Dynamics of infrared excitations in boron doped diamond

We report on the investigation of relaxation dynamics of optical excitations in IIb high pressure high temperature (HPHT) diamond doped by natural boron and isotopically enriched 11boron. The measurements were performed with a pump-probe technique using short pump pulses from a wavelength-tunable infrared free electron laser. Lifetimes of excited boron states ranging from a few picoseconds to a few hundred picoseconds, have been derived from the obtained data. The relaxation rates depend on the pumped states, the pump intensity and the diamond lattice temperature. We discuss possible contributions to the optical and nonradiative intracenter relaxation rates observed in these experiments. Theoretical simulations support ultrafast relaxation by multiple phonon emission, for the electronic states with the energy gap exceeding the energy of optical phonon. From the left to the right: Schematic presentation of optical intracenter excitation and two-phonon nonradiative relaxation in boron doped diamond. Temporal dependence of the decay of the optical pump induced transparency measured by the probe beam. Experimental data have been fitted with the three-level cascade relaxation model. Inset: a photo of the boron doped diamond crystal. Temporal dependence of the population on boron levels right after the optical pulsed pumping derived from the three-level cascade relaxation model. [Display omitted] •We observed ultrafast relaxation of charge carriers bound to boron impurity states in IIb diamond.•Decay to the boron ground state involves single- and two-phonon-assisted relaxation processes.