Upconversion circularly polarized luminescence with dissymmetry factor up to 1.80 from flexible Perovskite-Liquid crystal membranes

Abstract

Upconversion circularly polarized luminescence (UC-CPL) which refers to the emission of circularly polarized light upon excitation with low-energy photons through photon upconverion process, has garnered significant attention due to its distinctive photonic properties. However, achieving high dissymmetry factors for UC-CPL through a simple thin-film design remains a challenge. Here, a flexible UC-CPL membrane device is reported, consisting of a composite film of upconversion nanoparticles (UCNPs) and perovskite nanocrystals (PNCs) integrated with a cholesteric liquid crystal (CLC) polymer film. The UCNPs and PNCs composite was synthesized via a one-step in-situ method, facilitating efficient nonradiative Förster resonance energy transfer (FRET) from UCNPs to PNCs, as evidenced by the shortened time-resolved fluorescence decay lifetime of the UCNPs. By designing the CLC film with a photonic bandgap that matches the emission peak of the PNCs, a UC-CPL with a dissymmetry factor of 1.8 was achieved. This is attributed to the circular polarization selection characteristics induced by the periodic helical structure of the CLC. The membrane device is fully solution-processable and exhibits ultra-flexibility as the emission intensity remains unchanged after repeated 300 bending cycles. Microscale pattern was inscribed on the membrane using femtosecond laser direct writing (FsLDW), and the pattern, with dual-mode CPL capability, exhibit distinct colors under different excitation wavelengths and reading modes. These findings represent the demonstration of perovskite based UC-CPL from a flexible membrane device with a high $g_{\mathit{lum}}$$g_{\mathit{lum}}$, providing valuable insights for practical applications for micro/nano-scale optical information encryption and anti-counterfeiting.