Bright quantum confined luminescence due to band-to-band recombination can be obtained from Si/SiO2 superlattices. To further enhance their light emitting properties, we have studied the effect of placing them in a one-dimensional optical microcavity. The Si/SiO2 superlattices were grown on various substrates in a magnetron sputtering system. The effect of the additional optical confinement on the photoluminescence (PL) results in a pronounced modulation of the PL intensity with emission wavelength, as a consequence of the standing wave set up between the substrate and air interfaces. The modulation in the case of a quartz substrate is much weaker, because of the low reflectance (similar to 1%) between the superlattice and the quartz. For a Si substrate, absorption of light reduces the PL efficiency, but for an Al-coated glass substrate the PL intensity is twice that of the quartz substrate case. These results show that a suitably designed planar microcavity cannot only considerably increase the efficiency of luminescence in Si/SiO2 superlattices but can also be used to decrease the bandwidth and selectively tune the peak wavelength.