Dominant free-exciton (FE) recombination radiation has been obtained from high-purity Chemical vapor deposition (CVD) diamond synthesized on Cu substrates by means of microwave plasma CVD using CH4 + O2 diluted with H2. The intensity of FE emission is almost constant between 80 K and 170 K, and is reduced by two orders of magnitude at room temperature. The emission increases in proportion to the incident beam current from 1 × 10–9 A to 2 × 10–6 A. The spectrum shapes between 200 nm and 600 nm do not depend on the beam current. In addition, the isotopic effect on the FE emission peak shift has been observed in the spectrum from13C-enriched (96.6%) CVD diamond for the first time.
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