Electron‐paramagnetic‐resonance study of silver halide photochromic glasses: Darkening mechanism Available to Purchase

The mechanism of darkening of standard silver halide photochromic glass is studied by electron paramagnetic resonance (EPR) of photogenerated divalent copper ions. A time resolution of the EPR spectra was obtained by recording the evolution with the irradiation time of the EPR intensity at various magnetic‐field strengths. It is shown that only one copper species is photogenerated during darkening. This species is a Cu^II‐silver vacancy complex oriented along a [110] direction. The electron ground state has a predominantly dz² character. The activation energy of the formation of this complex, E=0.06±0.01 eV, is controlled by the migration of interstitial silver ions. It is also shown that the silver vacancy of the complex is generated during the hole trapping by the monovalent copper ion.