Diamond nanocrystals containing Nitrogen-Vacancy (NV) color centers have been used in recent years as fluorescent probes for near-field and cellular imaging. In this work we report that an infrared (IR) pulsed excitation beam can quench the photolumi
nescence of NV color center in a diamond nanocrystal (size < 50 nm) with an extinction ratio as high as ~90%. We attribute this effect to the heating of the nanocrystal consecutive to multi-photon absorption by the diamond matrix. This quenching is reversible: the photoluminescence intensity goes back to its original value when the IR laser beam is turned off, with a typical response time of hundred picoseconds, allowing for a fast control of NV color center photoluminescence. We used this effect to achieve sub-diffraction limited imaging of fluorescent diamond nanocrystals on a coverglass. For that, as in Ground State Depletion super-resolution technique, we combined the green excitation laser beam with the control IR depleting one after shaping its intensity profile in a doughnut form, so that the emission comes only from the sub-wavelength size central part.
We present results showing the potential of diamond nanoparticles with size less than 50 nm as photoluminescent nanoprobes for serving as stable point-like emitters attached at the tip apex of a near-field optical microscope to achieve enhanced spatial resolution.
