Power-dependent photophysical pathways of upconversion in BaTiO3:Er3+.

Lanthanide incorporated perovskite is one of the most promising systems for efficient energy conversion or light-emitting materials in terms of upconversion (UC). Investigation of the photophysical mechanism of UC in the lanthanide-doped system is here continued. However, research on the ⁴I_13/2 energy state in Er³⁺ is rare and more is still needed. In our work, BaTiO₃:Er³⁺ (E-BT) was irradiated by a 1532 nm laser which is a resonance to the energy between ⁴I_13/2 and the ground ⁴I_15/2 state in Er³⁺. Bright 1532 nm-pumped UC was generated, and the UC color changed from red to yellow under increasing laser power. In addition, pump-power-dependent UC contained interesting clues about the photophysical pathway of UC. By analyzing photon numbers for each UC (green: ²H_11/2/⁴S_3/2 → ⁴I_15/2, red: ⁴F_9/2 → ⁴I_15/2, infrared: ⁴I_9/2 → ⁴I_15/2), we found that changes in photon number with pump-power increase contain three different phases (P). P1 is a red UC phase with a small cross-relaxation between Er³⁺ ions. However, in P2, there is a rapid decrease in the photon number with green UC generation, which is due to the enhancement of ⁴I_13/2-populating cross-relaxation. Finally, in P3, a saturated ⁴I_13/2 state causes little increase of photon number (compared with P2), with different mechanistic cross-relaxation enhancement. With these three different phases under 1532 nm pumping, photophysical mechanisms in E-BT are interpreted. [ABSTRACT FROM AUTHOR]