The effect of nitrogen removal agents on diamond quality during annealing

Abstract

Diamond is a unique material with numerous outstanding properties, now widely applied across various fields. Nitrogen (N) is a common impurity in diamond, and its concentration and form directly influence diamond's performance and applications. Annealing is an effective method for altering the form of nitrogen atoms within diamond. Currently, there is limited research on the annealing behavior of diamond crystals with different nitrogen contents. This study aims to investigate the properties of diamonds with varying nitrogen contents after annealing treatment. First, 4 sets of (111) diamond single crystals with different nitrogen contents were prepared by adding varying proportions of Ti to an Fe₆₀Co₄₀ catalyst. Subsequently, the characteristics of the 4 diamond crystals before and after annealing were examined using detection equipment, including X-ray diffraction (XRD), Raman spectroscopy, infrared spectroscopy, and photoluminescence (PL) spectroscopy. The experiments demonstrated that as the proportion of the nitrogen getter Ti increased, the color of the diamond lightened. Using 0.5% nitrogen getter yielded a bright yellow diamond with a nitrogen content of 54 ppm. Annealing lightened or completely removed the yellow coloration in diamond single crystals; crystals with a nitrogen content below 54 ppm became colorless after annealing. Infrared spectroscopy calculations indicated that C-center nitrogen in the crystals converted to A-center nitrogen at a conversion rate exceeding 90%. UV spectroscopic characterization revealed that all annealed diamond samples contained nitrogen at the A center, with the concentration gradually decreasing as the amount of nitrogen getter increased, corroborating the findings of infrared spectroscopy. Based on PL spectroscopy, the post-annealed diamonds exhibit the disappearance of the defect (613 nm) peak position, with the emergence of peaks representing NV⁰ color centers (575 nm) and NV⁻ color centers (637 nm). Based on the results of infrared spectroscopy and photoluminescence (PL) spectroscopy, UPS testing revealed that the annealing process modulates the Fermi level within the diamond, thereby promoting the formation of NV⁻ color centers. This study provides a basis for determining the dosage of nitrogen getters in gem-quality diamond production and offers a process reference for diamond fabrication in the field of quantum communication.