Abstract

UV-visible transmission measurements were performed on GexSe₁-ₓ chalcogenide glasses at room temperature over the spectral range of 200-800nm. The transmission spectra exhibited transient relaxation behavior particularly evident in the 700-800nm range. Notably, this relaxation behavior could not be adequately described using the conventional Debye model. Instead, the relaxation dynamics were analyzed using the Kohlrausch-Williams-Watts (KWW) function:

While the KWW model typically assumes stretched exponential behavior with β in the range 0<β<1, the relaxation in these samples was better described using compressed exponential functions, with β values observed in the range 2.7<β<3.5. This compressed relaxation indicates a departure from conventional glassy (liquid-like) dynamics, instead reflecting solid-like behavior. It is interpreted as arising from the clustering of atomic groups or GeSe₄/₂ tetrahedral units, where increasing structural compactness or compression leads to a decrease in characteristic relaxation time (τ). This behavior contrasts with the typical diffusive motion seen near the glass transition in more fluid-like systems. Furthermore, the analysis links the shape parameter β to the degree of structural linearity or nonlinearity, thereby relating it to micro-collapse mechanisms and dynamic heterogeneity in the glass network. The variation in β serves as a dynamic signature of the underlying structural organization, offering insight into the relationship between atomic-scale structure and macroscopic optical response.

Keywords:Debye relaxation; Chalcogenide glasses; Absorption; Nonlinearities; Photo-relaxation; Relaxation dynamics