Radiation-induced modification in network glass formers such as binary arseno-chalcogenides As-X (X=S, Se) is critically reexamined accepted possibility of volume restrictions in their realization. Destruction of covalent bonds in these glasses under above-bandgap exposure or high-energy irradiation is accompanied by relaxation into a new state. When this process occurs via switching of hoteronuclear (As-X) bonds into homonuclear (As-As) and (X-X) ones, like under intrinsic decomposition in As₂X₃, an additional volume appears in the glass, resulting in a red shift of the optical absorption edge (darkening effect). Assuming that double-bond-based quasi-tetrahedral X=As(X_1/2) ₃ units are stabilized in a glass due to inner pressure developed in nanoconfined geometry, an opposite blue shift (bleaching effect) is expected. This analysis, based on ab initio quantum-chemical modeling of atomic clusters, critically resolves speculations about quasi-tetrahedral X=As(X1/2)3 units as the principal species facilitating self-organization in arseno-chalcogenide networks.

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