In situ 3D characterization of polymer microstructures: Electric field-induced autofluorescence confocal microscopy imaging and stimulated emission mechanisms

Achieving high-precision, in situ, three-dimensional (3D) characterization of microscale defects within material interiors and at interfaces through non-destructive methods has remained a persistent challenge. Herein, this study reports a novel phenomenon: electric fields induce autofluorescence in various intrinsically non-fluorescent polymers. This enables non-destructive, in situ 3D imaging of surface and internal microstructures and facilitates real-time characterization of dynamic evolution of internal electrical tree defects in polymers. Studies integrating quantitative fluorescence spectroscopy with molecular dynamics and quantum chemical calculation modeling demonstrate that the application of moderate-strength electric fields induce conformational changes in polymer molecules, thereby generating fluorescent emission. Under laser excitation, these molecules transition from the ground state to excited states, releasing fluorescent photons during spontaneous relaxation. By precisely capturing these photons and mapping their spatial relationship with radiation sites, the 3D structural characteristics of materials within the excited radiation regions can be reconstructed. This approach provides a robust, non-destructive tool for polymer microstructure imaging, representing a significant complement to established techniques such as scanning electron microscopy and X-ray computed tomography. Validated across glassy, rubbery, and semi-crystalline polymers, it exhibits broad applicability in polymer electronics, composite durability assessment, and failure mechanism investigations, thereby expanding the scope for advanced material characterization. • Novel electric field-induced autofluorescence in non-fluorescent polymers enables non-destructive microstructural imaging. • Simulations + experiments reveal the mechanism: electric fields bend polymer chains to trigger fluorescence. • Multi-spectroscopy confirms molecular conformational changes and links electric field parameters to autofluorescence intensity.