We report a novel microcavity design that allows the control in wavelength of the resonant modes of a microcavity operating in the visible spectrum. We have been able to shift the modes by up to 56 nm. The device is comprised of a thin film of a fluorescent semiconducting polymer combined with an electrically switchable liquid crystal layer, which are sandwiched between the two cavity mirrors. This structure serves as a tool for further experimental studies of the properties of microcavities and also has considerable technological potential, providing, for example, an efficient wavelength converter or tunable light source. ©1998 American Institute of Physics.