Temporally stochastic and abrupt photoluminescence (PL) intermittency/blinking between bright and dark intensity levels has been long recognized as a characteristic feature of single quantum-emitters. Apart from single fluorescent molecules, proteins and conjugate polymers, a variety of quantum confined semiconductor quantum dots (QDs) and nanocrystals (NCs) do exhibit PL blinking, which is generally attributed to Auger assisted non-radiative (NR) recombination due to charging-discharging of NCs, or long-lived carrier trapping in surface defects, or trap mediated NR recombination. However, PL intermittency is rarely reported beyond nanoscale dimensions because of (i) average out of spatiotemporally uncorrelated intensity fluctuations in ensemble, and (ii) low surface-to-volume ratio decreases the number of surface defects and its significance for NR recombination in bulk crystal. While there are a few rare examples of PL intermittency in spatially extended (~ μm sized) yet nano-confined (1 or 2-D) systems [1-2], such blinking is spatiotemporally heterogeneous. Of late, the inorganic/organic metal halide perovskites (MHPs) have attracted enormous attention owing to their remarkable material and opto-electronic properties, and outstanding performances in photovoltaic and light-emitting applications. In recent years, extensive PL intermittency has been observed in various individual nano-/micro-crystals of MHPs [3-5]. Since, the NR recombination of photo-carriers may have adverse effect for device applications, there is always a general concern to understand the origin and nature of NR defects, and the involved blinking mechanisms.

Here, we present the highly unusual phenomenon, where entire individual bulk crystalline methyl ammonium lead bromide (MAPbBr₃) micro-rods/wires (MRs/MWs), with no dimensional confinement, undergo discrete and prominent intensity fluctuations between multiple levels on top of base intensity. Interestingly, for shorter MWs (~1-2 μm) blinking is found to be spatio-temporally synchronous over entire crystal. However, for longer wires, blinking becomes locally synchronous, where adjacent nano-domains exhibit correlated PL fluctuations at distinct time intervals. We explain this intriguing observation using a phenomenological model which involves the formation/annihilation of transient NR quenchers (traps) and long-range (> μm) excitation energy transfer to distal locations. The sphere of influence (SOI) of a quencher depends on both quenching efficiency (capture and recombination cross-section) of quencher, and energy migration length of photo-carriers. If the SOI of a quencher/s covers entire crystal, the highly mobile charge carriers recognize their presence and efficiently migrate to quenching sites, leading to correlated PL fluctuation over entire individual MWs. However, with simultaneous presence of multiple transient quenchers at distal locations with overlapping SOI results in locally synchronous PL intermittency with incorporation of additional intensity levels at overlapped region (Figure). This work will elaborate on likely causes and plausible mechanisms as well as implications of such long-range spatially correlated blinking dynamics in microcrystals.