Engineering Polarons for Circumventing Energy Gap Law: Nd-doped CdTe Quantum Dots With High-efficiency Emission at
Qin Xu1, Yijie Hou1, Shuaiqi Li1
1State Key Laboratory of Digital Medical Engineering, Key Laboratory of Biomedical Engineering of Hainan Province, School of Biomedical Engineering, Hainan University, Sanya, China.
Abstract:
Despite widespread attention in near-infrared IIb/c (NIR-IIb/c, 1500-2000 nm) fluorescence for deep-tissue bioimaging, the development of NIR-IIb/c emissive materials with high photoluminescence quantum yield (PLQY) remains hindered by the energy gap law (EG law). Herein, we propose a polaron engineering strategy to circumvent the EG law via accelerating the radiative recombination rate by 150-fold through increased charge localization. By incorporating Nd3+ into CdTe quantum dot lattice, we achieved broadband NIR-IIb/c emission peak at 1730 nm, with PLQY of 11.34 ± 0.79% in aqueous solution and a Stokes shift exceeding 900 nm. We demonstrate Nd3+ substitution introduces beneficial defects that perturb electronic structure and local symmetry. Upon 808 nm excitation, these defects trap photoexcited carriers, inducing lattice distortions and strong electron-phonon coupling, which leads to the formation of polarons with high NIR-II emission efficiency. The resulting QDs enable clinical-grade NIR-II imaging via dual modes, including low-power (10 mW cm- 2) real-time deep-tissue imaging and white-light-activatable fluorescence-guided surgery navigation. This study provides a promising approach to bypass the EG law, offering a pathway toward highly emissive emitters in the NIR regime.
