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Description
Type Ib diamonds containing ~200 ppm substitutional nitrogen were irradiated with 4.8 MeV/n swift heavy ions ($^{48}$Ca, $^{197}$Au, $^{238}$U) to investigate radiation-induced defect formation and evolution. A comprehensive spectroscopic approach combining on-line ionoluminescence, spatially resolved photoluminescence/Raman spectroscopy, UV/vis absorption, and infrared spectroscopy was employed to characterize defect dynamics across fluences from $10^9$ to $2 \times 10^{13}$ cm$^{-2}$.
Ionoluminescence spectroscopy revealed broad emission bands at ~530 nm and ~885 nm, attributed to 3H centers and NiV$^-$ centers, respectively. The integrated luminescence signal degraded rapidly, retaining only 20% of initial intensity after $2 \times 10^{11}$ cm$^{-2}$ $^{197}$Au irradiation. At higher fluences ($>10^{12}$ cm$^{-2}$), blue emission from 3.188 eV and 2.807 eV centers emerged.
Spatially resolved measurements with 1-2 µm resolution probed different energy loss regimes along ion trajectories. Vacancy-related GR1 centers showed maximum intensity at electronic energy loss dominated regions near the surface, while diamond lattice degradation (monitored via Raman intensity) was most pronounced at nuclear energy loss dominated end-of-range regions. The 3H center intensity peaked at vacancy densities of $4.4 \times 10^{18}$ cm$^{-3}$, scaling with the electronic-to-nuclear energy loss ratio.
Complementary UV/vis and FT-IR absorption spectroscopy confirmed the identified defect centers and revealed direct nitrogen A/B center formation without significant aggregation.
These results demonstrate strong sensitivity of various color centers to electronic energy loss, challenging the common assumption that radiation damage in diamond is solely nuclear energy loss driven. The findings provide crucial insights for diamond detector applications in heavy ion environments and advance understanding of defect formation mechanisms under swift heavy ion irradiation.
