The latest issue of “Advances Materials” published a research article entitled with “Electric Field Regulated Energy Transfer in Chiral Liquid Crystal for Enhancing Upconverted Circularly Polarized Luminescence through Steering the Photonic Bandgap”, which is accomplished by a research team led by Prof. Pengfei Duan from the National Center for Nanoscience and Technology (NCNST), the Chinese Academy of Sciences. This work will not only provide a novel strategy to obtain the upconverted circularly polarized luminescence, but also show the first example for achieving high dissymmetry factor of UC-CPL by steering the photonic band gap.
In recent years, Prof. Duan’s group has been focusing on the study of circularly polarized luminescence (CPL) based on anti-Stokes wavelength shift, named upconverted circularly polarized luminescence (UC-CPL). Previous works from his group have shown that the first example of UC-CPL based on the mechanism of triplet-triplet annihilation-based photon upconversion, in which photon upconversion process can significantly amplify the circular polarization (J. Am. Chem. Soc. 2017, 139, 9783). Besides, lanthanide-doped upconversion nanoparticles (UCNPs) were found to emit upconverted circularly polarized light after encapsulated into chiral supramolecular organogels (ACS Nano 2019, 13, 2804). Recently, new system of UC-CPL based on the two-photon absorption mechnism has been demonstrated in chiral perovskite nanocrystals (J. Phys. Chem. Lett. 2019, 10, 3290). However, the obtained dissymmetry factor (glum) value of all the UC-CPL, which is used to evaluate the level of CPL, is very low. Therefore, pursuing large glum value is an emergent issue in UC-CPL research field.
In numerous chiroptical materials, chiral nematic liquid crystals (N*LC), as one kind of quasi one-dimensional (1D) photonic crystal, possess unique optical properties, enabling N*LC an excellent matrix for achieving circularly polarized luminescence with large glum value. Therefore, in this work, by incorporating UCNPs and CsPbBr3 perovskite nanocrystals (PKNCs) into the N*LC, enhanced UC-CPL based on radiative energy transfer (RET) process from UCNPs to CsPbBr3 PKNCs has been successfully implemented. CsPbBr3 PKNCs and UCNPs were used as the energy acceptor and donor, whose emission spectra were located at the center and edge of photonic band gap of N*LC, respectively. Through this ambidextrous design, the obtained UC-CPL of CsPbBr3 PKNCs showed the extremely large glum value and overcame the emission suppression from the photonic band gap. In addition, the UC-CPL of CsPbBr3 PKNCs and the process of RET could be switched off by the electric field and recovered by the mechanical force for multiple cycles, enabling an electric field-controlled UC-CPL switch (Adv. Mater. 2020, 32, 2000820).
Dr. Xuefeng Yang is the first author of this work, Prof. Pengfei Duan supervised the entire project as corresponding authors. This work was financially supported by the National Natural Science Foundation of China，Strategic Priority Research Program of Chinese Academy of Sciences （B） and the Ministry of Science and Technology of the People's Republic of China.