Two types of stimulated emission in HPHT diamond with a high concentration of NV centers

The paper presents the results of experimental observation of two types of stimulated emission (SE) under pulsed laser pumping at 532 nm in diamond with NV centers. A comprehensive spectroscopic characterization of multisectorial HPHT diamond plate was performed. At low pumping power, the stimulated emission from NV¯ centers was recorded as a broad (≥80 nm wide) band with a maximum at 706 nm in the {111} and {311} sectors of the diamond plate. As the pump power increased in the {111} sector, narrow-band stimulated emission (<10 nm wide) was detected, with a maximum at 716 nm and a luminescence impulse duration of 1.5–3 ns. As the pump density increased, a fine structure in the spectrum of narrow-band stimulated emission was revealed for the first time. The concentration of NV¯ centers in the {111} and {311} growth sectors was ≈10 ppm. However, there were considerable differences in the concentrations of C (35 and 3.5 ppm) and C⁺ centers (6.1 and 3.2 ppm, respectively). It was demonstrated that the presence of a high concentration of NV¯ centers is not the only necessary condition for the initiation of narrow-band SE in the 710–720 nm range. In the {311} sector, lighting at 360, 405, and 488 nm reduced the concentration of NV¯ centers by 15 % while increasing the concentration of C⁺ centers in the {311} sector. This effect is weak in the {111} sector. The authors suggested a model for narrow-band SE at the transition Valence Band → C⁺ with charge-state conversion of C↔C⁺ and NV⁰↔NV¯ centers. Further research on the dynamic processes is required in order to a detailed understanding of the operation of NV centers in diamond during SE generation.