EVANESCENT LUMINESCENCE AND NANOMETER-SIZE LIGHT-SOURCE

Subwavelength light sources have been constructed with the aid of luminescent materials. These EXCITOR (exciton transmitted optical radiation) sources are of both theoretical and practical interest. The production of evanescent luminescence may test some of the predictions of quantum electrodynamics concerning the interactions of matter and radiation (e.g., when the emission process and the "subsequent" absorption process are no longer independent). Furthermore, the scannable luminescent tip can be applied to near-field optical microscopy, to scanning exciton microscopy, and to sub-microspectroscopy. An example of an EXCITOR consists of a gold-plated glass micropipette with an inner diameter tapering down to 50 nanometer, "plugged" with an anthracene microcrystal or a polymeric matrix doped with a laser dye. Design considerations involve optical, excitonic, photochemical, and mechanical properties of the luminescent point source. In the ideal limit, the luminescent source consists of a single active chromophore (analogous to the photosynthetic reaction center). As it is scanned over a sample, it senses a variety of perturbations on the atomic or molecular scale such as quenching or external heavy atom effect.