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Condensed Matter and Interphases
Kondensirovannye Sredy i Mezhfaznye Granitsy https://journals.vsu.ru/kcmf/
Original articles
Original article
https://doi.org/10.17308/kcmf.2021.23/3294
Spectral manifestations of the exciton-plasmon interaction of Ag2S quantum dots with silver and gold nanoparticles
I. G. Grevtseva, T. A. Chevychelova, V. N. Derepko, O. V. Ovchinnikov®, M. S. Smirnov, A. S. Perepelitsa, A. S. Parshina
Voronezh State University,
1 Universitetskaya pl., Voronezh 394018, Russian Federation Abstract
The purpose of our study was to develop methods for creating hybrid nanostructures based on colloidal Ag2S quantum dots, pyramidal silver nanoparticles, Au nanorods, and to determine the spectral-luminescent manifestations of exciton-plasmon interactions in these structures. The objects of the study were Ag2S quantum dots passivated with thioglycolic acid (Ag2S/ TGA QDs) and 2-mercaptopropionic acid (Ag2S/2-MPA QDs), gold nanorods (Au NRs), silver nanoparticles with pyramidal geometry (Ag NPs), and their mixtures. The spectral properties were studied using a USB2000+ with a PMC-100-20 photomultiplier system (Becker & Hickl Germany). The article considers the transformation of the luminescence spectra of colloidal Ag2S/TGA QDs and Ag2S/2-MPA QDs in mixtures with pyramidal Ag NPs and Au NRs. The study demonstrated the presence of the effects of the contour transformation of the luminescence spectra due to the Fano effect, as well as the luminescence quenching following direct contact between QDs and NPs.
Keywords: silver and gold nanoparticles, silver sulfide quantum dots, hybrid nanostructures, luminescence spectrum Acknowledgements: The reported study was supported by a grant of the President of the Russian Federation to support leading scientific schools of the Russian Federation, project No. NSh-2613.2020.2. The results of transmission electron microscopy were obtained using the equipment of the Center for Collective Use of Scientific Equipment of Voronezh State University.
For citation: Grevtseva I. G., Chevychelova T. A., Derepko V. N., Ovchinnikov O. V., Smirnov M. S., Perepelitsa A. S., Parshina A. S. Spectral manifestations of exciton-plasmon interaction of Ag2S quantum dots with silver and gold nanoparticles. Kondensirovannyesredy i mezhfaznyegranitsy = Condensed Matter and Interphases. 2021;23(1): 25-31. https:// doi.org/10.17308/kcmf.2021.23/3294
Для цитирования: Гревцева И. Г., Чевычелова Т. А., Дерепко В. Н., Овчинников О. В., Смирнов М. С., Перепелица А. С., Паршина А. С. Спектральные проявления плазмон-экситонного взаимодействия квантовых точек Ag2S с наночастицами серебра и золота. Конденсированные среды и межфазные границы. 2021;23(1): 25-31. https://doi. org/10.17308/kcmf.2021.23/3294
И Oleg V. Ovchinnikov, e-mail: ovchinnikov_o_v@rambler.ru
© Grevtseva I. G., Chevychelova T. A., Derepko V. N., Ovchinnikov O. V., Smirnov M. S., Perepelitsa A. S., Parshina A. S., 2021
The content is available under Creative Commons Attribution 4.0 License.
I. G. Grevtseva et al. Original articles
1. Introduction
Metal nanoparticles (NPs), semiconductor quantum dots (QDs), and hybrid structures based on them can be used to solve certain basic and applied science problems in biology, medicine, chemistry, optoelectronics, photocatalysis, etc. [1-10]. Most of these spheres require sensors which can be used for various purposes. These sensors include fluorescent thermometers, pH sensors, fluorescent indicators of impurity ions, and biosensors based on the luminescence of QDs and dyes as well as on light scattering from plasmonic NP, etc. It is possible to control the spectral position of the plasmon resonance of metal NPs using their size [3, 4], shape [11], and dielectric environment [12], as well as by changing the structure of their interface. Thus, NPs can be decorated with semiconductor QDs, whose luminescence spectra partially or completely overlap with the plasmon peak of the extinction spectrum. Creation of hybrid structures with plasmon-exciton coupling based on plasmonic NPs and semiconductor QDs, may result in the high sensitivity of the structures' spectra to impurities, the environment, and the properties of the surrounding solution or matrix. As a result, hybrid nanostructures demonstrate both the additive properties of their components and novel unique sensory properties arising from direct interaction between the components and their close proximity to each other [6-18]. Variations in the regime of exciton-plasmon coupling (weak, intermediate and strong) enable resonance spectral-luminescent effects in the weak (Purcell effect), intermediate (Fano effect), and strong (Rabi splitting) regimes of exciton-plasmon coupling [14, 19-21]. The type of interaction and the distance between the components are crucial for such hybrid nanostructures. Of vital importance is to predict the spectral-luminescent properties of hybrid nanostructures. This problem has not been thoroughly studied yet. It is thus important to study the optical properties of synthesised nanostructures. To solve this problem, it is necessary to develop approaches to the synthesis of hybrid nanostructures based on technologies that allow for various regimes of exciton-plasmon interaction of metal NPs with QDs and dye molecules, as well as for the tuning of the
optical resonance of the components of hybrid nanostructures.
The purpose of our study was to develop methods for creating hybrid nanostructures based on colloidal Ag2S quantum dots (Ag2S QDs), pyramidal silver nanoparticles (Ag NPs), gold nanorods (Au NRs), and to determine the spectral-luminescent manifestations of exciton-plasmon interactions in these structures.
2. Experimental
2.1. Samples
Colloidal Ag2S QDs, passivated using molecules of thioglycolic acid (Ag2S/TGA QDs) and 2-Mercaptopropionic acid (Ag2S/2-MPA QDs) with an average size of 2.0 nm and 2.8 nm respectively, were synthesised using a one-step method. The method involves using TGA and 2-MPA molecules in the crystallisation both as the sources of sulphur and as passivators of QDs interfaces [22,23]. The approach involves mixing the initial reagent AgNO3 (2.4 mM) and TGA (2-MPA) (4.8 mM). When TGA was used to passivate the QDs interfaces, distilled water was used as a solvent. When 2-MPA was used, the synthesis was performed in viscous medium (ethylene glycol).
The method of synthesising pyramidal Ag NPs was based on a combination of two methods: reduction of Ag with trisodium citrate (Na3C6H5O7) and reduction of Ag with sodium borohydride (NaBH4). To do this we subsequently poured 0.5 ml of PVP (0.003 М) , 3 ml of Na3C6H5O7 (0.03 М), 0.2 ml of H2O2 (30%), and 0.5 ml of NaBH4 (0.05 моль) into the AgNO3 (50 мл, 0.02 М) aqueous solution with constant stirring at room temperature. At this stage the formed particles were predominantly spherical. When the constantly stirred colloidal solution was subjected to optical radiation with a wavelength of 520 nm, pyramidal Ag NPs were formed.
The colloidal synthesis of Au nanorods was performed in the presence of a surface-active substance (SAS), cetyltrimethylammonium bromide (CTAB), whose aqueous solution forms cylindrical micelle, thus creating anisotropic environment for the growth of NRs. Au NRs were formed in several stages, which included subsequent preparation and mixing of the seeds and growth solutions. As a seed solution we used spherical Au NPs (3 nm), obtained by means of the
I. G. Grevtseva et al.
Original articles
chemical reduction of HAuCl4 (7 ]l, 0.36 M) with a NaBH4 solution (1.0 ml, 5mM) in the presence of CTAB (20 ml, 0.02 mM). The growth solution was a mixture of HAuCl4 (28 ]l, 0.36 M), CTAB (50 ml, 0.1 mM), AgNO3 (100 ]l, 0.02 M), and C6H8O6 (5 ml, 0.05 ]M). After adding the seed solution to the growth solution, the reaction mixture gradually becomes blue, purple, or brown-red depending on the ratio of the length of the Au NRs to their diameter. By adding variable concentrations of AgNO3 to the growth solution we could regulate the ratio of the length of the Au NRs to their diameter. The obtained Au NRs were purified from reaction products by means of several cycles of centrifugation and dispersion.
Hybrid structures were formed by mixing colloidal solutions of Au NRs (pyramidal Ag NPs) and Ag2S ODs/TGA (or Ag2S ODs/2-MPA) with a molar ratio of [v(NPs)]:[v(ODs)] ~ 10-4 mole fraction (m.f.).
2.2. Methods of experimental studies
The size and morphology of Ag2S/TGA ODs, Ag2S/2-MPA ODs, pyramidal Ag NPs and Au NRs were determined by means of a Libra 120 transmission electron microscope (TEM) (Carl Zeiss, Germany). The absorption properties were studied using a USB2000+ spectrometer (Ocean Optics, USA) with a USB-DT light source (Ocean Optics, USA). The luminescence spectra and the luminescence decay kinetics of Ag2S/TGA ODs, Ag2S/2-MPA ODs, and their mixtures with plasmonic NPs were studied using the USB2000+ and a TimeHarp~260 system for time correlated photon counting (PicoOuant Germany) with a PMC-100-20 photomultiplier tube (Becker&Hickl
Germany) with a time resolution of 0.2 ns. A diode laser NDV7375 (Nichia, Japan) with a wavelength of 405 nm (200 mW) was used to stimulate the luminescence.
3. Results and discussion
Figure 1 presents TEM images of pyramidal Ag NPs and Au NRs. The analysis of TEM images demonstrated that pyramidal Ag NPs are formed with an average edge length of 19 nm (Fig. 1a). The photo-induced transformation of Ag NPs from spherical to pyramidal, followed by a growth in size, results in the shift of the extinction peak to longer wavelengths, from 480 nm to 590 nm (Fig. 2a, dotted line).
The described approach to the synthesis of Au NRs allowed us to obtain Au NRs with a size from 20^9 nm to 25^9 nm (Fig. 1b) and regulate their average size (ratio of the length to the diameter) by adding 100 ]l and 70 ]l of AgNO3 (0.02 M) to the growth solution of Au NRs. The; increased length of Au NRs results in the shift of the extinction peak to longer wavelengths, from 640 to 690 nm respectively (Fig. 2b, dotted line).
According to the results of TEM, the suggested methods of synthesising Ag2S ODs and Ag and Au NPs provided for the compatibility of the components and the formation of hybrid structures. TEM images demonstrate that the largest number of ODs are observed next to Ag and Au NPs (Fig. 1).
The spectra of optical absorption of Ag2S/ TGA ODs and Ag2S/2-MPA ODs shifted to shorter wavelengths relative to the edge of the fundamental absorption of single crystals of silver sulphide (1.09 eV). This happened due
a b
Fig. 1. TEM images demonstrating the formation of associates of Ag2S ODs with pyramidal Ag nanoparticles (a) and Au nanorods (b)
I. G. Grevtseva et al. Original articles
to the quantum size effect. In the absorption spectrum of colloidal Ag2S/TGA QDs, we observed a specific feature in the 590 nm region, which was characteristic of the most probable excitonic transition in the absorption spectrum. When colloidal Ag2S/TGA QDs were excited at the wavelength of405 nm, we observed recombination luminescence, with the absorption band peak at 615-620 nm (Fig. 2a, b).
The absorption spectrum of colloidal Ag2S/2-MPA QDs has a prominent peak at about 690 nm, corresponding to the most probable excitonic transition in the optical absorption spectrum. For colloidal Ag2S/2-MPA QDs a recombination luminescence was observed with the peak at 820 nm (Fig. 2c).
Thus, the geometry and size of pyramidal Ag NPs (19 nm) and Au NRs (20^9) ensured a significant overlap between their extinction
spectra and the luminescence spectra of Ag2S/ TGA QDs (620 nm) (Fig. 2a, b). The mixture of Au NRs (25^9) and Ag2S/2-MPA QDs (820 nm) did not yield any significant overlap between their extinction spectra and the luminescence spectra of Ag2S/2-MPA QDs (Fig. 2c).
Mixtures of Ag2S/TGA QDs and Ag2S/2-MPA QDs with plasmonic pyramidal Ag NPs and Au NRs demonstrated complex bands in the extinction spectra, which were not simply a sum of the spectra of mixtures components. It was also noted that the optical density increased over the whole extinction spectrum, when QDs and NPs were mixed. The difference in the location of the stop band peaks of the components and redistribution of the intensity within the resulting contours indicate the presence of exciton-plasmon interaction between the components.
Fig. 2. The extinction spectra of pyramidal Ag NPs (a) and Au NRs with size of (20^9) nm (b) and (25^9) nm (c), the luminescence spectra of Ag2S/TGA QDs (a and b), Ag2S/2-MPA QDs (c), and their mixtures with NPs
I. G. Grevtseva et al. Original articles
The most interesting patterns, however, were observed in luminescence spectra of QDs mixed with plasmonic NPs. Mixtures of Ag2S/TGA QDs (luminescence peak at 620 nm) with Ag NPs (light extinction peak at 590 nm) demonstrated a decrease in the luminescence intensity of QDs by 8 times (Fig. 2a) together with a decrease in the luminescence lifetime by 5-7 %. The observed patterns indicate that the effects of exciton-plasmon coupling are dominated by the carrier phototransfer between the components of the associates. The phototransfer blocks QDs luminescence, when the overlap between the extinction peak of Ag NPs (nanoresonator mode) and Ag2S/TGA QDs luminescence is not complete [10, 24].
On the contrary, when the overlap between the luminescence spectra (620 nm) and the plasmon peak (640 nm) was greater, mixtures of the same samples of Ag2S/TGA QDs with plasmonic Au NPs (20^9 nm), demonstrated an increase in luminescence quantum yield by 1.5 times (Fig. 2b). At the same time, the intensity of QDs recombination luminescence fell below the luminescence level of the initial QD sample after a 20-second exposure to luminescence excitement. The initial increase in the intensity of Ag2S/TGA QDs luminescence is accounted for by the Purcell effect, which presumes greater probability of optical transition in proximity to the nanoresonator [25]. However, the following significant decrease in the luminescence intensity may be caused by the photo-stimulated charge transfer between the components of the studied associates, which, as we know, blocks the luminescence [10, 24]. Incomplete luminescence quenching indicates that some of QDs are not in full contact with NPs, which is necessary for the injection of photostimulated charge carriers.
Mixtures of Au NRs (25^9 nm, extinction peak at 690 nm) and Ag2S/2-MPA QDs demonstrated a decrease in QDs luminescence intensity at the band peak (820 nm). In this case, a dramatic transformation of the spectral contour of Ag2S/2-MPA QDs luminescence band was registered. However, the peak intensity grew in the region with the wavelengths shorter than 700 nm (Fig. 2b). Apparently, such a behaviour of the luminescence spectrum is connected with the quantum interference (Fano antiresonance)
during exciton-plasmon interaction [26]. At the same time, the average luminescence lifetime increased from 94 to 115 ns at the wavelength of 750 nm and decreased from 94 to 16 ns at the wavelength of 820 nm. This also indicates the presence of exciton-plasmon interaction. The enhancement of luminescence at 700 nm may be accounted for by the Purcell effect, when there is direct contact between a plasmonic nanoparticle and quantum dots. A slowdown in the luminescence decay is explained by a decrease in the effectiveness of the non-radiative recombination caused by the difference in the immediate environment of the QDs.
4. Conclusions
The article suggests a new method for synthesising hybrid associates based on Ag2S/TGA QDs, Ag2S/2-MPA QDs, pyramidal Ag NPs, and Au NRs. The study determined the transformation effects of the luminescence spectra contours resulting from the quantum interference (the Fano effect), and the luminescence quenching occurring when there is direct contact between QDs and NPs. The observed interaction between Ag2S QDs and plasmonic NPs indicates the possibility to regulate the spectrum and the quantum efficiency of QDs IR luminescence. However, the results of the latest experiments definitely indicate the complexity of exciton-plasmon interaction in the studied systems, as several effects are observed at the same time, including the Purcell effect, the Fano effect, and the photo-induced charge transfer between QDs and NPs.
Conflict of interests
The authors declare that they have no known competing financial interests or personal relationships that could have influenced the work reported in this paper.
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Information about the authors
Irina G. Grevtseva, PhD in Physics and Mathematics, lecturer, Department of Optics and Spectroscopy, Voronezh State University, Voronezh, Russian Federation; e-mail: grevtseva_ig@inbox.ru. ORCID iD: https://orcid.org/0000-0002-1964-1233.
Tamara A. Chevychelova, postgraduate student Department of Optics and Spectroscopy, Voronezh State University, Voronezh, Russian Federation; e-mail: t.chevychelova@rambler.ru. ORCID iD: https://orcid.org/0000-0001-8097-0688.
Violetta N. Derepko, postgraduate student Department of Optics and Spectroscopy, Voronezh State University, Voronezh, Russian Federation;
e-mail: viol.physics@gmail.com. ORCID iD: https:// orcid.org/0000-0002-9096-5388
Oleg V. Ovchinnikov, DSc in Physics and Mathematics, Professor, Department of Optics and Spectroscopy, Voronezh State University, Voronezh, Russian Federation; e-mail: ovchinnikov_o_v@rambler.ru. ORCID iD: https://orcid. org/0000-0001-6032-9295
Mikhail S. Smirnov, PhD in Physics and Mathematics, Associate Professor, Department of Optics and Spectroscopy, Voronezh State University, Voronezh, Russian Federation; e-mail: smirnov_m_s@mail.ru. ORCID iD: https://orcid.org/0000-0001-8765-0986
Aleksey S. Perepelitsa, PhD in Physics and Mathematics, senior lecturer, Department of Optics and Spectroscopy, Voronezh State University, Voronezh, Russian Federation; e-mail: a-perepelitsa@ yandex.ru. ORCID iD: https://orcid.org/0000-0001-8097-0688.
Anna S. Parshina, master's degree student, Department of Materials Science and Nanotechnology, Voronezh State University, Voronezh, Russian Federation; e-mail: anyuta_parshina@mail.ru. ORCID iD: https://orcid.org/0000-0002-9455-2062
All authors have read and approved the final manuscript.
Received25 December2020; Approved after reviewing 13 January 2021; Accepted 15 March 2021; Published online 25 March 2021
Translated by Yulia Dymant Edited and proofread by Simon Cox
