CsPbBrxI_(3-x)全无机钙钛矿量子点的组分及浓度对电子结构及荧光性质影响研究

Study on the Influence of Component and Concentration of CsPbBrxI_(3-x)All-inorganic Perovskite Quantum Dots on Electronic Structure and Fluorescence Properties

全无机铯-卤化铅钙钛矿材料因其优异的性能在光电领域具有广泛的应用前景.本工作通过第一性原理计算和稳态、瞬态荧光光谱实验研究了CsPbBr_(x)I_(3-x)(x=3,2,1,0)全无机钙钛矿量子点卤素组分和量子点浓度对其电子结构及荧光性质影响规律.通过对材料CsPbBr_(x)I_(3-x)进行能带结构和态密度的计算,发现这种钙钛矿的带隙类型都为直接带隙,带隙值随着I原子的不断取代,带隙变窄,表明了可通过增加I含量来实现量子点的能带调控.通过对Cs Pb B_(r3)和Cs Pb B_(r2)I全无机钙钛矿量子点进行稳态发光和皮秒时间分辨单光子计数实验,发现随着量子点浓度的增加,发射光谱红移,光致发光强度先增大后减小,荧光辐射寿命增加.这些现象主要是由于量子点的量子限制效应以及自吸收效应导致的.随着量子点的浓度增加,量子点因发生团聚效应而尺寸增大,导致发射光谱红移.当量子点浓度大到一定程度时,量子点的吸光度逐渐饱和,自吸收效应会使发射荧光部分被吸收,导致荧光发射强度先增大后减小.随着钙钛矿量子点浓度的增加,量子限制效应导致量子点团聚,尺寸增大,进而使其荧光辐射寿命增加.随着I含量的增加,量子点捕获态产生导致晶体结构的扭曲,因而荧光寿命变短.这些结果表明激子重组过程可通过调节浓度和卤素组分进行控制.

All-inorganic cesium lead halide perovskite materials have broad application prospects in the field of optoelec-tronics due to their excellent performance.The influences of component and concentration on the electronic structure and fluorescence properties of the CsPbBrxI_(3-x)(x=3,2,1,0)all-inorganic perovskite quantum dots using the first-principles cal-culations and steady-state and transient fluorescence spectroscopy experiments were investigated.The band structure and density of states of the perovskites CsPbBrxI_(3-x)are calculated to find that the bandgap types are all direct bandgaps and the bandgap becomes narrow with the continuously supplanting of I atoms.This indicates that increasing the I content can achieve the band gap regulation of quantum dots.The steady-state luminescence and picosecond time-correlated single pho-ton counting experiments are completed for CsPbB_(r3)and CsPbBr_(2I)all-inorganic perovskite quantum dots,it is found that with the increase of quantum dot concentration,the emission spectrum is red-shifted,the photoluminescence intensity first increases and then decreases,and the fluorescence radiation lifetime also increases.These phenomena are mainly caused by the quantum confinement effect and self-absorption effect of quantum dots.As the concentration of quantum dots increases,the size of quantum dots increases due to agglomeration effects,resulting in a red shift in the emission spectrum.When the concentration of quantum dots reaches a certain level,the absorbance of quantum dots gradually saturates,and the self-absorption effect will cause the emission of fluorescence to be absorbed,leading to an increase and then a decrease in fluorescence emission intensity.As the concentration of perovskite quantum dots increases,the quantum confinement effect leads to the size increase of quantum dots due to the aggregation effect,thereby increasing their fluorescence radiation lifetime.With increasing I content,the quantum dot trapping states lead to a distortion of the crystal structure,and thus the fluorescence lifetime becomes short.These results suggest that the exciton recombination process can be controlled by regulating concentration and halogen components.