The M-Center Luminescence in KCl and KBr Crystals

Abstract

The M-center luminescence in KCl and KBr crystals has been investigated extensively over a temperature range from about 4°K to 370°K. From the temperature dependence of the band width of the luminescence, vibrational frequencies influencing the M center in the excited states are estimated as 3.9×10¹² cps and 3.8×10¹² cps, respectively, in KCl and KBr crystals. By stimulating the crystal with M₄ light almost the same luminescence as that by M₁ light is observed in KCl. New absorption bands, M_L, being associated with the M center and located at 360 mμ, 308 mμ, 250 mμ, and 400 mμ, 325 mμ, 275 mμ in KCl and KBr crystals, respectively, have been found, which may be analogous to the L bands of the F center. By comparing with the quantum yield of the F-center luminescence, the quantum yield of the M-center luminescence is estimated as 0.37±0.05 in KCl crystals at liquid nitrogen temperature. From the temperature dependence of the M-center luminescence intensity the energy gap between the first excited state and the bottom of the conduction band is found to be 0.38±0.01 eV and 0.13±0.02 eV in KCl and KBr crystals, respectively.