Optische Absorption und Fluoreszenz von NH ⁻₂ - und ND ⁻₂ -Ionen in Alkalihalogenidkristallen

Abstract

The centers are produced by different methods. Either the crystal, containingF centers in a high concentration, is annealed in an atmosphere of ammonia. Or the NH ⁺₄ doped crystal is reduced withF centers.

The optical absorption in the near infrared at 21 °K shows a well resolved doublett and another band at longer wavelengths. In the case of deuterated centers these bands are shifted by about √2 to longer wavelengths. These bands belong to the two stretching vibrations and the bending vibration of the NH ⁻₂ .

In the UV a strong absorption band appears with satellites on its short wavelength side. Its maximum follows a Mollwo-Ivey relation. The satellites come from the simultaneous excitation of internal vibrations of the NH ⁻₂ . Their energy distance to the main maximum depends strongly on the hydrogen isotope.

Excitation in the UV bands yields a flourescence in the visible region. It consists of two bands. They are interpreted as 0–0 transitions relative to the internal vibrations of the center. Their relative hight strongly depends on the temperature. We think that both bands are due to different positions of the amide ion in the excited state within the anion vacancy. From a detailed study of this temperature dependance typical activation energies can be derived.