Effect of ion irradiation on the structure and luminescence characteristics of porous silicon impregnated with tungsten-telluride glass doped by Er and Yb impurities

Using transmission electron microscopy and elemental analysis, it has been shown that tungsten telluride glass (TTG) containing erbium and ytterbium as impurities penetrates into pores of porous silicon (PS) when melted in vacuum at 500°C. It has been found that the intensity of photoluminescence (PL) of erbium at the wavelength of 1.54 μm in PS: TTG layers increases by a factor of up to 5 in the layers irradiated by P⁺ and Ar⁺ ions. This is assigned to ion mixing which favors interaction among the Er ions and PS-embedded Si nanocrystals initiating sensitization of the PL, as well as to broadening of the glass-impregnated PS region. Implantation of the lighter Ne⁺ ions affects only weakly the PL of erbium ions.     

Photoluminescence of porous silicon saturated with tungsten-tellurite glass with rare-earth metal impurities

It has been shown that the presence of silicon nanoparticles in a layer of porous silicon saturated with tungsten-tellurite glass causes an increase in the photoluminescence quantum efficiency of erbium (1530 nm) by an order of magnitude in the case of long-wavelength excitation and an enhancement of the ytterbium photoluminescence (980 nm) by almost 50 times and erbium photoluminescence by 25 times in the case of short-wavelength pumping. This luminescence enhancement is explained by the formation of additional channels of transfer of external excitation by silicon nanocrystallites in porous silicon to impurity ytterbium and erbium ions in tungsten-tellurite glass.     

Photoluminescence and EPR of porous silicon formed on <Emphasis Type="Italic">n</Emphasis><Superscript>+</Superscript> and <Emphasis Type="Italic">p</Emphasis><Superscript>+</Superscript> single crystals implanted with boron and phosphorus ions

The effect of combined doping by shallow donor and acceptor impurities on boosting the quantum yield of porous-silicon photoluminescence (PL) in the visible and near IR range was studied using phosphorus and boron ion implantation. Nonuniform doping of samples and subsequent oxidizing annealing were performed before and after porous silicon was formed on silicon single crystals strongly doped by arsenic or boron up to ≈10¹⁹ cm^?3. The concentration of known P_b centers of nonradiative recombination was controlled by electron paramagnetic resonance. It is shown that there is an optimal joined content of shallow donors and acceptors that provides a maximum PL intensity in the vicinity of the red part of the visible spectrum. According to estimates, the PL quantum yield in the transitional n ⁺⁺-p ⁺ or p ⁺⁺-n ⁺ layer of porous silicon increases by two orders of magnitude as compared to that in porous silicon formed on silicon not subjected to ion irradiation.     

Investigation of the long-range effect of light irradiation by means of Rutherford backscattering/ion channeling spectroscopy

This paper presents the results of the first experiments on the observation of the long-range effect by means of Rutherford backscattering/ion channeling spectroscopy under irradiation of a silicon crystal by visible light.     

Influence of the ion synthesis and ion doping regimes on the effect of sensitization of erbium emission by silicon nanoclusters in silicon dioxide films

The photoluminescence spectra of erbium centers in SiO₂ films with ion-synthesized silicon nanoclusters under nonresonant excitation were investigated. Erbium was introduced into thermal SiO₂ films by ion implantation. The dependences of photoluminescence intensity on the dose, the order of ion implantation of Si and Er, the annealing temperature, and additional Ar⁺ and P⁺ ion irradiation regimes, i.e., factors determining the influence of radiation damage and doping on sensitization of erbium luminescence by silicon nanoclusters, were determined. It was found that the sensitization effect and its amplification due to doping with phosphorus are most pronounced under the conditions where nanoclusters are amorphous. The quenching of photoluminescence due to radiation damage in this case manifests itself to a lesser extent than for crystalline nanoclusters. The role of various factors in the observed regularities was discussed in the framework of the existing concepts of the mechanisms of light emission and energy exchange in the system of silicon nanoclusters and erbium centers.     

Phonon-assisted radiative electron-hole recombination in silicon quantum dots

The temperature dependence of the photoluminescence (PL) spectrum of silicon quantum dots (QDs) is studied both theoretically and experimentally, and the time of the corresponding electron-hole radiative recombination is calculated. The dependence of the recombination time on the QD size is discussed. The experiment shows that the PL intensity decreases by approximately 60% as the temperature increases from 77 to 293 K. The calculated characteristic recombination time has only a weak temperature dependence; therefore, the decrease in the PL intensity is associated primarily with nonradiative transitions. It is also shown that the phonon-assisted radiation is much more efficient than the zero-phonon emission. Moreover, the zero-phonon recombination time depends on the QD radius R as R⁸, whereas the phonon-assisted recombination time depends on this radius as R³.     

Mechanism of quantum dot luminescence excitation within implanted SiO2:Si:C films

Results of the investigation of photoluminescence (PL) mechanisms for silicon dioxide films implanted with ions of silicon (100 keV; 7 × 10(16) cm(-2)) and carbon (50 keV; 7 × 10(15)-1.5 × 10(17) cm(-2)) are presented. The spectral, kinetic and thermal activation properties of the quantum dots (Si, C and SiC) formed by a subsequent annealing were studied by means of time-resolved luminescence spectroscopy under selective synchrotron radiation excitation. Independent quantum dot PL excitation channels involving energy transfer from the SiO(2) matrix point defects and excitons were discovered. A resonant mechanism of the energy transfer from the matrix point defects (E' and ODC) is shown to provide the fastest PL decay of nanosecond order. The critical distances (6-9 nm) of energy transport between the bulk defects and nanoclusters were determined in terms of the Inokuti-Hirayama model. An exchange interaction mechanism is realized between the surface defects (E(s)'-centres) and the luminescent nanoparticles. The peculiarities of an anomalous PL temperature dependence are explained in terms of a nonradiative energy transfer from the matrix excitons. It is established that resonant transfer to the luminescence centre triplet state is realized in the case of self-trapped excitons. In contrast, the PL excitation via free excitons includes the stages of energy transfer to the singlet state, thermally activated singlet-triplet conversion and radiative recombination.     

Influence of ion irradiation on the morphology, structure, and optical properties of gold nanoparticles synthesized in SiO2 and Al2O3 dielectric matrices

Irradiation of fused quartz (SiO₂) and sapphire (Al₂O₃) by Ne⁺ and F⁺ ions with medium energies and their subsequent annealing enables us to control the intensity and frequency of surface plasmon resonance in Au nanoparticles (NPs) synthesized in oxide matrices. The control process can be implemented because NPs dissolve during irradiation and undergo partial reconstruction at annealing. The degree of reconstruction depends on the matrix material and the type and dose of ions. It has been found that the difference in the results obtained by means of irradiation with ions with similar masses is substantially affected by the chemical nature of the ions. The composition, morphology, and structure of the unirradiated and irradiated layers are investigated by transmission electron microscopy, X-ray photoelectron spectroscopy, and spectroscopic ellipsometry.     

Formation of gold nanoparticles in single-layer and multi-layer ensembles of light-emitting silicon nanocrystals using ion implantation

The possibility of ion beam formation of gold nanoparticles in SiO2 and Al2O3 matrices with presynthesized single-layer and multi-layer ensembles of silicon nanocrystals is revealed by analyzing the spectra of optical transmission. The parameters of gold nanoparticles are estimated. It is shown that luminescent properties of Si nanocrystals are preserved under irradiation with gold ions.     

A mechanical model of amorphization under ion bombardment

A mechanical model is proposed for the amorphization of solids. The model is based on a concept according to which the accumulation of radiation-induced defects gives rise to forces and force moments that act on local volumes of the material and are responsible for fragmentation. The estimates obtained demonstrate that the proposed model can adequately describe the amorphization of solids only with allowance made for strain waves generated during reactions between defects. This model is consistent with the paracrystalline structure of silicon layers transformed into the amorphous state under ion bombardment.