Switching green to red emission in tridoped ZrO2:Yb3+–Er3+–Bi3+ nanocrystals

• Green–yellow broadband emission from Bi3+.
• Forward and backward energy transfer.
• Switch from green–yellow to red emission.
• Enhancement of the red band from Er3+ with Bi3+.

Tridoped ZrO2:Yb3+–Er3+–Bi3+ nanophosphor was synthesized by hydrothermal process and demonstrated the possibility of switching from a strong green–yellow broadband signal to red emission due to Bi3+ and Er3+ ion by changing excitation from 350 nm to 970 nm, respectively. The green–yellow band is associated to the transition 3P1 → 1S0 and was overlapped with the green band associated to the transition 2H11/2 + 4S3/2 → 4I15/2 of Er3+ as a result of the energy transfer from Bi3+ to Er3+. The strong red band is associated to 4F9/2 → 4I15/2 transition of Er3+ and enhanced by a factor of 3 as a result of the forward and backward energy transfer process (Er3+ → Bi3+ → Er3+). This sink effect where electrons can be stored temporally and released back can be useful to enhance the emitted signal of other lanthanides.