Recombination and excited-state absorption at photoluminescence centres in crystalline and amorphous arsenic triselenide

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Abstract
Results are presented of a detailed study of optical transitions from the excited states of the photoluminescence (PL) centres in c-As2Se3, including the first observation of photo-induced optical absorption (PA) arising from these states. It is inferred from observations of the decay rates and polarization dependences of the PL and PA that the lowest excited state of the PL centre is a triplet exciton state, and that the singlet-triplet splitting is 4 × 10−3 eV. The PA in the spectral range measured (0·4–2 eV) appears to probe transitions from the excttcd PL centres to states in the continuum. Also observed for the first time is PA from the excited states of the PL centres in a-As2Se3. The properties of the PL centres in a-As2Se3 and c-As2Se3 are compared.