Nanoscale Vacancy-Mediated Aggregation, Dissociation, and Splitting of Nitrogen Centers in Natural Diamond Excited by Visible-Range Femtosecond Laser Pulses

Abstract

Natural IaA+B diamonds were exposed in their bulk by multiple 0.3 ps, 515 nm laser pulses focused by a 0.25 NA micro-objective, producing in the prefocal region (depth of 20–50 μm) a bulk array of photoluminescent nanostructured microtracks at variable laser exposures and pulse energies. These micromarks were characterized at room (25°) and liquid nitrogen cooling (−120 °C) temperatures through stationary 3D scanning confocal photoluminescence (PL) microspectroscopy at 405 and 532 nm excitation wavelengths. The acquired PL spectra exhibit a linearly increasing pulse-energy-dependent yield in the range of 575 to 750 nm (NV0, NV- centers) at the expense of the simultaneous reductions in the blue–green (450–570 nm; N3a, H4, and H3 centers) and near-IR (741 nm; V0 center) PL yield. A detailed analysis indicates a low-energy rise in PL intensity for B2-related N3a, H4, and H3 centers, while at higher, above-threshold pulse energies it decreases for the H4, H3, and N3a centers, converting into NV centers, with the laser exposure effect demonstrating the same trend. The intrinsic and (especially) photo-generated vacancies were considered to drive their attachment as separate species to nitrogen centers at lower vacancy concentrations, while at high vacancy concentrations the concerted splitting of highly aggregated nitrogen centers by the surrounding vacancies could take place in favor of resulting NV centers.

Electron Paramagnetic Resonance Sensing of «Hidden» Atomistic and Cooperative Defects in Femtosecond Laser-Inscribed Photoluminescent Encoding Patterns in Diamond

“…On the other hand, the concentrations of the B2 (platelets, layers of interstitial carbon), N2 (fragments of the structure with broken C-C bonds), and H3 (N-V-N) centers containing vacancies, as well as the NV 0 and NV − centers, have increased. These findings, in particular, about the conversion of substitutional N atoms into NV centers, are in agreement with the previous experimental [21,24,25,[29][30][31]34] and theoretical [26][27][28] studies of IIa diamonds, while the diminishing of A center abundance and the rise of H3 center abundance in laser-modified natural diamonds were revealed in [23,32,33]. Meanwhile, laser-driven variation of more complex N2, W7, and B2 centers was observed for the first time and deserves its detailed discussion.…”

“…In diamond samples with higher-ppm-level-concentrations of nitrogen impurities in different aggregation forms, a number of analytical methods-Fourier-transform infrared (FT-IR), optical (UV-near-IR), and photoluminescence (PL) microspectroscopy-were utilized to envision their atomistic transformations, driven by the photoinjected intrinsic defects [23,29]. Moreover, clustering and cooperative processes in the laser-generated microscale dense clouds of intrinsic defects lead to different forms of damage to the diamond lattice, which can be analyzed by the same methods [30][31][32][33][34]. The complementary optical and EPR spectral analysis could shed an informative light on the optically active and optically blind ("hidden") defects resulting from femtosecond laser irradiation.…”