Blue Light-Emitting Si Quantum Dots with Mesoporous and Amorphous Features: Origin of Photoluminescence and Potential Applications

Abstract

Recently, Si quantum dots (QDs) with porous and amorphous characteristics have shown tremendous potential applications in photovoltaics and biomedical fields. However, in general, their preparation involves meticulous synthetic procedures. Herein, we present the first report of the synthesis of Si QDs in aqueous solution with amorphous and porous features using γ-ray irradiation, which is a facile, one-pot, and reproducible approach. Fourier transform infrared and X-ray photoelectron spectroscopy indicated the formation of a shell of Si oxides (SiO x , 0 < x < 2) surrounding the Si core. The Brunauer–Emmett–Teller method confirmed the formation of mesoporous structure with a specific surface area of ∼53 m2/g. The average size of the QDs was <2 nm, as determined from high-resolution transmission electron microscopy. Moreover, the size of the QDs could be tuned by varying the dose, as was indicated from the shift in their absorption peaks. The QDs displayed bright blue emission under ultraviolet light. Detailed and systematic investigations involving various sets of experiments such as aging, annealing, acid treatment, and temperature-dependent PL studies of the QDs indicate the origin of the blue photoluminescence (PL) is the radiative processes originating from the defects located in the oxide shell as well as at/or near the Si/SiO x interface. This has been further substantiated from the size-independent emission spectra at various absorbed doses and short PL lifetime (in nanoseconds). Nonetheless, these QDs showed highly sensitive and robust thermosensing properties, as their PL intensity varied linearly and reproducibly with temperature, ranging from 278 to 338 K. In addition, the QDs were found to be noncytotoxic and therefore can be utilized in cell imaging. Furthermore, the blue PL and the nontoxic aspects of these QDs can be utilized in anticounterfeiting measures, the potential application of which is also demonstrated in this work. The possible mechanism behind the formation of Si QDs and the role of the total dose in the introduction of mesoporous and amorphous features are proposed and explained in this paper.

Size Tuning, Phase Stabilization, and Anticancer Efficacy of Amorphous Selenium Nanoparticles: Effect of Ion-Pair Interaction, −OH Functionalization, and Reuse of RTILs as Host Matrix

“…A control experiment was conducted wherein Se NPs were synthesized in aqueous solution in the absence of RTILs. The reaction mixture comprised a N 2 -bubbled aqueous solution of SeO 2 and tert -butanol (1 M; to quench • OH). ,,, The experimental parameters (such as absorbed dose and precursor concentration) were kept the same as in the case of experiments in the presence of RTILs. On irradiation of the reaction mixture, Se NPs were formed, as was indicated from the appearance of the red-orange color.…”

“…In this perspective, a methodology of clubbing the radiation-mediated technique with the host matrix of solvents such as room-temperature ionic liquids (RTILs) could be a promising approach. − Electron beam-induced nanomaterial synthesis is a versatile technique with several inherent advantages, such as facileness, nanocharacteristic-maneuvering parameters (such as absorbed dose and dose rate), time efficiency, scale-up potential, and not requiring any external reducing agents. − In the current work, an electron beam was used to generate reducing species, deriving nucleation that eventually leads to the formation of α-Se NPs, while RTILs played multiple roles: as a host matrix, a source of reducing species, and a stabilizer. Nonetheless, apart from the synthesis of α-Se NPs with prolonged stabilization, the main objective of the current work was to investigate the effect of the nature of cation–anion combinations (in RTILs) on the size and phase stability of α-Se NPs.…”

Water-Induced Dimensionality Reduction in Metal-Halide Perovskites

“…Essentially, lattice strain typically exists in nanoscale materials, which could influence the band structure of indirect band gap materials. In addition, dissolution–recrystallization processes caused by water might initiate the formation of emissive centers which could be possibly generated by defects or surface states in PRMs. ,,− It is well-known that surface defects can be easily generated by oxygen- or moisture-induced reorientation of crystal structure or decomposition. Indeed, we also observed that PL inactive CsPb 2 Br 5 single crystals emit green photoluminescent after prolonged exposure to a humid atmosphere (Figure S8).…”

Facile Synthesis, Enhanced Photostability, and Long-term Cellular Imaging of Bright Red Luminescent Organosilica Nanoparticles

“…In the Si 2p XPS spectrum (Figure 3C), the broad peak was fitted by three components at 102.15, 102.55, and 103.22 eV, corresponding to Si atoms involved in Si−C, Si−O−H, and Si−O−Si species, respectively, which were consistent with the formation of silica networks via hydrolysis and condensation of APTMS during the reaction. 38,39 In the N 1s spectrum (Figure 3D), the broad peak was fitted by two components at 399.36 and 400.26 eV, assigned to the N atoms in N−C and N−H bonds, respectively. 17,40 It was deduced that there were plenty of amino and silanol groups on the surface of the OSi NPs, which are responsible for their excellent dispersity in the aqueous phase.…”

“…TEM observation revealed that the product was nanoparticles nearly spherical in shape, with an average size of 3.4 ± 0.4 nm (Figure A), corresponding to a hydrodynamic diameter of 5.8 nm (Figure S4). XRD pattern of the powdered nanoparticles showed a broad peak centered at 2θ = 21.5° (Figure S5), revealing the amorphous character of the nanoparticles. , MALDI-TOF mass spectrometry was employed to identify the composition of the nanoparticles (Figure B). The peak at the mass to charge ratio ( m / z ) of 2618.9 was assigned to the composition of [(ICG′) 2 (hAPTMS) 9 + Na] + , in which hAPTMS represents the hydrolytic APTMS molecules that may cross-link each other to construct the silica network, and ICG′ represents the product from the ICG molecule after the addition reaction.…”