Abstract

Clusters, consisting of a small number of atoms, have been in the focus of physical and chemical research for several decades. They often show dramatic size effects. The addition of a single atoms can change their properties rather abruptly because of, for example, the discreteness of shell filling (Knight et al. 1984) or sphere-packing effects (Echt et al. 1981). When clusters become larger and reach the nanometer scale, other effects are observed, such as quantum confinement; the intense red fluorescence observed for nanostructured silicon (Canham 1990; Cullis and Canham 1991; Wilson et al. 1993; Lockwood 1994; Cullis et al. 1997) is a popular and frequently cited example of this effect. The discovery of fluorescent nanoscale silicon at room temperature by Canham (Canham 1990) increased the already quite intense research into silicon clusters further, and to date numerous examples of nanostructured forms of fluorescent silicon have been reported (Takagi et al. 1990; Brus et al. 1995; Hirschman et al. 1996; Borsella et al. 1997; Ehbrecht et al. 1997; Cullis et al. 1997; Huisken et al. 1999; Pavesi et al. 2000; Belomoin et al. 2000, 2002; Falconieri et al. 2005; Mangolini et al. 2005; Brewer and von Haeften 2009; Vincent et al. 2010; He et al. 2011; Dasog et al. 2014; Li et al. 2016). Hence, we have a rich set of data available on electronic and structural properties that underpin our understanding of the fluorescence of silicon clusters and nanoparticles.