1, 2 and 3 Dimensional Photonic Materials Made Using Ion Beams: Fabrication and Optical Density-of-States

Abstract

The spontaneous emission rate of an optical probe atom is strongly dependent on its optical environment. This concept is well known in one-dimensional geometries, e.g. for an atom placed near a mirror, a dielectric interface, or in a microcavity.1,2,3,4,5,6 With the recent development of two- and three-dimensional photonic crystals it becomes possible to tailor optical modes and the local optical density-of-states (DOS) to a much greater extent. Large effects on the spontaneous emission rate of optical probe ions are expected in these materials. In order to study these effects, accurate and reproducable methods of optical doping must be developed. Ion implantation is a technique with which ions can be introduced at a well defined depth and concentration into any material, in a reproducible fashion. In this paper we demonstrate this concept for Cr ions implanted near the surface of an Al2O3 single crystal. In this one-dimensional system the DOS near the interface can be calculated from Fermi’s Golden rule. It can be experimentally varied by bringing liquids with different refractive index in contact with the crystal surface, as we will show. In this way it becomes possible to determine the radiative decay rate and quantum efficiency of Cr in Al2O3. These well-characterized samples can then be used to study the changes in spontaneous emission in more complicated systems such as absorbing and strongly scattering materials. We also study the DOS in a one-dimensional system with two interfaces: a SiO2 thin film on a Si substrate. Er ions are implanted in the SiO2 thin film, and their radiative decay rate is derived from experiments in which the DOS is varied. Using these data it becomes possible to study the effect of a varying DOS in a 3-dimensional system composed of Er-doped SiO2 colloidal particles. Large effects on the spontaneous emission rate are observed, as will be shown. Finally, we will discuss the design and fabrication of two-dimensional photonic crystals in silicon. A method to incorporate a luminescent dye in these crystals is described which may be used to study the DOS.