Luminescence due to the indirect band-gap transition activated by the inter-valence transition of Se clusters confined in 13X zeolite

Nanoclusters of Se have been incorporated in the supercage of 13X zeolite. Raman scattering results have established that the Se clusters confined in 13X mainly take the form of chain molecules. Intensive near-infra-red light emission at 1.54 eV is recorded in the photoluminescence measurements. Such a low-energy band-gap transition has not been reported in other forms of selenium. The luminescence is assigned to the exciton of the indirect optical transition between lone-pair and σ* bands of Se chains. The FTIR measurements show an inter-valence-gap transition at 0.38 eV (3064 cm−1) which activates the indirect band-gap transition. The blue shift of the excitonic energy of the indirect band in Se/13X, from that of the bulk t-Se, is very small.