Theoretical Study On Nonlinear Optical Properties Of Atom-doped Carbon Nanomolecules And Black Phosphorus Quantum Dots

Due to the wide application in the fields of optical data storage,transmission,dynamic image processing,and other laser equipment,nonlinear optical materials have become one of the most intriguing materials among advanced functional materials.Researchers have paid great efforts to find new NLO materials with high performance.In this work,（super）alkali metal-doped carbon nanomolecules and black phosphorous quantum dots systems are designed as new nonlinear optical molecules.The geometric structures,electrical properties,and hyperpolarizabilities of these systems are systematically studied by using the density functional theory（DFT）method.The main contributions are as follows:1.The nonlinear optical（NLO）properties of the BP-（B₃N₃）_nand Li@BP-（B₃N₃）_n（n=1–4）systems have been systematically investigated using the density functional theory（DFT）.When the carbon rings are replaced by B₃N₃units in the biphenylene,the new system exhibits a large static first hyperpolarizability（β₀）.And the position and the number of B₃N₃unit have an important effect on theβ₀value.Moreover,when one Li atom is adsorbed on the surface of B₃N₃-substituted BP,theβ₀values of these systems are further enhanced.The investigations also show that small transition energy is the decisive factor for their largeβ₀values.These studies may provide theoretical guidance for the design of new high-performance NLO materials based on BP flakes.2.A new class of graphyne superalkali complexes,OM₃⁺@（GYs）^–（M=Li,Na,K;GYs=GY,GDY,GTY）,have been designed and investigated by DFT method.These complexes with high stability can be regarded as novel superalkali salts of graphynes due to electron transfer from OM₃to GYs.These superalkali salts exhibit large first hyperpolarizabilities（β₀）,and the atomic number of alkali atom in superalkali and the pore size of graphyne have important influence onβ₀values.In addition,these superalkali salts of graphynes have deep-ultraviolet working region,thus they can be a new kind of high-performance deep-ultraviolet NLO molecules.3.Based on density functional theory（DFT）method,the geometric,electronic,and nonlinear optical properties of novel alkali and alkaline-earth metal atoms doped on the black phosphorus quantum dots（BPQDs）systems,M@BPQDs（M=Li,Na,K,Be,Mg,and Ca）,were systematically investigated.The metal atom M doping can remarkably enhance the second hyperpolarizability（γ₀）of BPQDs,due to electron transfer from M to BPQDs.M@BPQDs complexes possess large second hyperpolarizabilities（γ₀）in the range of0.81×10^-33–3.94×10^-33esu,where the alkali-doped complexes are much superior to the alkaline-earth doped complexes.The type of metal atom and the size effect of the BPQDs have an essential influence on the NLO response.Furthermore,doping heavier K atom on the large-sized BPQDs can obtain the largestγ₀value of 3.94×10^-33esu.These metal-doped complexes have the deep-ultraviolet（deep-UV）transparent region at wavelength≤200 nm,and hence are new deep-UV NLO molecules.