Date: August 13th 2019 (Tuesday)
Time: 3:30 PM
Venue: Committee Room (MS710), Chemistry Department, 6th Floor
Abstract: Temporally random, fluorescence or photoluminescence (PL) intermittency between bright and dark intensity levels (often referred to as blinking) has been long recognized to be characteristic of single quantum-emitters. Apart from fluorescent molecules, proteins and conjugated polymers, a variety of quantum-confined semiconductor nanocrystals (such as quantum-dots) also exhibit blinking upon continuous photo-illumination. In contrast however, such PL instability is seldom reported for crystals beyond nanoscale dimensions primarily because (i) spatiotemporally uncorrelated intensity fluctuations average out over the ensemble, and (ii) contributions of surface-states in radiative-recombination processes become far less significant compared to that of the bulk material. Moreover, while there are a few rare examples of PL blinking in spatially extended (~µm) yet quantum-confined (1 or 2-D) systems [1-2], such phenomenon is spatiotemporally inhomogeneous. Recently, we showed that organo-metal (hybrid) halide microcrystals (MCs) without dimensional confinement, such as polycrystalline films of methylammonium (MA) lead iodide, can exhibit optical instability (blinking) within local nanodomains . Upon investigation of other variants of hybrid mixed halide perovskite films, we discovered a remarkable phenomenon where entire individual micron-sized MAPbBr3 disks undergo multi-level blinking . Intriguingly, such flickering or sparkling is found to be spatially-synchronous across each crystal, implying long-range (>µm) communication amongst carriers photogenerated at distal locations. Based on a phenomenological model which invokes transient non-radiative traps, I will discuss the possible mechanisms which may lead to such a bizarre phenomenon.