Hot Electron- and Spin-Flip-Assisted Upconversion Excitation in the La_0.7Sr_0.3MnO₃/BiFeO₃ Heterojunction

Strongly correlated electron materials, such as La0.7Sr0.3MnO3 (LSMO), have exhibited abundant physical properties due to the interaction between their multiple degrees of freedom including electron, spin, and lattice. In this work, we found that NIR pump-induced hot electrons in majority spin states of LSMO are transferred to minority spin states through spin–lattice relaxation-induced spin-flip. The transferred electrons de-excite with visible emission. This upconversion process is accompanied by the metal–insulator transition and prolonged carrier lifetime from subpicosecond to subnanosecond. In the BiFeO3 (BFO)/LSMO heterojunction, the spectral results have exhibited evidence of excited electrons transferring from LSMO to BFO, enabling excitation of BFO (band gap of 2.7 eV) by visible to NIR pump light (440 to 2400 nm). This finding exhibits perspectives for NIR light harvesting and energy conversion, as well as spin-dependent electron excitation and transfer in correlated electron materials and their heterojunctions.