When Blinking Helps: Suppressed Biexciton Emission in Lead Halide Perovskite Quantum Dots

TL;DR

The paper reveals a novel STE-mediated blinking regime in Ni-doped CsPbBr3 PQDs where dark states exhibit improved single-photon purity due to selective suppression of biexciton formation. Using time-resolved TCSPC and state-resolved $g^{(2)}( au)$ measurements, the authors quantify how exciton and biexciton quantum yields decline along a linear FLID trajectory, with $g^{(2)}_0$ decreasing from about $0.16$–$0.19$ in bright states to as low as $0.12$ in dark states, driven by self-trapped excitons that quench biexciton pathways. A simple STE-based model and a two-photon excitation framework account for the observed suppression of biexciton emission, contrasting with conventional A/BC blinking where dark states worsen single-photon purity. These findings highlight lattice self-trapping as a tunable mechanism to engineer perovskite quantum emitters with intrinsically reduced multiphoton events and point toward design strategies for robust, high-purity room-temperature single-photon sources. Overall, the work expands the understanding of multiexciton dynamics in lead-halide perovskites and demonstrates a lattice-driven route to improved quantum-light performance in PQDs.

Abstract

Blinking and multiphoton emission in metal halide perovskite quantum dots (PQDs) limit their use as single-photon quantum emitters. Conventional models distinguish between trion-related A-type blinking and defect-assisted BC-type blinking, both expected to degrade single-photon purity in a dark state. Here, time-resolved spectroscopy on individual PQDs reveals a qualitatively different regime in which low emitting dark states exhibit higher single-photon purity than bright states. For those PQDs state-resolved $g^{(2)}(τ)$ analysis shows that the exciton photoluminescence quantum yield decreases by a factor of $\sim 8$, while the biexciton one is suppressed by a factor of $\sim 10$. This leads to a moderate improvement of single-photon purity with $g^{(2)}_0$ decreased from 0.155 to 0.120. In contrast, PQDs with fluorescence lifetime--intensity distribution patterns characteristic for A-type blinking, display the expected increase of $g^{(2)}_0$ in charged, trion-dominated states. To explain the observed improvement of single-photon purity of low-emitting dark states, we propose a self-trapped-exciton (STE) mechanism that selectively blocks biexciton formation by diverting hot excitons into long-lived, weakly emissive STE configurations. This STE-mediated blinking channel explains why certain low-emitting states improve, rather than degrade, single-photon purity and suggests a lattice-driven route to perovskite quantum emitters with intrinsically suppressed multiphoton events.

Figures (4)

• Figure 1: Properties of ensemble (a-c) and single (d-f) PQDs. (a) Representative TEM image of PQDs. (b) Normalized PL and absorption spectra of the PQDs ensemble in solution at room temperature. (c) Ensemble PL decay with a biexponential fit. (d) Emission spectrum of a representative single PQD at room temperature with Lorentzian fit. (e) Representative all-photon second-order correlation function $g^{(2)}(\tau)$. (f) All-photon $g^{(2)}_0$ as a function of average PL lifetime for 21 PQDs at room temperature. Grey cross represents mean values with standard deviations
• Figure 2: (a-e) PL parameters of different blinking states of individual PQD exhibiting single-photon blinking at room temperature. (a) FLID map with regions corresponding to bright (green circle), intermediate (yellow diamond), and dark (blue square) states. The red dashed line is a guide for the eye. (b) PL decay curves and biexponential fits of bright (green), intermediate (yellow), and dark (blue) states. (c, d, e) State-resolved normalized $g^{(2)}(\tau)$ for the (c) bright, (d) intermediate, and (e) dark states. (f) $g^{(2)}_0$ as a function of average lifetime for bright states (green circles), intermediate states (yellow diamonds), and dark states (blue squares) of 9 PQDs exhibiting single-photon blinking at room temperature.
• Figure 3: (a-f) PL parameters of different blinking states of individual PQD with a conventional A/BC blinking at room temperature. (a) FLID map with regions corresponding to bright (green circle), intermediate (yellow diamond), trion (red triangle) and dark (blue square) states. Red dashed lines are guides for an eye. (b) PL decay curves and biexponential fits of bright (green), intermediate (yellow), trion (red) and dark (blue) states. (c,d,e,f) State-resolved normalized $g^{(2)}(\tau)$ for the (c) bright, (d) intermediate, (e) trion and (f) dark states. (g) $g^{(2)}_0$ as a function of average lifetime for bright states (green circles), intermediate states (yellow diamonds), trion states (red triangles) and dark states (blue squares) of 12 PQDs exhibiting conventional A/BC blinking at room temperature.
• Figure 4: Schematic illustration of the STE-based model explaining suppressed two-photon emission.