PROPERTIES OF THE 800-NM LUMINESCENCE BAND IN NEUTRON-IRRADIATED MAGNESIUM-OXIDE CRYSTALS

We present results on the luminescence at 800 nm which occurs upon excitation of the 573-nm optical absorption band attributed to an aggregate defect in neutron-irradiated MgO crystals both pure and doped. The study was undertaken to evaluate the suitability of this luminescence for a tunable laser. Absorption, luminescence, and excitation spectra were measured before and after isochronal annealing, with the goal of optimizing the luminescence intensity and stability of the responsible defect, and reducing the background absorption in the crystal. The emission intensity is highest after annealing at approximately 550 K independent of dose. A thermally induced absorption band at 565 nm, which emerges at approximately 550 K, does not contribute to the emission at 800 nm. Under low-intensity continuous excitation, the 573-nm absorption band is not susceptible to photoconversion. However, when pumped with high-intensity laser light, the band exhibits a decay which recovers within 0.5 s. The luminescence has a single-exponential decay time of 15.5 ns at room temperature, and the band shape remains essentially constant throughout the decay. Tests for laser action using pulsed and cw pump lasers were unsuccessful at 77 and 300 K.