Force-Induced Luminescence Suppression in Colloidal Clusters Revealed by Optical Tweezers

Colloidal clusters often undergo aggregation, leading to luminescence suppression, which limits their potential as efficient luminescent materials. We employ noncontact optical tweezers, generated by autofocusing beams, to measure the intercluster forces of Cs₃Cu₂I₅ perovskite in n-hexane, investigating how these interactions influence luminescence intensity. Our results show that when the average intercluster distance exceeds 235 nm, both van der Waals attraction and electrostatic double-layer repulsion weaken, resulting in a small net force. This enhanced stability prevents aggregation, allowing a higher concentration of luminescent clusters and improving the photoluminescence intensity. However, when the intercluster distance drops below this critical threshold, van der Waals attraction dominates, leading to aggregation and significant photoluminescence suppression. By accurately measuring the intercluster forces, we determine the critical distance at which the force approaches zero, allowing the calculation of the shortest intercluster distance and highest concentration required for optimal luminescent performance. These findings offer essential theoretical insights into the design and fabrication of high-performance luminescent materials and provide a comprehensive explanation of the force-induced luminescence suppression mechanism.