Multiphoton excited singlet/triplet mixed self-trapped exciton emission.

Rui Zhou, Laizhi Sui, Xinbao Liu, Kaikai Liu, Dengyang Guo, Wenbo Zhao, Shiyu Song, Chaofan Lv, Shu Chen, Tianci Jiang, Zhe Cheng, Sheng Meng, ChongXin Shan

OAI: oai:www.repository.cam.ac.uk:1810/348537 • DOI: 10.17863/CAM.95968

Multiphoton excited luminescence is of paramount importance in the field of optical detection and biological photonics. Self-trapped exciton (STE) emission with self-absorption-free advantages provide a choice for multiphoton excited luminescence. Herein, multiphoton excited singlet/triplet mixed STE emission with a large full width at half-maximum (617 meV) and Stokes shift (1.29 eV) has been demonstrated in single-crystalline ZnO nanocrystals. Temperature dependent steady state, transient state and time-resolved electron spin resonance spectra demonstrate a mixture of singlet (63%) and triplet (37%) mixed STE emission, which contributes to a high photoluminescence quantum yield (60.5%). First-principles calculations suggest 48.34 meV energy per exciton stored by phonons in the distorted lattice of excited states, and 58 meV singlet-triplet splitting energy for the nanocrystals being consistent with the experimental measurements. The model clarifies long and controversial debates on ZnO emission in visible region, and the multiphoton excited singlet/triplet mixed STE emission is also observed.