Study on fluorescence collection enhancement of NV color centers in diamond by anti-reflection gradient refractive index diamond-like coatings

Abstract

The nitrogen-vacancy (NV) color centers in diamond, recognized as the most prevalent defect centers, are extensively utilized in fields such as quantum communication and quantum sensing. However, the high reflectance at the diamond-air interface results in low fluorescence collection efficiency of NV color centers. To address this challenge, this paper proposes the deposition of an anti-reflection gradient refractive index diamond-like coating (DLC) on the diamond substrate to enhance light transmittance and, consequently, improve the fluorescence collection from the NV color centers. By employing the finite-difference time-domain method in conjunction with a gradient refractive index distribution, we simulate the number of DLC layers and their thickness to assess the effects of the anti-reflection coating on transmittance, reflectance, and emission efficiency of the NV color centers within the diamond substrate. This analysis elucidates the mechanisms by which the anti-reflection coating enhances fluorescence collection in the NV color centers. Furthermore, we prepared the diamond substrate using the microwave plasma chemical vapor deposition method and applied the anti-reflection coating via the magnetron sputtering technique. Testing demonstrated that with the addition of the anti-reflection coating, reflectivity was reduced to a mere 1.7 %, reduce by about 1/10 lower than without the coating. Additionally, following the deposition of the anti-reflective coating, the fluorescence collection of the NV⁰ and NV^- color centers was significantly enhanced, with the fluorescence collection of the NV⁰ color centers increasing by 1.7 times and that of the NV^- color centers increasing by 1.9 times.