Synthesis And Photoluminescence Properties Of Low-Dimensional Ternary Cu(?)-Based Halides Nanocrystals

Metal halide perovskites have become leading edge materials,for their unique optoelectronic properties,such as tunable band gap energy,short lifetime,high quantum efficiency,etc.,attracting the attention of scientists from different fields.Although impressive progress has been made so far,the poor stability of lead-halide perovskites and the toxicity of lead cannot match social development.Therefore,obtaining high-stability lead-free new perovskite luminescent materials is very important for future high-tech applications and has becoming a challenging frontier subject.Based on these,Cu(I)-based ternary metal halide perovskites gradually stepped into the sight of researchers.At present,they have been considered as one of the most promising systems to replace lead halide perovskites.Main objective of the current research still focused on developing controllable synthesis strategies,characterizing the structure and optical properties of this kind of materials,while the structure evaluation,structure–property relationships and emission tunability have not been fully exploited.In this paper,we chose the copper cesium iodide and the copper chloride as the research objects.The crystal-growth mechanism and model of structure evolution were revealed in our work.Besides,the relationship between structural parameters and photoluminescence properties are proposed.Main research contents are as follows:(1)Crystal growth and structure evaluation of CsCu₂I₃ nanocrystals(NCs):In this work,we investigated the growth and structural evolution of CsCu₂I₃ nanocrystals.At low temperature and in the presence of a high dosage of oleic acid(OA)and oleylamine(OAm),Cs₃Cu₂I₅ nanoparticles,rather than CsCu₂I₃ NCs,preferred to form in the hot-injection reaction system.Increasing the reaction temperature promoted the formation of CsCu₂I₃ nanorods.Phase-pure CsCu₂I₃ nanorods were steadily obtained at 180°C.Structural evolution from less copper-containing NCs to copper-rich ones in the low-temperature reaction condition is highly related to the coordination of copper ions with OAm.More importantly,accompanying the growth of nanorods and structural evolution from Cs₃Cu₂I₅ to CsCu₂I₃,the color of photoluminescence emission of NCs changed from blue to nearly white and to yellow.(2)Synthesis optimization and optical quality evaluation of Cs₃Cu₂Cl₅:In this work,we report a systematically optimized finds for the colloidal synthesis conditions of Cs₃Cu₂Cl₅ NCs.The Cs₃Cu₂Cl₅ NCs are modulated from nanoparticles to nanorods and to nanoplates by adjusting reaction temperature and reaction time.Cs₃Cu₂Cl₅nanorods give a wide emission at 510 nm,being caused by self-trapped exciton state with exciton binding energy of 137 me V and phonon–electron interaction of 25 me V as determined by temperature-dependent photoluminescence spectra.The photoluminescence quantum yield(PLQY)of the nanorods that were reacted at 150°C for 1200 s,an optimal reaction condition,reaches up to 80.19%.We also find for the first time that the optical quality of Cs₃Cu₂Cl₅ NCs is positively related to the full width at half maximum of main peak in X-ray diffraction pattern.