Optical and Thermal Properties of Sulfur-Perturbed F2+ Centers in NaCl as the Laser Active Center

The optimum sample preparation, optical properties, and stability against light and heat for sulfur-perturbed F₂⁺ centers (F₂⁺:S^-) in NaCl have been investigated to determine the potential quality as a laser material. F₂⁺:S^-’s were introduced into NaCl doped with Na₂S by additive coloration and subsequent photoaggregation. Absorption and luminescence bands occurred at 1.18 and 0.832 eV at 80 K, respectively. The excitation spectra for the luminescence showed two maxima at 1.18 and 2.71 eV. The luminescence efficiency was 0.84± 0.03 between 80 and 290 K. Photoexcitation of the F₂⁺ center in F₂⁺:S^- to the 2pπ_u state at 80 K converted the configuration of F₂⁺:S^- into the most compact form, and also rotated the F₂⁺ axis by 60°, while the photoexcitation above about 190 K destroyed F₂⁺:S^-. F₂⁺:S^- was expected to be stable for ∼19 days at 290 K, and ∼400 days at 268 K in the dark.