Abstract: An electroluminescent solid state device includes an active body member that is formed of a single crystalline metal oxide, such as aluminum oxide, that is doped with a rare earth element, such as erbium and/or terbium and an activator atom such as oxygen and/or fluorine. The metal oxide body member is electron excited by kinetic electrons that are emitted by a cold cathode. The ends of the metal oxide body member are polished to form a Fabry-Perot resonator, thus providing for coherent radiation from the device. As an alternative to the use of a Fabry-Perot cavity, an acoustic wave generator is associated with the metal oxide body member in order to launch acoustic waves into the body member. The frequency of energization of the acoustic wave generator operates to select a radiation wavelength from one or more emission wavelengths that are produced by doping the metal oxide body member with one or more rare earth elements.