Ultrafast X-ray Pump-Probe Investigation of the Formation Dynamics of SiV Centers in Diamond

Color centers in diamond are promising single-photon sources for quantum technologies and biomedical applications. We studied the formation dynamics of negatively charged silicon-vacancy (SiV) centers during diamond nucleation using time-resolved X-ray pump-probe experiments at the European X-ray Free-Electron Laser Facility. A silicon-containing adamantane precursor was flash-heated within diamond anvil cells using ultrashort femtosecond X-ray pulses at a 2.2-MHz repetition rate. We captured the structural evolution of diamond with X-ray diffraction patterns separated by 443 ns. Correlating these dynamics with postexperiment SiV photoluminescence reveals, for the first time, a link between ultrafast diamond nucleation and color-center inclusion. SiV formation is contingent on diamond formation and occurs only above pressure-dependent energy-delivery-rate thresholds: 34.3 J·s^-1 at 17.8 GPa and 178.4 J·s^-1 at 14.4 GPa. Our findings define synthesis windows for generating SiV and reveal a kinetic regime in which diamond nucleates without optically active SiV, informing rate- and pressure-aware strategies for producing various color centers.