Broadband Downconversion of Ultraviolet Light to Near‐Infrared Emission in Bi 3+ –Yb 3+ ‐Codoped Y 2 O 3 Phosphors

The metal ion Bi 3+ has been shown to be an efficient broadband sensitizer for Yb 3+ ion in the Y 2 O 3 host lattice. Upon ultraviolet‐light excitation in the allowed 1 S 0 → 3 P 1 transition of Bi 3+ ions, the characteristic near infrared luminescence of Yb 3+ ions due to the 2 F 5/2 → 2 F 7/2 transition was observed as a result of energy transfer from Bi 3+ to Yb 3+ ions. It demonstrates that cooperative downconversion can be realized for Bi 3+ –Yb 3+ coupling. Yb 3+ ‐concentration‐dependent quantum efficiency was evaluated and the maximum efficiency reached 173.8%. These phosphors are promising for the enhancement of energy efficiency of crystalline Si solar cells via spectrum shifting.