Synthesis And Optical Properties Of Highly Luminescent Zero-dimensional Metal Halide Materials

In recent years,metal halide materials have gained considerable attention.There is huge potential for metal halide materials in the field of optoelectronic devices,such as solar cells,photodetectors and light-emitting diodes,due to their high luminescent quantum efficiency and good stability.Currently,most work focused on the synthesis,properties and device applications of three-dimensional metal halide materials.In contrast,the preparation and mechanism studies of luminescence in zero-dimensional metal halide materials still lag behind.In this thesis,two kinds of zero-dimensional metal halide materials,Cs4PbBr6 and(C9NH20)2SnBr4 are used to invesitigate the crystal growth process and further clarify their luminescence mechanism.Overall,our work can be summarized as following:First,we proposed a simple and scalable dissolution-recrystallization room-temperature self-assembly strategy,and successfully synthesized Cs4PbBr6/CsPbBr3 metal halide composites by using low-cost and low-toxicity reaction precursors,which owned nearly 100%photoluminescence quantum efficiency,good stability,and high synthesis yield(up to 71%).A series of experimental and theoretical characterizations(e.g.synchrotron X-ray technique)illustrated that high-efficiency luminescence originated from a small amount of CsPbBr3 nanocrystals wrapped by zero-dimensional Cs4PbBr6,and this finding has resolved the long-standing controversy over the mechanism of Cs4PbBr6 green light emission.Additionally,a white light-emitting device with good blue-light excitation stability combining the green-emitting Cs4PbBr6/CsPbBr3 composites with red-emitting K2SiF6:Mn4+was constructed.Next,in order to study the influence of defects on the luminescence properties of zero-dimensional metal halides,we chose zero-dimensional(C9NH20)2SnBr4 as the research object,and found the luminescence phenomena of double-band emission and anti-thermal quenching.We prepared(C9NH20)2SnBr4 single crystal by controllable synthesis method and found that it has two emission bands at 490 nm and 690 nm,exhibiting anti-thermal quenching luminescence over a wide temperature range.On the basis of thorough experimental examinations(e.g.optical spectroscopy,variable-temperature synchrotron X-ray diffraction)and first-principle calculations,we proposed that both two emission bands originated from an asymmetric coordination geometry of Sn2+ with a 5s2 electronic configuration,and anomalous thermal quenching of luminescence was associated with trap states introduced by structural defects of(C9NH20)2SnBr4 crystal.