A fluorescent color center in meteoritic Lonsdaleite
Lonsdaleite -- hexagonal diamond -- has only recently been proposed as a wide-bandgap host capable of supporting optically active point defects, but no such centres have yet been observed. Here we provide the first experimental evidence that lonsdaleite does in fact host photoluminescent color centres. In meteoritic lonsdaleite grains from the ureilite NWA7983, we identify a new defect, RU1, which exhibits bright and stable emission across 550-800 nm, with optimal blue excitation (~455 nm) and a peak at ~700 nm. Time-resolved photoluminescence reveals an excited-state lifetime of 14 ns with no detectable blinking, bleaching, or charge conversion. From the excitation-emission energetics we infer an unresolved zero-phonon line near 550 nm. Correlative electron microscopy confirms the lonsdaleite host lattice, and compositional analysis suggests N, Si, or Ni as plausible defect constituents. These results suggest lonsdaleite could become a new quantum-grade crystalline platform and indicate that hexagonal-diamond color centres may form a new and unexplored family of solid-state quantum emitters.