"Flash" Synthesis Of Thick Shells And Optical Property Of Core/shell Quantum Dots

Owing to luminescence tuning et al.,colloidal quantum dots(QDs)have good potential applications in detection,display and solid-state lighting et al.Aiming at the enhancements of photostability and photoluminescence(PL)of QDs,the "flash" synthesis of giant shells of QDs and the optical properties of Mn-doped type-? and type-? QDs were mainly studied in this work.The photostability of QDs can be enhanced by the thick-shell coating on QDs with a wide-bandgap inorganic material.The giant ZnS shell of?20 monolayers(MLs)can be rapidly prepared within 6 min,and the mechanism of "flash" synthesis is discussed.An optimized "flash" synthesis favors the narrower size distribution,the higher QY,and the breakthrough of the size limitation of QDs."Flash" synthesis of thick shells not only enhances QDs's photostability but also reduces the preparation cost,in favor of the industrialized application of QDs.For the combination strategy of one-pot growth doping and "flash" synthesis,the injection and growth temperature were reduced to 340 ? and 315 ? respectively to suppress the Mn2+ diffusion.For Mn-doped CdS/ZnS QDs(ZnS shell:?14 MLs),the PL quantum yield(QY)was increased from 25%to 36%.Further,inner-doped core/giant-shell QDs(ZnS shell:?18 MLs)with high QY(40%)were prepared by the optimized combination strategy of hot-injection nucleation doping and optimized "flash" synthesis.The QDs were encapsulated on a LED chip and showed high photostability for practical application during photostability testing.In type-? QDs,both the cooling of hot excitons and the radiative recombination of cold excitons are slow,and then excitons are easily trapped by traps,leading to a low PLQY of type-? QDs.Accordingly,Mn2+ ions were introduced as exciton couplers to enhance the QY of type-? PL from CdS/ZnSe/ZnS QDs(timescale of PL lifetime:?100 ns)from?35%to?60%.Transient absorption and PL spectra reveal that the enhancement of CT exciton emission is attributed to the couplings:1.the rapid energy transfer(ET)from hot excitons to Mn2+ ions(?220 ps),2.the strong bidirectional couplings between cold excitons and Mn2+4T1.