Interfacial Charge Flow Modulation of CaF 2 /CaAl 12 O 19 :Dy Heterojunctions for Enhanced Mechanoluminescence in Flexible Composites

Abstract Mechanoluminescence (ML) flexible composites show broad application prospects in stretchable optoelectronics and wearable devices. However, challenges such as low brightness, inadequate repeatability, and restricted self‐recoverability hinder their practical use. Aiming to these issues, this work demonstrates the effectiveness of the heterojunction strategy on the interfacial triboelectricity‐induced ML in flexible composites. Herein, the typical interfacial triboelectricity‐dependent ML material of CaF 2 :Dy is in situ grown on the trap‐controlled ML material of CaAl 12 O 19 :Dy (CA 6 :Dy) because of their high crystal lattice matching ability. Compared with the single‐phase materials, the CaF 2 /CA 6 :0.06Dy heterojunctions exhibit outstanding ML performance in the flexible polydimethylsiloxane matrix, which can achieve repeatable ML for over 10 000 times with a self‐recovery degree of ca. 91.60%. The trap‐controlled mechanism and interfacial triboelectrification‐induced electron bombardment model are both responsible for the ML of CaF 2 /CA 6 :0.06Dy heterojunctions. Theoretical calculation results suggest that the construction of heterojunction interfaces via F─Al─O and F─Ca─O bonds can effectively prompt the charge flow from CA 6 to CaF 2 . This endows CaF 2 /CA 6 :0.06Dy with enhanced interfacial triboelectricity and enriched trap structure, leading to improved ML properties. This work confirms that rational heterojunction design can overcome the limitations of single‐phase materials in flexible matrices, offering a robust platform for the development of high‐performance and flexible ML materials.