Pavel A. Frantsuzov

Colloidal semiconductor quantum dots are promising materials for numerous applications due to their tunable emission and high quantum yields. However, emission instability in the form of luminescence blinking remains a significant obstacle to their practical implementation. While recent advances in synthesis and surface engineering have demonstrated partial or complete blinking suppression, the quantitative assessment of the “quality” of this suppression remains challenging. Existing criteria typically rely on threshold-based classification into ON and OFF states, which becomes inherently ambiguous owing to the continuous distribution of emission intensities in single quantum dots. Here, we propose a threshold-free two-dimensional quantitative criterion based on the variance of the recombination rate and the relative quantum yield, both of which can be extracted from standard time-correlated single-photon counting measurements. We validate the criterion using simulated blinking trajectories covering all major blinking mechanisms and demonstrate that it cleanly separates them into distinct regions of the two-dimensional parameter space while providing a quantitative measure of the degree of suppression. This approach directly quantifies the temporal stability of emission without requiring arbitrary state definitions, thereby providing a robust metric for comparing different blinking suppression strategies and for guiding their further optimization.

Reaction-diffusion processes play an important role in a variety of physical, chemical, and biological systems. Conventionally, the kinetics of these processes are described by the law of mass action. However, there are various cases where these equations are insufficient. A fundamental challenge lies in accurately accounting for the microscopic correlations that inevitably arise in bimolecular reactions. While approaches to describe microscopic correlations in many specific cases exist, no general theory for multistage reactions has been established. In this article, we apply the quantum field theory approach to derive kinetic equations for general multistage reactive systems termed complete modified encounter theory (CMET). CMET can be formulated as a set of coupled partial differential equations that can be easily integrated numerically, thereby serving as a versatile tool for investigating reaction-diffusion processes. Across multiple case studies, we demonstrated that CMET reproduces the kinetics predicted by many other theories within their respective scopes of applicability.

Schematic of light scattering in a wIR-PHI experiment where cold and hot states exhibit distinct scattering contributions, producing a crossover in photothermal contrast for nanoparticles embedded in a Nujol dielectric medium.

We propose a single CsPbBr ₃ nanocrystal luminescence blinking model. The model successfully reproduces the two-dimensional distributions of the PL emission components, the photon distribution function and the power spectral density.

The phenomenon of sub-bandgap light induced luminescence switching for lead tribromide perovskite microcrystals with excess lead was recently discovered by Wan et al., Adv. Mater. 35, 2209851 (2023). It was found that the photoluminescence caused by the high energy excitation light is suppressed by the control light, the photon energy of which is less than the bandgap of the crystal, and is restored after switching off the control light. We propose an original model of this phenomenon, taking into account the spatially distributed kinetics of charge carrier recombination and the creation/annihilation of trap states induced by both light sources. The model successfully reproduces the main features of light induced luminescence switching.

We present a fundamentally new model of colloidal semiconductor quantum dot blinking. The blinking is caused by fluctuations of the non-radiative exciton relaxation rate, induced by variations of the electron–phonon coupling value.

The photoluminescence (PL) of metal halide perovskites can recover after light or current‐induced degradation. This self‐healing ability is tested by acting mechanically on MAPbI₃ polycrystalline microcrystals by an atomic force microscope tip (applying force, scratching, and cutting) while monitoring the PL. Although strain and crystal damage induce strong PL quenching, the initial balance between radiative and nonradiative processes in the microcrystals is restored within a few minutes. The stepwise quenching–recovery cycles induced by the mechanical action is interpreted as a modulation of the PL blinking behavior. This study proposes that the dynamic equilibrium between active and inactive states of the metastable nonradiative recombination centers causing blinking is perturbed by strain. Reversible stochastic transformation of several nonradiative centers per microcrystal under application/release of the local stress can lead to the observed PL quenching and recovery. Fitting the experimental PL trajectories by a phenomenological model based on viscoelasticity provides a characteristic time of strain relaxation in MAPbI₃ on the order of 10–100 s. The key role of metastable defect states in nonradiative losses and in the self‐healing properties of perovskites is suggested.

Metal halide perovskites are an important class of emerging semiconductors. Their charge carrier dynamics is poorly understood due to limited knowledge of defect physics and charge carrier recombination mechanisms. Nevertheless, classical ABC and Shockley-Read-Hall (SRH) models are ubiquitously applied to perovskites without considering their validity. Herein, an advanced technique mapping photoluminescence quantum yield (PLQY) as a function of both the excitation pulse energy and repetition frequency is developed and employed to examine the validity of these models. While ABC and SRH fail to explain the charge dynamics in a broad range of conditions, the addition of Auger recombination and trapping to the SRH model enables a quantitative fitting of PLQY maps and low-power PL decay kinetics, and extracting trap concentrations and efficacies. However, PL kinetics at high power are too fast and cannot be explained. The proposed PLQY mapping technique is ideal for a comprehensive testing of theories and applicable to any semiconductor.