Rapid-darkening, wavelength-tunable photochromic compositions, systems, and methods

Abstract

Rapid-darkening and wavelength-tunable photochromic compositions and systems are disclosed. Nanoparticles photochromically darken in response to incident light by photo-oxidizing a dopant to reversibly create an optically absorbing mid-gap electronic state. The wavelengths that trigger photochromic darkening as well as the absorbed wavelengths may be tuned by changing the nanoparticle composition, the nanoparticle size, and/or the dopant. The time for reversal of darkening may be tuned using hole-accepting ligands attached to the nanoparticles as well as hole-accepting molecules adjacent to the nanoparticles. Some variations provide a photochromic composition comprising: semiconductor nanoparticles that do not include ZnS, ZnSe, ZnTe, or ZnInS; transition-metal dopant particles; and organic ligands bonded to the semiconductor nanoparticles, wherein the organic ligands contain a carboxylate functional group, a thiol functional group, an amine functional group, or a combination thereof. In the disclosed systems, there is an on/off switch for the photochromic function. Many photochromic uses are described.