Luminescence and Raman Spectroscopy of Polycrystalline Diamond Films with Nitrogen-Vacancy Centers for Converters of Vacuum Ultraviolet Radiation

Diamond has shown great promise as solid-state converter for radiation, especially in the vacuum ultraviolet (VUV) spectrum, due to its bandgap and scintillation provided by nitrogen-vacancy (NV) centers. In the present work, we study polycrystalline diamond films synthesized via plasma-enhanced chemical vapor deposition (PECVD), incorporating varying levels of nitrogen doping by adding N2 flow from 0% to roughly 2.3% relative to the hydrogen-methane mixture. Raman and luminescence mapping have revealed correlation between diamond peak and NV luminescence distributions, indicating that the grown structures are successfully formed with the content of NV centers, since the initial diamond clusters of the seed layer have only a weak luminescence in this region. Further analysis of the panoramic Raman spectra uncovered distinct trends: a progressive increase in the contribution from sp2 carbon with higher N2 content in the gas flow, a relative decline in NV0 luminescence compared to the diamond signal, and a rise in NV–/NV0 ratio, indicating a shift toward charge states. At higher N2 doping levels, signals from nanocrystalline diamond became evident. However, based on analysis of Raman and luminescence maps, an increase in the ratio of luminescence to the diamond Raman peak is observed across the layer, with rapid saturation already at 0.3–0.5% N2 in the gas flow.