Revised fine splitting of excitons in diamond

We study low-strain synthetic high pressure, high temperature diamonds by c athodoluminescence and observe novel fine structure in the free exciton and the boron-bound exciton emission. The basic spectral structure is a double t with Delta E approximate to 11 meV common lo both exciton spectra. This r esolves the previously found inequivalence of free exciton (approximate to 7 meV) and bound exciton (approximate to 12 meV) fine splitting. It is argu ed that for a spin-orbit interaction Delta(0) much smaller than the exciton ic binding (E-x approximate to 80 meV) and the excitonic localization (E-lo c approximate to 51 meV) at the boron acceptor, the orbital momentum and th e spin of the particles constituting the electron-hole pair are recoupled t o form spin singlet and triplet exciton states as the elementary excitation s.