Size effect in electron paramagnetic resonance spectra of impurity centers in diamond particles

Abstract

The experiments have shown qualitative changes in electron paramagnetic resonance (EPR) spectra with decreasing average size of diamond particles from 100 μm to 18 nm. The characteristic hyperfine splitting in the EPR spectrum due to the interaction of an unpaired electron of a neutral impurity (nitrogen atom) in the diamond lattice with its nuclei disappears, and the resulting EPR spectrum is a superposition of two singlet Lorentzian lines. The reason for the observed effect is the indirect exchange interaction of electrons localized on bulk impurity centers through electrons localized on surface dangling bonds. Such an interaction of electrons localized on bulk centers becomes possible due to the resonant energy transfer between them. The transfer is result of the exchange interaction with electrons of surface centers. It is shown, that the energy of the indirect exchange interaction depends on the size of the diamond particle; therefore, the effect can be observed only in the case when particle size is smaller than a critical value R cr . The calculated value of the R cr based on the suggested model fitted well with experimental data.