Synthesis And Fluorescence Adjustment Of Copper Nanoclusters Self-assembly Materials

Metal nanoclusters（MNCs）are usually composed of several to hundreds of metal atoms.The size of MNCs is close to the Fermi wavelength,which is usually less than2 nm.Within this size range,continuous energy levels are transformed into discrete energy levels.Due to the limitation of the molecular dimensions of metal atoms and the special discrete energy levels,MNCs have many unique characteristics,for example size-dependent fluorescence emission and strong light absorption.Such properties make MNCs of great application potetial in chemical sensors,biological imaging,and lighting display devices（LED）.Moreover,these properties also have size/structure-dependence properties,so MNCs with different sizes or structures can be constructed according to the demands of practical applications.For feeding the applications in future,enriching the types of MNCs and reducing the cost have become the main research direction.Compared with gold,silver and other precious metals,copper has large reserves and low price,which is more suitable for large-scale production.However,due to the complexity and heterogeneity of the structure of Cu NCs,it is very challenging to characterize the clear structure of Cu NCs at atomic level,which lead to poor fluorescence stability,narrow emission tuning range and low fluorescence intensity.To solve the problems above,the self-assembly strategy is used to make Cu NCs orderly and closely stack through weak interaction,which induced luminescence enhancement of Cu NCs.Also,X-ray crystal diffraction and mass spectrometry are used to reveal the fine structure of the surface of Cu NCs on the atomic scale,and explore the relationship between its structure and fluorescence properties.Based on the above discussion,this paper will further expand the related research by constructing new Cu NCs and exploring their fluorescence potetial.In the second chapter,solely by altering the pre-dissolving solvents for the copper source to construct homogeneous and heterogeneous phase of reaction conditions,we can engineer the Cu₁₂DT₈,Cu₁₅DT₉,and Cu₂₆DT₁₅NCs self-assemblies by renovating the coordination condition of Cu atoms.Further studies corroborate the difference in the composition and size of Cu NCs make the emission color show significant bathochromic-shift and the adjustable range from 490 nm to 650 nm.Besides,with the size of Cu NCs increases,the photoluminescence quantum yields（PLQYs）significantly improve to 15.8%.The enhancement of PLQYs is mainly attributed to the increased Cu（I）,facilitating the relaxation of excited electrons via a radiative pathway by Cu（I）-Cu（I）metallophilic interaction.Based on the obtained manifold color-emitting of fluorescent powders,the white light emitting diodes（WLED）by composition of pure Cu NCs self-assemblies are prepared with color temperature of5122 K.In the third chapter,the halogen effects are utilized to tune the emission of the Cu nanocluster self-assembly nanosheets（NSASs）.By varying cuprous halides as the Cu source,Cl,Br and I are respectively introduced into the structure motif of Cu NSASs.Theoretical calculations demonstrate that with the introduced halogens varying from Cl,Br to I,the S₀T₁gap is narrowed and the SOC is enhanced in the Cu NCs,thus generating cyan,yellow and red emissive Cu NSASs.Simply mixing different types of cuprous halides results in Cu nanocluster co-assembly nanosheets（NCASs）.The emission color of the Cu NCASs can be successively tuned and white emission can be directly obtained.The Cu NSASs are further employed as down-conversion phosphors for fabricating monochromic LEDs and white light emitting diodes WLEDs.These WLEDs exhibit high color rendering index（CRI）over 80 and controllable color temperature from 4313 to 6559 K.In the fourth chapter,we selected three Cu NCs with three primary colors emission and composited with PVA and obtained composite films with bright emission.The Cu NCs/PVA composite films not only inherit the emissive property of the Cu NCs,but also possess the merits of high transparency,flexibility,stability and self-healing ability from PVA.As a proof of concept,the Cu NCs/PVA composite films are further employed as down-converters to build remotetype monochromic and white LEDs,which exhibit a maximum color rendering index（CRI）of 86 and correlated color temperature（CCT）ranging from 5582 to 9490 K.