Isotopic fingerprints of gold-containing luminescence centers in 28Si

We have recently shown that the dramatic reduction in linewidth of many deep luminescence centers in highly enriched 28Si can lead to the observation of isotopic fingerprints, revealing not only that a specific element is involved in the defect complex, but also the number of atoms of that element. This has led to many surprises regarding the actual constituents of supposedly well known luminescence centers, as well as the discovery of new members of a family of four-atom centers where the constituents can be chosen from Cu, Ag, Au and Li. Obtaining the isotopic fingerprint of Au is problematic, since only 197Au is stable, but we have now used the relatively long-lived 195Au to reveal the presence, and the number, of Au atoms in several of these centers. We find a series of four-atom centers containing one Au plus Cu and/or Li. Surprisingly, the Au isotopic fingerprint also reveals a series of five-atom centers containing a single Au plus Cu and/or Li. Further evidence for the ubiquity of these four- and five-atom defects is provided by two previously observed Pt-related centers, with luminescence at 884 and 777 meV, which are present in these samples due to the decay of 195Au to 195Pt. In addition to Pt, these centers are found to contain three and four Cu atoms, respectively.