Absorption and emission of light in spark-processed silicon

Spark-processed Si (sp-Si) exhibits blue, green and red photoluminescence at around 385, 525 and 650 nm, depending on the wavelength of excitation. Its optical absorption spectrum reveals bands peaked approximately at 245, 277, 325 and 389 nm. The centers where absorption takes place were modeled as Si and silica clusters in an amorphous SiOxNy matrix using various embedding schemes. Geometry optimizations were applied prior to calculations of the absorption spectra of the clusters. The measured absorption spectrum of sp-Si and calculated absorption spectra were compared. Best agreement is achieved for Si particles embedded in amorphous SiOxNy matrix. The importance of the various embedding schemes is discussed and conclusions for the centers of emission are established.