Power-dependent photophysical pathways of upconversion in BaTiO 3 :Er 3

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 4 I 13/2 energy state in Er 3+ is rare and more is still needed. In our work, BaTiO 3 :Er 3+ (E-BT) was irradiated by a 1532 nm laser which is a resonance to the energy between 4 I 13/2 and the ground 4 I 15/2 state in Er 3+ . 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: 2 H 11/2 / 4 S 3/2 → 4 I 15/2 , red: 4 F 9/2 → 4 I 15/2 , infrared: 4 I 9/2 → 4 I 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 Er 3+ ions. However, in P2, there is a rapid decrease in the photon number with green UC generation, which is due to the enhancement of 4 I 13/2 -populating cross-relaxation. Finally, in P3, a saturated 4 I 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.