Photoluminescence sites on MCM-48

Photoluminescence (PL) was used to study the emission of light from siliceous MCM-48 that had undergone rapid thermal annealing. Two PL bands were observed at 1.9 and 2.16 eV and assigned to the non-bridging oxygen hole centers (NBOHCs) and the NBOHCs associated with broken bonds, respectively. The PL intensity is enhanced after rapid thermal annealing. Based on the surface chemistry, the enhancement is explained by the generation of NBOHCs that originate from the hydrogen-bonded and single silanol groups on the MCM-48 surface. The PL intensity in MCM-48 degrades with time during photoexcitation. The dominant mechanism of PL degradation involves the formation of the chemisorbed oxygen-related complexes (probably O2 molecules) on the surface, which are adsorbed onto the surface and act as an efficient quencher of PL. The PL features of MCM-41 are also discussed.