Synthesis Of White Light Mn-Doped 2D Perovskite-related Nanoplatelets

Lead halide perovskite with high photoluminescence quantum yields(PL QY),extremely narrow emission bandwidths,and broad emission spectra tunability has been a research hotspot of monochromatic and white LEDs.Though simply mixing of blue,green,and red color emission nanocrystals(NCs)on a background chip can prepare white LEDs,the self-absorption,phase separation,and color instability are always serious problems for the multiple components of NCs color conversion layers.To avoid these problems,using single component NCs with white fluorescence as a single-color conversion layer becomes a solution.However,their practical applications have been hindered by the relative low PL QY.On this basis,this work mainly focuses on the synthesis of highly white luminescent single-component perovskite NCs.The main contents are as follows.Firstly,we synthesized Mn-doped 2-dimensional(2D)perovskite-related CsPb2ClxBr5-x nanoplatelets with a pure white emission from a single component.The highest PL QY is up to 49%,which is a new record for white-emitting nanocrystals with single component.PL dynamics reveals that unlike Mn-doped perovskite nanocubes with insufficient energy transfer efficiency,the current reported Mn-doped 2D perovskite-related CsPb2ClxBr5-x nanoplatelets show a 10 times higher energy transfer efficiency from perovskite to Mn impurities at the required emission wavelengths(about 450 nm for perovskite emission and 580 nm for Mn emission).As a result,the Mn/perovskite dual emission intensity ratio surprisingly elevates from less than 0.25 in case of Mn-doped nanocubes to 0.99 in the current Mn-doped CsPb2ClxBr5-x nanoplatelets,giving rise to a pure white light emission with Commission Internationale de l’Eclairage(CIE)color coordinates of(0.35,0.32).These highly luminescent nanoplatelets can be blended with polystyrene(PS)without changing the white light emission but dramatically improving perovskite stability.The perovskite-PS composites are available not only as a good solution processable coating material for assembling LED,but also as a superior conversion material for achieving white light LED with a single conversion layer.Secondly,we developed a novel one-pot method to accelerate the synthesis of Mn-doped CsPbClxBr3-x NCs by merit of sonochemical technique.The localized hot spots,as well as an excellent stirring action of ultrasonic preparation facilitate the substitution of Mn2+ and Pb2+ in perovskite lattice within 15 minutes.Compared to the conventional post-synthetic cation exchange approaches or high-temperature preparation,time and energy consumption for cation exchange of Pb have been decreased enormously.Besides,further reaction kinetics investigation reveals an apparent decrease of reaction order from original method(2.4)to our ultrasound-assisted method(1.0).This ultrasonic-assisted method opens a new route for synthesis and doping strategy of perovskite materials.