The role of some shallow-trap centres in the photochromism of
Institut de Physique et Chimie des Matériaux de Strasbourg Groupe d'Optique
Nonlinéaire et d'Optoélectronique Unité mixte 380046 CNRS-ULP-EHICS
23 rue du Loess, 67037 Strasbourg Cedex, France
Accepted: 17 February 1999
A close correlation between thermally stimulated conductivity and thermally bleached photochromism experiments allows us to propose a charge transfer mechanism: free electrons are generated by an appropriate illumination, which either ionizes deep donor centres or creates band-to-band transitions. These electrons are trapped on shallow levels. Three of them act as reservoirs and in turn populate a deeper level which constitutes the fundamental state of the photochromic transitions. The model well explains the variation of the magnitude of the photochromism under variable optical excitation and de-excitation as well as its thermal stability.
PACS: 72.20.Jv – Charge carriers: generation, recombination, lifetime, and trapping / 65.90.+i – Other topics in thermal properties of condensed matter / 42.70.Gi – Light-sensitive materials
© EDP Sciences, 1999