Interface models for the photochromism and thermochromism of glasses with nanocrystals

Abstract A study was made of the (UV, X-ray)/temperature induced absorption spectra of glasses with AgCl or CuCl nanocrystals. New models are proposed for photochromic and thermochromic effects in these glasses. Bleaching of the photochromic CuCl-glass after irradiation goes synchronously with diminishing of the burned out spectral hole’s depth. The CuCl nanocrystal exciton dissociation due to the Coulomb field of carriers injected into traps at the glass/nanocrystal interface can account for this spectral hole burning. The photochromic induced spectra display excellent fit with the bands of well-known silicate glass radiation color centers. Trap parameters at the interface are estimated. In case of the thermochromic spectra, the transformation at temperatures above nanocrystal melting temperatures of a two-band absorption spectrum into a single narrow band is considered a unique argument for Mie Theory application. The data are interpreted in terms of a new model that involves reversible transformation of oblate spheroid silver metal particles to continuous silver coating at the inside surface of a cavity containing a nanocrystal or its melt.