Luminescence from natural and man-made diamond in the near infrared

Abstract

Attention is directed to a number of newly discovered luminescence bands between ≈ 0.7 eV and ≈ 2.2 eV which appear to be characteristic of diamonds possessing various concentrations and configurations of the major impurity, nitrogen. A broad band peaking near 1.25 eV and observed in type Ia diamond is identified with the radiative recombination of free holes with electrons in the platelet nitrogen donor impurity band. The previously reported 1.40 eV luminescence system has been found in all natural and man-made type Ib diamonds so far examined, and a ground state splitting of 2.9 meV has been observed. This system is still believed to be associated with dispersed neutral nitrogen donors, although reasons for rejecting a previous interpretation in terms of indirect gap bound excitons are discussed. A band centred near 1.8 eV containing much fine structure has been found in all natural type IIb diamonds, and a vibronic system with a peak energy near 1.2 eV has been found in all natural diamonds except type Ib. Finally, the intense excitation density obtainable with the electron beam technique has facilitated observation of the surprisingly weak luminescence of the GR1 low temperature irradiation damage centre, and the absorption and luminescence are compared under high resolution.