu(3+) concentration is 35 mol%, and the red emission peaks due to the (5)D(0) →(7)F(J) (J = 1 and 2) transitions of Eu(3+) ions are further enhanced by energy transfer from a sensitizer pair of Ce(3+) and Tb(3+). The triple doping of Ce, Tb, and Eu into the LiYF(4) host more effectively enhances the Eu(3+) emission than the core/shell strategies of LiYF(4):Eu(35%)/LiYF(4):Ce(15%), Tb(15%) and LiYF(4):Ce(15%), Tb(15%)/LiYF(4):Eu(35%) architectures. Efficient energy transfer from Ce(3+) to Eu(3+) through Tb(3+) results in three times higher Eu(3+) emission intensity from LiYF(4):Ce(15%), Tb(15%), Eu(1%) nanophosphors compared with LiYF(4):Eu(35%), which contains the optimized Eu(3+) concentration. Owing to the energy transfer of Ce(3+) → Tb(3+) and Ce(3+) → Tb(3+) → Eu(3+), intense green and red emission peaks are observed from LiYF(4):Ce(13%), Tb(14%), Eu(1-5%) (LiYF(4):Ce, Tb, Eu) nanophosphors, and the intensity ratio of green to red emission is controlled by adjusting the Eu(3+) concentration. With increasing Eu(3+) concentration, the LiYF(4):Ce, Tb, Eu nanophosphors exhibit multicolor emission from green to orange. In addition, the successful incorporation of LiYF(4):Ce, Tb, Eu nanophosphors into polydimethylsiloxane (PDMS) facilitates the preparation of highly transparent nanophosphor-PDMS composites that present excellent multicolor tunability.