Silicon nanocrystals are an extensively studied light-emitting material due to their inherent biocompatibility and compatibility with silicon-based technology. Although they might seem fall behind rival, namely, direct band gap based semiconductor nanocrystals, when it comes the emission of light, room for improvement still lies in exploitation various surface passivations. In this paper, we report on original way, taking place at temperature ambient pressure, replace silicon oxide shell...

The three-dimensional photonic crystals used in this study were synthetic opals, composed of submicron silica spheres, close-packed a face-centered cubic structure with period 200 nm, that exhibit stopbands around 600 nm. We present measurements the optical gain CdS quantum dots (QDs) embedded inside interstitials between spheres. Unlike usual spectra QDs glass matrices, which display maximum at energies first quantum-confined transitions, for is shifted toward high-frequency edge stopband...

We discuss applicability of the variable stripe length method to experimental investigation optical gain in a luminescent layer that behaves like planar waveguide. show an interplay between output direction guided light modes and numerical aperture collection optics may lead artifact manifesting itself as apparent but false gain. propose way circumvent this inconvenience by using “shifting excitation spot” complementary measurement. The is demonstrated on Si nanocrystals embedded into...

In this paper, we discuss the validity of band structure concept in silicon nanocrystals a few nanometers size. We introduce general method which allows reconstruction fuzzy electronic from ordinary real-space calculations. A comprehensive study realistic nanocrystal is given including full geometric and relaxation with surface passivating groups. particular, combine large-scale density functional theory calculations to obtain insight into luminescence properties up 3 nm size depending on...

Silicon, a semiconductor underpinning the vast majority of microelectronics, is an indirect‐gap material and consequently inefficient light emitter. This hampers ongoing worldwide effort towards integration optoelectronics on silicon wafers. Even though nanocrystals are much better emitters, they retain nature. Here, we propose solution to this long‐standing problem: can be transformed into with fundamental direct bandgap via concerted action quantum confinement tensile strain. We document...

Colloidal suspensions of small silicon nanoparticles (diameter around 2 nm) with fast and efficient ultraviolet–blue photoluminescence (PL) band are fabricated by enhanced electrochemical etching Si wafers. The detailed study excitation spectra in a wide range photon energies (270–420 reveals specific behavior the Stokes shift PL that agrees well theoretical calculation optical transitions nanocrystals is distinct from emission dioxide defects.

Small oxidized silicon nanocrystals of average sizes below 3.5 nm are prepared using modified electrochemical etching a wafer. Modifications introduced in the procedure together with postetching treatment H2O2 lead to decrease nanocrystalline core size and also, some extent, changes surface oxide. The interplay between these two factors allows us blueshift photoluminescence (PL) spectrum from 680 down 590 nm, which is accompanied by PL dynamics. This continual development, however, stops at...

We collect a large number of experimental data from various sources to demonstrate that free-standing (FS) oxide-passivated silicon nanocrystals (SiNCs) exhibit considerably blueshifted emission, by 200 meV on average, compared those prepared as matrix-embedded (ME) ones the same size. This is suggested arise compressive strain, exerted their matrix, which plays an important role in light-emission process; this strain has been neglected up now opposed impact quantum confinement or surface...

Porous silicon grains embedded in the phosphorus doped SiO2 matrix exhibit improved photoluminesce properties and better stability comparison with native porous samples. We have tested this material for presence of room temperature optical amplification under femtosecond (100 fs, 395 nm) excitation. Combined variable stripe length shifted excitation spot experiments reveal positive gain, net modal gain coefficient reaching 25 cm−1 at a pump intensity 1.1 W/cm2 (mean power). The spectrum is...

Abstract Spectra of individual silicon nanocrystals within porous Si grains are studied by the wide‐field imaging microspectroscopy and their ON – OFF blinking is detected confocal single‐photon‐counting microscopy. Observed spectral properties comprise all features reported before in differently prepared single (SiNCs). Former apparently contradictory results shown to be due different experimental conditions. When effect dark periods ( switching) removed common ultimate photoluminescence...

We report on a detailed study of the dynamics photoexcited carriers in red-emitting porous silicon at room temperature after excitation by 532-nm picosecond laser pulses. Experimental techniques time-resolved absorption (pump and probe) photoluminescence are used to cover very large time interval ${10}^{\mathrm{\ensuremath{-}}11}$--${10}^{\mathrm{\ensuremath{-}}4}$ s. The exhibits fast slow components. component (\ensuremath{\sim}${10}^{\mathrm{\ensuremath{-}}10}$ s) is interpreted as...

In this paper we study the influence of progressing oxidation on photoluminescence spectra small silicon nanocrystals (SiNCs). H-terminated SiNCs exhibit only a fast approximately nanosecond component at ∼525 nm, quenched and redshifted to ∼550 nm by oxidation. At same time new microsecond appears, intensity which progressively increases its peak position redshifts continuously from 575 up 660 nm. We interpret our observations in terms quasidirect core electron-hole pair recombination...

Silicon nanocrystals (SiNCs) smaller than 5 nm are a material with strong visible photoluminescence (PL). However, the physical origin of PL, which, in case oxide-passivated SiNCs, is typically composed slow-decaying red–orange band (S-band) and fast-decaying blue–green (F-band), still not fully understood. Here we present interpretation F-band based on results an experimental study, which combine temperature (4–296 K), temporally (picosecond resolution) spectrally resolved luminescence...

We investigate the blue photoluminescence of Si+-implanted SiO2 films under picosecond UV excitation. The emission intensity exhibits a nonlinear increase with increasing excitation intensities, accompanied by pulse shortening. decays nonmonoexponentially in time. However, nonlinearities are not associated significant spectral narrowing. To explain results, we propose and numerically kinetic model based on competition between radiative (both spontaneous stimulated) nonradiative recombination...

Photoluminescence dynamics in silicon nanocrystals measured by a femtosecond up-conversion technique are reported. The samples were prepared embedding porous grains sol-gel derived SiO2 matrix. Efficient initial relaxation of the excess energy photoexcited carriers with effective rate ⩾3.8eV∕ps was observed. A fast decay component (400fs) photoluminescence signal found and interpreted terms quenching interior exciton radiative recombination carrier trapping on nanocrystal surface. ultrafast...

We present a study of ultrafast carrier transfer from highly luminescent states inside the core silicon nanocrystal (due to quasidirect transitions) on nanocrystal-matrix interface.This leads sub-picosecond luminescence decay, which is followed by slower decay component induced relaxation lower interface states.We investigate dynamics for two different surface passivation types and we propose general model describing spectral dependence dynamics.Our results stress crucial role energy...

Silicon nanocrystals (Si-ncs) of sufficiently small size, emitting luminescence at short wavelengths (which implies the occurrence quasi-direct radiative recombination) and being densely packed in a planar thin film ensures stimulated emission (StE) lifetime) can become suitable active material for observation StE visible region. In this paper, we describe fabrication method nanostructures type, based on enhanced electrochemical etching silicon wafers followed by embedding porous grains into...

In this paper we present time-resolved optical gain spectroscopy using the variable stripe length technique in combination with shifting excitation spot under pumping nanosecond laser pulses. Measurements reveal positive on a time scale at 430 nm (F-band), accompanied by spectral narrowing and threshold behaviour of amplified spontaneous emission as function intensity. We show that presence slow-red (S-band) component critically influences observation stimulated from F-band.

Abstract The article presents a short overview of the worldwide experimental activity directed towards vindicating occurrence positive optical gain in dense assemblies luminescent silicon nanocrystals. In spite an intense interest field, achieved results are non‐uniform till now. Hints how to proceed further given.

Strain-engineered silicon nanocrystals (SiNCs) have recently been shown to possess direct bandgap. Here, we report the observation of a rich structure in single-nanocrystal photoluminescence spectra strain-engineered direct-bandgap SiNCs temperature range 9–300 K. The relationship between individual types is discussed, and numerical modeling spectral diffusion experimentally acquired reveals common origin for most types. intrinsic shape be that contains three peaks, approximately 150 meV...

A new emission band in AgBr is attributed to electron-hole-liquid recombination. Excitonic molecules appears only at higher excitation and temperature, corresponding a limited region of the ($T, n$) plane called biexciton pocket.