Photoluminescence Of Silicon Nanocrystals Research Articles

Oxygen backed silicon hydride in correlation with the photoluminescence of silicon nano-crystals

Converting silicon hydride (–SiH) to oxygen backed silicon hydride (–OSiH) on porous silicon leads to a shift in the wavelength of photoluminescence (PL) maximum from 670 to 605 nm, corresponding to an increase of 0.2 eV on emission energy.

Photoinduced Electron-Transfer Quenching of Luminescent Silicon Nanocrystals as a Way To Estimate the Position of the Conduction and Valence Bands by Marcus Theory

Photoluminescence of silicon nanocrystals (SiNCs) in the presence of a series of quinone electron acceptors and ferrocene electron donors is quenched by oxidative and reductive electron transfer dynamic processes, respectively. The rate of these processes is investigated as a function of (a) the thermodynamic driving force of the reaction, by changing the reduction potentials of the acceptor or donor molecules, (b) the dimension of SiNCs (diameter = 3.2 or 5.0 nm), (c) the surface capping layer on SiNCs (dodecyl or ethylbenzene groups), and (d) the solvent polarity (toluene vs dichloromethane). The results were interpreted within the classical Marcus theory, enabling us to estimate the position of the valence and conduction bands, as well as the reorganization energy (particularly small, as expected for quantum dots) and electronic transmission coefficients. The last parameter is in the range 10–5–10–6, demonstrating the nonadiabaticity of the process, and it decreases upon increasing the SiNC dimensions: this result is in line with a larger number of excitons generated in the inner silicon core for larger SiNCs and thus resulting in a lower electronic coupling with the quencher molecules.

Size vs surface: tuning the photoluminescence of freestanding silicon nanocrystals across the visible spectrum via surface groups.

The syntheses of colloidal silicon nanocrystals (Si-NCs) with dimensions in the 3-4 nm size regime as well as effective methodologies for their functionalization with alkyl, amine, phosphine, and acetal functional groups are reported. Through rational variation in the surface moieties we demonstrate that the photoluminescence of Si-NCs can be effectively tuned across the entire visible spectral region without changing particle size. The surface-state dependent emission exhibited short-lived excited-states and higher relative photoluminescence quantum yields compared to Si-NCs of equivalent size exhibiting emission originating from the band gap transition. The Si-NCs were exhaustively characterized using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier transformed infrared spectroscopy (FTIR), and their optical properties were thoroughly investigated using fluorescence spectroscopy, excited-state lifetime measurements, photobleaching experiments, and solvatochromism studies.

Effect of surface Si-Si dimers on photoluminescence of silicon nanocrystals in the silicon dioxide matrix

The effect of surface states of silicon nanocrystals embedded in silicon dioxide on the photoluminescent properties of the nanocrystals is reported. We have investigated the time-resolved and stationary photoluminescence of silicon nanocrystals in the matrix of silicon dioxide in the visible and infrared spectral ranges at 77 and 300 K. The structures containing silicon nanocrystals were prepared by the high-temperature annealing of multilayer SiOx/SiO2 films. The understanding of the experimental results on photoluminescence is underlain by a model of autolocalized states arising on surface Si-Si dimers. The emission of autocatalized excitons is found for the first time, and the energy level of the autolocalized states is determined. The effect of these states on the mechanism of the excitation and the photoluminescence properties of nanocrystals is discussed for a wide range of their dimensions. It is reliably shown that the cause of the known blue boundary of photoluminescence of silicon nanocrystals in the silicon dioxide matrix is the capture of free excitons on autolocalized surface states.

The Effect of the MeV Si-Ion Irradiation on the Photoluminescence of Silicon Nanocrystals

Silicon nanocrystals embedded in silicon nitride films were irradiated with Si-ions at 8 MeV in order to modify their optical response. The samples were characterized by means of Rutherford Backscattering Spectrometry, Elastic Recoil Detection Analysis, High-Resolution Transmission Electronic Microscopy and Photoluminescence analysis. It was found a blue-shift in the photoluminescence emission from the as-grown films after they were irradiated with high energetic silicon ions. According to the quantum confinement theory, this fact is related to a decrease in size of the silicon nanocrystals, which means that a higher silicon fluence irradiation is related with a diminishing in silicon nanocrystal size.

Luminescence and structure of nanosized inclusions formed in SiO2 layers under double implantation of silicon and carbon ions

Luminescent and structural characteristics of SiO2 layers exposed to double implantation by Si+ and C+ ions in order to synthesize nanosized silicon carbide inclusions have been investigated by the photoluminescence, electron spin resonance, transmission electron microscopy, and electron spectroscopy methods. It is shown that the irradiation of SiO2 layers containing preliminary synthesized silicon nanocrystals by carbon ions is accompanied by quenching the nanocrystal-related photoluminescence at 700–750 nm and by the enhancement of light emission from oxygen-deficient centers in oxide in the range of 350–700 nm. Subsequent annealing at 1000 or 1100°C results in the healing of defects and, correspondingly, in the weakening of the related photoluminescence peaks and also recovers in part the photoluminescence of silicon nanocrystals if the carbon dose is less than the silicon dose and results in the intensive white luminescence if the carbon and silicon doses are equal. This luminescence is characterized by three bands at ∼400, ∼500, and ∼625 nm, which are related to the SiC, C, and Si phase inclusions, respectively. The presence of these phases has been confirmed by electron spectroscopy, the carbon precipitates have the sp 3 bond hybridization. The nanosized amorphous inclusions in the Si+ + C+ implanted and annealed SiO2 layer have been revealed by high-resolution transmission electron microscopy.

Influence of electric field on the photoluminescence of silicon nanocrystals

We studied the effect of electric field generated on photoluminescence (PL) of silicon nanocrystals embedded in SiO2 films. We show that the application of electric field generated by means of surface acoustic waves (SAW) results in an increase of the PL intensity of nanocrystal photoluminescence by as much as 10% at a field amplitude of 12 kV/cm at temperatures below 15 K. At temperatures above 20 K the PL intensity decreases as the electric field is applied. The results are discussed within the frame of the self-trapped exciton model.

Photoluminescence of Silicon Nanocrystals under the Effect of an Electric Field

The effect of an electric field on photoluminescence (PL) of silicon nanocrystals formed in silicon dioxide by ion implantation with subsequent annealing has been studied. Application of an electric field leads to an increase in PL intensity by ∼10% at low temperatures and an electric field strength of 12 kV/cm and to its decrease at temperatures above 20 K. The increase in exciton PL intensity in an electric field is inconsistent with the model of recombination of quantum-confined excitons in nanocrystals. The effect can be described in terms of a model of recombination of self-trapped excitons formed at the interface between a Si nanocrystal and SiO2.

Quantum confinement effect of silicon nanocrystals in situ grown in silicon nitride films

Silicon nanocrystals were in situ grown in a silicon nitride film by plasma-enhanced chemical vapor deposition. The size and structure of silicon nanocrystals were confirmed by high-resolution transmission electron microscopy. Depending on the size, the photoluminescence of silicon nanocrystals can be tuned from the near infrared (1.38eV) to the ultraviolet (3.02eV). The fitted photoluminescence peak energy as E(eV)=1.16+11.8∕d2 is evidence for the quantum confinement effect in silicon nanocrystals. The results demonstrate that the band gap of silicon nanocrystals embedded in silicon nitride matrix was more effectively controlled for a wide range of luminescent wavelengths.

Quantum confinement effect of silicon nanocrystals in situ grown in silicon nitride films

AbstractSilicon nanocrystals were in situ grown in a silicon nitride film by plasma enhanced chemical vapor deposition. The size and structure of silicon nanocrystals were confirmed by high-resolution transmission electron microscopy. Depending on the size, the photoluminescence of silicon nanocrystals can be tuned from the near infrared (1.38 eV) to the ultraviolet (3.02 eV). The fitted photoluminescence peak energy as E(eV) = 1.16 + 11.8/d2 is an evidence for the quantum confinement effect in silicon nanocrystals. The results demonstrate that the band gap of silicon nanocrystals embedded in silicon nitride matrix was more effectively controlled for a wide range of luminescent wavelengths.

Influence of doping concentration on the photoluminescence of silicon nanocrystals

Photoluminescent silicon films have been fabricated starting from p-type silicon powders, by means of a purely wet-chemical process at different doping concentrations. Their light emission properties have been investigated by means of continuous wave and time-resolved photoluminescence measurements. In all the samples Auger saturation has been observed, showing that light emission from quantum confined Si nanocrystals occurs. The doping level influences the spectra, the decay times and the reactivity towards oxidizing environment. The same features are observed in samples obtained from simultaneously processing p- and n-type silicon powders. Hence, our results support the hypothesis that, during the chemical reaction, merging of p- and n-type silicon nanocrystals and subsequent doping neutralization occurs.

Effect of passivation and aging on the photoluminescence of silicon nanocrystals

Silicon nanocrystals were prepared by laser pyrolysis of silane in a gas flow reactor and deposited on substrates by cluster beam deposition. The evolution of the photoluminescence was measured as a function of the time the samples were exposed to air. With gradual air exposure and oxidation, the photoluminescence increases in intensity and its peak wavelength shifts to the blue. At the same time, the photoluminescence band becomes wider. To remove the oxide layer, the samples were exposed to hydrofluoric acid (HF) vapor. The HF attack has no influence on the band position but leads to a smaller width. The observations can be explained in terms of quantum confinement as the origin of the photoluminescence. Only for the smallest Si nanocrystals, an interface state seems to limit the maximum photoluminescence energy to 2.1 eV.

The recombination statistics of the visible photoluminescence of silicon nanocrystals

AbstractA pulsed, high-power TEA CO2 laser with Unes in the region from 9.2 to 10.6 μm has been used to irradiate luminescent porous Si samples. The IR laser pulses heat the sample on a time scale much shorter than the PL decay time which is at 300 K for the PL at 1.65 eV in the order of tenth of μs. One IR pulse serves to increase the temperature of the luminescing particles in ∼2 μs up to 100°C. This increase of temperature leads to a efficient reduction of the photoluminescence (PL) intensity. However, the PL decay times are almost not affected by the heating pulse. Based on this measurement a picture of the recombination statistics that takes account of the granular Nature of the material is developed.