Surface brightens up Si quantum dots: direct bandgap-like size-tunable emission

• DOI: 10.1038/lsa.2013.3
• Publication Date: 2013-01-04T07:18:51Z
• Authors: Kateřina Dohnalová; Alexander N Poddubny; Alexei A Prokofiev; Wieteke DAM de Boer; Chinnaswamy P Umesh; Jos MJ Paulusse; Han Zuilhof; Tom Gregorkiewicz
• Keywords: nanoclusters; IR-89895; 02 engineering and technology; 530; dependent photoluminescence; 7. Clean energy; 620; optical-properties; silicon nanocrystals; confinement; luminescence; origin; METIS-293901; functionalization; nanoparticles; 0210 nano-technology; alkyl

Colloidal semiconductor quantum dots (QDs) constitute a perfect material for ink-jet printable large area displays, photovoltaics, light-emitting diode, bio-imaging luminescent markers and many other applications. For this purpose, efficient light emission/absorption spectral tunability are necessary conditions. These currently fulfilled by the direct bandgap materials. Si-QDs could offer solution to major hurdles posed these materials, namely, toxicity (e.g., Cd-, Pb- or As-based QDs), scarcity QD with In, Se, Te) and/or instability. Here we show that combining confinement dedicated surface engineering, biggest drawback of Si—the indirect nature—can be overcome, ‘direct bandgap’ variety is created. We demonstrate transformation on chemically synthesized using state-of-the-art optical spectroscopy theoretical modelling. The carbon termination gives rise drastic modification in electron hole wavefunctions radiative transitions between lowest excited states attain bandgap-like’ (phonon-less) character. This results fast emission, tunable within visible range size. findings fully justified tight-binding model. When C replaced oxygen, emission converted into well-known red luminescence, microsecond decay limited tunability. In way, convert ‘traditional’ form, thoroughly investigated past. Surface engineering provide silicon photoluminescence region. finding Kateřina Dohnalová colleagues from University Amsterdam Wageningen Netherlands, who studied properties alkyl-capped dots. They believe can modify energy band structure dot allow ‘direct-bandgap-like’ blue photoluminescence. tuned across spectrum changing size has rate 100,000 times stronger than bulk silicon. future, such prove useful making diodes as label experiments, wide