CERN ISOLDE Setup Confirms GeV- Center via 82.3-Minute Radiotracer Decay in Diamond

The team built an optical microscope coupled to a fiber-fed Czerny-Turner spectrometer at the ISOLDE beamline and performed room-temperature measurements on diamond samples after low-energy radioactive ion implantation. Radioactive 75Ga served as a precursor that beta-decays to 75Ge, allowing the temporal correlation between nuclear decay and optical signal to be measured directly over several hours. This approach bypasses the ambiguity of conventional photoluminescence assignments that rely only on spectral position or theoretical calculations.

The observed 600 nm band decayed with a half-life of 82.3 +2.5/-2.3 min, statistically consistent with the accepted 82.78(4) min half-life of 75Ge. No other known impurity produces both this emission and this precise temporal signature, providing the first direct experimental proof that the center contains germanium. The method extends established radiotracer techniques from electrical and hyperfine studies to optical defects in wide-bandgap materials.

Existing literature on GeV- centers has relied on indirect evidence such as ion implantation fluence dependence and ab-initio modeling; the new decay correlation removes the remaining doubt about the chemical identity. Industrial diamond growers and quantum-sensor developers can now use the technique for rapid quality control of color-center purity, potentially accelerating device qualification timelines from months to days.

Future runs at ISOLDE will target other candidate centers in diamond, silicon carbide, and hexagonal boron nitride using the same isotope library. A portable version of the setup could be adapted to synchrotron beamlines, broadening access beyond CERN.