We report photoluminescence and electroluminescence at room temperature in diodes based on Si/SiO2 multilayers. The multilayers are fabricated by alternating Si and SiO2 layers, whose thickness is, respectively, 2 and 5 nanometers. In photoluminescence, a single band is observed, centered at 800 nm, which is due to electron-hole pair recombination under quantum confinement. On the other hand, in electroluminescence, two bands are reported. The first band is in the infrared spectrum, and is blackbody radiation. The second band is visible, and is originated by relaxation of a single type of electrical carrier (electrons), as suggested by a fast decay time (less than 0.1 µs). Possible mechanisms can be hot-electron relaxation or coupling with surface plasmon-polaritons.