Subscriber access provided by University of Sunderland
Interfaces: Adsorption, Reactions, Films, Forces, Measurement Techniques, Charge Transfer, Electrochemistry, Electrocatalysis, Energy Production and Storage
PHOTOLUMINESCENCE OF DRYING DROPLETS WITH SILICON NANOPARTICLES Vladimir I. Yusupov, and Victor N. Bagratashvili Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.8b01721 • Publication Date (Web): 28 Sep 2018 Downloaded from http://pubs.acs.org on September 29, 2018
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Langmuir
PHOTOLUMINESCENCE OF DRYING DROPLETS WITH SILICON NANOPARTICLES Vladimir. I. Yusupov*, Victor N. Bagratashvili
Institute of Photon Technology Federal Scientific Research Center "Crystallography and Photonics" of Russian Academy of Sciences, Moscow, Troitsk, Russia *
[email protected] ABSTRACT This study is dedicated to the formation of structures during drying of droplets of sols of silicon nanoparticles (SiNP) in dimethylsulfoxide (DMSO) with diameter of 1-5 mm on the horizontal glass and mica surfaces. Drying of such droplets with pinning (sticking) of the droplet contact line causes gradual gathering of SiNP on its edge with formation of a thin ring. It has been found that the integral photoluminescence intensity IPL greatly varies during the drying process. At the initial stage, IPL monotonically decreases by several orders of magnitude and then abruptly increases several times at the final stage of ring formation. It has been shown that the rate of IPL decrease is maximal at a very early stage and depends both on aggregative state (solid film SiNP/sols of SiNP) and volume of the SiNP sols. It is minimal for the solid film SiNP and gradually increases as the volume of SiNP sol in DMSO decreases (optical cell → big droplet → small droplet). The obtained experimental dependencies between luminescence decrease rate and aggregative state and volumes of SiNP sol in DMSO are attributed to combination of three mechanisms of luminescence quenching: photobleaching, quenching with atmospheric oxygen and Förster resonance energy transfer (FRET) quenching. The appearing of luminescence leap at the final stage of ring formation is associated with the emergence of cracks in the ring. KEYWORDS sols of silicon nanoparticles, DMSO, luminescence quenching, cracks in the ring
ACS Paragon Plus Environment
Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
INTRODUCTION A liquid contains micro-nanocomponents that form various hierarchically-related structures as a result of complex interactions and self-organization during drying of the liquid [1-7]. Interest towards this process is both theoretical and practical. Thus, the study of morphological structure of dried droplets of biological fluids is used in medical diagnosis [8]. The resulting picture obtained after evaporation of liquid with nanoparticles, which reflects the result of their self-assembly, allows to define some physical and chemical characteristics of these particles [2-8]. Features of this process must be taken into account for the formation of nanostructures of composite and hybrid materials, obtaining of micro-and nano-objects with specified properties. In many cases, evaporation of droplets of liquid containing solid micronanoparticles on a horizontal solid surface gradually causes these particles to gather on its edge, forming a ring ("coffee ring") [1-6]. This pattern is observed at pinning (sticking) of the drop contact line. Silicon nanoparticles (SiNP) are especially interesting due to the prospects of their application in photonics and biomedicine [9-11]. SiNP are biologically compatible and possess bright photoluminescence (PL) in the red-near infrared spectral regions [12, 13]. Study of the luminescence of drying droplets with luminescent nanoparticles can give additional data on occurring processes and structural changes. Preliminary observation has shown that during drying of droplets of sols of SiNP nanoparticles in different solvents (viscous and slowly evaporating DMSO or low-viscous and quickly evaporating ethylene dichloride) PL signal undergoes unexpected changes. Initially, it gradually weakens (much more than in case of thin solid films with SiNP) and then grows stepwise at the final stage of ring formation. The aim of this work was to obtain new data on the spatial-temporal characteristics of photoluminescence in drying droplets of nanoparticles of SiNP sols with different diameters and to clarify mechanisms leading to the significant temporal changes of PL signal. EXPERIMENTAL SECTION In our experiments we used sols of SiNP nanoparticles in DMSO and also thin films obtained through successively drying of several (5-7) layers of droplets of the original sol on the surface of microscope slides. DMSO is a viscous solvent and we chosen it because it ensures slow evaporation. This allowed detailed study of the photoluminescence temporal patterns during drying of droplets with different diameter. Drying droplets with diameter of 1.1±0.1; 2.0±0.1; 3.3±0.2 and 4.3±0.2 mm (ten replications of each size). The SiNP nanoparticles were obtained through CSSM method [13, 14]. Such nanoparticles consist of silicon core 2.5-3 nm in size and Si nanocrystals coated by the silicon suboxide SiOx (1< x< 2) [13]. At the first stage of the SiNP synthesis use is made of the disproportionation reaction of fine-grained silicon monoxide, 2mSiO→mSi+mSiO2, run at temperatures from 298 to 1223 ºK, where m is the number of silicon atoms in a nanoparticle, followed by the dissolution and elution of silicon dioxide in an aqueous HF solution. Nanocrystalline silicon is formed in the bulk of SiOx produced during the course of annealing of silicon monoxide, a process similar to the decomposition of solid solutions. It is precisely annealing in air that leads to the formation of the SiNP nanoparticles whose oxide coat contains so-called oxygen-deficient centers responsible for photoluminescence in the red–infrared region of the spectrum. The photoluminescent sediment thus obtained was placed in a silica test tube containing dimethylsulfoxide (DMSO) and roiled by ultrasound (40 W). The brightest PL is attained with silicon monoxide annealed at a temperature of 1223 ºK. The details of the CSSM method used to synthesize the SiNP nanoparticles can be found in [14]. The SiNP sol in DMSO was placed in an optical cell with thickness 1.5 mm and diameter 5 mm equipped with 0.15 mm thick windows of cover glass. In order to obtain SiNP film samples, a droplet of the initial sol with nanoparticles 1-3 mm in diameter was air-dried on a cover glass at room temperature. In order to excite photoluminescence (PL), SiNP samples (sols and films) were irradiated with a CW diode laser with wavelength λ=405 nm and intensity 0.1 W·cm-2. We ACS Paragon Plus Environment
Page 2 of 27
Page 3 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Langmuir
used fiber optic spectrometer Model USB4000 (Ocean Optics) to measure spectra and dynamics of the laser-induced PL of the SiNP samples. PL excitation and electronic absorption spectra of the SiNP samples were measured with Fluorescence Spectrophotometer Model Cary Eclipse (Varian) and UV-Visible Spectrophotometer Model Car 50 (Varian), respectively. The samples were studied using an HRM-300 Series optical 3D microscope (Huvitz, Korea), a Micros MC 300 microscope (Micros, Austria) with a luminescence unit. Profiles of dried droplets were studied using atomic force microscopy Solver PRO (NT-MDT, RU). SiNP were characterized by Transmission electron microscope (TEM) FEI Osiris (FEI Company, USA). We used thermal imager FLIR A655sc (FLIR Systems AB, Sweden) for registration of temperature fields. It allows obtaining of 14-bit images (640×480 pixels) with resolution o17 µm and sensitivity
