Coarse and fine-tuning of lasing transverse electromagnetic modes in coupled all-inorganic perovskite quantum dots
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of Natural Science, Ulsan National Institute of Science and Technologh, Ulsan 44919, Republic of Korea Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford, OX1 3PU, UK 3 Centre for Quantum Technologies, National University of Singapore, Science Drive 2, Singapore 117543, Singapore § Youngsin Park, Guanhua Ying, and Atanu Jana contributed equally to this work. 2
© The Author(s) 2020 Received: 20 May 2020 / Revised: 10 August 2020 / Accepted: 11 August 2020
ABSTRACT Inorganic perovskite lasers are of particular interest, with much recent work focusing on Fabry-Pérot cavity-forming nanowires. We demonstrate the direct observation of lasing from transverse electromagnetic (TEM) modes with a long coherence time ~ 9.5 ps in coupled CsPbBr3 quantum dots, which dispense with an external cavity resonator and show how the wavelength of the modes can be controlled via two independent tuning-mechanisms. Controlling the pump power allowed us to fine-tune the TEM mode structure to the emission wavelength, thus providing a degree of control over the properties of the lasing signal. The temperature-tuning provided an additional degree of control over the wavelength of the lasing peak, importantly, maintained a constant full width at half maximum (FWHM) over the entire tuning range without mode-hopping.
KEYWORDS perovskite quantum dots, coherent lasing, transverse electromagnetic mode, stimulated emission
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Introduction
All-inorganic lead halide perovskites such as alkali-metal caesium lead halides (CsPbX3, X = Cl, Br or I) are emerging as highly promising materials for optoelectronic devices, from solar cells to light emitting diodes, due to their higher stability and robustness compared to organic–inorganic lead halides [1–8]. Lasing has so far been demonstrated in CsPbBr3 nanowires (NWs) with Fabry-Pérot cavity modes bounded on the either end by the facets of single-crystal NWs [7–10] whose diameter needs to exceed ~180 nm to confine efficiently emission at a wavelength ~ 535 nm [7] and to increase the spectral coherence of laser devices. A key factor is the narrowness of the emission line measured at the full width at half maximum (FWHM). It is noteworthy that lasing from CsPbBr3 arises from self-assembled clusters of nanocrystals that encapsulate the quantum dots (QDs) without reliance on an external cavity resonator, unlike the confinement provided by their singlecrystal nanowire counterparts. The nanocrystals are distributed homogeneously with a spacing ~ 20–30 nm between each nanocrystal inside a self-assembled cluster characterized by a regular cuboidal geometry with facets ~ 1–2 m in diameter (Fig. 1(a)). The QDs were synthesized by solution-based processing (see the Electronic Supplementary Material (ESM) for Chemicals and Synthesis) and show a broad spectral linewidth of ~ 5 nm [11, 12]. Although an improved spectral linewidth of ~ 2 nm can be achieved by embedding colloidal quantum dots into silica spherical cavities, this approach is not
suitable for practical applications [11].
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