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Article Dans Une Revue Optics Letters Année : 2020

Enhanced spontaneous emission from two-photon-pumped quantum dots in a porous silicon microcavity

Résumé

(IN) Received XX Month XXXX; revised XX Month, XXXX; accepted XX Month XXXX; posted XX Month XXXX (Doc. ID XXXXX); published XX Month XXXX Photoluminescence (PL)-based sensing techniques have been significantly developed in practice due to their key advantages in terms of sensitivity and versatility of the approach. Recently, various nanostructured and hybrid materials have been used to improve the PL quantum yield and spectral resolution. The near-infrared (NIR) fluorescence excitation has attracted much attention because it offers deep tissue penetration and avoiding the autofluorescence of the biological samples. In our study, we have shown both spectral and temporal PL modifications under two-photon excitation of quantum dots (QDs) placed in one-dimensional porous silicon photonic crystal (PhC) microcavities. We have demonstrated an up to 4.3-fold Purcell enhancement of the radiative relaxation rate under two-photon excitation. The data show that the use of porous silicon PhC microcavities operating in the weak coupling regime permits the enhancement of the PL quantum yield of QDs under two-photon excitation, thus extending the limits of their biosensing applications in the NIR region of optical spectrum. © 2020 Optical Society of America Light-matter resonance interaction enables control over spontaneous photoluminescence (PL) emission properties of various luminophores, including organic dyes [1,2], rare-earth ions [3], 2D metal dichalcogenides [4], and fluorescent nanocrystals [5,6]. The so-called "weak" coupling regime makes it possible to change the spectral, spatial, and temporal properties of the luminophore PL emission by varying the local electromagnetic environment [7]. The use of photonic crystals (PhCs) is one of the most promising approaches to controlling the electromagnetic field distribution and, hence, to coupling it to the emitters placed inside the PhC microcavities (MCs) [1,3,4,7]. This approach is of special interest in the field of sensing in such emerging areas as the healthcare, environmental monitoring, and food safety [8,9]. Recent studies have demonstrated significant advances of PL-based sensors employing PhC structures in order to improve the critical properties of PL labels [9,10]. Porous silicon (pSi) MCs have been shown to be promising for biosensing applications due to the simplicity and scalability of fabrication and highly developed pore structure making the sensor surface easily accessible for analytes [11-13]. However, the necessity of selective excitation of majority of conventional dyes in the visible region of optical spectrum, low photostability, brightness, and background due to the autofluorescence of biological samples remain the obstacles to wider use of PL-based biosensor techniques. Excitation of the PL probes in the near-infrared (NIR) transparency window of biological samples could resolve some of these problems, allowing one deeper tissue penetration, higher spectral resolution and avoiding the autofluorescence. The nonlinear regime of two-photon excitation is a way to obtain visible-range fluorescence using NIR light sources. Moreover, the use of semiconductor quantum dots (QDs) with uniquely high two-photon absorption cross-sections compared to conventional dyes [14,15] allows one to reach the unprecedentedly high values of fluorescence contrast [16]. In addition, QDs are the excellent probes for sensing due to their wide one-and two-photon absorption [17,18] and narrow PL spectra, high quantum yield [19], and excellent photostability [20,21]. In this study, we have investigated the spontaneous PL emission of CdSe(core)/ZnS/CdS/ZnS(multishell) QDs placed inside a porous silicon MCs under two-photon excitation. We have measured the spectral and temporal characteristics of the spontaneous PL emission of QDs under two-photon pumping, as well as their dependence on the pump power. Significant enhancement of the QD PL at the wavelength corresponding to the MC eigenmode and its suppression within the photonic bandgap were observed. The change in the QD PL spectrum inside the porous silicon microcavity depended on the excitation energy density because the relaxation rates of the PL signal in the spectral regions where it was enhanced or suppressed were different. The increase in the emission rate corresponding to the weak coupling between the exciton transition of QDs and the eigenmode of the MC has been shown, and Purcell factor was determined to be about 4.3.
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Dates et versions

hal-02933862 , version 1 (08-09-2020)
hal-02933862 , version 2 (13-09-2020)

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Dmitriy Dovzhenko, Victor Krivenkov, Irina Kryukova, Pavel Samokhvalov, Alexander Karaulov, et al.. Enhanced spontaneous emission from two-photon-pumped quantum dots in a porous silicon microcavity. Optics Letters, 2020, 45 (19), pp.5364-5367. ⟨10.1364/OL.400300⟩. ⟨hal-02933862v2⟩

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