Issues concerning the nitrogen-vacancy center in diamond

The nitrogen-vacancy (N-V) center in diamond has been extensively studied and several novel properties identified. As a consequence the center has interesting applications. However, the center is not completely understood. In this work a new electronic model is proposed which accounts for the fine structure of the excited state and for many of the associated properties of the center. In addition the paper discusses the remaining difficulties and indicates the studies required to resolve the outstanding issues.