Key Laboratory of Spectral Measurement and Analysis of Shanxi Province, College of Physics and Information Engineering, Shanxi Normal University, Linfen 041004, China
Fund Project:Project supported by the National Natural Science Foundation of China (Grant No. 11974229) and the Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi, China (Grant No. 2021L257)
Received Date:13 May 2021
Accepted Date:10 June 2021
Available Online:12 October 2021
Published Online:20 October 2021
Abstract:Owing to their excellent optical properties, perovskite quantum dots become ideal materials for conventional optoelectronic devices such as solar cells, light-emitting diodes, lasers, detectors, and non-classical quantum light sources such as single photon sources and entangled photon sources. The research on the photoluminescence blinking dynamics of single perovskite quantum dots can provide technical support for the preparation of nano-optoelectronic devices. In recent years, some achievements have been made based on the photoluminescence lifetime and photoluminescence intensity of single perovskite quantum dots. In this paper, the bright (on) state probability density and the dark (off) state probability density are extracted from photoluminescence intensity trajectories of single quantum dots and fitted by the (truncated) power-law function. It is found that the on-state probability density of single perovskite quantum dot under weak excitation condition can be fitted by a power-law function, which indicate that the photoluminescence blinking originates from the activation and deactivation of surface trap states. Under strong excitation condition, the on-state probability density of single perovskite quantum dot obeys exponential truncated power-law statistics, which indicate that the photoluminescence blinking is affected not only by the surface trap state, but also by the charging and discharging process. Keywords:perovskite/ single quantum dot/ photoluminescence blinking/ power law distribution
不同激发光功率激发下单个CsPbBr3钙钛矿量子点的积分时间为10 ms的荧光强度随时间变化轨迹如图2(a)中黑色曲线所示, 绿色曲线为背景荧光, 右侧为相应的强度分布柱状图. 其中$ \langle N\rangle $是每脉冲平均吸收光子数, 由量子点的吸收截面和激发光的功率密度决定[23]. 在激光激发下单量子点的荧光强度在亮态(bright state)和暗态(dark state)之间来回切换, 该现象被称为单量子点的荧光闪烁. 在弱光激发($ \langle N\rangle = 0.02 $)下, 量子点的荧光强度主要分布在亮态, 随着激发功率的提高, 量子点的荧光闪烁越来越剧烈, 且柱状图表示量子点荧光强度的分布向暗态集中. 图 2 (a)左侧为不同激发功率下单个CsPbBr3钙钛矿量子点的荧光强度随时间变化轨迹图, 右侧为相应的荧光强度分布图; (b)图(a)中各方框区域内荧光相应的衰减曲线(颜色一一对应)及相应的单指数拟合曲线(绿色), 灰色曲线为仪器响应函数; (c)绿色曲线为相应的二阶关联函数, 粉色曲线为门控二阶关联函数 Figure2. (a) Typical photoluminescence intensity time trajectories and corresponding intensity distributions of a single CsPbBr3 QD under different excitation powers; (b) photoluminescence decay curves obtained from the corresponding square in Figure (a); the green and gray curves are single exponential fitted curves and instrument response function, respectively; (c) corresponding second-order correlation function curves (green) and time-gated second-order correlation function curves (pink).
在量子点荧光闪烁特性研究中, 通过对荧光亮、暗态概率密度分布($ {P_{{\text{on}}/{\text{off}}}}\left( t \right) $)进行拟合也同样可以获得量子点充、放电过程以及量子点表面俘获态对量子点荧光闪烁特性的影响. 在荧光强度上设一个阈值将荧光轨迹分为两个态: 阈值以上为亮态(on-state), 阈值以下为暗态(off-state). 阈值强度取背景荧光强度的平均值加三倍方差[28-30]. 通过统计不同激发功率下单个CsPbBr3钙钛矿量子点的荧光在亮、暗态的持续时间可以得到概率密度分布, 如图3(a)—(c)所示. 弱光激发($ \langle N\rangle = 0.02 $)下单量子点的亮、暗态概率密度分布服从幂律统计: 图 3 (a)?(c)不同功率激发下单个CsPbBr3钙钛矿量子点的亮、暗态概率密度分布及相应的拟合曲线. On-state代表亮态, Off-state代表暗态; (d)不同功率激发下亮态到暗态以及暗态到亮态的转换速率 Figure3. (a)?(c) The probability density distributions and fitted curves of the bright (on) and dark (off) states of a single CsPbBr3 perovskite quantum dot under different power excitations; (d) conversion rate from bright state to dark state and dark state to bright state under different power excitations.
$ {P_i}\left( t \right) \propto {t^{ - {\alpha _i}}}_{}^{} {{,~~ (}} i = {\rm{on}} \;{\rm{or}} \;{\rm{off}}) . $
表1不同功率激发下单个CsPbBr3钙钛矿量子点的亮、暗态概率密度分布的拟合参数 Table1.Fitted parameters for the probability density distributions of the bright and dark states of a single CsPbBr3 perovskite quantum dot under different power excitations.