ELECTRIC-FIELD MODULATION OF LUMINESCENCE-EXCITATION IN NATURAL DIAMOND IN SPECTRAL ENERGY RANGE 5.0-6.0 EV

An investigation has been made of the effect of high electric fields, up to 50kV cm-1, on the luminescence-excitation spectrum of natural diamond in the spectral energy range 5-6 eV, using ac fields and phase-sensitive detection. The major effect observed is an over-all reduction in luminescence efficiency at energies above the fundamental absorption edge. This luminescence quenching is interpreted in terms of the acceleration of free carriers by the applied field, increasing the probability of nonradiative decay at surface states and decreasing the probability of radiative electron-hole recombination at aluminum-acceptor-nitrogen-donor pairs. In some crystals, notably those in which the luminescence efficiency is very low, an increase in luminescence is observed near the fundamental absorption edge. The maxima in the differential luminescence-excitation spectra are found to coincide with the threshold energies for indirect transitions to a free exciton state, and are interpreted in terms of electric-field broadening of the free-exciton state. Electroabsorption spectra can also be obtained in this region from a small number of extremely pure crystals, and these spectra are also consistent with transitions to a free-exciton state. The low resolution observed in both the differential luminescence-excitation spectra and the electroabsorption spectra, which are field-independent, is attributed to interference from extrinsic absorption in the region of the intrinsic absorption edge associated with the impurity complexes responsible for the luminescence. © 1968 The American Physical Society.