  Lanthanides are vital components in lighting, imaging technologies and future
quantum memory applications due to their narrow optical transitions and long
spin coherence times. Recently, diamond has become a preeminent platform for
realization of many experiments in quantum information science. In this work,
we demonstrate a promising approach to incorporate Eu ions into single crystal
diamond and nanodiamonds, providing a means to harness the exceptional
characteristics of both lanthanides and diamond in a single material.
Polyelectrolytes are used to electrostatically assemble Eu(III) chelate
molecules on diamond and subsequently chemical vapor deposition is employed for
the growth of a high quality diamond crystal. Photoluminescence,
cathodoluminescence and time resolved fluorescence measurements show that the
Eu atoms retain the characteristic optical signature of Eu(III) upon
incorporation into the diamond lattice. Computational modelling supports the
experimental findings, corroborating that Eu3+ in diamond is a stable
configuration within the diamond bandgap. The versatility of the synthetic
technique is further illustrated through the creation of the well-studied Cr
defect center. Together these defect centers demonstrate the outstanding
chemical control over the incorporation of impurities into diamond enabled by
the electrostatic assembly together with chemical vapour deposition growth.
