Color center fluorescence and spin manipulation in single crystal,   pyramidal diamond tips
  We investigate bright fluorescence of nitrogen (NV)- and silicon-vacancy color centers in pyramidal, single crystal diamond tips which are commercially available as atomic force microscope probes. We coherently manipulate NV electronic spin ensembles with $T_2 = 7.7(3)\,\mu$s. Color center lifetimes in different tip heights indicate effective refractive index effects and quenching. Using numerical simulations, we verify enhanced photon rates from emitters close to the pyramid apex; a situation promising for scanning probe sensing. 
Richard Nelz, Philipp Fuchs, Oliver Opaluch, Selda Sonusen, Natalia   Savenko, Vitali Podgursky, and Elke Neu
cond-mat.mtrl-sci cond-mat.mes-hall physics.optics quant-ph