Photochromism induced in an electrolytically pretreated Mo03 thin film by visible light

Abstract

PHOTOCHROMIC materials, whose optical absorption properties change in response to light, are important for a number of technological applications. A stable, reusable photochromic thin-film could be used, for example, in optical displays and high-density memories. Thin films of some transition-metal oxides can be coloured blue by band-gap excitation using ultraviolet light^1–6. For use with common semiconductor laser sources, however, photo-chromic materials are required that respond to visible light. Here we report on the preparation of visible-light-sensitive, reversibly photochromic films of MoO₃. Pretreated, vacuum-evaporated MoO₃ thin films were slightly blued by cathodic polarization in a non-aqueous electrolyte; subsequent irradiation with visible light in air produced a strong colour enhancement. The photochromism could be erased by anodic polarization, and the coloration–decoloration process was repeatable over at least five cycles. The behaviour of these films contrasts with those blued by band-gap irradiation, which were not responsive to visible light.