Seminar


Department of Chemistry
Indian Institute of Technology Delhi

Blink, Wink, Flicker and Sparkle: Optical Instabilities of Single Perovskite Crystals



Prof. Arindam Chowdhury

Department of Chemistry, IIT Bombay, Mumbai

Email:arindam@chem.iitb.ac.in

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 [3]. 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 [4]. 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.

    References:
  1. Protasenko, V.V.; Hull, K. L.; Kuno, M. Adv. Mater. 2005, 17, 2942.
  2. Si, J.; Volkán-Kacsó, S.; Eltom, A.; Morozov, Y.; McDonald, M.P.; Kuno, M.; Jankó, B. Nano Lett. 2015, 15, 4317.
  3. Halder, A.; Chulliyil, R.; Subbiah, A.S.; Khan, T.; Chattoraj, S.; Chowdhury, A.; Sarkar, S.K. J. Phys. Chem. Lett. 2015, 6, 3483.
  4. Pathoor, N.; Halder, A.; Mukherjee, A.; Mahato, J.; Sarkar, S.K.; Chowdhury, A. Angew. Chem. Int. Ed. 2018, 57, 11603.

    All are cordially invited to attend.
    Convener (Seminar)