Photoluminescence of Au− formed in 12CaO · 7Al2O3 single crystal by Au+-implantation

Au+ ion implantation with fluences from 1 × 1014 to 3 × 1016 cm−2 into 12CaO · 7Al2O3 (C12A7) single crystals was carried out at a sample temperature of 600 °C. The implanted sample with the fluence of 1 × 1015 cm−2 exhibited photoluminescence (PL) bands peaking at ∼3.1 and ∼2.3 eV at ⩽150 K when excited by He–Cd laser (325 nm). This was the first observation of PL from C12A7. These two PL bands are possibly due to intra-ionic transitions of an Au− ion having the electronic configuration of 6s2, judged from their similarities to those reported on Au− ions in alkali halides. However, when the concentration of the implanted Au ions exceeded the theoretical maximum value of anions encaged in C12A7 (∼2.3 × 1021 cm−3), surface plasmon absorption appeared in the optical absorption spectrum, suggesting Au colloids were formed at such high fluences. These observations indicate that negative gold ions are formed in the cages of C12A7 by the Au+ implantation if an appropriate fluence is chosen.