O. A. Shalygina

Comparative study of photoluminescence of undoped and erbium-doped size-controlled nanocrystalline Si∕SiO2 multilayered structures

Spectra and transients of the photoluminescence (PL) of undoped and Er-doped size-controlled nanocrystalline Si∕SiO2 multilayered structures with mean nanocrystal size of 1.5–4.5nm have been comparatively investigated. The Er-doped structures exhibit a strong Er-related PL band at 0.81eV, while the efficiency of the intrinsic PL band of Si nanocrystals at 1.2–1.7eV decreases by several orders of magnitude in comparison with the undoped structures. At low temperature the PL spectra of the Er-doped structures show several dips separated by the energy of Si TO-phonon and bound to the transition energies between the second and third excited states to the ground state of Er3+. The Er-related PL is characterized by lifetimes of around 3–5ms, a weak temperature quenching, and a high efficiency, which is comparable or even stronger than that of the intrinsic PL in the corresponding undoped samples. This efficient sensitizing of the Er-related luminescence is explained by the structural properties of the samples, ...

Highly efficient sensitizing of erbium ion luminescence in size-controlled nanocrystalline Si/SiO2 superlattice structures

Comparative studies of photoluminescence (PL) of undoped and Er-doped size-controlled nanocrystalline Si/SiO2 superlattice structures show that the optical excitation of Si nanocrystals can be completely transferred to the Er3+ ions in surrounding SiO2, resulting in a strong PL line at 1.5 μm. The PL yield of the Er-doped structure increases for higher photon energy of excitation and for smaller nanocrystal sizes. This highly efficient sensitizing of the Er-related PL is explained by a strong coupling between excitons confined in Si nanocrystals and neighboring Er3+ ions in their upper excited states.

Population inversion of the energy levels of erbium ions induced by excitation transfer from the semiconductor matrix in Si-Ge based structures

Population inversion of the energy levels of Er3+ ions in Si/Si1−xGex:Er/Si (x = 0.28) structures has been achieved due to electron excitation transfer from the semiconductor matrix. An analysis of the photoluminescence kinetics at a wavelength of 1.54 μm shows that up to 80% of the Er3+ ions are converted into excited states. This effect, together with the high photoluminescence intensity observed in the structures studied, shows good prospects for obtaining lasers compatible with planar silicon technology.

Erbium ion luminescence of silicon nanocrystal layers in a silicon dioxide matrix measured under strong optical excitation

The photoluminescence (PL) spectra and kinetics of erbium-doped layers of silicon nanocrystals dispersed in a silicon dioxide matrix (nc-Si/SiO2) are studied. It was found that optical excitation of nc-Si can be transferred with a high efficiency to Er3+ ions present in the surrounding oxide. The efficiency of energy transfer increases with increasing pumping photon energy and intensity. The process of Er3+ excitation is shown to compete successfully with nonradiative recombination in the nc-Si/SiO2 structures. The Er3+ PL lifetime was found to decrease under intense optical pumping, which implies the establishment of inverse population in the Er3+ system. The results obtained demonstrate the very high potential of erbium-doped nc-Si/SiO2 structures when used as active media for optical amplifiers and light-emitting devices operating at a wavelength of 1.5 μm.

Nonmonotonic Dependence of the Photoluminescence Peak Position of Cadmium Selenide Nanocrystals as a Function of the Excitation Photon Energy

The photoluminescence properties of colloidal CdSe quantum dots with a mean size of 3 nm were studied. The experimental results revealed the nonmonotonic dependence of the photoluminescence peak’s position as a function of the excitation photon energy being varied from 2.41 to 3.68 eV. This effect can be explained by the size distribution of the nanocrystals and the spectral dependence of their absorption coefficients.

Carrier capture and recombination in CdSe/ZnSe quantum dots

Time-resolved photoluminescence (PL) spectra of self-assembled CdSe/ZnSe quantum dots (QDs) are measured with a view to identifying the QD-size dependence of carrier capture and recombination in a single QD. The PL is excited by optical absorption in the ZnSe barrier layers under weak and strong irradiation with femto-and nanosecond laser pulses, respectively. In the case of weak excitation, the PL dynamics observed in a QD and the barrier layers are attributed to (i) fast carrier diffusion in the barrier layers, (ii) intense capture of carriers by the QD, (iii) fast carrier relaxation to the QD ground state, and (iv) dependence of the carrier capture and recombination times on the QD size. In the case of strong excitation, PL spectra are measured for different levels of excitation intensity and PL intensity is examined as a function of excitation intensity. It is established that (i) an increase in excitation intensity has a stronger effect on a high-frequency part of the spectrum and (ii) the intensity characteristic is essentially nonlinear. These findings are explained by state filling and/or decrease in carrier capture rate as the QD becomes increasingly full.

Photoluminescence of erbium ions in heterostructures with silicon nanocrystals

Photoluminescence properties of erbium-doped silicon dioxide layers containing silicon nanocrystals with 1.5–4.5 nm average size are investigated. It is found that the intensity and mean lifetime of the Er3+-ion photoluminescence depend on the nanocrystal size, optical pump intensity, and temperature. The results obtained are explained both by the effect of the local environment on Er3+ ions and by the manifestation of nonradiative deexcitation of ions caused by the transfer of energy back into the solid-state matrix and the Auger processes.

Photoluminescence of Er3+ ions in layers of quasi-ordered silicon nanocrystals in a silicon dioxide matrix

The spectra and kinetics of photoluminescence from multilayered structures of quasi-ordered silicon nanocrystals in a silica matrix were studied for undoped samples and samples doped with erbium. It was shown that the optical excitation energy of silicon nanocrystals could be effectively transferred to Er3+ ions, which was followed by luminescence at a wavelength of 1.5 µm. The effectiveness of energy transfer increased as the size of silicon nanocrystals decreased and the energy of exciting light quanta increased. The excitation of erbium luminescence in the structures was explained based on dipole-dipole interaction (the Förster mechanism) between excitons in silicon nanocrystals and Er3+ ions in silica surrounding them.

Magnetic and magnetooptical properties of Au/Cu-wedge/15-Å-NiFe sandwiches

The results of an investigation of the magnetic and magnetooptical properties of Au/Cu-wedge/15-Å-NiFe sandwiches are reported. Oscillations of the equatorial Kerr effect as a function of the copper wedge thickness are observed. The period of these oscillations is found to be of the order of 5–6 Å. The experimentally observed oscillations of the equatorial Kerr effect are attributed to a quantum size effect.

Plasmon induced modification of silicon nanocrystals photoluminescence in presence of gold nanostripes

We report on the results of theoretical and experimental studies of photoluminescense of silicon nanocrystals in the proximity to plasmonic modes of different types. In the studied samples, the type of plasmonic mode is determined by the filling ratio of a one-dimensional array of gold stripes which covers the thin film with silicon nanocrystals on a quartz substrate. We analyze the extinction, photoluminesce spectra and decay kinetics of silicon nanocrystals and show that the incident and emitted light is coupled to the corresponding plasmonic mode. We demonstrate the modification of the extinction and photoluminesce spectra under the transition from wide to narrow gold stripes. The experimental extinction and photoluminescense spectra are in good agreement with theoretical calculations performed by the rigorous coupled wave analysis. We study the contribution of individual silicon nanocrystals to the overall photoluminescense intensity, depending on their spacial position inside the structure.