Density-dependent exciton kinetics in synthetic diamond crystals

We have measured transients of excitonic luminescence under pulsed excitation of single-crystal diamond, synthesized by a high-temperature high-pressure method. The longest decay time of 80 ns is measured at a lattice temperature around 100 K in nondoped samples. The decay kinetics strongly depends on the excitation power density and the impurity concentration. Based on the impurity concentrations determined from infrared and ultraviolet absorption coefficients, we simulate the carrier kinetics by solving rate equations for free and bound exciton densities. It is found that annihilation of free excitons via capture to impurity sites and via collection to electron-hole droplets plays an important role at low temperatures.