We discuss the enhancement of spontaneous emission of fluorescent organic dyes when placed in micropillar microcavities and also in an optical nanocavity. We show experimentally that an enhancement in the spontaneous-emission rate of 1.78 +/- 0.04 times can be realized by placing a thin-film of the molecular dye Lumogen Red dispersed in a polymer matrix into a 3 mu m diameter micropillar having a Q-factor of 680. We then model the optical properties of Noda nanocavities in vertically symmetric and asymmetric slab waveguides using TiO2 as a high-index dielectric, with the cavity mode wavelength tuned to 713 nm. We estimate that such cavities will have a maximum Q-factor of 4455 and a Purcell Factor (maximum enhancement in the spontaneous-emission rate) of 340. (C) 2007 Elsevier B.V. All rights reserved.