Triboluminescence from diamond

Abstract

The process by which diamonds wear when they are facetted using traditional diamond polishing has been the subject of much debate. The absence of a plausible wear mechanism to describe the process has been due in part to the lack of reliable data; a multitude of variables are involved with the process. In recent years, the enhancement of sophisticated analytical techniques has led to the discovery that diamond undergoes a phase transformation during polishing, although the process by which this occurs is unclear. One of the more interesting observations seen during diamond polishing is the occasional emission of light from a polishing diamond. Since this emission is a direct consequence of physical processes at the polishing interface, it provides us with detailed and direct information about electronic processes occurring as diamond bonds that are broken and/or transformed. These light emissions have loosely been described as triboluminescence, although no detailed study of the phenomenon occurring in diamond has ever been published. This paper describes an investigation into the light emitted during fracture (such as that obtained when diamond is scratched) and during polishing. In each case, the spectral emissions are different. During fracture, the overall spectral envelope is dominated by light emission due to frictional sliding and to a lesser extent by photoluminescence, demonstrated by the appearance of the 'N3' centre. During polishing, it is suggested that the mechanism by which light emission occurs is via electroluminescence.