Photoactivation of CdSe Quantum Nanoplatelet Luminescence
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ANOPHOTONICS
Photoactivation of CdSe Quantum Nanoplatelet Luminescence1 V. N. Smelova, *, V. G. Maslova, F. M. Safina, S. A. Cherevkova, A. V. Baranova, and A. V. Fedorova a
ITMO University, St. Petersburg, 197101 Russia * e-mail: [email protected]
Received January 18, 2020; revised January 18, 2020; accepted April 20, 2020
Abstract—The impact of irradiation with higher and lower quantum energy than that corresponding to the fundamental absorption band of CdSe nanoplatelets has been studied. We show that the irradiation wavelength and oxygen strongly influence the photoluminescence of nanoplatelets. We demonstrate also that irradiation of CdSe nanoplatelets dry layers leads to a reversible change in their photoluminescence quantum yield. Keywords: semiconductor nanoplatelet, excitonic luminescence, trap states, intermittent irradiation DOI: 10.1134/S0030400X20080342
INTRODUCTION Colloidal semiconductor nanoplatelets (NPs) are 2D quantum nanocrystals with a flat geometry [1]. NPs are characterized by a large lateral size that can be varied from tens to hundreds of nanometers, depending on a synthetic protocol, and a tiny, about several nanometers, thickness [1]. The latter provides strong confinement of carriers, i.e., an electron and a hole, in the NP thickness [2]. The properties of NPs significantly differ from those of Quantum Dots (QDs). Firstly, it is possible to control the NP thickness at the atomic level through the synthesis protocol. It ensures narrower exciton absorption and photoluminescence (PL) bands of NPs than QD bands. Secondly, their flat 2D geometry allows considering NPs as substrates for growing other nanostructures [3]. It is known that a prolonged QD irradiation with light absorbed by QDs can significantly change the PL quantum yield of QDs due to photochemical processes on their surface [4]. This phenomenon, known as “photoactivation,” was first observed in 2000 [5]. The QD photoactivation is a rather complex process because it includes charge transfer, i.e. electron or hole, from QD exciton to the QD surface trap-states and interaction of these charged states with QD environments, i.e., water molecules, oxygen and some radicals [6]. As a result, the photoactivation efficiency and its sign, i.e., whether this process leads to the increase or to the decrease of QD PL quantum yield, depend on the QD surface properties, QD synthetic protocol, QD environments, i.e., solutions, polymer 1 The 2nd International School-Conference for young researchers
“Smart Nanosystems for Life,” St. Petersburg, Russia, December 10–13, 2019.
or glass matrices, dry mono- or multilayers onto dielectric or conductive surfaces, etc. In this paper, we demonstrate that irradiation of CdSe NPs leads to NP photoactivation, and the photoactivation rate, efficiency, and sign depend on oxygen concentration and irradiation doze and wavelength. We also show for the first time that low-intensity light with a wavelength outside the NP absorption spectrum, for example, 640 nm, can be used for reversible efficient photoactivat
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