Fine Structure of the Boron Bound Exciton in Diamond

Low temperature cathodoluminescence has been measured on boron-doped natural and synthetic diamond crystals that show very narrow line widths due to low internal strain. This allows us to resolve a novel fourfold fine structure in both components of the bound exciton doublet, which is known from previous work. Temperature-controlled measurements lead to a level scheme with a 2 meV ground state splitting of the neutral boron acceptor and a 3.3 meV splitting in either of the two initial doublet exciton states. The ground state splitting is in excellent agreement with data from former excitation spectroscopy on boron acceptors in the IR and from recent Raman spectroscopy on boron-doped diamonds. The initial state-splitting which we measured to be 11.4 meV is discussed in terms of spin-orbit interaction of the holes. The 3.3 meV exciton splitting remains unidentified. (Author)