Recently, the team of Han Keli, a researcher of the reaction kinetics group of complex molecular systems at the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, has achieved broad-band white light emission by regulating the self-trapped excitons of non-lead perovskite colloidal nanocrystals, and effectively improved Luminous quantum yield.
Efficient and stable white light emission is of great significance for indoor lighting. The traditional white light emitting device has the disadvantages of easy discoloration and loss of efficiency (self-absorption), while the single-matrix white light emitting material can be avoided. Unlike band-side emission fluorescence generated by free carrier recombination, self-trapped exciton luminescence exhibits characteristics of large spectral bandwidth and large Stokes shift. Due to the "soft" lattice, the low-dimensional lead-based perovskite materials are prone to form trapped excitons and exhibit broad-band white light emission. However, lead is toxic and the luminous efficiency of low-dimensional lead-based perovskites is usually low. Recently, studies have reported that non-leaded double perovskite materials with trapped exciton luminescence, but colloidal nanocrystals with high efficiency and broad band white light emission rarely appear.
In recent years, the Hankli team has devoted itself to the study of carrier dynamics of non-lead perovskite nanocrystals, and for the first time realized the transition from non-lead double perovskite nanocrystals from indirect band gap to direct band gap in 2018 (J. Am. Chem. Soc.). To further study the effect of the bandgap type on self-trapped exciton luminescence, the team delved into two different bandgap types of non-lead perovskite nanocrystals Cs2AgBiCl6 (indirect band gap) and Cs2AgIn0.9Bi0.1Cl6 (direct band Gap) of trapped exciton dynamics. The results show that in the indirect bandgap nanocrystals, the recombination process of photon absorption and carrier is accompanied by a strong electron-phonon coupling effect, and self-trapped excitons recombine mainly in the form of non-radiative transitions. No fluorescence is emitted; in the direct bandgap perovskite, the electron-phonon coupling strength is relatively moderate, and the trapped excitons recombine mainly through radiation transitions, so the direct bandgap nanocrystals exhibit bright broad-band white light emission.
Based on the above mechanism, the team further synthesized K+/Ag+ and Li+/Ag+ alloy double perovskite colloidal nanocrystals with direct band gaps. Femtosecond transient absorption spectroscopy studies have found that K+/Ag+, Li+/Ag+ alloy double perovskite colloidal nanocrystals can further suppress the non-radiative transition recombination of trapped excitons, so the colloidal nanocrystals exhibit higher luminescence quantum Yield and wider emission spectrum. In addition, the team also used the colloidal nanocrystalline material to prepare simple LED devices with white light emission. This work deepens the understanding of the dynamics of the self-deficient exciton of non-lead perovskite, and has guiding significance for the design and synthesis of white light-emitting non-lead perovskite materials.
Related research was published in the "Science Bulletin". This work was supported by key projects of the National Natural Science Foundation of China, key national research and development plans, and scientific challenge plans.
Fluorescence diagram and color coordinate diagram of Cs2AgIn0.9Bi0.1Cl6, K+/Ag+, Li+/Ag+ alloy double perovskite nanocrystals
Electric Actuator,Mini Electric Valve,Electric Actuator Valve,Electric Rotary Actuator
WENZHOU FOREVER CLASSIC TECHNOLOGY CO.,LTD , https://www.fballvalve.com