Full length article Twenty-fold plasmon-induced enhancement of radiative emission rate in silicon nanocrystals embedded in silicon dioxide S Gardelis a,b,n , V. Gianneta a , A.G Nassiopoulou a a NCSR Demokritos INN, Terma Patriarchou Grigoriou, Aghia Paraskevi,15310 Athens, Greece b Solid State Physics Section, Physics Department, National and Kapodistrian University of Athens, Panepistimioupolis, Zografos, 15784 Athens, Greece article info Article history: Received 24 July 2015 Received in revised form 7 October 2015 Accepted 14 October 2015 Available online 10 November 2015 Keywords: Photoluminescence Plasmons Ag nanoparticles Silicon nanocrystals abstract We report on a 20-fold enhancement of the integrated photoluminescence (PL) emission of silicon nanocrystals, embedded in a matrix of silicon dioxide, induced by excited surface plasmons from silver nanoparticles, which are located in the vicinity of the silicon nanocrystals and separated from them by a silicon dioxide layer of a few nanometers. The electric field enhancement provided by the excited surface plasmons increases the absorption cross section and the emission rate of the nearby silicon nanocrystals, resulting in the observed enhancement of the photoluminescence, mainly attributed to a 20-fold enhancement in the emission rate of the silicon nanocrystals. The observed remarkable improvement of the PL emission makes silicon nanocrystals very useful material for photonic, sensor and solar cell applications. & 2015 Elsevier B.V. All rights reserved. 1. Introduction Light emission from silicon nanostructures has been studied vigorously since the observation of efficient room temperature visible photoluminescence from porous silicon in 1990 by Canham [1]. Similar photoluminescence was observed in silicon nano- crystals (SiNCs) embedded in a silicon dioxide matrix [2–5]. Effi- cient light emission at room temperature does not occur in bulk Si due to its indirect bandgap. It is observed only in silicon nanos- tructures with sizes less than the exciton Bohr radius of bulk Si, i.e. less than 5 nm [6] and is attributed to quantum confinement of the generated carriers within the nanostructures [1–5]. The spatial confinement of the electron and the hole within nanostructures smaller than the critical value of the exciton Bohr radius increases the oscillator strength for radiative recombination compared to bulk Si [7]. Further to quantum size effects, the surface chemistry of the Si nanostructure affects the energetics and dynamics of the emission. For example, hydrogen passivation favors band to band transitions, whereas passivation with silicon dioxide introduces energy states within the energy band gap of the nanostructures that are involved actively in the emission process, whereas surface dangling bonds quench the luminescence [8–10]. Today, lots of methods are available in order to fabricate silicon nanostructures with controllable sizes and thus emission of controllable energies [1–3,11,12]. Also, many applications in various scientific domains have been either proposed or realized including biology, medicine, due to the compatibility of Si with the leaving organisms, photo- nics, solar cells and optoelectronics [3,5,13,14]. It still remains though the need for even higher light emission efficiencies from silicon nanostructures, which would benefit their use in the aforementioned applications, for example in the case of using light emitting silicon nanocrystals as down-shifters for the improve- ment of conversion efficiencies of silicon-based solar cells [15,16]. One way towards this direction is light emission enhancement by the use of localized surface plasmons originating from metal nanoparticles mainly, silver and gold, which are deposited in close proximity to the emitting nanostructures [17–37]. Localized sur- face plasmons in metal nanoparticles can be excited by the electric field of a laser light of suitable energy. When this happens a peak in the absorption spectrum of the nanoparticles appears in a cer- tain range of energies. The energetics of the spectrum depends on the metal and the size of the metal nanoparticles [37,38]. Enhancement of the emission rate of an emitter can occur when metal nanoparticles are placed in the vicinity of the emitter, separated from it by a dielectric of suitable thickness, so as to assure an overlap between the absorption spectrum of the excited localized surface plasmons and the emission spectrum of the emitter [21,39]. Plasmonic enhancement of the emission rate has been established in several organic and inorganic emitters such as organic molecules and quantum dots, respectively [17–34,40,41]. However, little work has been done regarding plasmonic engi- neering of the emission rate in silicon nanocrystals [17–29]. Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jlumin Journal of Luminescence http://dx.doi.org/10.1016/j.jlumin.2015.10.029 0022-2313/& 2015 Elsevier B.V. All rights reserved. n Corresponding author at: Solid State Physics Section, Physics Department, National and Kapodistrian University of Athens, Panepistimioupolis, Zografos, 15784 Athens, Greece. E-mail address: sgardelis@phys.uoa.gr (S. Gardelis). Journal of Luminescence 170 (2016) 282–287