Photoluminescence of Nitrogen-Vacancy Centers by Ultraviolet One- and Two-Photon Excitation of Fluorescent Nanodiamonds

Fluorescent nanodiamonds contain nitrogen-vacancy (NV) centers as quantum defects. When exposed to a continuous-wave 325 nm laser or a femtosecond 344 nm laser, the particles emit red fluorescence from NV0 centers at similar to 620 nm. Power dependence measurements of the emission strength revealed a predominantly linear behavior at the laser peak intensity lower than 1 GW.cm(-2), contributed mainly by photoexcitation of electrons from the valence band of diamond to the NV0 centers, followed by relaxation via electronhole recombination. In the higher power regions, however, nonresonant two-photon interband excitation of the diamond matrix dominates the photoluminescence processes. Best fits of the experimental data to semiempirical models revealed an ionization coefficient of similar to 1 cm(-1) for the one-photon valence-to-defect excitation and a saturation intensity of 180 +/- 60 GW.cm(-2) for the two-photon interband excitation. The study provides new insight into the photoionization of NV0 centers and the interband excitation properties of diamond in the UV region.

Automated summary

The study reveals that fluorescent nanodiamonds emit red fluorescence when exposed to specific wavelength lasers. At low power, the emission is mainly due to excitation of electrons from the valence band of diamond to the NV0 centers, while at high power, nonresonant two-photon interband excitation dominates.