Spontaneous transitions to enhanced fluorescence for GeV centers in a single microcrystalline diamond Natalia A. Lozing, Maxim G. Gladush, Ivan Yu. Eremchev, Eugeniy A. Ekimov and Andrey V. Naumov EPJ Web Conf., 190 (2018) 04012 Published online: 26 September 2018 DOI: 10.1051/epjconf/201819004012