Nonlinear optical effects in porous silicon: Photoluminescence saturation and optically induced polarization anisotropy

Optical Properties of Si Nanocrystals

“…Since the efficiency of occupation is now dependent on the insurface plane direction of the electric field of the pump beam, I k and I c components of the probe beam-induced PL and, therefore, r have to exhibit angular in-plane anisotropy. The exact dependence of r on the angle between pump and probe beam accounting Optical Properties of Si Nanocrystals for the real geometry of nanoparticles has been calculated in [97,104] and found to be in a good agreement with experimental data. Fig.…”

“…PL saturation and hole burning effects are seen especially clearly in polarization-resolved mode [97,104]. As was discussed above, using the polarized light of an optical pump beam, we can selectively excite crystals whose largest dimension is parallel to the polarization of the pump and in this way prepare a temporary or permanent anisotropic in-surface plane distribution of unexcited or not permanently charged nanocrystals.…”

“…Again two phonon replicas and a forbidden gap known from the resonant PL measurements are observed. The degradation becomes less efficient at low detection energies as in the case of the nonresonant fatigue effect [97,104]: the energy gained by the carrier is equal to 2E gap and at small E gap may not be enough to overcome the potential barrier. At low temperatures, the spectrum of the``holeº and its magnitude do not change at least during tens of hours.…”

“…This is not the case when PL saturation experiments are performed in a pump±probe technique. We have used an intense CW laser to achieve a permanent average occupation of nanocrystals by e±h pairs while monitoring the response to a weak probe pulse or modulated CW excitation source [97]. Lifetimes, measured as a function of the pump beam intensity, do not change at low pump beam intensity but decrease in the PL saturation regime (see Fig.…”

Polarization memory effect on nonlinear photoluminescence of semimagnetic semiconductor Cd0.8Mn0.2Te

“…In the first case, PL is emitted by an anisotropic luminous body or ensemble of it. For example, ensemble of CdSe nano-rods [1], a carbon nanotube [2], porous Si nanocrystals which have nonspherical shape [3]. The mechanism of this case is as below.…”