Gabriele Raino1 2 Michael Becker4 3 Roman Vaxenburg5 Georgian Nedelcu1 2 Maryna I. Bodnarchuk1 2 Pete Sercel6 M. J. Mehl7 J. Michopoulos8 S. Lambrakosh8 David Norris3 R. F. Mahrt4 Thilo Stöferle4 Alexander Efros8 Maksym Kovalenko1 2

1, Institute of Inorganic Chemistry, Zurich, , Switzerland
2, Laboratory for Thin Films and Photovoltaics, Dubendorf, , Switzerland
4, IBM Research – Zurich Research Laboratory, Rüschlikon, Zurich, Switzerland
3, Optical Materials Engineering Laboratory, Zurich, , Switzerland
5, George Mason University, Fairfax, Virginia, United States
6, T. J. Watson Laboratory of Applied Physics, Pasadena, California, United States
7, U.S. Naval Acadamy, Annapolis, Maryland, United States
8, Naval Research Laboratory, Washington, District of Columbia, United States

Besides conventional optoelectronic devices (LEDs and Laser), colloidal nanocrystals (NCs) are pursued as non-classical light sources (i.e. single photon emitters) that might be playing a pivotal role in future quantum technologies (quantum cryptography, quantum sensing, quantum communication). Due to strongly reduced charge trapping on surface states, perovskite NCs become attractive as alternative single photon emitters.
Fully inorganic cesium lead halide (CsPbX3, where X=Cl, Br, I) perovskite NCs are characterized by narrow emission lines, achieve ultrahigh photoluminescence quantum yields of up to 90% and are tunable over a wide energy range.1 Furthermore, they are interesting due to their facile solution processability and their potential in diverse optoelectronic devices. Nevertheless, the origin of their exceptional photophysical properties at the single quantum dot level still needs to be completely uncovered.
Here we show that single CsPb(Br/Cl)3 NCs exhibit stable, blinking-free emission at cryogenic temperatures.2 An in-depth investigation of the trion dynamics revealed the absence of non-radiative quenching processes, such as Auger recombination, even without any shell passivation. We examined the origin of the composition dependent ultrafast (sub-ns) radiative recombination dynamic, and assigned it to a giant oscillator transition. For CsPb(Br/Cl)3 nanocrystals the radiative lifetime is in the order of 200-250 ps, representing a significant enhancement compared to other colloidal II-VI NCs or organic molecules. Using polarization dependent high resolution spectroscopy, we further elucidated the complex nature of the exciton fine structure splitting revealing the unique character of bright triplet excitons.3
Due to their high oscillator strength, high quantum yield and wide range of composition and size tunability, CsPbX3 NCs are versatile quantum light sources and offer a clear pathway for integration into optical microcavities and for the generation of more complex quantum states of ligth (i.e. multiphoton entangled-states).


1) Protesescu, L. et al. Nanocrystals of Cesium Lead Halide Perovskites (CsPbX 3 , X = Cl, Br, and I): Novel Optoelectronic Materials Showing Bright Emission with Wide Color Gamut. Nano Lett. 15, 3692–3696 (2015).
2) Rainò, G. et al. Single Cesium Lead Halide Perovskite Nanocrystals at Low Temperature: Fast Single-Photon Emission, Reduced Blinking and Exciton Fine Structure. ACS Nano 10, 2485 (2016).
3) Becker, M. et al. Bright triplet excitons in lead halide perovskites. arXiv:1707.03071