Silicon nanocrystals: from bio-imager to erbium sensitizer

The work in this thesis has been centred on the light emitting properties of silicon nanocrystals and the possible applications of this particular material platform to various topics ranging from bio-imaging to erbium ion sensitization. Silicon nanocrystals as bio-imaging agent have been investigated by employing colloidal dispersion of individual silicon nanocrystals where surface properties could be controlled to a great extent. By using a suitable functionalization scheme, high quality hydrophilic luminescent nanoparticles were produced. Using the improvements in the physical coating, bio-imaging on living cells (in vitro) was demonstrated showing that silicon nanocrystals have a great potential in bio-imaging and offer a promising alternative to commonly used fluorescence dyes. A part from being good light emitters, silicon nanocrystals could also amplify the light. This is a reason why the part of the work in this thesis has been dedicated to the investigation of silicon nanocrystals as a gain material. While most of the studies on this topic are concentrated on the nanocrystal surface as a driving mechanism behind the optical amplification, the work presented in this thesis concerns the study of a zero phonon (direct) optical transition as a possible source of optical amplification in this material system. To this scope, investigation of the dynamics of the system on a nanosecond time-scale and under high excitation conditions has been employed. Additional insight on ultrafast dynamics has been obtained by using optical cavities in the form of optically active free-standing micro-disk resonators. Finally, in the last part of this thesis a study of Er3+-doped Silicon-Rich-Oxide (SRO) materials and Er3+-doped SRO based devices is presented. This part of the work differs from the rest of the work reported in this thesis as is not focused on the light emitting properties of silicon nanocrystals but mostly on their non-radiative process engineering (energy transfer to erbium ions). Er3+ doped SRO opens the route towards compact waveguide amplifiers and lasers and allows for the possibility of electrical injection schemes, which are not realizable in standard erbium amplifiers used in EDFA for telecom applications. To that end, novel opto-electronic structures were proposed, modeled and manufactured and preliminary results of their performance were presented. The sensitization mechanism between silicon nanoparticles and erbium ions was studied and its complex nature was illustrated. Although, the acquired knowledge of physics involved was not sufficient for formulation of a complete working theory of the energy transfer process, some important physical aspects of this process have been elucidated paving the way towards its complete understanding.