Mechanically steered photon upconversion and circularly polarized luminescence in stretchable photonic crystal films

Photon-upconverted circularly polarized luminescence (UC-CPL) based on triplet-triplet annihilation (TTA) holds considerable promise for innovative applications. However, existing strategies encounter difficulties in concurrently achieving tunable TTA photon upconversion (TTA-UC) performance and a high luminescence dissymmetry factor (glum) in the solid state. In this study, we design and fabricate flexible and stable upconverted stretchable photonic crystal (SPC) films. These films demonstrate dynamically tunable TTA-UC intensity and UC-CPL in response to mechanical stretching. Notably, while the TTA-UC intensity initially diminishes upon stretching the upconverted SPC film, it subsequently exhibits significant enhancement when the photonic bandgap edge aligns with the TTA-UC emission wavelength. Furthermore, stretching the upconverted SPC film can invert the circular polarization direction of the UC-CPL, with the glum value varying from +0.50 to -0.60. Consequently, these upconverted SPC films, characterized by their tunable structural color and adjustable UC-CPL, achieve visual flexible dynamic information display and encryption. This research offers promising perspectives for the development of advanced chiral UC-CPL materials and their potential applications in fields such as information encryption and flexible 3D displays.