Showing papers by "G. N. Ramachandran published in 1946"

The luminescence of diamond excited by X-radiation

Abstract: D*AMOND can be made to iuminesce in a variety of ways, e.g., by irra6iating with ultra-violet rays, cathode rays of X-rays or by the action of heat or friction. The fluorescente spectra and various other properties assoeiated with fluorescence, such as the local variations of colour and intensity, have been studied by a number of workers in this laboratory using ultra-violet excitation (Nayar, 1941; Mani, 1944, 1945; Sunanda Bai, 1944; Rendall, 1946). John (1930) has reported a study of the fluorescent spectrum when exposed to cathode rays. The present paper describes the investigations made by the author on the fluorescente of diamond when irradiated with X-rays. Among the various phenomena that were studied may be mentioned the fluorescence spectra, the fluorescence patterns, the correspondence of otherwise of these with those produced by ultra-violet excitation and the influence, of the hardness and intensity of X-rays on the intensity of luminescence. A discussion is also included on the probable mechanism by which the luminescence is produced by the impact of X-rays.

Luminescence as “forbidden” electronic transitions in diamond

Abstract: Arguments are adduced to show that the doublet centred at 4152 A occurring in the spectrum of all fluorescing diamonds arises from ‘forbidden’ transitions analogous to the forbidden3P-1S transitions in the spectrum of C I. On the basis of this analogy, fluorescence lines are also expected to occur at about 8816 A and 7849 A, analogous to the3P-1D and1D-1S transitions in C I. Of these, the former should also occur in absorption, while the latter should not occur in absorption and should be emitted only if the exciting radiation has a wavelength shorter than 4152 A. A line has actually been found at 7930 A, satisfying the latter conditions. The former line could not be recorded being outside the limit of sensitivity of the photographic plate.

On the crystal symmetry of diamond and its X-ray reflections

Abstract: The problem of the symmetry of the diamond structure in relation to its X-ray behaviour is considered in a formal manner. It is shown that the presence or absence of the 200 or the 222 reflection cannot uniquely decide whether the symmetry is tetrahedral or octahedral. The 200 reflection is shown to be absent if the structure is either completely symmetric or antisymmetric with respect to the centre of inversion at 1/8, 1/8, 1/8 or if the two distributions are superposed in any arbitrary ratio. The 222 reflection is, however, absent only in the fully antisymmetric case. Making use of these results, the nature of the structures that are possible for the tetrahedral and the octahedral modifications of diamond are discussed.