Quantum cutting downconversion by cooperative energy transfer from Bi³⁺ to Yb³⁺ in Y₂O₃ phosphor

Bi³⁺ and Yb³⁺ codoped cubic Y₂O₃ phosphors are prepared by pechini sol—gel method. Strong near-infrared (NIR) emission around 980 nm from Yb^{3 +} (²F_{^{5 / 2}} → ²F_{^{7 / 2}}) is observed under ultraviolet light excitation. A broad excitation band ranging from 320 to 360 nm, owing to the 6s² → 6s6p transition of Bi^{3 +} ions, is recorded when the Yb^{3 +} emission is monitored, which suggests a very efficient energy transfer from Bi^{3 +} ions to Yb^{3 +} ions. The Yb^{3 +} concentration dependences of both the Bi^{3 +} and the Yb^{3 +} emissions are investigated. The decay curve of Bi^{3 +} emission under the excitation of 355 nm pulse laser is used to explore the Bi^{3 + →} Yb^{3 +} energy transfer process. Cooperative energy transfer (CET) is discussed as a possible mechanism for the near-infrared emission.