CHAPTER 1. FLUORESCENT SILICON CLUSTERS 26 techniques have been explored. Responses to various chemical treatments and correlation to fluorescence performance, as well as chemical analysis, have been employed. The results are not always consistent. Konkievicz and co-workers prepared porous silicon films and investigated photoluminescence over a wide spectral range. Under photoexcitation with 193 nm excimer laser radiation, they observed red luminescence. After annealing in an oxygen atmosphere with 2% organochlorine, blue luminescence around 400 nm appeared. The blue band appeared at annealing temperatures of 750 $^{0}$C and increased in intensity up to temperatures of 1050 $^{0}$C, after which no fur- ther increases were seen (Kontkiewicz et al., 1994). Fourier transform infrared (FTIR) measurements showed the presence of silicon oxide. This preparation was also repeated in a nitrogen atmosphere. Annealing in nitrogen did not pro- duce blue luminescence. This led to the conclusion that the blue luminescence originates from oxidised nanostrutured silicon, although later work showed a cor- relation between blue fluorescence intensity and nitrogen content (Dasog et al., 2013). Results similar to those of Konkievicz and co-workers have also been reported from porous Si that was oxidized and annealed at 880 $^{0}$C (Kanemitsu et al., 1994). Depending on the production method, the band maxima range from 400 to 460 nm (Yu et al., 1998). The specific response of red and blue luminescence intensity to repeated etching and oxidation was investigated by Lockwood and co-workers, leading them to the conclusion that, at least, quan- tum confinement cannot be responsible for the blue luminescence (Lockwood et al., 1996). An important aspect of chemical treatment is how silicon nanoparticles in- teract with an aqueous environment. This is because water is a strong oxidising agent, but also because of the relevance of nanoparticles to biomedical applica- tions. Water may also be expected to quench fluorescence because of its dense