Spectral analysis of the fatigue of the photoluminescence and of the creation of paramagnetic centres in amorphous Ge_xSe_1–x

Abstract

We report an extensive experimental study of the fatigue of the photo-luminescence and the photocreation of paramagnetic centres in a series of amorphous Ge _x Se_{1 – x} glasses. For each composition of this series, from pure selenium to Ge_0·4Se_0·6, we have studied the effect of the energy of the excitation light on these two photoinduced metastable phenomena. The experimental results are analysed by means of a model of progressive saturation across the sample from the illuminated area. This analysis allows us to define cross-sections for the fatigue of a luminescence centre and for the photocreation of a paramagnetic centre, respectively F and F_S. The energy spectra for F and F_S are quite different. This fact is inconsistent with the model of Street and Mott (1975) which predicts a single process for the photoluminescence fatigue and for the creation of paramagnetic centres. Therefore we discuss our results within the framework of several other models: variations on point-defect models and a model without defects. Finally, we propose a hybrid model where the photoluminescence and its fatigue are related to point defects as in the Street and Mott model, but where the paramagnetic centres originate from distorted ‘soft’ regions without point defects.