Photophysical Properties of Blue-Emitting Silicon Nanoparticles

Abstract

Silicon nanoparticles with strong blue photoluminescence were synthesized by electrochemical etching of silicon wafers and ultrasonically removed under N2 atmosphere in organic solvents to produce colloids. Thermal treatment leads to the formation of colloidal Si particles of 3 ± 1 nm diameter, which upon excitation with 340 – 380 nm light exhibited room temperature luminescence in the range from 400 to 500 nm. The emission and the one- and two-photon excitation spectra of the particles are not sensitive to surface functionalization with methyl 2-methylprop-2-enoate. However, the derivatized particles show higher emission quantum yields in air-saturated suspensions (44%) than the underivatized particles (27%), as well as higher stability of its dispersions. FTIR and XPS spectra indicate a significant surface oxidation of the particles. The Si:O:C ratio at the surface of the derivatized particles estimated from XPS is Si3O6(C5O2Hy)1, with y = 7 - 8. Vibronic spacing is observed in both the emission and excitation spectra. The information obtained from one-photon excitation experiments (emission and excitation spectra, photoluminescence quantum yields, luminescence decay lifetimes and anisotropy correlation lifetimes), as well as from two-photon excitation fluorescence correlation spectroscopy (brightness and diffusion coefficients) and TEM indicate that the blue-emitting particles are monodisperse and ball-shaped. Particle size clearly determines the emission and excitation spectral region, as expected from quantum confinement, but the presence and extent of Si-O species on the silicon networks seem crucial for determining the spectrum features and intensity of emission. The nanoparticles could hold great potential as quantum dots for applications as luminescence sensors in biology and environmental science.

EXAFS and DFT study of the cadmium and lead adsorption on modified silica nanoparticles

“…The N-H stretch absorption over the 3300-3400 cm À1 present in APTES [24] is masked by the O-H absorption present in silica [21]. Any absorption due to the vibration modes assigned to the SiAOAC moiety is shrouded by the strong SiAOASi absorption signals at 1100 cm À1 [22]. Absorption at 1332 and 1630 cm À1 was assigned to CO 2 trapped by surface NH 3 + giving rise to an amine bicarbonate moiety in coincidence with that reported for protonated (3-aminopropyl) triethoxysilane films and aged silicon particles modified with propylamine groups [25].…”

“…These bands are also present in the spectrum of APTES. The bands in the 3000-2800 cm À1 region are assigned to the CH 2 stretching [22]. Absorption bands in the region 1575-1450 cm À1 may be assigned to NÀH vibrations in protonated amines [23].…”

Electrochemical Properties of Screen-Printed Carbon Nano-Onion Electrodes

“…After peak fitting, two different contributions can be observed ( Table S3 in Supplementary Materials ). The most intense peak at 102.3 eV corresponds to Si atoms in the siloxane (Si–O–Si) and Si-C groups present in the chemical structure of the plasticiser [ 42 , 43 , 44 ], while the peak at 104.4 eV is assigned to the native oxide layer (SiO 2 ) of the Si substrate employed for the analyses [ 41 , 45 ].…”

Generation of Chemisorbed Benzyl Radicals on Silica Nanoparticles

“…The ratio of the intensity of the bands due to Si–OH absorption at 3400–3450 cm −1 and those assigned to Si–O–Si at 1100 cm −1 is smaller for the modified silica particles than for the bare ones; therefore a considerable diminution of the amount of silanol groups occurs after functionalization, as expected from the covalent bonding between the nanoparticles and the organic molecules, reaction 1 . Any IR absorption due to the vibration modes assigned to Si–O–C bonds (29) is masked by the strong Si–O–Si absorption signals at 1100 cm −1 .…”

“…To increase the signal-to-noise ratio, the crosspolarization (CP) technique was applied. NMR spectra of 13 C and 29 Si were obtained with pulse repetition of 1 and 3 s and contact times of 1 and 3 ms, respectively.…”