Synthesis And Optical Properties Of All Inorganic Halide Perovskite For LEDs

All-inorganic CsPbX₃(X=Cl,Br,and I)perovskite materials have gained significant attention owing to their high photoluminescence quantum yield,narrow emission line width,defecttolerance,and wide range of band gaps tunable by control of both composition and morphology.The promise of CsPbX₃materials has been examined in the context of their applications in optoelectronic devices,such as light emitting diodes,asing,and photovoltaics.Due to the ability of high diffusion/migration of halogen ions in CsPbX₃,a new method for efficient and green anion exchange was developed,and complete tunable composition of CsPbX₃and emission covering the full visible spectral range with narrow band widths can be achieved.Most important of all,these intrinsic superior properties have yet to be fully realized in practical applications mainly due to the obstacles from the toxicity of lead and unsatisfactory stability.Hence,nontoxic and stable perovskite alternatives must be urgently developed.In this thesis,lead-free perovskite materials with high fluorescence properties were synthesized,and their optical properties and stability were improved by doping metal ions and heat-treatment.The details are as follows:(1)we report the shape and phase evolution of cesium lead halide nanocrystals,including the hexagonal Cs₄Pb Br₆ nanocrystals(NCs),perovskite Cs Pb Br₃ NCs,and tetragonal Cs Pb₂Br₅ crystallite by adjusting the Cs-oleate concentrations.When the Cs-oleate concentrations are gradually reduced,the absorption peak and the emission peak of the sample are blue shifted,and the fluorescence lifetime is gradually reduced,which are mainly caused by the change of phase state and the quantum size effect.(2)we propose one facile anion exchange method assisted by ultrasonication to tune the composition and optical properties of the Cs Pb Br₃ nanocrystals.Compared to most of the reported anion exchange methods,this anion-exchange scheme is very facile and environment-friendly.Most importantly,the reaction can be carried out under normal condition,instead of the inert and anhydrous conditions.By adjusting the reaction time or the Cs X aqueous solution,complete tunable composition of CsPbX₃NCs and emission covering the full visible spectral range with narrow band widths can be achieved.(3)we provide data on how visible emission of Cs₂SnCl₆:Bi and Cs₂SnCl₆:Sb lead-free perovskites phosphors was tubed by heat-treatment.The photoluminescence peaks Cs₂SnCl₆:Bi show obvious red shift from 455 to483nm by heat-treatment,and the PLQY holding upto 50.8%.For Cs₂SnCl₆:Sb are reported still as orange-red phosphors with photoluminescence peak at 630nm upon heat-treatment,and the PLQY increased from 19.8%to 41.6%.Because of the large decomposition enthalpy and low solubility of Cs₂SnCl₆ in water,our phosphors showed excellent very good thermal and chemical stability.Lastly,by incorporating Cs₂SnCl₆:Bi-300(cyan-emitting)and Cs₂SnCl₆:Sb-300(orange-red-emitting)in to commercial 365 nm light-emitting diodes(LEDs)chips,a warm white LED with correlated color temperature of 4888 K,chromaticity coordinates of(0.347,0.345)was obtained.(4)We prepared lead-free VA-doped Cs₂ZrCl₆ double pervoskites as blue-emitting phosphors via a simple co-precipitation method.Cs₂ZrCl₆:Bi³⁺exhibits emission of light in the blue region with high efficiency at 460 nm,with 105 nm being the Stokes shift and PLQY?36%for 355 nm light excitation.Cs₂ZrCl₆:Sb³⁺exhibits emission of light in the orange region with high efficiency at 605 nm for 325 nm light excitation.Blue LEDs are constructed by combining Cs₂ZrCl₆:Bi with commercial UV LED chips.