This work studies the use of Photoluminescent NanoDiamonds (PNDs) for bio-imaging applications. The work is divided in two parts. The first part concerns the study of the optical properties of nitrogen-vacancy (NV) color centers and the optimization of the NV center concentration in nanodiamonds. To enhance the imaging contrast of internalized by cells PNDs, we applied time gated imaging and studied the 2-photon excitation properties of NV centers. While implementing a pulsed excitation laser, we discovered that simultaneous one and two-photon excitation quenches the signal of PNDs. We...